vacuum gravity experiment

WATCH: A Bowling Ball And Feather Fall in World's Biggest Vacuum Chamber

It was Galileo himself who first discovered that in a vacuum, if you were to drop two objects from the same height, they'd hit the ground at exactly the same time, regardless of their respective weights. Of course, on Earth, we rarely - if ever - get the change to see this at play, thanks to a phenomenon known as air resistance .

The combination of bowling ball and feather is the perfect way to demonstrate air resistance, also known as drag. Because the shape of the feather allows it to endure way more air resistance than the bowling ball, it takes much longer to fall to the ground.

British physicist Brian Cox wanted to see this primary-school problem play out in a vacuum, where there is zero air resistance to mess with the results. Filming for his new BBC 2 show, Human Universe , he travelled to the US and visited the NASA Space Power Facility in Ohio. The facility is the world's largest vacuum chamber, measuring 30.5 metres by 37.2 metres, and has a volume of 22,653 cubic metres. 

When not in use, the chamber contains around 30 tonnes of air, but when it's turned on, all but around 2 grams of air are sucked out to create an artificial vacuum. Watch above to see what happens when a bowling ball and feather are dropped in the chamber under 'normal' conditions and then in a vacuum. If it's enough to make even the most seasoned NASA scientist grin with childlike wonder, you know it's gotta be good.

Source:  io9

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Watch a Feather and Bowling Ball Fall At the Same Speed

Gravity - air = video gold.

Over 400 years ago, the story goes, Galileo stood atop the Leaning Tower of Pisa and dropped two balls of different masses over the edge. As we all know, both balls smacked the ground at the same time, proving that gravity affects objects’ acceleration regardless of mass. (Though whether that was a real experiment or merely a thought experiment is  still debated .)

Regardless, it’s a great, memorable visual. But be prepared to replace it with an even better one.

To demonstrate the effects of air — not gravity — on falling objects, physicist Brian Cox of the  BBC Two  program  Human Universe   visited the largest vacuum chamber in the world: NASA’s Space Power Facility in Ohio.

In this video, you see Galileo’s centuries-old concept illustrated quite dramatically. A bowling ball and a feather both fall at the same speed when all the air has been removed from the massive chamber.

Read more : 20 Things You Didn’t Know About Gravity

Yeah, it makes sense, but it’s still surreal to see a massive bowling ball and a delicate feather fall at an identical speed.

Although the demonstration is certainly impressive here on Earth, let’s not forget Apollo 15 astronaut David Scott’s rendition of the famous experiment — from the moon. Both a falcon feather and a hammer fall at the same speed, but without the encumbrance of a massive vacuum chamber.

Gravity: it has a certain pull on the human curiosity.

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Science project, do heavier objects fall faster gravity in a vacuum.

Do heavier objects fall faster? Newton observed the infamous apple falling from a tree, and drew important conclusions about the behavior of everyday objects under the force of gravity. In the case of a feather and a coin, one would believe that a feather will always fall more slowly to the ground, and the coin faster. However, as we will explore below, heavier objects do not always fall to the ground more quickly than lighter objects do! When dropped from the same height, objects fall to the earth at the same time when there is no major amount of air mass acting on them. Let’s discover why this is!

First, some background info: Mass, the quantity of matter an object contains, is (typically) constant in an object and does not change. In comparison, weight is the measurement of gravitational force being acted upon a particular object. Think about it this way: The mass of your body is the same on earth as it would be on the Moon, while your weight on earth would be much heavier here because the earth’s gravity is much stronger than the moon’s. This experiment aims to remove the variable of air mass acting on objects so we can measure the effect of gravitational acceleration produced by the earth’s gravity.

• 1 vacuum pump with tube and end caps (available at scientific supply stores)
• Assemble vacuum pump but do not turn it on.
• Leaving the pump lying horizontal, place a feather and a coin in top end of the pump.
• Turn the pump vertically and record your observations.
• Return the feather and the coin to the top of the vacuum pump.
• Seal both ends of the vacuum pump. Turn the pump on to remove the air.
• Now, turn the pump vertically and record your observations.

Observations & Results

The vacuum created an airless chamber for both items to fall freely. You should have noticed that the second time you dropped the feather and the coin, they both fell together at the same speed.

Gravitational acceleration was constant both times you dropped the items. The only difference from one trial to the next was the presence of air mass acting upon the feather: because the feather is an object of low density (it has a low ratio of mass to volume), the feather encounters more drag as it falls through the air. By removing most of the air, the feather should fall the same speed as the denser penny.

This experiment shows us that weight does not determine the rate at which something falls—only air resistance does. Try other things in the tube: a paper clip and a cotton ball, a crayon and a small leaf. Disregarding air resistance, can you believe a piano and pea would hit the ground at the same time if dropped from the same height? You bet!

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Gravity Experiments for Kids

July 5, 2021 By Emma Vanstone Leave a Comment

These gravity experiments are all fantastic demonstrations of gravity and a great way to learn about Isaac Newton and Galileo ‘s famous discoveries. If you enjoy them, do check our my book This IS Rocket Science which is full of exciting space activities demonstrating how rockets overcome gravity and other forces to launch into space followed by a tour of the solar system with an activity for each planet.

What is Gravity?

Gravity is the force that pulls objects towards the Earth. It’s the reason we walk on the ground rather than float around.

Gravity also holds Earth and the other planets in their orbits around the Sun.

Did you know – gravity exists on the Moon but it is not as strong as on Earth, which is why astronauts can jump higher on the Moon than on Earth. This article from ScienceAlert tells you how high you could jump on each planet in the Solar System compared to Earth.

Great Gravity Experiments for Kids

Galileo and gravity.

Galileo was a famous scientist in the 16th and 17th Century. His most famous observation was that two objects of the same size but slightly different mass (how much “stuff” it is made of) hit the ground at the same time, as far as he could tell, if they are dropped from the same height. This happens because the acceleration due to gravity is the same for both objects and that actually this acceleration has nothing to do with the mass of an object. This fact has been demonstrated many times, even on the moon with a feather and a hammer.

Back on our air-filled planet, if a feather and a ball are dropped from the same height they clearly do fall at different rates. This is because gravity is not the only force acting on the falling object, air resistance is also a factor and that does depend on quite a few properties of the object and the fluid it is falling in. This does include its mass, the surface area and how fast it is moving. The feather suffers a lot here being so light and having a much greater surface area.

Galileo dropped two balls of different weights but the same size off the Leaning Tower of Pisa, giving a hint that the mass of an object doesn’t affect how fast it falls.

However if a ball and feather are dropped in a vacuum , where there is no air resistance as there’s no air, the ball and feather will fall together and hit the ground at the same time.

Bottle Drop Experiment

Following on from the ball and feather experiment another great example of Galileo’s discovery is to half fill one plastic bottle and leave another ( the same size ) empty. If dropped from the same height they will hit the ground at the same time!

Issac Newton and Gravity

According to legend Issac Newton was sitting under an apple tree when an apple fell on his head, which made him wonder why if fell to the ground.

Newton published the Theory of Universal Gravitation in the 1680s, setting out the idea that gravity was a force acting on all matter. His theory of gravity and laws of motion are some of the most important discoveries in science and have shaped modern physics.

Film Canister Rocket

A film canister rocket is a fantastic demonstration of all three of Newton’s Laws of Motion , but it falls back to the ground thanks to gravity.

Water powered bottle rockets are another great fun example of gravity and lots of other forces too!

Defy gravity with a magnet

Did you know you can defy gravity using magnets. We love this activity as you can theme it however you want. Your floating object could be a spaceship in space, a flower growing towards the sun or even a plane in the sky.

The magnet holds the paperclip in the air as if it’s floating!

Straw Rockets – Gravity Experiment

Create your own straw rockets and launch at different angles to investigate how the trajectory changes. Of course these don’t have to be rockets, they could be anything you want, so get creative!

Parachutes are another great gravity experiment and perfect for learning about air resistance too!

Marble Runs

A DIY marble run is another hands on way to demonstrate gravity. Can you build one where the ball has enough energy to move uphill?

DIY Sling Shot

Finally, a simple slingshot is a brilliant and simple STEM project and perfect for learning about gravity as a shower of pom poms fall to the ground!

Last Updated on May 25, 2022 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

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Falling Feather

In a famous demonstration, Galileo supposedly dropped a heavy weight and a light weight from the top of the Leaning Tower of Pisa to show that both weights fall at the same acceleration. However, this rule is true only if there is no air resistance. This demonstration lets you repeat Galileo's experiment in a vacuum.

Note: While Snacks were originally conceived to require only low-cost materials, a few Snacks—such as this one—require materials that are notably costly (but there is a reasonable chance these materials might be found in a middle- or high-school classroom). If your school has such items, then this Snack may be appropriate. If not, its usefulness may depend on your ability to obtain or improvise suitable substitutes.

• Three feet (three meters) or more of clear, plastic, rigid-walled tube (available at your local plastics store) with an inner diameter of at least 1 inch (2.5 cm)
• Two solid rubber stoppers—one with a hole through it, one without—to fit in the ends of the plastic tube
• Copper tubing about 4 in (10 cm) long that fits tightly in the hole in the rubber stopper (glass tubing can be used—just be especially careful so it doesn't break)
• About six feet (180 cm) of thick-walled, flexible plastic or rubber vacuum tubing
• A feather or a small piece of paper
• Vacuum pump (use a regular lab vacuum pump if available; if not, use a small hand pump such as Mityvac®)
• 2 hose clamps
• A partner (preferably an adult)
• Insert the solid rubber stopper (the one without the hole) firmly into one end of the plastic tube. Turn the tube so the stopper is on the bottom.
• Put the coin and the feather (or piece of paper) in the tube.
• Push the copper tube through the one-hole stopper and firmly insert the stopper into the open end of the plastic tube.
• Push the vacuum tubing over the copper tube and secure it with a hose clamp, if needed. Attach the other end of the vacuum tubing to the pump; again, use a hose clamp if needed.
• The final assembly should look like the diagram below (click to enlarge).

Invert the tube and let the objects fall. Notice that the feather falls much more slowly than the coin.

Now pump the air out of the tube and invert it again (the pump can remain attached while you invert the tube). Notice that the feather falls much more rapidly than before—in fact, it falls almost as fast as the coin.

Let the air back into the tube and repeat the experiment. (Try to avoid rubbing the wall of the tube; otherwise, static electricity may make the feather stick to it.)

Galileo predicted that heavy objects and light objects would fall at the same rate. The reason for this is simple. Suppose the coin has 50 times as much mass as the feather. This means that the earth pulls 50 times as hard on the coin as it does on the feather. You might think this would cause the coin to fall faster. But because of the coin's greater mass, it's also much harder to accelerate the coin than the feather—50 times harder, in fact! The two effects exactly cancel out, and the two objects therefore fall with the same acceleration.

This rule holds true only if gravity is the only force acting on the two objects. But if the objects fall through air, then air resistance must also be taken into account.

Larger objects experience more air resistance than smaller objects. Also, the faster an object falls, the more air resistance it encounters. When the retarding force of the air just balances the downward pull of gravity, the object will no longer gain speed; it will have reached what is called its terminal velocity .

Since the feather is so much lighter than the coin, the air resistance on it very quickly builds up to equal the pull of gravity. After that, the feather gains no more speed, but just drifts slowly downward. The heavier coin, meanwhile, must fall much longer before it gathers enough speed so that air resistance will balance the gravitational force on it. The coin quickly pulls away from the feather.

The terminal velocity of a human being falling through the air with arms and legs outstretched is about 120 miles per hour (192 kilometers per hour)—slower than a lead balloon, but a good deal faster than a feather!

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Science News

Galileo’s famous gravity experiment holds up, even with individual atoms.

Different types of atoms fall with the same acceleration due to gravity

Individual atoms fall at the same rate due to gravity, scientists report, reaffirming a concept called the equivalence principle.

vchal/iStock/Getty Images Plus

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By Emily Conover

October 28, 2020 at 6:00 am

According to legend, Galileo dropped weights off of the Leaning Tower of Pisa, showing that gravity causes objects of different masses to fall with the same acceleration. In recent years, researchers have taken to replicating this test in a way that the Italian scientist probably never envisioned — by dropping atoms.

A new study describes the most sensitive atom-drop test so far and shows that Galileo’s gravity experiment still holds up — even for individual atoms. Two different types of atoms had the same acceleration within about a part per trillion, or 0.0000000001 percent, physicists report in a paper in press in Physical Review Letters .

Compared with a previous atom-drop test, the new research is a thousand times as sensitive. “It represents a leap forward,” says physicist Guglielmo Tino of the University of Florence, who was not involved with the new study.

Researchers compared rubidium atoms of two different isotopes, atoms that contain different numbers of neutrons in their nuclei. The team launched clouds of these atoms about 8.6 meters high in a tube under vacuum. As the atoms rose and fell, both varieties accelerated at essentially the same rate, the researchers found.

In confirming Galileo’s gravity experiment yet again, the result upholds the equivalence principle, a foundation of Albert Einstein’s theory of gravity, general relativity. That principle states that an object’s inertial mass, which determines how much it accelerates when force is applied, is equivalent to its gravitational mass, which determines how strong a gravitational force it feels. The upshot: An object’s acceleration under gravity doesn’t depend on its mass or composition.

So far, the equivalence principle has withstood all tests. But atoms, which are subject to the strange laws of quantum mechanics, could reveal its weak points. “When you do the test with atoms … you’re testing the equivalence principle and stressing it in new ways,” says physicist Mark Kasevich of Stanford University.

Kasevich and colleagues studied the tiny particles using atom interferometry, which takes advantage of quantum mechanics to make extremely precise measurements. During the atoms’ flight, the scientists put the atoms in a state called a quantum superposition, in which particles don’t have one definite location. Instead, each atom existed in a superposition of two locations, separated by up to seven centimeters. When the atoms’ two locations were brought back together, the atoms interfered with themselves in a way that precisely revealed their relative acceleration.

Many scientists think that the equivalence principle will eventually falter. “We have reasonable expectations that our current theories … are not the end of the story,” says physicist Magdalena Zych of the University of Queensland in Brisbane, Australia, who was not involved with the research. That’s because quantum mechanics — the branch of physics that describes the counterintuitive physics of the very small — doesn’t mesh well with general relativity, leading scientists on a hunt for a theory of quantum gravity that could unite these ideas. Many scientists suspect that the new theory will violate the equivalence principle by an amount too small to have been detected with tests performed thus far.

But physicists hope to improve such atom-based tests in the future, for example by performing them in space, where objects can free-fall for extended periods of time. An equivalence principle test in space has already been performed with metal cylinders , but not yet with atoms ( SN: 12/4/17 ).

So there’s still a chance to prove Galileo wrong.

More Stories from Science News on Quantum Physics

Physicists measured Earth’s rotation using quantum entanglement

Scientists propose a hunt for never-before-seen ‘tauonium’ atoms 

Two real-world tests of quantum memories bring a quantum internet closer to reality

The neutrino’s quantum fuzziness is beginning to come into focus

A maverick physicist is building a case for scrapping quantum gravity

The development of quantum dots wins the 2023 Nobel prize in chemistry

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Quantum computers could break the internet. Here’s how to save it

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Gravity Falling Experiment: Feather in a Vacuum!

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UCSC Physics Demonstration Room

Demonstration Resources for UCSC

Ball and Foil – Free fall in a vacuum

Description:

This apparatus simultaneously drops a ball and a square of aluminum foil into an evacuated cylinder to demonstrate the independence of mass and gravitational acceleration. It is a good idea to drop the ball and foil by hand in front of the audience and then follow this procedure.

Materials :

• Plexiglass cylinder with copper coils at the top (Figure 1)
•  Vacuum with tube (Figure 4)
• Cap with valve (Figure 2)
• 9V Battery (Figure 3)
• 2x battery leads with alligator clips (red/black) (Figure 4)
• 1x Magnetic ball, 1x paper clip, and aluminum foil
• Clamp stand for cylinder

• Connect the battery leads to the 9v battery attached to the tube to allow a current through the coils, thus creating a magnetic field.
• Lift the cap off of the cylinder and place the ball and foil onto the magnetic holders at the top of the tube. The foil can be held onto the magnet using a paper clip.
• Gently press the cap into top of the cylinder, and connect the vacuum to the valve via the tube provided, making sure the valve is open.
• To evacuate the cylinder, turn on the vacuum and wait till the pressure gauge has maximized (Usually around 27 inHg). Then, shut the valve and turn off the vacuum.
• To release the ball and foil, unclip one of the leads from the battery so that the coil is no longer magnetized. The two objects should fall at the same rate.
• To retrieve the ball and foil, release the valve gradually to let air in, then remove the cap. One can either remove the cylinder from the clamp and flip it upside down, or feed a string with a magnet towards the bottom of the tube and lift the objects out.

Explanation:

We can explain why in the vacuum the ball and the piece of foil fall at the same acceleration by using Newton’s second law of motion, F = ma. Here we need to distinguish between two quantities, the acceleration due to gravity, which is constant (mostly, at sea level); and the force acting on the object due to gravity. We will show that the forces due to gravity are different with math, but you can also tell for yourself with a simple experiment.

If we hold a piece of foil in our hand, it requires less force to hold it in equilibrium. Remember that to hold an object in equilibrium, the forces must be balanced. You can then tell the relative force of gravity just by seeing what force is required to keep it still (how heavy it is!). A plastic ball with a magnet within has a greater force due to gravity, and you have to exert more force to keep it in equilibrium with your hand (it weighs more). The differences in the force due to gravity are because the masses are different, and according to F = ma, a greater mass leads to a greater force. Take a 1kg brick and a 1 gram feather under the acceleration of gravity (9.8 m/s2). FgB is the force of gravity acting on the brick, and FgF is the force of gravity acting on the feather.

FgB = mB a = (1kg)(9.8m/s2) = 9.8 N FgF = mF a = (0.001 kg)(9.8m/s2) = 0.0098 N

This shows us that the gravitational force acting on each object is different, but the force of gravity is not the only thing governing the motions of objects in free fall. Inertia plays an equally important part.

Inertia can be explained by Newton’s first law of motion: an object at rest will stay at rest unless acted on by an external force; an object in motion will continue in motion at constant speed and direction unless acted on by an external force. The greater mass an object has, the greater its tendency to resist a force acting on it. You can see this with another simple experiment: place two bricks, one of cement and the other of styrofoam on a table and push them. The styrofoam brick will begin to move with a much smaller force than is needed to move the cement brick. This shows how mass affects inertia.*

This concept of inertia is displayed in the vacuum tube, and explains why even though the ball has a greater force of gravity acting on it compared to the foil, they fall with the same acceleration. Because the foil is lighter than the ball, it has less inertia and therefore has a smaller tendency to oppose a change in motion. This means that less force is required to start moving it. Conversely, because the ball is heavier than the foil, it has a greater tendency to oppose any force applied to it, and it needs a greater force to begin moving from rest. This means that a ball and foil will fall with the same acceleration because they are opposing the change in motion (from rest to falling with gravity) to different degrees, proportional to their masses. The small Fg on the foil is enough to start it moving, where the ball needs a substantially larger Fg to get it moving.

Now it is obvious to wonder why the vacuum tube is necessary to demonstrate this property of objects. All objects that fall in the atmosphere are affected to a certain degree by the force of air resistance, which opposes all direction of motion. The vacuum tube creates a vacuum so there is no air for air resistance to play a part. The two most important contributing factors to air resistance are the cross-sectional area of the object and the speed of the object. An increase in either of these will lead to an increase in the air resistance acting to oppose the direction of motion.

Terminal velocity is the speed at which an object is falling such that the force of air resistance (FAR) opposing the direction of motion is equal to the force of gravity acting on an object. Because at this point the forces are balanced, the object will stop accelerating and will maintain a constant velocity (VT). For a more massive object which has a greater Fg, it will require a greater FAR to balance the forces to stop the object from accelerating. Because air resistance is proportional to velocity, it will need to accelerate to a greater velocity to achieve the FAR necessary to balance the forces. Equally, for a light object, there is a very small Fg. This means that there will need to be a very small FAR acting in the opposite direction to stop the acceleration. A small air resistance force can be achieved at very low speeds (especially if there is a large cross-sectional area), so it will reach terminal velocity shortly after it begins accelerating. This is shown in the following image with the example of an elephant and a feather.

Notes: Works well but can only be seen from the first few rows without a video camera Works best at max vacuum pressure (27-30 inHg on gauge)

Written by Sophia Sholtz

College of Liberal Arts & Sciences

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Instructional Resources and Lecture Demonstrations

1c20.10 - free-fall in a vacuum (penny and feather demo).

The vacuum tube may have to be taken apart for cleaning.  Check the oil in the vacuum pump and maintain at the proper level.  Using the triangular variable wedge will help insure that the tube will not roll off the table.

A small ball of cotton may be substituted for the feather.

A way to do this without the vacuum system is to take a large text book and place a piece of paper directly on top of it.  When this is dropped the paper will drop at the same speed as the textbook and stay directly on top of the book.

• Hollis Williams, "A High-Speed Test of the Equivalence Principle", TPT, Vol. 60, #7, Oct. 2022, p. 594.
• Elida de Obaldia, Norma Miller, Fred Wittel, George Jaimison, and Kendra Wallis, "Bridging the Conceptual Gap Between Free Fall and Drag-Dominated Regimes", TPT, Vol. 54, #4, Apr. 2016, p. 233.
• Christopher L. Vaughan and Moshe Nissan, "Teaching Mechanics with a Digital Camera", TPT, Vol. 25, #7, Oct. 1987, p. 445.
• "M-088: Coin and Feather in Tube", DICK and RAE Physics Demo Notebook.
• George M. Hopkins, "Falling Bodies--Inclined Plane--The Pendulum", Experimental Science, p. 38.
• Julien Clinton Sprott, "1.1, Guinea and Feather Tube", Physics Demonstrations, ISBN 0-299-21580-6, p. 2.
• John Henry Pepper and Henry George Hine, "Gravitation", The Boy's Playbook of Science, p. 14.
• "The Paradox of the Falling Bodies", The Boy Scientist.
• Ron Hipschman, "Falling Feather", Exploratorium Cookbook III, p. 137-1.
• "Falling Feather", The Exploratorium Science Snackbook, p. 50-1.
• Christopher P. Jargodzki and Franklin Potter, "397. Was Galileo Right?", Mad About Physics, p. 154, 297.
• Borislaw Bilash II and David Maiullo, "Falling Together", A Demo a Day: A Year of Physics Demonstrations, p. 27.
• "This Month in Physics History", APS News, Vol. 26, #2, Feb. 2017, p. 2 - 3.
• Borislaw Bilash II, “Falling Together“, A Demo A Day – A Year of Physical Science Demonstrations, p. 238.
• "Guinea and Feather Tube", Pike's Illustrated Catalogue of Scientific & Medical Instruments, 1984, p. 207.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.

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Bowling ball and feathers dropped at same time in giant vacuum chamber

Which will hit the ground first when you drop them together from the same height: a bowling ball, or a feather? Now suck out all the air in the room, and turn on a high-speed camera and watch the astonishing result below.

Tap to view if on News app.

BBC's Brian Cox brought the old high school experiment to NASA's Space Power Facility, used to test spacecraft in a giant vacuum chamber meant to resemble the conditions of outer space. By removing all the air out of the room, we'd finally be able to see how gravitation truly effects objects without any interference.

The video takes Galileo's famous experiment to a new level, where both heavy and light objects are dropped at the same time to see which will hit the ground faster. Spoiler: the answer is that they will all fall at the exact same rate. Though some objects, like feathers, seem to fall slower because of air resistance. In order to see the true nature of gravity effecting the feathers, you need to remove all the air in the room.

By employing high-speed cameras to capture every fraction of a second, there is no denying the result.

After the chamber is made into a complete vacuum, the bowling ball and feathers are released, falling gracefully to the ground with neither accelerating father than the other. The objects both stay in unison as they descend more than 30 feet, smashing into the wooden crate below at the exact same time, all in beautiful slow-motion.

The findings produced by the original experiments made by Galileo and Sir Isaac Newton lead to the theory of gravitation, though also became the foundation of Albert Einstein's theory of relativity.

In explaining Einstein's theory, Cox said, "The reason the bowling ball and the feather fall together is because they're not falling. They are standing still. There is no force acting on them at all."

"(Einstein) reasoned that if you couldn't see the background, there would be no of knowing that the ball and the feathers were accelerating toward the Earth."

Now try wrapping your head around that.

What two objects should they drop together next? Let us know in the comments below.

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Brian Cox’s Galileo experiment is mind-blowing (video)

by Gordon Hunt

Still of Brian Cox on BBC

BBC presenter Brian Cox’s gravity experiment a few days ago was spectacular.

Cox , a physicist and former musician, went to America, to NASA’s Space Power Facility (SPF), to observe the gravitational force applied when dropping a bowling ball, and a feather, from a height.

Near Cleveland, Ohio, NASA’s SPF  is the world’s biggest vacuum chamber. It’s used to test spacecraft in the conditions of outer space, doing so by pumping out the 30 tonnes of air in the chamber, until there’s just two grammes left.

According to Galileo Galilei’s discovery, in vacuum, if two objects were dropped from the same height, they would fall on the surface at exactly the same time. The theory states that the weight of the objects should not affect the experiment.

Before the vacuum took place, Cox released the bowling ball and feather from a significant height in the chamber, explaining how both objects, according to the laws of gravity, should drop at the same speed.

“Galileo’s experiment was simple: He took a heavy object and a light one and dropped them at the same time to see which fell fastest,” explains Cox as the objects are released.

What happened, rather more predictably, was the bowling ball travelling at a far higher velocity – the wind resistance on the feather was too great, slowing it down significantly.

The scientists at the SPA then spent three hours pumping the air out of the facility, setting up new conditions to test the drop in.

This time, both the feather and the bowling ball fell at the exact same rate, not a flicker in the feather, just straight down like a dart, hitting the ground at the same time – gravity at work in its purest sense.

But Cox then spoke of Albert Einstein’s “happiest thought”.

“The reason the bowling ball and the feather fall together is because they’re not falling. They’re standing still,” he says.

“There’s no force acting on them at all. He reasoned that, if you couldn’t see the background, there would be know way of knowing that the objects were accelerating to the earth. So he concluded… that they weren’t.”

Mind successfully blown.

Related: electronics

Gordon Hunt was a journalist with Silicon Republic

[email protected]

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How does gravity overpower a vacuum?

While watching experiments with vacuum chambers, I had a thought.

If you put a sealed box at normal atmospheric pressure inside a vacuum chamber, pumped out the air and pierced the pressurized box I'd feel confident predicting the pressurized air would push out into the vacuum chamber, seeking equalization.

I would further predict that the above would be true no matter where precisely the piercing was located on the box - bottom or top.

If the box was pierced on the top side, the air would push out against the force of gravity.

So, my question is: If gravity can't overcome the equalization pressure of a relatively weak vacuum at sea level gravity, how does gravity hold on to Earth's atmosphere up on the fringes of space where it is weaker and against a far more powerful vacuum?

• atmospheric-science

• 9 $\begingroup$ Gravity at the fringes of space is still pretty strong. Eg, at 100 km the acceleration is ~96.9% of g at sea level. sagecell.sagemath.org/… $\endgroup$ –  PM 2Ring Commented Jun 14 at 4:59
• 15 $\begingroup$ Size matters. If your sealed box were several hundreds of kilometers tall, and standing on the surface of the Earth, then I think you would find that the gas pressure was not the same everywhere inside of it. $\endgroup$ –  Solomon Slow Commented Jun 14 at 10:01
• 3 $\begingroup$ The atmosphere is not a pressurised container. It's a smooth gradient all the way out. $\endgroup$ –  OrangeDog Commented Jun 14 at 13:56
• 1 $\begingroup$ Vacuums don't have power so it's meaningless to talk about 'overpowering' a vacuum. $\endgroup$ –  JimmyJames Commented Jun 14 at 16:34
• 2 $\begingroup$ "A more powerful vacuum" is cute ;-). $\endgroup$ –  Peter - Reinstate Monica Commented Jun 14 at 16:47

3 Answers 3

The escape velocity of the Earth is 11.2 km/s . In other words, you need to move faster than 11.2 km/s to leave the Earth permanently. The Earth's gravity is strong enough to attract everything moving slower back to Earth.

Meanwhile, the speed of an air molecule depends on 1) what type the molecule it is, heavier molecules move slower and 2) the temperature. If you work through that, then you find that an order of magnitude estimate for oxygen and nitrogen (which make up most of air) is about 300 to 400 m/s. This is obviously much slower than 11.2 km/s, and hence they do not escape to the fringes of space.

The experiment you describe is not relevant; in particular you seem to assume that the vacuum in your vacuum chamber is "relatively weak" while the vacuum in space is "far more powerful". That's not wrong , but it's not precise. What causes air to flow into your vacuum chamber is the pressure difference. If the vacuum in your vacuum chamber has pressure 3 kilopascals, while the vacuum in outer space has pressure 100 micropascals , then you can indeed say that outer space is a much-better vacuum, but that's not what is important, what matters is the pressure difference. The difference in pressure is $101 kPa - 3 kPa$ (where $101 kPa$ is the atmospheric pressure) in one case and $101 kPa - 100 \mu Pa$ in the other, and the difference between those two is not that big.

• 1 $\begingroup$ While what you say is true but you mix two ways of looking at things: The single-molecule way and the "gas is a continuum with pressure" way. "What causes air [molecules] to flow into your vacuum chamber" is that there are not enough molecules colliding with them on the way out, or even flying in the opposite direction. $\endgroup$ –  Peter - Reinstate Monica Commented Jun 14 at 16:51
• 5 $\begingroup$ You don't need to move 11.2km/s to escape Earth's gravity. You could escape if you moved at .001mph as long as your acceleration was constant . Escape velocity means "moving that fast to begin with" $\endgroup$ –  Richard Commented Jun 14 at 19:36
• $\begingroup$ @Richard But once you are realistically past the top of the atmosphere there's nothing to push off of. Thus you need to be moving 11.2km/sec to escape. $\endgroup$ –  Loren Pechtel Commented Jun 15 at 22:23

In addition, there is no point in the atmosphere where there is sudden "pressure to vacuum", like your question suggests. Pressure is the highest at sea level, and drops as we move higher, so that at the highest points the pressure is the same as it is in space.

how does gravity hold on to Earth's atmosphere up on the fringes of space where it is weaker and against a far more powerful vacuum

Note that at sea level, pressure is a lot higher than it is in the upper atmosphere/space. At sea level, if you put air in a small parcel and placed it in a partial vacuum, because of the large pressure difference, it will push on the insides of the parcel trying to escape into the vacuum. How hard it pushes depends on the difference in pressure. As we approach the highest points in the atmosphere, this pressure difference becomes zero.

There is no "far more powerful vacuum"; just no more pressure differential.

• 17 $\begingroup$ Slight correction, the pressure doesnt decrease because the decrease in gravity (it doesnt change a whole lot as you go higher in the atmosphere), but because there is less air above it pushing down, the same as how hydrostatic pressure works. $\endgroup$ –  JMac Commented Jun 14 at 11:39
• 3 $\begingroup$ What JMac said. The variation in g is pretty small. The variation in temperature is much more important. But the main factor is simply the weight of atmosphere at any given height. See en.wikipedia.org/wiki/Scale_height $\endgroup$ –  PM 2Ring Commented Jun 14 at 14:11
• 2 $\begingroup$ Indeed, you'd still have decreasing pressure with height even if the force of gravity increased as you went higher. Any type of gravity gradient will make the air want to move downward, and since there isn't an infinite amount of air, the atmosphere has to end somewhere in a vacuum with 0 pressure. $\endgroup$ –  Nuclear Hoagie Commented Jun 14 at 17:23
• $\begingroup$ @JMac ...Noted. $\endgroup$ –  joseph h Commented Jun 14 at 21:27

I think you are making a common error when thinking about vacuums. We tend to intuitively to think about vacuums as 'pulling' but that's not really the right way to think about it and while it seems like a workable model in certain circumstances, thinking about vacuums as generating a force will definitely lead you astray. Note that we are not talking about ' vacuum energy '. That isn't relevant to the question at hand.

I think one of the more relatable ways to think about this is drinking through a straw. The intuitive way I think most people think about this is that you 'suck' on the straw and that pulls the drink into your mouth. But that's not really how it works. What happens is that you are reducing the pressure in your mouth below that of the atmosphere. This creates a pressure differential and the atmosphere 'pushes' the drink up the straw.

Centuries ago, there was a great mystery around pumps . No matter how powerful a vacuum pump or suction pump was, no one could get them to pump water higher than a little over 10 meters. Even Galileo wasn't able to figure out. The answer requires understanding that the vacuum doesn't apply any force. It's the weight of the air that pushes the water up. There's only so much air above us and that's the reason for the limit. To pump water higher than that, you increase the pressure pushing the water upwards.

Going back to the straw example, imagine some sort of setup where there is a drink is inside a vacuum chamber with a tube that extends out of the drink. If you try to suck the drink up, it won't work. There's nothing pushing the drink up the tube.

The last thing to point out here is that, as mentioned above, it's the weight of the air in the atmosphere that creates the net force on a vacuum pump or drinking straw. Another way to say it is that the weight of the air that creates atmospheric pressure. That is to say, it is gravity that creates air pressure. Gravity is not in opposition to the earth's atmospheric pressure. It's what causes the earth's atmospheric pressure.

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Purdue physicists throw world's smallest disco party - Elmore Family School of Electrical and Computer Engineering - Purdue University

Purdue physicists throw world's smallest disco party

Physicists at Purdue are throwing the world’s smallest disco party.  The disco ball itself is a fluorescent nano diamond, which they have levitated and spun at incredibly high speeds. The fluorescent diamond emits and scatters multicolor lights in different directions as it rotates. The party continues as they study the effects of fast rotation on the spin qubits within their system and are able to observe the Berry phase. The team, led by  Tongcang Li , professor in the Elmore Family School of Electrical and Computer Engineering at Purdue University, published its results in  Nature Communications .  Reviewers of the publication  described this work as “arguably a groundbreaking moment for the study of rotating quantum systems and levitodynamics” and “a new milestone for the levitated optomechanics community.”

“Imagine tiny diamonds floating in an empty space or vacuum. Inside these diamonds, there are spin qubits that scientists can use to make precise measurements and explore the mysterious relationship between quantum mechanics and gravity,” explains Li, who is also a professor in the Department of Physics and Astronomy and a member of the  Purdue Quantum Science and Engineering Institute .  “In the past, experiments with these floating diamonds had trouble in preventing their loss in vacuum and reading out the spin qubits. However, in our work, we successfully levitated a diamond in a high vacuum using a special ion trap. For the first time, we could observe and control the behavior of the spin qubits inside the levitated diamond in high vacuum.”

The team made the diamonds rotate incredibly fast—up to 1.2 billion times per minute! By doing this, they were able to observe how the rotation affected the spin qubits in a unique way known as the Berry phase.

“This breakthrough helps us better understand and study the fascinating world of quantum physics,” he says.

The fluorescent nanodiamonds, with an average diameter of about 750 nm, were produced through high-pressure, high-temperature synthesis. These diamonds were irradiated with high-energy electrons to create nitrogen-vacancy color centers, which host electron spin qubits. When illuminated by a green laser, they emitted red light, which was used to read out their electron spin states.  An additional infrared laser was shone at the levitated nanodiamond to monitor its rotation. Like a disco ball, as the nanodiamond rotated, the direction of the scattered infrared light changed, carrying the rotation information of the nanodiamond.

The authors of this paper were mostly from Purdue University and are members of Li’s research group: Yuanbin Jin (postdoc), Kunhong Shen (PhD student), Xingyu Gao (PhD student) and Peng Ju (recent PhD graduate). Li, Jin, Shen, and Ju conceived and designed the project and Jin and Shen built the setup. Jin subsequently performed measurements and calculations and the team collectively discussed the results. Two non-Purdue authors are Alejandro Grine, principal member of technical staff at Sandia National Laboratories, and Chong Zu, assistant professor at Washington University in St. Louis. Li’s team discussed the experiment results with Grine and Zu who provided suggestions for improvement of the experiment and manuscript.

“For the design of our integrated surface ion trap,” explains Jin, “we used a commercial software, COMSOL Multiphysics, to perform 3D simulations. We calculate the trapping position and the microwave transmittance using different parameters to optimize the design. We added extra electrodes to conveniently control the motion of a levitated diamond. And for fabrication, the surface ion trap is fabricated on a sapphire wafer using photolithography. A 300-nm-thick gold layer is deposited on the sapphire wafer to create the electrodes of the surface ion trap.”

So which way are the diamonds spinning and can they be speed or direction manipulated? Shen says yes, they can adjust the spin direction and levitation.

“We can adjust the driving voltage to change the spinning direction,” he explains. “The levitated diamond can rotate around the z-axis (which is perpendicular to the surface of the ion trap), shown in the schematic, either clockwise or counterclockwise, depending on our driving signal. If we don’t apply the driving signal, the diamond will spin omnidirectionally, like a ball of yarn.”

Levitated nanodiamonds with embedded spin qubits have been proposed for precision measurements and creating large quantum superpositions to test the limit of quantum mechanics and the quantum nature of gravity.

“General relativity and quantum mechanics are two of the most important scientific breakthroughs in the 20th century. However, we still do not know how gravity might be quantized,” says Li. “Achieving the ability to study quantum gravity experimentally would be a tremendous breakthrough. In addition, rotating diamonds with embedded spin qubits provide a platform to study the coupling between mechanical motion and quantum spins.”

This discovery could have a ripple effect in industrial applications. Li says that levitated micro and nano-scale particles in vacuum can serve as excellent accelerometers and electric field sensors. For example, the US Air Force Research Laboratory (AFRL) are using optically-levitated nanoparticles to develop solutions for critical problems in  navigation and communication .

“At Purdue University, we have state-of-the-art facilities for our research in levitated optomechanics,” says Li. “We have two specialized, home-built systems dedicated to this area of study. Additionally, we have access to the shared facilities at the Birck Nanotechnology Center, which enables us to fabricate and characterize the integrated surface ion trap on campus. We are also fortunate to have talented students and postdocs capable of conducting cutting-edge research. Furthermore, my group has been working in this field for ten years, and our extensive experience has allowed us to make rapid progress.”

This research was supported by the National Science Foundation (grant number PHY-2110591), the Office of Naval Research (grant number N00014-18-1-2371), and the Gordon and Betty Moore Foundation (grant DOI 10.37807/gbmf12259). The project is also partially supported by the Laboratory Directed Research and Development program at Sandia National Laboratories.

Source: Purdue physicists throw world’s smallest disco party

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August 14, 2024

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Physicists throw world's smallest disco party with a levitating ball of fluorescent nanodiamond

by Purdue University

Physicists at Purdue are throwing the world's smallest disco party. The disco ball itself is a fluorescent nanodiamond, which they have levitated and spun at incredibly high speeds. The fluorescent diamond emits and scatters multicolor lights in different directions as it rotates. The party continues as they study the effects of fast rotation on the spin qubits within their system and are able to observe the Berry phase.

The team, led by Tongcang Li, professor of Physics and Astronomy and Electrical and Computer Engineering at Purdue University, published their results in Nature Communications . Reviewers of the publication described this work as "arguably a groundbreaking moment for the study of rotating quantum systems and levitodynamics" and "a new milestone for the levitated optomechanics community."

"Imagine tiny diamonds floating in an empty space or vacuum. Inside these diamonds, there are spin qubits that scientists can use to make precise measurements and explore the mysterious relationship between quantum mechanics and gravity," explains Li, who is also a member of the Purdue Quantum Science and Engineering Institute.

"In the past, experiments with these floating diamonds had trouble in preventing their loss in vacuum and reading out the spin qubits. However, in our work, we successfully levitated a diamond in a high vacuum using a special ion trap. For the first time, we could observe and control the behavior of the spin qubits inside the levitated diamond in high vacuum."

The team made the diamonds rotate incredibly fast—up to 1.2 billion times per minute! By doing this, they were able to observe how the rotation affected the spin qubits in a unique way known as the Berry phase.

"This breakthrough helps us better understand and study the fascinating world of quantum physics," he says.

The fluorescent nanodiamonds, with an average diameter of about 750 nm, were produced through high-pressure, high-temperature synthesis. These diamonds were irradiated with high-energy electrons to create nitrogen-vacancy color centers, which host electron spin qubits.

When illuminated by a green laser, they emitted red light, which was used to read out their electron spin states. An additional infrared laser was shone at the levitated nanodiamond to monitor its rotation. Like a disco ball, as the nanodiamond rotated, the direction of the scattered infrared light changed, carrying the rotation information of the nanodiamond.

The authors of this paper were mostly from Purdue University and are members of Li's research group: Yuanbin Jin (postdoc), Kunhong Shen (Ph.D. student), Xingyu Gao (Ph.D. student) and Peng Ju (recent Ph.D. graduate). Li, Jin, Shen, and Ju conceived and designed the project and Jin and Shen built the setup.

Jin subsequently performed measurements and calculations and the team collectively discussed the results. Two non-Purdue authors are Alejandro Grine, principal member of technical staff at Sandia National Laboratories, and Chong Zu, assistant professor at Washington University in St. Louis. Li's team discussed the experiment results with Grine and Zu who provided suggestions for improvement of the experiment and manuscript.

"For the design of our integrated surface ion trap," explains Jin. "We used a commercial software, COMSOL Multiphysics, to perform 3D simulations. We calculate the trapping position and the microwave transmittance using different parameters to optimize the design. We added extra electrodes to conveniently control the motion of a levitated diamond. And for fabrication, the surface ion trap is fabricated on a sapphire wafer using photolithography. A 300-nm-thick gold layer is deposited on the sapphire wafer to create the electrodes of the surface ion trap."

So which way are the diamonds spinning and can they be speed or direction manipulated? Shen says yes, they can adjust the spin direction and levitation.

"We can adjust the driving voltage to change the spinning direction," he explains. "The levitated diamond can rotate around the z-axis (which is perpendicular to the surface of the ion trap), shown in the schematic, either clockwise or counterclockwise, depending on our driving signal. If we don't apply the driving signal, the diamond will spin omnidirectionally, like a ball of yarn."

Levitated nanodiamonds with embedded spin qubits have been proposed for precision measurements and creating large quantum superpositions to test the limit of quantum mechanics and the quantum nature of gravity.

"General relativity and quantum mechanics are two of the most important scientific breakthroughs in the 20th century. However, we still do not know how gravity might be quantized," says Li. "Achieving the ability to study quantum gravity experimentally would be a tremendous breakthrough. In addition, rotating diamonds with embedded spin qubits provide a platform to study the coupling between mechanical motion and quantum spins."

This discovery could have a ripple effect in industrial applications. Li says that levitated micro and nano-scale particles in vacuum can serve as excellent accelerometers and electric field sensors. For example, the US Air Force Research Laboratory (AFRL) are using optically-levitated nanoparticles to develop solutions for critical problems in navigation and communication .

"At Purdue University, we have state-of-the-art facilities for our research in levitated optomechanics," says Li. "We have two specialized, home-built systems dedicated to this area of study. Additionally, we have access to the shared facilities at the Birck Nanotechnology Center, which enables us to fabricate and characterize the integrated surface ion trap on campus. We are also fortunate to have talented students and postdocs capable of conducting cutting-edge research. Furthermore, my group has been working in this field for ten years, and our extensive experience has allowed us to make rapid progress."

Journal information: Nature Communications

Provided by Purdue University

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The potential of microgravity: How companies across sectors can venture into space

When companies try to differentiate themselves from the pack, the same options emerge: developing innovative products, overhauling portfolios, capturing different customer segments, or opening new locations. Now, in a twist that may startle attendees at routine strategy meetings, they have another possibility: expanding their business into space.

The unique properties of space

In space, research and manufacturing benefits come from a combination of three properties (exhibit):

• Microgravity. Gravity decreases significantly with distance from Earth. As long as objects remain in Earth’s orbit, however, they will not experience zero gravity; they will be in microgravity, a much weaker condition akin to a free fall. Multiple experiments have shown that organic and inorganic matter alter their characteristics in response to gravitational changes. Living cells, for instance, may “sense” decreased gravity though their gravireceptors, specialized receptors and nerve endings, found throughout the body, that influence intracellular metabolism and send the brain information about the body’s position and equilibrium, as well as the direction of gravitational forces. Similarly, inorganic matter will demonstrate a different degree of buoyancy in space because microgravity decreases the importance of weight.
• Radiation. In space, radiation—energy released in the form of particle or electromagnetic waves—can be 15 to 650 times stronger than it is on Earth. 1 According to NASA, people in space are exposed to 50 to 200,000 millisieverts (mSv) over six months, compared with 620 mSv on Earth. The radioactive ions could lead to DNA breaks that cause cell mutations, which may alter morphology, growth rates, and gene expression in living systems.
• A continuous near-vacuum. Space is a partial vacuum, devoid of matter for long stretches and completely airless. The pressure in the lower orbit, where satellites usually operate and the first microgravity experiments are supposed to occur, is vastly lower than the pressure on Earth. The effect of a vacuum on living cells is under investigation, but some early experiments have already shown that it may cause dehydration and increasingly permeable membrane breaks. With inorganic matter, a vacuum may reduce the chance that gases will introduce impurities, as they do on Earth, when two substances combine.

Researchers have found ingenious ways of replicating aspects of space environments on Earth, but the limitations are significant. Take preparations for space walks. Astronauts may train in planes that make sharp climbs and steep dives, allowing them to escape gravity and achieve weightlessness, but the effects persist for only a few seconds.

It may seem far-fetched for any company outside the aerospace or defense sectors to pursue such opportunities, but a growing number of businesses are excited by the potential and are increasingly backing their plans with solid investments. Space offers a unique research and manufacturing environment to a broad range of sectors because of its near-vacuum state, microgravity (which confers weightlessness), and higher levels of radiation. These features may enable new processes or reveal new insights. (For more information, see sidebar “The unique properties of space.”)

Many companies believe that the environment of space could help them discover new products, enhance their current offerings, or decrease development timelines. The number of patents with “microgravity” in the title or abstract soared from 21 in 2000 to 155 in 2020. To obtain greater clarity about the burgeoning opportunities in the space economy, we interviewed more than 20 industry experts and researched potential applications. We focused on four sectors: pharmaceuticals, beauty and personal care, food and nutrients, and semiconductors.

In addition to examining the impact and feasibility of different use cases for space, we also explored value pools and business models. The full impact of any commercial space opportunity is now difficult to estimate, but some exciting discoveries could benefit both businesses and society as a whole. If space-based R&D allows researchers to make breakthroughs in oncology compounds, for instance, the insights could save millions of lives.

A few caveats

In space, as in any nascent sector, the revenues from commercial growth opportunities are still uncertain. For this reason, a few caveats are necessary as companies contemplate next steps and potential partnerships with space companies.

First, cost is an issue. Before embarking on promising opportunities, researchers must determine if they could get the same insights in their terrestrial labs, which are less expensive to build and operate. It may be necessary to repeat these assessments periodically because scientific and technological advances may improve the accuracy and value of Earth-based experiments over time.

The next caveat relates to timelines. During our feasibility assessment, we did not estimate precisely when commercial opportunities might become possible, because so many constantly changing factors will influence the space economy. Launch costs are decreasing, for instance, but they must drop even further to allow most companies to take advantage of space-based R&D and manufacturing.

Would you like to learn more about our Aerospace & Defense Practice ?

Finally, for any endeavor to succeed, traditional businesses and space companies must focus on forming close, mutually beneficial relationships. The space company must be fully integrated into the industry’s ecosystem rather than a distant partner that provides occasional advice. If companies do not forge these strong ties, their space applications are likely to progress slowly.

Beyond the factors that could slow progress, it is important to note caveats related to the potential value of space use cases. We have analyzed current R&D spending and other factors to predict value, but the estimates are always subject to change.

The potential for real business impact, from faster drug evaluation to greater innovation with semiconductors

An assessment of commercial opportunities in space: our methodology.

When we looked at commercial opportunities in space, we evaluated three factors:

• Impact. This included the potential market for companies across industries, including the likelihood that companies would invest in space and the potential social and environmental benefits of space-based R&D, such as the ability to reduce waste.
• Value creation and business models. Our focus here was on pathways for creating and capturing value, as well as potential partnerships with space companies.
• Feasibility. This assessment considered basic issues, such as whether a suitable environment for manufacturing or R&D could exist in space, the essential technologies, the required skills and resources, and regulatory and safety standards.

We did not estimate when commercial opportunities might become possible, because so many factors will influence timelines. The experts we interviewed believe they may overcome obstacles if enough companies invest in solutions. Overall, we believe that most use cases will become viable and mature in the late 2020s, although later developments might alter this view.

In our industries of focus, we pinpointed several promising opportunities after assessing three factors: the holistic impact, the feasibility, and the value creation possibilities and business models. (For more information, see sidebar “An assessment of commercial opportunities in space: Our methodology.”) If even one opportunity pans out, it could create a virtuous cycle in which more businesses begin exploring similar applications.

Our early analysis suggests that the opportunities in our chosen industries could potentially capture billions of dollars in value (exhibit). Here are a few possible applications in pharmaceuticals, beauty and personal care, food and nutrients, and semiconductors.

Pharmaceuticals

The pharmaceutical industry spends about $280 billion annually on R&D and $80 billion on work with contract research organizations (CROs)—businesses that specialize in conducting clinical trials. Space companies may eventually capture some of this funding if they can increase the returns from innovation, improve the success rates for compounds in development, or cut product development timelines. Consider a few potential use cases:

• Cell cultures for predicting disease models. These cultures develop in well-known patterns on Earth, but the novel environment in space would shift growth patterns and reveal new insights. Such variations, which scientists are still attempting to identify and understand, might depend on the cell involved. Similarly, space radiation might change gene expression and growth patterns, which could yield new insights.
• Organoids. These miniaturized and simplified versions of organs resemble living human tissues and can be used as 3-D models to evaluate disease. Scientists now create organoids in labs through a lengthy, resource-intensive process that requires complex scaffolds to promote 3-D growth. But in a few recent collaborations between academic institutions and space organizations, scientists grew organoids from embryoid bodies to greater maturity levels, without scaffolds, during unattended missions in orbit. Other potential benefits of space-based R&D in organoid production are still largely theoretical, but exciting. For instance, scientists have hypothesized that the environment of space might enable the production of organoids from specific adult stem cells—something not possible today.
• Direct drug research. To understand the benefits of this use case, consider oncology drugs, now the industry’s largest product group. Many of these compounds fail in development, so the risk–return ratio is very poor. If companies explore new R&D methods for developing oncology drugs in space, they might achieve breakthroughs that would increase their success rates, accelerate product development cycles, identify new targets for potential drugs, or differentiate their candidates from existing products. Our early analysis suggests that companies that develop one novel oncology drug through space-based R&D could obtain an average net present value of $1.2 billion.

Many other use cases, including the manufacture of retinas in space, are under investigation. Overall, our research on hypothetical use cases suggests that companies could potentially obtain $2.8 billion to $4.2 billion in revenues from pharmaceuticals in space.

Beauty and personal care

In the beauty and personal-care segment, skin care has emerged as one of the most promising segments for space opportunities: it is expected to account for more than 34 percent ($208 billion) of industry revenues by 2025. To date, R&D spending has been relatively low in this area, but trends suggest that it may soon rise, especially since many consumers are increasingly interested in products that have scientific data supporting their efficacy.

Overall, two areas stand out. The first, premium skin care, has an estimated compound annual growth rate (CAGR) of 13 percent through 2024 (compared with 3 percent for mass-market products). It is expected to reach $93 billion in value by 2025. Space-based R&D may unlock new insights about skin care because the harsh space environment, including high radiation levels, accelerates aging. Any new findings from space may carry a lot of weight with consumers who want scientific evidence of efficacy. These findings could also help differentiate and market products.

Another important use case involves the production of active ingredients—vitamins, retinol, and other substances directly responsible for a skin care product’s effects. R&D spending in this area, now about $460 million annually, has an estimated CAGR of 19 percent. By 2025, such active ingredients are expected to generate $1.5 billion in value. Space-based R&D might help companies to develop or manufacture active ingredients in skin care products: microgravity reduces the sedimentation rate and the impact of buoyancy, making it easier to combine different substances, including those in yeast extracts. Preliminary scientific studies have also demonstrated that yeast cultivated in space have a higher growth rate and metabolic production, which could make products more effective.

Food and nutrients

The human-nutrition industry accounts for about $10 trillion in value. Within this segment, nutraceuticals—any food-derived product that has health benefits in addition to basic nutrition—are expected to represent $17 billion in value by 2025.

Probiotics—foods containing live bacteria and yeast with health benefits—are particularly popular within the nutraceuticals category and may be a good target for commercial activities in space. They are gaining popularity thanks to increased consumer interest in health and wellness issues, including those related to the immune system. The R&D intensity of probiotics is among the highest in the food ingredient industry. They represent about 30 percent of overall nutraceutical R&D spending.

Space-based R&D could help companies discover and develop new probiotics—routinely in demand from consumers—since the growth and metabolic expression of these products may differ in space. Space experiments might, for instance, help scientists better understand environmental influences on probiotics and increase the efficacy of probiotic products. Research suggests that consumers may be willing to pay a premium for innovative probiotics and that the discovery of a novel probiotic strain with health benefits could generate $100 million or more in commercial value.

Another potential use case involves the production of probiotics. As with beauty products, researchers may find that space provides a favorable environment for culturing and harvesting certain microbes, such as lactobacillus strains, found in probiotics. Microbes may, for example, grow more rapidly in suspension in space, given the lack of shearing effects in bioreactors.

Semiconductors

Semiconductors represent one of the largest global markets, with sales estimated to reach about $725 billion by 2025, when research spending will hit about $90 billion.

Fabrication in space could reduce the number of gravity-induced defects (from contaminants landing on chips) and increase output. The benefits would be relatively small, however, because semiconductor yields—the amount of usable chips—are already 97 to 99 percent, since many processes occur in highly sanitized clean rooms. A more important advantage might come from the natural vacuum in space, which could potentially facilitate innovative thin-layering techniques by reducing or eliminating gases during production. If space-based R&D could lead to the creation of smaller semiconductor structures, the benefits could be huge.

A few efforts to manufacture products in space are already under way. In 2020, for instance, a company received a NASA grant to investigate an autonomous and high-throughput process for creating, in orbit, high-quality chips at lower cost. But our analysis suggests that it may be ten years or more before large-scale, cost-efficient semiconductor manufacturing occurs in space. Among other obstacles, the heavy equipment now used in manufacturing would be difficult to transport there.

If space manufacturing does become possible, it might produce some environmental benefits, since the terrestrial manufacturing process requires high amounts of energy and other resources. If companies can use solar power in space or otherwise decrease resource requirements, that could both reduce costs and promote sustainability .

Some of the most visionary researchers and corporate leaders have been imagining space-based R&D , manufacturing, or other business activities since the early 1960s, when the first crewed flights took place. These ideas seemed implausible for many years, but recent technological advances—including those in robotics and AI, seamless space–earth communication, and unattended cell-feeding machines—have changed the game. Launch costs have also fallen, making space more accessible to businesses in traditional industries. Other technologies, including cubesats, a class of nanosatellites, are much less expensive.

After decades of research, artificial intelligence is finally enabling powerful new computing algorithms. Space-based R&D and manufacturing could also be nearing the point when they transform business and society. Much is still unknown, and many technological advances must still be made. But if large-scale space-based R&D and manufacturing do prove viable, companies that forge ahead now could become the pioneers directing the course for years to come.

Carsten Hirschberg is a senior partner in McKinsey’s Berlin office, where Tobias Sodoge is a consultant; Ireen Kulish is a senior associate in the Frankfurt office; and Ilan Rozenkopf is a partner in the Paris office.

This article was edited by Eileen Hannigan, a senior editor in the Waltham, Massachusetts, office.

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Living Reviews in Relativity: “Gravity experiments with radio pulsars”

• by Frank Schulz
• 2024/08/14 2024/08/15

The open-access journal Living Reviews in Relativity has published a new review article on 22 July 2024:

Paulo C. C. Freire and Norbert Wex, Gravity experiments with radio pulsars. Living Rev Relativ 27, 5 (2024). https://doi.org/10.1007/s41114-024-00051-y

Abstract: The discovery of the first pulsar in a binary star system, the Hulse-Taylor pulsar, 50 years ago opened up an entirely new field of experimental gravity. For the first time it was possible to investigate strong-field and radiative aspects of the gravitational interaction. Continued observations of the Hulse-Taylor pulsar eventually led, among other confirmations of the predictions of general relativity (GR), to the first evidence for the reality of gravitational waves. In the meantime, many more radio pulsars have been discovered that are suitable for testing GR and its alternatives. One particularly remarkable binary system is the Double Pulsar, which has far surpassed the Hulse-Taylor pulsar in several respects. In addition, binary pulsar-white dwarf systems have been shown to be particularly suitable for testing alternative gravitational theories, as they often predict strong dipolar gravitational radiation for such asymmetric systems. A rather unique pulsar laboratory is the pulsar in a hierarchical stellar triple, that led to by far the most precise confirmation of the strong-field version of the universality of free fall. Using radio pulsars, it could be shown that additional aspects of the Strong Equivalence Principle apply to the dynamics of strongly self-gravitating bodies, like the local position and local Lorentz invariance of the gravitational interaction. So far, GR has passed all pulsar tests with flying colours, while at the same time many alternative gravity theories have either been strongly constrained or even falsified. New telescopes, instrumentation, timing and search algorithms promise a significant improvement of the existing tests and the discovery of (qualitatively) new, more relativistic binary systems.

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• Published: 13 August 2024

Pathfinder experiments with atom interferometry in the Cold Atom Lab onboard the International Space Station

• Jason R. Williams   ORCID: orcid.org/0000-0002-3798-4424 1 ,
• Charles A. Sackett   ORCID: orcid.org/0000-0001-6741-0571 2 ,
• Holger Ahlers 3 ,
• David C. Aveline 1 ,
• Patrick Boegel   ORCID: orcid.org/0000-0002-3606-2452 4 ,
• Sofia Botsi   ORCID: orcid.org/0000-0001-9100-3650 1 ,
• Eric Charron   ORCID: orcid.org/0000-0003-1660-6368 5 ,
• Ethan R. Elliott 1 ,
• Naceur Gaaloul   ORCID: orcid.org/0000-0001-8233-5848 6 ,
• Enno Giese   ORCID: orcid.org/0000-0002-1126-6352 7 ,
• Waldemar Herr   ORCID: orcid.org/0000-0002-3685-2729 3 ,
• James R. Kellogg 1 ,
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• Norman E. Lay 1 ,
• Matthias Meister   ORCID: orcid.org/0000-0001-7210-8588 8 ,
• Gabriel Müller   ORCID: orcid.org/0009-0004-5980-5740 6 ,
• Holger Müller   ORCID: orcid.org/0000-0003-0636-5951 9 ,
• Kamal Oudrhiri 1 ,
• Leah Phillips 1 ,
• Annie Pichery   ORCID: orcid.org/0009-0007-8426-6445 5 , 6 ,
• Ernst M. Rasel 6 ,
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• Matteo Sbroscia 1 ,
• Wolfgang P. Schleich   ORCID: orcid.org/0000-0002-9693-8882 4 , 10 , 11 , 12 ,
• Christian Schneider 1 ,
• Christian Schubert 3 ,
• Bejoy Sen 2 ,
• Robert J. Thompson   ORCID: orcid.org/0000-0002-2160-3201 1 &
• Nicholas P. Bigelow   ORCID: orcid.org/0000-0003-1854-5757 13  

Nature Communications volume  15 , Article number:  6414 ( 2024 ) Cite this article

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• Astronomical instrumentation
• Matter waves and particle beams
• Quantum metrology
• Ultracold gases

Deployment of ultracold atom interferometers (AI) into space will capitalize on quantum advantages and the extended freefall of persistent microgravity to provide high-precision measurement capabilities for gravitational, Earth, and planetary sciences, and to enable searches for subtle forces signifying physics beyond General Relativity and the Standard Model. NASA’s Cold Atom Lab (CAL) operates onboard the International Space Station as a multi-user facility for fundamental studies of ultracold atoms and to mature space-based quantum technologies. We report on pathfinding experiments utilizing ultracold 87 Rb atoms in the CAL AI. A three-pulse Mach–Zehnder interferometer was studied to understand the influence of ISS vibrations. Additionally, Ramsey shear-wave interferometry was used to manifest interference patterns in a single run that were observable for over 150 ms free-expansion time. Finally, the CAL AI was used to remotely measure the Bragg laser photon recoil as a demonstration of the first quantum sensor using matter-wave interferometry in space.

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Quantum gas mixtures and dual-species atom interferometry in space

A space-based quantum gas laboratory at picokelvin energy scales

Observation of Bose–Einstein condensates in an Earth-orbiting research lab

Introduction.

NASA’s Cold Atom Lab (CAL) was launched to the International Space Station (ISS) in 2018 as a multi-user facility for fundamental physics investigations with ultracold atoms enabled by a persistent microgravity environment. The flight instrument incorporates a toolbox of capabilities for flight Principal Investigators (PIs) to pursue space-enabled studies with interacting quantum gases 1 . Initial commissioning efforts for the flight instrument used laser and evaporative cooling of rubidium gases to produce Bose-Einstein Condensates (BECs) in orbit and characterized these quantum gases after freefall times exceeding 1 s 2 . Subsequent science demonstrations by the CAL investigators included enhanced techniques for cooling, manipulation, and control for quantum gases such as decompression cooling via adiabatic relaxation 3 , shortcut to adiabaticity and delta-kick collimation techniques for preparing atoms with effective temperatures as low as 52 picokelvin 4 , as well as the development of RF-dressed potentials and the study of ultracold rubidium gases in bubble-shaped geometries 5 . Recently, sympathetic cooling of bosonic potassium using evaporated 87 Rb gases as a reservoir has also been utilized in CAL to produce ultracold gases of either 41 K or 39 K and coexisting and interacting BECs of 41 K and 87 Rb 6 .

Accommodation of CAL on the ISS not only provides the unique infrastructure, support, and effective real-time download of science data needed for daily operations, but also allows for on-orbit repair and upgrades by the resident astronaut crew. Notably, a replacement science module (SM-3) was launched to ISS onboard the commercial resupply services mission SpaceX-19 and was installed into CAL by astronauts Christina Koch and Jessica Meir. SM-3 was equipped with an optical beam path to enable experiments with atom interferometry. This article details the initial pathfinder experiments by CAL investigators utilizing matter-wave interferometry with ultracold 87 Rb gases in orbit.

Precision metrology based on light-pulse atom interferometry is a quintessential utilization of the wave-like nature of matter that is at the heart of quantum mechanics. Here, pulses of laser light generate a superposition of motional states of atoms whose momenta differ by discrete units of the photon recoil. Subsequent laser pulses then induce the components of the atomic wave functions to recombine and constructively or destructively interfere (see “Methods” for more details). The final result is an interference pattern that provides a phase-sensitive readout of effects such as accelerations, rotations, gravity, and subtle forces that could signify new physics acting on matter. Due to the quantum nature of ultracold atomic gases and the phase sensitivity of matter waves in extended freefall, atom interferometry can enable unprecedented applications for both applied and fundamental physics 7 . Such applications include gravimetry 8 , 9 , 10 , 11 , 12 and gravity gradiometry 13 , 14 , 15 , investigating gravity at microscopic scales 16 , tests of the universality of free fall (UFF) with quantum matter 17 , 18 , 19 and measurement of relativistic effects with delocalized quantum superpositions 20 , 21 , 22 , 23 , 24 , 25 , 26 , measurements of fundamental constants 27 , 28 , 29 , 30 , 31 , realization of an optical mass reference 32 , tests of contemporary dark matter 33 and dark energy 34 , 35 candidates, and tests of theories of modified gravity 36 , 37 .

On Earth, atom interferometers of various designs have been studied to capitalize on the favorable quadratic scaling of inertial-force sensitivities with matter-wave evolution times between the interferometry light pulses. Notably, high-precision measurements of UFF have been achieved with atom interferometers utilizing 10-meter-tall atomic fountains operating in Stanford University 18 and the Wuhan Institute of Physics and Mathematics 17 . Further, long-baseline interferometers using alkaline earth metals are under construction at the Leibniz University of Hanover 38 and Stanford University 39 for precision fundamental physics experiments. Quantum gas experiments at the 100-meter drop tower in Bremen Germany have provided an enabling platform for developing cooling protocols and demonstrating atom interferometry in microgravity 40 , 41 , 42 . The Einstein Elevator and the GraviTower Pro expand this capability with greater than 100 drops per day providing 4 and 2.5 s of freefall, respectively 43 , 44 . Experiments have also been conducted in suborbital parabolic flights to detect inertial effects 45 and to test the UFF with a dual-species atom interferometer in microgravity 46 . Finally, the 100-meter-long MAGIS interferometer 39 , the MIGA large scale atom interferometer 47 , and the AION interferometer network 48 are being developed for gravitational wave detection. Such work is expected to continue in multiple terrestrial facilities dedicated to the fundamental study of ultracold gases in microgravity conditions.

Developing matter-wave interferometry to operate in a space environment can address similar goals with significant advantages, including: (1) access to essentially unlimited freefall time in a compact instrument, (2) enabling novel schemes such as extreme adiabatic cooling and delta-kick collimation for achieving ultra-low effective temperatures in atomic gases 2 , 3 , 4 , and (3) implementation and maturation of this quantum technology on a flight platform to support upcoming space missions where high-precision inertial sensing will be needed, including Earth observers and missions to test fundamental physics 36 , 49 , 50 , 51 , 52 . Even for trapped atom interferometers, which have demonstrated unprecedented coherence times for interferometry and provide localized gravity measurements 53 , microgravity can be beneficial since the need for a relatively strong potential to support the atoms against gravity is no longer a constraint. In 2017, the MAIUS sounding rocket mission provided a seminal demonstration of cold atom technologies by operating for 6 min in-space flight and achieved the production of BEC of 87 Rb atoms along with Bragg splitting and matter-wave interferometry 52 , 54 . As part of the commissioning efforts for SM-3 in the CAL instrument, a dual-species atom interferometer in space was also recently demonstrated using simultaneously interrogated 41 K and 87 Rb atoms with a single-laser atom interferometer beam 6 .

We report on a series of seminal experiments in which CAL investigators performed pathfinding investigations with single-species 87 Rb BECs to mature atom interferometry and quantum sensing on an Earth orbiting platform. Our results include (1) the demonstration of high-visibility Mach–Zehnder interferometry (MZI) at relatively short times, (2) signatures of atom interferometer sensitivities and visibility degradation due to the ISS vibration environment, (3) the use of shear-Ramsey atom interferometry to extract contrast and phase shifts in a single experimental run, (4) observation of interference fringes persisting for greater than 150 ms during freefall in the compact CAL science cell, and (5) the use of the CAL AI to perform a photon recoil measurement to demonstrate its utility as the first quantum matter-wave sensor in space.

The CAL AI permits sensing of inertial forces onboard the ISS and is intended as a technology demonstrator for future space-borne fundamental physics experiments. Figure  1 a gives an overview of the interior layout within the physics package at the heart of SM-3. This atom-interferometer-capable science module is based on the original CAL design 1 , 2 . Primary upgrades are a redesigned atom chip and the inclusion of a laser beam, which propagates from the atom interferometer platform above the science cell, through the center of a 3-mm diameter on-chip window (and through a set of atom-chip wires separated by 2 mm), and is retro-reflected from an in-vacuum mirror at the bottom of the science cell. The CAL AI utilizes Bragg diffraction laser pulses 11 , 55 operating at 785 nm for matter-wave beam splitters and mirrors. The Bragg beam waist is approximately 0.5 mm (1/ e 2 ) within the science cell, and propagates at a 4° angle off the normal to the atom chip such that the laser wave vector k is nominally aligned with Earth’s gravity vector along z . Specifics of the design and implementation of the CAL AI were given previously 6 , with additional details in the “Methods” section.

a Cut of the upper region of the physics package of SM-3 to expose the interior components and the path of the retro-reflected Bragg beam (red) inside the vacuum system. The expanded region shows the beam entering the vacuum chamber through a window and between pairs of Z- and U-traces (blue) and H-traces (yellow) on the atom chip. Dimensions of the upper vacuum cell are given to illustrate the compactness of the science region accommodating our AI experiments. Note that the entire CAL payload occupies only 0.4 m 3 on the ISS with a mass of approximately 230 kg. b Space-time diagram of an ideal Mach–Zehnder interferometer, where three retro-reflected laser pulses (red) are applied in a sequence of \(\frac{\pi }{2}\) - π - \(\frac{\pi }{2}\) pulses, with pulse separation times T , to create a superposition and then recombination of the initial atom cloud into two motional states ( \(\left| {p}_{+}\right\rangle\) and \(\left| {p}_{0}\right\rangle\) given by blue and yellow clouds respectively). c Ramsey atom interferometer diagram using a sequence of \(\frac{\pi }{2}\) - \(\frac{\pi }{2}\) pulses to explore shear-wave atom interferometry at long time-of-flight t TOF . For sufficiently short T , used for photon recoil measurements, the outputs are similar to that of the MZI.

For all experiments described in this article, ultracold gases of bosonic 87 Rb are produced in the flight system using an atom-chip-based BEC source, producing up to 10 4 degenerate atoms approximately once per minute 1 , 2 , 6 . Thereafter, a multi-stage transport protocol is used to quasi-adiabatically displace the magnetic trap minimum to position the atoms near the center of the Bragg beam, approximately 1 mm below the on-chip window. After transport, atoms in the \(\left| F=2,\, {m}_{F}=2\right\rangle\) internal state are confined in a nearly harmonic potential with measured trap frequencies ( ω x ,  ω y ,  ω z ) = 2 π  × (13.8, 23.4, 18.8) Hz, characterized using dual-axis absorption imaging. Atoms rapidly released from this center trap serve as the starting point for the following atom-interferometer experiments.

Mach–Zehnder interferometer

A three-pulse MZI 8 , illustrated in Fig.  1 b, was first demonstrated in Earth’s orbit including eight repeated measurement campaigns over a span of 38 days. Here, 87 Rb atoms were prepared and released from the center trap such that the cloud expands to less than 100 μm FWHM over 100 ms of freefall, and moves with the center-of-mass velocity v  =  p / m  = ( v x ,  v y ,  v z ) = (2.0, 1.0, 7.8) mm/s. The relatively large initial velocity ( p 0 / m  =  v 0  ≈  v z ) along the laser wave vector k was intentionally applied so that the Bragg transitions to \(\left| {p}_{\pm }\right\rangle \equiv \left| {p}_{0}\pm 2\hslash k\right\rangle\) are nondegenerate, as this choice simplifies the interferometer operation and suppresses double diffraction 56 (see “Methods” for details on the relevant Bragg processes). For this demonstration, the Bragg laser contains two frequencies separated by δ  = 34.82 kHz to compensate for the Doppler shift of the 87 Rb atoms along the direction of the beam. During the first 17 ms of freefall, atoms were transferred to the magnetically-insensitive \(\left| F=2,\, {m}_{F}=0\right\rangle\) state via Adiabatic Rapid Passage, leaving no atoms detected in any of the unwanted m F  ≠ 0 levels (see “Methods”). Thereafter, three square pulses of the Bragg laser approximating ( π /2,  π ,  π /2) transitions were applied for (0.13 ms, 0.25 ms, 0.13 ms), respectively, with T  = 0.5 ms pulse separation times.

The phase difference ϕ between the two paths of a MZI is sensitive to external perturbations on the atoms, including accelerations a , rotations Ω , and the Bragg laser phase 57 . In leading order, ϕ can be expressed by:

where k eff is the effective two-photon wave vector with amplitude ≈ 2 k that defines the transferred momentum during diffraction. To map out an interference fringe, the differential phase of two simultaneous frequency tones in the final Bragg laser pulse ϕ laser was varied between 0 and 360°. After the final Bragg pulse, the atoms were allowed to propagate freely for t TOF  = 15 ms so that the different momentum components, constituting the exit ports of the atom interferometer, could separate in position. The populations of atoms N 0 and N + , occupying the \(\left| {p}_{0}\right\rangle\) and \(\left| {p}_{+}\right\rangle\) output momentum states, respectively, were then measured using absorption imaging as shown in the lower inset of Fig.  2 . Note that a small population in the spurious exit port N − , corresponding to atoms driven toward the atom chip via off-resonant transitions into the \(\left| {p}_{-}\right\rangle\) state, was also produced as a result of the finite cloud temperature, moderate two-frequency detunings of the Bragg laser, and hardware limitations that practically inhibited the use of smooth (e.g., Gaussian-shaped) pulses 52 , 54 , 56 . Figure  2 shows the characteristic sinusoidal variation of the excitation fraction N + / N tot with ϕ laser (see “Methods” Eq. ( 7 )), providing a clear and repeatable signature of matter-wave interference with visibility V  = 0.36(2).

The main plot shows the relative population of rubidium atoms in the \(\left| {p}_{+}\right\rangle\) state after a Mach–Zehnder pulse sequence with T  = 0.5 ms duration between Bragg pulses. Scanning the phase ϕ laser of the traveling wave for the final laser pulse reveals a corresponding sinusoidal variation of N + / N tot . Eight independent data sets were analyzed, with up-to eight repetitions for each set. To increase the signal-to-noise ratio, the repeated images in each phase set were first summed, and the corresponding averaged images were fit to Thomas–Fermi profiles as described in “Methods”. The data plotted in light blue then yield the average N + / N tot for each ϕ laser , with error bars given by the standard deviations. (Lower Inset) The first set of averaged absorption images after MZI, showing atoms oscillating between the \(\left| {p}_{+}\right\rangle\) and \(\left| {p}_{0}\right\rangle\) momentum states as ϕ laser is increased. A small population occupying the \(\left| {p}_{-}\right\rangle\) state can also be seen. (Upper Inset) The influence of ISS vibrations is modeled (see “Methods”), with 2 ms granularity, to illustrate limitations to the atom-interferometer visibility for single-source 87 Rb BECs at larger T . Data for the acceleration a z in the z -direction from the SAMS 121F04 accelerometer on the ISS was used for each day during which the MZI experiments were conducted, with dashed lines to guide the eye. Experimental results for T  = 0.5 ms and 10 ms are included (orange triangles) for comparison.

The limited visibility of the interferometer with short T can be attributed to two effects: (1) Condensates released from the trap expand due to mean-field interactions, leading to a Thomas–Fermi velocity spread along the k -direction of Δ v 0  ≈ 1.6 mm/s. Both the Bragg pulse efficiencies and the phases developed during free evolution depend on the atomic velocity. (2) Analysis of the Bragg pulse efficiencies suggests that the atoms experience a relative spread in Bragg beam intensity of approximately ±25%. This variation is significantly larger than the approximately 5% variation expected from the spatial inhomogeneity of the Bragg beam if it had an ideal Gaussian profile. However, optical simulations indicate that the collimation lens used in the Bragg beam fiber coupler produces an imperfect Gaussian with substantial wings at large radii. The wings are clipped by the 2-millimeter aperture given by the atom-chip traces (see “Methods”) and the resulting diffraction pattern produces significant intensity modulation. We confirmed this effect by applying long-duration pulses of Bragg light to a 87 Rb BEC and observing the transverse motional excitation produced by the BEC propagating through this diffraction pattern.

Increasing T from 0.5 ms to 10 ms causes the interferometer visibility to drop to a value consistent with zero. However, the effective contrast at longer T was determined by fitting the histograms of the excitation fractions at T  = 0.5 ms and T  = 10 ms with a Probability Distribution Function (PDF) for a double-peaked distribution indicative of a sinusoidal excitation fraction with Gaussian noise (given by Eq. ( 9 )). The effective contrast decreases by approximately 30% as T is increased from 0.5 ms to 10 ms, signifying that phase noise is still dominating the signal at T  = 10 ms 58 , but other sources of visibility degradation are also growing as T is increased. The rising influence of phase noise with T is consistent with the simulated T -dependent visibility degradation, shown in the upper inset of Fig.  2 , which was modeled using ISS-SAMS 121F04 accelerometer data measured along the z direction. Details of the PDF fits and the visibility degradation simulation due to ISS vibrations are given in the “Methods” section.

Shear-wave atom interferometry

In Fig.  1 c, a two-pulse Ramsey interferometer geometry 59 is illustrated. Here, two π /2 pulses of the Bragg laser beam are applied in relatively rapid succession so that the atomic wave functions split from the first laser pulse still sufficiently overlap as to interfere and reveal a spatially resolved interference pattern at imaging. Depending on the expansion energy of the atoms and the freefall time after the second pulse t TOF , as well as the timings of the interferometer sequence and ϕ laser , such shear-wave interferometers 60 can provide direct information about both the atoms and the experimental apparatus. In particular, the spatially resolved interference pattern can in general be a very useful tool for diagnosing phase shifts that vary across the atom cloud as for instance induced by optical dipole forces from the Bragg beam or further diffraction from stray laser light 52 .

For this interferometer arrangement, sufficient t TOF is implemented after the pulse sequence so that spatial fringes are visible in a single experimental shot, as shown in Fig.  3 . The fringes persist for over 150 ms time of flight, which would be challenging to observe in a similarly compact terrestrial instrument. Here, two π /2 Bragg laser pulses, each with a square-pulse time distribution lasting 0.16 ms and separated by 1 ms, are applied 2 ms after release of the BEC from the trap. Approximately 60 ms after the second pulse, weak stripe patterns emerge in both the undiffracted cloud ( \(\left| {p}_{0}\right\rangle\) state) and the cloud that was diffracted by the Bragg beam toward the atom chip (defined here as the \(\left| {p}_{+}\right\rangle\) state). A weak third cloud, not shown in Fig.  3 , consists of atoms off-resonantly excited to the \(\left| {p}_{-}\right\rangle\) state. The images cannot be reliably analyzed for times greater than 150 ms because atoms in the \(\left| {p}_{+}\right\rangle\) state propagate into the region near the chip which exhibits degraded signal quality and, eventually the ultracold cloud is destroyed as the atoms come into contact with the chip itself. Due to resolution limits of the detection system and the size of the BEC being smaller than the fringe spacing for very short times, the nonlinear behavior of the fringe spacing shown in Fig.  3 could not be resolved. However, there is promise in exploring this nonlinear regime with greater resolution in the future.

a Fringe spacing λ fr of a shear-Ramsey interferometer aboard CAL as a function of the free-evolution time t TOF of the BEC after release from the magnetic trap. The BEC is split coherently with two π /2 Bragg pulses each lasting 0.16 ms with a separation of 1.0 ms between them to achieve the characteristic interference pattern for both exit ports within a single experimental run. The measured fringe spacings (blue dots for data and dashed line for the fit) show excellent agreement with the theoretical prediction (purple line) based on the expansion dynamics of the BEC in the Thomas–Fermi regime and a proper treatment of the finite pulse duration as expressed by Eq. ( 2 ). Exemplary 2D-density distributions for two different expansion times are shown in the top row (189 × 189 μm 2 area, with densities normalized for each image individually) with the integrated 1D densities (black lines) displayed below together with the fit results (red lines). b The contrast of the interference fringes (green dots) increases with expansion time and saturates at a maximum of around 45%. Error bars represent 1-sigma confidence bounds of fitting the density distributions.

Fits to extract the contrast and fringe spacing for the two primary clouds were obtained by first integrating the density distribution of the clouds along a direction parallel to the stripes, and then fitting each cloud to a Gaussian distribution with sinusoidal oscillations and a constant phase difference of π . Figure  3 gives the measured fringe spacing λ fr and contrast as a function of t TOF . Each point represents data from a single experimental run with error bars given by the fit uncertainty. A theoretical prediction for the fringe spacing (purple line) with no adjustable parameters shows excellent agreement with the fringe spacing data. The model, which takes into account the expansion dynamics of a BEC in the time-dependent Thomas–Fermi approximation, gives the following result for the fringe spacing 61 :

Here, R ( t TOF ) is the Thomas–Fermi radius, which follows from the scaling approach 62 . The asymptotic constant expansion rate is determined by the initial trap frequencies and the number of atoms and T eff , the effective time separation of the two Bragg pulses taking into account the finite duration of each pulse. We calculated T eff by solving the Schrödinger equation in the presence of the Bragg optical potential, giving a value of T eff  = 1.204 ms. When instead we fit the data to determine T eff , we obtain a value of 1.21(1) ms, in excellent agreement with the calculated value.

Because the shear-Ramsey interferometer yields an interference pattern in a single run, it is not sensitive to dephasing by vibrational phase noise. The ability to observe the pattern after long freefall times illustrates the potential for exploring long-time interference effects in microgravity. A similar terrestrial experiment, limited to expansion times of a few milliseconds, illustrated the effects of atomic interactions on the fringe patterns 63 . For our weak initial trap and low atom numbers, however, interactions between the two clouds can be safely neglected.

Photon recoil measurement

The two-pulse Ramsey interferometer configuration described in the previous section can also be used to perform a proof-of-principle recoil frequency measurement. Notably, in between the two Bragg pulses, the atomic wave packets develop a phase difference that depends on the recoil frequency ω r  ≡  ℏ k 2 /2 m . High-precision terrestrial measurements of ω r are used to determine the fine structure constant 28 , 29 . These efforts could be supported in microgravity by the availability of long interrogation times and low atom-cloud expansion rates. Many systematic errors are reduced for atoms remaining in a fixed position relative to the apparatus, and the impact of errors that impart a fixed phase shift (including laser phase errors 64 ) is reduced at longer interrogation times where the recoil phase is larger. Alternatively, even low-precision recoil frequency measurements could provide a useful method to calibrate the Bragg wave number k in a space environment where no conventional wavemeter instrument is available.

The phase evolution of a free atom is governed by its kinetic energy p 2 /2 m . The interferometer is sensitive to the phase difference between wave packets with momenta p ± and p 0 , which results in ϕ atom  = −(4 ω r  ± 2 k v 0 ) T for pulse separation time T (see “Methods” Eq. ( 5 )). In addition, the laser phase evolves as δ T  +  ϕ 0 , where δ is the difference between frequencies in the Bragg laser and ϕ 0 is the phase offset of the second Bragg pulse. The measured phase (from “Methods” Eq. ( 8 )) is therefore:

In order to interferometrically determine both ω r and v 0 , we measure ϕ as a function of T for both signs of the Bragg momentum kick.

In these experiments v 0  ≈ 2.5 mm/s, so for the \(\left| {p}_{0}\right\rangle \to \left| {p}_{+}\right\rangle\) transition away from the atom chip we set δ  = 2 π  × 21 kHz and for \(\left| {p}_{0}\right\rangle \to \left| {p}_{-}\right\rangle\) we set δ  = 2 π  × 9 kHz. The net phase was determined by scanning ϕ 0 , as shown in the inset of Fig.  4 . The data are fit to a sinusoidal function to extract ϕ atom at various values of T , with results shown in the main plot of Fig.  4 . From the slopes of these lines, we find ω r  = 2 π  × 3.77(6) kHz and v 0  = 2.4(1) mm/s. The recoil frequency is consistent with the expected value of 3.72 kHz, and the initial velocity is consistent with time-of-flight measurements.

Accumulated phase difference of the atomic wave packets as a function of interrogation time T . Circled points are obtained by fitting interference fringes as shown in the inset, and error bars represent the estimated fit uncertainties. The lines are linear fits for the Bragg transition \(\left| {p}_{0}\right\rangle \to \left| {p}_{+}\right\rangle\) with frequency δ  = 2 π  × 21 kHz and \(\left| {p}_{0}\right\rangle \to \left| {p}_{-}\right\rangle\) with 2 π  × 9 kHz. The phases for the two cases differ at T  = 0 because of different couplings to their respective off-resonant momentum states.

The precision of these measurements is low due to the limited interrogation time. At the maximum usable time of T  = 0.75 ms, the interference visibility has dropped to about 0.07 which is consistent with the expected coherence time R 0 / v B  ≈ 0.7 ms. Here, R 0  ≈ 8 μm is the initial condensate size in the trap and v B  ≡ 2 ℏ k / m  = 11.7 mm/s denotes the Bragg recoil velocity. Longer interaction times could be achieved by starting with atoms in a weaker trap, but a more effective method would be to use a closed interferometer configuration such a three-pulse contrast interferometer 65 .

In this article, we reported on three pathfinding experiments based on matter-wave interference of ultracold rubidium gases in orbital microgravity, which were each found to be robust and repeatable over timescales spanning months. We utilized the long freefall times available for atoms in space within the relatively compact CAL apparatus and compared the atom interferometer performance with ISS environmental data to gain insight into the high-frequency vibration environment experienced by the instrument. We further employed shear-wave interferometry to demonstrate the effects of matter-wave interference that are clearly visible in a single experimental run for more than 150 ms of freefall. Additionally, photon recoil measurements served to provide characterizations of the Bragg wave number using only the atomic feedback resulting from interferometer sequences, demonstrating the utility of CAL as the first quantum matter-wave sensor in space.

These efforts and findings serve as important milestones for maturing space-based atom interferometry for numerous mission concepts. Notably, observation of high-contrast interference fringes after long freefall times and within a single experimental run, as demonstrated here with shear-wave interferometry, is a technique that can be utilized for precision sensors 36 , allowing for shot-to-shot determination of AI contrast and phase shifts. AI-based measurements of the photon recoil in space is also promising for multiple applications. Experiments to determine the fine structure constant 28 , 29 are expected to benefit from the extended freefall environment of microgravity for higher precision and reduced systematic errors by achieving long T in a relatively compact and freely-falling apparatus. Additionally, measuring the frequency of the AI laser via atomic feedback, as directly demonstrated in this article, will enable characterization and control over leading systematics for future missions and can remove the need for launching dedicated wave meters for the AI lasers. Finally, understanding the influence of ISS vibrations to the Rb-based AI allows researchers to understand limitations and optimize near-term experiments using differential interferometry for fundamental physics investigations on the ISS.

Significant advancements and new sensing capabilities are expected to arise as differential interferometry (using either spatially-separated atom interferometers with the same atomic species in a gradiometer configuration or simultaneous interrogation of two distinct atomic species) is further explored with CAL 58 . The CAL AI is designed for precision dual-species simultaneous interferometry with 87 Rb and 39 K or 41 K, interrogated via absorption imaging for phase-sensitive measurements with two dissimilar quantum test masses. The operating frequency of the Bragg laser at 785 nm is near the magic wavelength where the two-photon Rabi frequencies are essentially identical for Rb and K species 36 . Hence, differential atom interferometer measurements in CAL are expected to be minimally impacted by common-mode noise sources including vibrations and laser noise. Initial experiments 6 on CAL demonstrating differential atom interferometry with 87 Rb and 41 K quantum gases at short T are particularly promising for PI-led efforts aiming to extend the capabilities of space-based dual-species differential atom interferometry.

A replacement for SM-3 on the ISS is already designed for reduced scattering of the beam before it enters the science cell and, hence, minimizing wavefront degradation. As a CAL follow-on, the BECCAL mission 49 is also expected to include numerous mechanisms to optimize visibility and allow long interrogation times with differential atom interferometers, including using relatively large beams and employing rotation compensation schemes to counter the effects of the ISS rotation as it orbits the Earth.

The experiments detailed in this article therefore serve as pathfinders for proposed space missions relying on sustained matter-wave interferometry with unprecedented sensitivity to inertial and fundamental physical forces, including tests of the Einstein Equivalence Principle 36 , 51 , 66 , gravitational wave detectors 39 , 48 , 67 , direct detection of dark matter and dark energy candidates 34 , 36 , Earth and planetary sciences including geodesy, seismology, and sub-surface mapping 15 , 50 , 68 , and advanced navigation and drag-free referencing 69 , 70 . With the successful utilization of CAL SM-3 for seminal, long-term PI-led studies of atom interferometry in Earth’s orbit, this first-of-its kind instrument has brought quantum sensing via atom interferometry into the list of technologies matured and flight-qualified by NASA toward expanding our fundamental understanding and exploration of the cosmos.

Upgraded Cold Atom Lab facility

The CAL AI is designed to be sensitive to the force of Earth’s gravity, rotations of the ISS, and also to utilize differential measurements from atom interferometers consisting of simultaneously interrogated rubidium and potassium gases. To this end, the on-orbit upgraded SM-3 includes four primary changes from the original CAL design to enable atom interferometry 6 , the first three of which are illustrated in Fig.  1 a. (1) Light from the Bragg laser system was delivered into the SM-3 via polarization maintaining optical fibers and routed to the atom interferometer platform, which is the optical bench used to shape and direct the beam as part of the upgraded physics package provided by ColdQuanta. (2) The atom chip was upgraded to allow the beam to propagate through the center of the 3-mm diameter window on the atom chip, which also serves as the top surface of the evacuated science cell. Passing the beam through the chip, as opposed to passing through the cell windows horizontal to the chip, was necessary to accommodate the desired orientation of the Bragg beam with respect to gravity. Providing clearance for the laser required the atom chip traces to be moved away from the center of the window, resulting in two pairs of in-vacuum traces (Z- and U-traces respectively), separated by approximately 2 mm along the x -axis, and a pair of wires on the atmospheric side of the chip (H-traces), separated by approximately 3 mm and oriented along the y -axis. (3) An in-vacuum mirror was mounted in the science cell on the side opposite to the atom chip, slightly off center and oriented at a 4° angle to allow retro-reflection of the Bragg beam while assuring clearance for the push beam and atom flux from the 2D MOT 2 . (4) The optical path for the through-chip imaging system was rerouted to accommodate detection through the chip window in combination with the atom interferometer platform.

The fiber-coupled Bragg laser was included as part of the original CAL flight system in anticipation of SM-3. Coherent light is provided by a single-wavelength external cavity diode laser operating at nominally 785 nm, which exhibits a narrow linewidth (<200 kHz) and continuous output of tens of milliwatts. The light is directed via optical fibers from the single locker to the quad-locker 2 where it is amplified using a Tapered Amplifier (TA). The TA input is shared between the 785 nm and 780 nm seed lasers and the output is directed either to the cooling light or atom interferometer beam paths via optical switches. Before the 785-nm light is directed into SM-3, it is passed through an acousto-optic modulator, operating at approximately 79 MHz as controlled by an arbitrary waveform generator (National Instruments PXI-5422). This design allows multiple frequency components to be written onto the Bragg laser. A narrow bandpass optical filter (Semrock Laser Clean-up MaxLine 785/3) on the atom interferometer platform passes 785-nm light while suppressing residual light near 780 nm by over three orders of magnitude, in order to avoid resonant scattering. The resultant Bragg beam was approximately collimated within the CAL science cell and retroreflected by the in-vacuum mirror with overlap of the incident and reflected beam, measured before launch to the ISS, better than 0.1 mm.

Source control and detection

Transfer of 87 Rb atoms from the magnetically sensitive \(\left| F=2,\, {m}_{F}=2\right\rangle\) state (within the 2 S 1/2 manifold) to the magnetically insensitive \(\left| F=2,\,m_F=0\right\rangle\) state is achieved with high-field adiabatic rapid passage (ARP) 71 . Here, the second-order Zeeman shift is made to be much larger than the Rabi frequency for RF coupling of atoms among magnetic sublevels, breaking the degeneracy that would otherwise arise when attempting to drive atoms among the five m F  -levels in the F  = 2 manifold. At an applied bias field of 29.2 G, the splitting between the sublevels is approximately 20 MHz, and the second-order Zeeman shift is 120 kHz. In comparison, the RF Rabi frequency for the \(\left| F=2,\,m_F=2\right\rangle \to \left| F=2,\,m_F=1\right\rangle\) transitions is approximately 9 kHz. The atoms are initially released from the center-trap and allowed to freefall for 5.2 ms while a B x  ≈ 31 G bias field along the x -axis is applied and allowed to stabilize. Single-tone RF at 20.4 MHz is then pulsed on for 5 ms while B x is linearly ramped down to approximately 29.2 G. Using this method, an ultracold rubidium gas is transferred from the \(\left| F=2,\,m_F=2\right\rangle\) to the \(\left| F=2,\,m_F=0\right\rangle\) state with no detectable signal remaining in other m F states. Thereafter, B x was turned off and a 10 mG magnetic field was applied along the y direction to maintain a field quantization axis throughout the freefall and atom interferometer stages.

Atomic density distributions are measured via one of two absorption imaging systems, which are nearly identical to those of the original CAL science module 2 , aside from the change to the through-chip imaging path discussed above. Here, the horizontal imaging system is used for detection of interference as it images the x – z plane. The vertical imaging system observes the atoms in the x – y plane through the atom chip and was used to help position atoms in the Bragg beam. At T  = 0.5 ms atom interferometer interrogation time, the average signal variation at a fixed ϕ laser  = 0° is σ  = 0.06, approximately an order of magnitude larger than the expected quantum projection-noise limit 72 for an ensemble of N tot  ~ 5 × 10 3 atoms. In comparison, the influence of detection noise and instabilities in the Bragg-pulse amplitudes was measured using an imbalance in timing between MZI pulses, with T 1  = 10 ms and T 2  = 8 ms so that the interferometer would not close at the final AI pulse, giving a mean excitation fraction of 0.53 with σ  = 0.03.

Bragg atom interferometry

The principles of light-pulse atom interferometry have been reviewed in detail elsewhere 8 , 59 , 73 . Here, we summarize the related theory for understanding the phases-shifts and fringes observed in Figs.  2 – 4 . For simplicity, we consider the ideal first-order Bragg process driven by a light pulse with two frequency components ω 1 and ω 2 , counter-propagating wave vectors k 1 and k 2 , and frequency difference δ  ≡  ω 1  −  ω 2 . For small detunings relevant to this study, k 1   ≃   k 2  =  k . The Bragg light pulse coherently couples atoms occupying an initial momentum state \(\left| {p}_{0}\right\rangle\) to the final states \(\left| {p}_{\pm }\right\rangle \equiv \left| {p}_{0}\pm 2\hslash k\right\rangle\) . Neglecting additional inertial forces, the evolution of the quantum state \(\left| {{\Psi }}(t)\right\rangle\) can be expressed in terms of time-dependent coefficients c 0 and c ± by:

which, up to an overall phase, is equivalent to:

with recoil frequency ω r  ≡  ℏ k 2 /2 m and initial velocity v 0  =  p 0 / m along k . If the two levels are coupled by a pulse with duration τ , Rabi frequency Ω, and frequency δ , then the detuning is Δ ±  = 4 ω r  ± 2 k v 0  −  δ and the probability of finding an atom in the \(\left| {p}_{\pm }\right\rangle\) state reads:

For the resonant case Δ ±  = 0, an equal superposition of \(\left| {p}_{0}\right\rangle\) and \(\left| {p}_{\pm }\right\rangle\) states is prepared for a π /2 pulse, where Ω τ  =  π /2 and atoms are fully transferred between states for a π pulse, when Ω τ  =  π .

Matter-wave interference can be observed by applying a series of π /2 and π pulses, with pulse separation time T , as illustrated in Fig.  1 . For each geometry, the output phase of the atom interferometer is observable from the population of atoms ( N 0 or N + ) occupying one of two final momentum states ( \(\left| {p}_{0}\right\rangle\) or \(\left| {p}_{+}\right\rangle\) , respectively) as:

where N 0  +  N +  =  N tot , N mean is the number of atoms occupying N 0 averaged over all interferometer phases ϕ , and V gives the atom interferometer visibility. Therefore, observing the fraction of atoms in each final momentum state allows us to extract the accumulated phase modulo 2 π . The measured phase can be decomposed into contributions from the Bragg laser and the atomic wave function evolution 57 :

These contributions depend on the environment and forces experienced by the atoms, the frequency stability of the laser pulses, geometric topological phase shifts, and the geometry of the atom interferometer itself  59 .

Fringe detection and data analysis

All interferometer data are acquired via absorption imaging, which yields the spatial distribution of the atoms at the end of the experimental sequence. Images with no atoms or other obvious errors are discarded. For the Mach–Zehnder and recoil measurements, images are cropped to a region of interest around the expected position of each output cloud, and the clouds are fit to independent Thomas–Fermi profiles in order to extract the atom number. All fits are confirmed visually. For the shear Ramsey atom interferometer measurements, absorption images were first processed using a principal component analysis of the whole data set to remove background imaging noise 74 . The resulting density profiles were then fitted to the Ramsey fringe model described in the main text.

For the recoil frequency measurements, data sets of about 50 points are acquired by scanning the Bragg phase ϕ 0 from 0 to 2 π . The resulting curves are fit to the form of Eq. ( 7 ), where here ϕ atom  = −4( ω r  ± 2 k v 0 ) T and ϕ laser  =  δ T  +  ϕ 0 . Uncertainty in ϕ is determined by the bounds for doubling the quality-of-fit parameter χ 2 . The uncertainty ranges from about 0.5 rad at small T up to as much as 2 rad for large T , which is consistent with the reduction in atom interferometer visibility at larger T . In comparison, uncertainties in ϕ 0 , δ and T are negligible.

Analysis of Mach–Zehnder interferometer output

To understand whether the loss of visibility observed at T  = 10 ms is attributed to phase noise (e.g., induced by ISS vibrations) or from other factors such as dipole forces across the atom cloud, the histograms for the excitation fractions for both T  = 0.5 ms and T  = 10 ms, shown in Fig.  5 , were fit to the probability density function (PDF) for a pure sine wave (double-peaked distribution with amplitude A and offset P 0 ) convoluted with a Gaussian noise distribution with standard deviation σ P 45 :

with normalization factor N . This model is well suited for distinguishing the influence of phase noise, which will wash out the sinusoidal dependence of N + / N tot vs. ϕ laser but will maintain the double-peaked density distribution, compared to other sources of noise or visibility loss that would also reduce A or increase σ P in the PDF.

The relative population of rubidium atoms in the excited state after Mach–Zehnder pulse sequences: (left-hand side) with respect to ϕ laser and the corresponding histograms (right-hand side). For both ( a ) T  = 0.5 ms, and ( b ) T  = 10 ms, N + / N tot was determined by fitting the images to Gaussian profiles for each experimental run and the fitting errors, shown for each N + / N tot , were propagated to the corresponding histogram errors using a Monte Carlo simulation. The histograms were fit with a PDF, described by Eq. ( 9 ), corresponding to a double-peaked distribution with amplitude A and offset P 0 and broadened into a nearly flat-top distribution by Gaussian noise with amplitude σ P (red curves). Although the characteristic sinusoidal dependence of N + / N tot with respect to ϕ laser is not observable for the T  = 10 ms data, a reasonable fit of the histogram with the double-peaked PDF, giving C  = 0.24 and SNR = 2.4, signifies that phase-noise is a major cause of the loss of AI visibility as T is increased to 10 ms for the CAL single-species 87 Rb atom interferometer.

For each data set, the histogram errors were extracted from N + / N tot fitting errors using Monte Carlo error propagation 75 . The fitted PDF parameters for the T  = 0.5 ms data are P 0 (0.5 ms) = 0.476(8), A (0.5 ms) = 0.163(8), and σ P (0.5 ms) = 0.055(9). It is evident that the T  = 10 ms data does not exhibit the characteristic sinusoidal dependence of the excitation fraction with ϕ laser that is clearly seen for the T  = 0.5 ms data, indicating a visibility at T  = 10 ms consistent with zero. However, the T  = 10 ms histogram still exhibits a flat-top profile that agreed well with a PDF fit with P 0 (10 ms) = 0.50(1), A (10 ms) = 0.12(1), and σ P (10 ms) = 0.05(1). For both data sets, a reasonable signal-to-noise ratio (SNR =  A / σ P ) and effective contrast ( C  =  A / P 0 ) are found, signifying that phase noise is a major contributor to the loss of visibility as T is increased for the single-species ( 87 Rb) CAL AI. It must be noted, however, that the decrease of effective contrast by ~30% compared to the T  = 0.5 ms data also shows that MZI noise (e.g., additive or offset noise 76 ) or sources of visibility degradation other than phase noise are also growing with T .

Phase noise can arise from acceleration noise (e.g., ISS vibrations as described in the next section) or from laser phase noise, which is highly suppressed in CAL by design. The two frequencies for Bragg AI are produced within a single acousto-optic modulator driven by the amplified multi-tone signal from the arbitrary waveform generator with phase stability better than −100 dBc/Hz 77 . This implementation removes differential path lengths for the two Bragg frequencies, and makes laser phase noise contributions arising from both the AWG noise and from environmental perturbations on the laser negligible 76 . To confirm this, the linewidth of the optical beatnote between two frequencies written onto the Bragg laser by the AOM, driven at 79 MHz and 79.035 MHz respectively, was measured to be below 10 Hz during the pre-launch checkout of CAL. Hence, the influence of ISS vibrations are found to be a leading source of visibility degradation for the ( 87 Rb) CAL AI at T  = 10 ms.

ISS vibrations study

Our analysis of the impact of the ISS vibrations on the atom interferometer visibility is based on a z data from the SAMS 121F04 three-axis accelerometer, which are provided publicly over NASA’s Principal Investigator Microgravity Services (PIMS) 78 . The accelerometer is located on the front panel of the CAL Instrument in front of SM-3. It has a sample rate of 500 sps and a bandwidth of 200 Hz. The Physics Package is attached via a flexure mount inside the science module which modifies the acceleration spectrum. However, we expect no major impact in the frequency range of interest and use the unmodified accelerometer data in our analysis for simplicity.

The SAMS accelerometer provides discrete measurements a z , i every Δ t  = 2 ms, giving a total of n  =  ⌊ 2 T /Δ t ⌋ measurements at our disposal for each Mach–Zehnder interferometer sequence. Equations for calculating the accumulated MZI phase from a z , k eff and the sensitivity function g s ( t ) 79 were discretized to utilize the PIMS data sets. The durations of the Bragg laser pulses were ignored since they are short compared to the overall atom interferometer interrogation time. We obtain:

with the discretized sensitivity function:

Although it was not feasible to correlate accelerometer measurements to individual atom interferometer experiments, the impact of vibrations was estimated for each day that MZI data was collected. Specifically, the accelerometer data set from a representative time frame of 2–4 h for each day was divided into blocks of n measurements. We then calculated the accumulated phase Φ( T ) for each block at T  = 2 ms, 4 ms, …, 30 ms. The phases follow Gaussian distributions (see Fig.  6 b, inset) with standard deviations σ Φ shown as a function of T in the main frame of Fig.  6 b.

a The spectra of the accelerations in z direction from the SAMS 121F04 accelerometer are compared to simulated Gaussian white noise spectra for different standard deviations σ z . The accelerometer spectra are averaged over relevant time frames of 2–4 h for days during which atom interferometer experiments were conducted (see legend). b The standard deviation ( σ Φ ) of the distribution of accumulated phases is depicted as a function of T . Distributions were obtained by calculating and binning the accumulated phases after dividing the acceleration data in blocks corresponding to the respective times T . (inset) Two examples of these distributions are given for T  = 4 ms and T  = 20 ms. Deviations of σ Φ from the expected T 2 -scaling for ISS data are attributed to deviations of the accelerometer spectra from that of ideal Gaussian white noise as shown.

The impact of the vibrational phase noise on the atom interferometer visibility was modeled using simulated data for an ideal fringe. For each T , Gaussian-distributed noise with the previously calculated σ Φ was added to the phase ϕ of ideal interferometer fringes. Fitting the resulting signals to Eq. ( 7 ) yielded the expected visibility shown in the upper inset of Fig.  2 . While the ISS vibration spectra remained similar over the roughly 3-month time span over which the MZI experiments were conducted, differences in the day-to-day vibrations are noticeable at larger T .

For short T , σ Φ due to ISS vibrations is larger than σ Φ from simulated Gaussian white noise. However, the behavior inverts for larger T , as shown in Fig.  6 b. A likely explanation for the deviation from the expected T 2 -behavior is that the harmonics in the real ISS vibration spectra are important for short T . The influence of small n for T  = 2 ms are also found to lead to slight deviations from an ideal Gaussian distribution even with simulated Gaussian white noise. However, for larger T , low frequency harmonics are less impactful and can essentially only contribute a maximum phase.

Data availability

All NASA CAL data are on a schedule for public availability through the NASA Physical Sciences Informatics (PSI) website ( https://www.nasa.gov/PSI ) at the time of publication.  Source data are provided with this paper.

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Acknowledgements

We gratefully acknowledge the contributions of current and former members of CAL’s operations and technical teams, and those of the team at Coldquanta Labs. We also recognize the continuing support of JPL’s Astronomy, Physics, and Space Technology Directorate, of the JPL Communication, Tracking, and Radar Division, the JPL Mission Assurance Office, the Payloads Operations Integration Center (POIC) cadre at NASA’s Marshall Space Flight Center, the International Space Station Program Office (ISSPO) at NASA’s Johnson Space Center in Houston, and ISS crew members. We are thankful for dedicated support from the Biological and Physical Sciences Division (BPS) of NASA’s Science Mission Directorate at the agency’s headquarters in Washington, D.C. Cold Atom Lab was designed, managed, and operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (Task Order 80NM0018F0581). CAL and the PI-led science teams, including J.R.W., C.A.S., D.C.A., S.B., E.R.E., J.M.K., H.M., K.O., L.P., M.S., C.Schn., B.S., R.J.T., and N.P.B., are sponsored by BPS of NASA’s Science Mission Directorate at the agency’s headquarters in Washington, D.C. and by ISSPO at NASA’s Johnson Space Center in Houston. E.M.R., G.M., W.P.S., P.B., E.G., A.P., and N.G. acknowledge support by the DLR Space Administration with funds provided by the Federal Ministry for Economic Affairs and Climate Action (BMWK) under grant numbers DLR 50WM2245-A/B (CAL-II), 50WM2253A (AI-quadrat), 50WM2250E (QUANTUS+), and 50WM2177 (INTENTAS). N.G. further acknowledges support from the Deutsche Forschungsgemeinschaft (German Research Foundation) under Germany’s Excellence Strategy (EXC-2123 QuantumFrontiers Grants No. 390837967) and through CRC 1227 (DQ-mat) within Project No. A05. A.R. is supported by the Q-GRAV Project within the Space Research and Technology Program of the German Aerospace Center (DLR). A.P. and E.C. acknowledge support by the “ADI 2019/2022” project funded by the IDEX Paris-Saclay, ANR-11-IDEX-0003-02. Any opinions, findings, and conclusions or recommendations expressed in this article are those of the authors and do not necessarily reflect the views of the National Aeronautics and Space Administration.

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Contributions

J.R.W., N.P.B., and C.A.S. are CAL Principal Investigators leading the teams who conducted experiments in the “Mach–Zehnder interferometer”, “Shear-wave atom interferometry”, and “Photon recoil measurement” sections, respectively. The atom interferometer was proposed as a CAL add-on by the CUAS consortium including N.G., M.M., H.M., E.M.R., A.R., W.P.S., and C.Schu. as part of the Bigelow team. D.C.A. led CAL’s ground testbed for the development, integration, and subsystem-level testing of the upgraded science module. E.R.E. led operation of CAL’s engineering model testbed for system-level testing of the upgraded science module with flight-like hardware. J.M.K. supported development of the atom interferometer platform and led the characterization of instrument telemetry. J.R.K. led development of ISS hardware installation procedures and operations. B.S. analyzed data for the recoil measurement experiments. L.P., M.S., J.M.K., and S.B. analyzed atom interferometry data and supported manuscript preparation. C.Schn. analyzed ISS vibration data and drafted the ISS vibrations study. A.R. proposed the shear-wave interferometry sequences and carried out a detailed theoretical modeling of the fringe spacing. H.A., P.B., M.M., G.M. and A.P., with support from E.C., E.G., and W.H., analyzed the shear-wave interferometry data. K.O. (CAL Project Manager) and N.E.L. led technical planning and supported testing across multiple subsystems during hardware development and science operations. R.J.T. proposed the CAL instrument and gave scientific guidance as Project Scientist from 2018–2020 and Cold Atom Program Scientist since 2021. J.R.W. was the CAL Project Scientist since 2021 and led the development of the flight atom interferometer system, with support from J.M.K., D.C.A., E.R.E., K.O., and H.M. The initial manuscript was drafted by J.R.W. along with C.A.S., M.M., N.G., and N.P.B. All authors read, edited, and approved the final manuscript.

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Williams, J.R., Sackett, C.A., Ahlers, H. et al. Pathfinder experiments with atom interferometry in the Cold Atom Lab onboard the International Space Station. Nat Commun 15 , 6414 (2024). https://doi.org/10.1038/s41467-024-50585-6

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DOI : https://doi.org/10.1038/s41467-024-50585-6

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