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Schrodinger's Cat (Simplified): What Is It & Why Is It Important?

In 1935 – two years after winning the Nobel Prize for his contributions to quantum physics – Austrian Physicist Erwin Schrödinger proposed the famous thought experiment known as Schrödinger’s cat paradox.

What Is Schrödinger’s Cat Paradox?

The paradox is one of the most well-known things about quantum mechanics in popular culture, but it isn’t merely a surreal and funny way to describe how the quantum world behaves, it actually strikes at a key criticism of the dominant interpretation of quantum mechanics.

It endures because it proposes the absurd idea of a simultaneously alive and dead cat, but it has some philosophical weight because, in a sense, this really is something that quantum mechanics might suggest is possible.

Schrödinger came up with the thought experiment for precisely this reason. Like many other physicists, he wasn’t completely satisfied by the Copenhagen interpretation of quantum mechanics, and he was looking for a way to convey what he saw as the central flaw in it as a way of describing reality.

The Copenhagen Interpretation of Quantum Mechanics

The Copenhagen interpretation of quantum mechanics is still the most widely-accepted attempt to make sense of what quantum physics actually means in a physical sense.

It essentially says that the wave function (which describes a particle’s state) and the Schrödinger equation (which you use to determine the wave function) tell you everything you can know about a quantum state. This might sound reasonable at first, but this implies a lot of things about the nature of reality that don’t sit well with many people.

For example, a particle’s wave function spreads across space, and so the Copenhagen interpretation states that a particle doesn’t have a definitive location until a measurement is made.

When you make a measurement, you cause wavefunction collapse, and the particle falls into one of several possible states instantly, and this can only be predicted in terms of a probability.

The interpretation says that quantum particles actually don’t have values of observables such as position, momentum or spin until an observation is made . They exist in a range of potential states, in what is called a “superposition” and can essentially be thought of as all of them at once, although weighted to acknowledge that some states are more likely than others.

Some take this interpretation more strictly than others – for example, the wave function could simply be viewed as a theoretical construct that allows scientists to predict the results of experiments – but this is broadly how the interpretation views quantum theory.

Schrödinger’s Cat

In the thought experiment, Schrödinger proposed placing a cat in a box, so it was hidden from observers (you can imagine this to be a sound-proof box, too) along with a vial of poison. The vial of poison is rigged to break and kill the cat if a certain quantum event takes place, which Schrödinger took to be the decay of a radioactive atom which is detectable with a Geiger counter.

As a quantum process, the timing of radioactive decay can’t be predicted in any specific case, only as an average over many measurements. So with no way to actually detect the decay and the vial of poison breaking, there is literally no way to know whether it has happened in the experiment.

In the same way as particles are not considered to be in a particular location prior to measurement in quantum theory, but a quantum superposition of possible states, the radioactive atom can be considered to be in a superposition of “decayed” and “not decayed.”

The probability of each could be predicted to a level that would be accurate over many measurements but not for a specific case. So if the radioactive atom is in a superposition, and the life of the cat depends entirely on this state, does this mean the cat’s state is also in superposition of states? In other words, is the cat in a quantum superposition of alive and dead?

Does the superposition of states only happen at the quantum level, or does the thought experiment show that it should logically apply to macroscopic objects too? If it can’t apply to macroscopic objects, why not? And most of all: Isn’t this all a bit ridiculous?

Why Is It Important?

The thought experiment gets to the philosophical heart of quantum mechanics. In one easy-to-understand scenario, the potential issues with the Copenhagen interpretation are laid bare and proponents of the explanation are left with some explaining to do. One of the reasons it’s endured in popular culture is undoubtedly that it vividly shows the difference between how quantum mechanics describes the state of quantum particles, and the way you describe macroscopic objects.

However, it also tackles the notion of what you mean by “measurement” in quantum mechanics. This is an important concept, because the process of wave function collapse depends fundamentally on whether something has been observed.

Do people need to physically observe the outcome of a quantum event (for example, reading the Geiger counter), or does it simply need to interact with something macroscopic? In other words, is the cat a “measuring device” in this scenario – is that how the paradox is resolved?

There isn’t really an answer to these questions that’s widely-accepted. The paradox perfectly captures what it is about quantum mechanics that is hard to stomach for humans accustomed to experiencing the macroscopic world, and indeed, whose brains ultimately evolved to understand the world in which you live and not the world of subatomic particles.

The EPR Paradox

The EPR paradox is another thought experiment intended to show issues with quantum mechanics, and it was named after Albert Einstein, Boris Podolsky and Nathan Rosen, who devised the paradox. This relates to quantum entanglement , which Einstein famously referred to as “spooky action at a distance.”

In quantum mechanics, two particles can be “entangled,” so that any one of the pair cannot be described without reference to the other – their quantum states are described by a shared wave function that cannot be separated into one for one particle and one for another.

For example, two particles in a specific entangled state can have their “spin” measured, and if one is measured as having spin “up,” the other must have spin “down,” and vice-versa, although this isn’t determined beforehand.

This is a little difficult to accept anyway, but what if, the EPR paradox proposes, the two particles were separated by a huge distance. The first measurement is made and reveals “spin down,” but then very shortly afterward (so fast that even a light signal couldn’t have traveled from one location to the other in time) a measurement is made on the second particle.

How does the second particle “know” the result of the first measurement if it’s impossible for a signal to have traveled between the two?

Einstein believed this was proof that quantum mechanics was “incomplete,” and that there were “hidden variables” at play that would explain seemingly illogical results like these. However, in 1964, John Bell found a way to test for the presence of the hidden variables Einstein proposed and found an inequality that, if broken, would prove that the result couldn’t be obtained with a hidden variable theory.

Experiments performed on the basis of this have found that Bell’s inequality is broken, and so the paradox is just another aspect of quantum mechanics that seems strange but is simply the way quantum mechanics works.

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About the Author

Lee Johnson is a freelance writer and science enthusiast, with a passion for distilling complex concepts into simple, digestible language. He's written about science for several websites including eHow UK and WiseGeek, mainly covering physics and astronomy. He was also a science blogger for Elements Behavioral Health's blog network for five years. He studied physics at the Open University and graduated in 2018.

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Schrödinger's cat: The favorite, misunderstood pet of quantum mechanics

Reference article: A brief, simple explanation of Schrödinger's cat.

The thought experiment known as Schrödinger's cat is one of the most famous, and misunderstood, concepts in quantum mechanics . By thinking deeply about it, researchers have come to spectacular insights about physical reality. 

Who came up with Schrödinger's cat? 

The Austrian physicist Erwin Schrödinger, who helped found the discipline of quantum mechanics, first conceived of his feline conundrum in 1935 as a commentary on problems originally posed by the luminary Albert Einstein, according to an article in Quanta Magazine . 

While developing their new understanding of the subatomic realm, most of Einstein and Schrödinger's colleagues had realized that quantum entities exhibited extremely odd behaviors. The Danish physicist Niels Bohr championed an understanding that particles like electrons did not have well-defined properties until they were measured. Before that, the particles existed in what's known as a superposition of states, with, for example, a 50% chance of being oriented "up" and a 50% chance of being oriented "down."

Einstein, in particular, did not like this indecisive explanation. He wanted to know how, exactly, the universe knows that someone is measuring something. Schrödinger highlighted this absurdity with his notorious conceptual cat.

Suppose one builds a strange contraption, Schrödinger wrote in a 1935 paper called " The Current Situation in Quantum Mechanics ." The apparatus consists of a box with a sealed vial of cyanide, above which is suspended a hammer attached to a Geiger counter aimed at a small lump of mildly radioactive uranium. Inside the box, there's also a kitty (and remember, this is a thought experiment that's never actually been carried out). 

The box is sealed, and the experiment is left to run for some set amount of time, perhaps an hour. In that hour, the uranium, whose particles obey the laws of quantum mechanics, has some chance of emitting radiation that will then be picked up by the Geiger counter, which will, in turn, release the hammer and smash the vial, killing the cat by cyanide poisoning. 

According to folks like Bohr, until the box is opened and the cat's status is "measured," it will remain in a superposition of both living and deceased. People like Einstein and Schrödinger balked at such a possibility, which doesn't accord with everything our ordinary experience tells us — cats are either alive or dead, not both at the same time.

"[Q]uantum physics lacked an important component, a story about how it lined up with things in the world," wrote science journalist Adam Becker in his book " What Is Real? " (Basic Books, 2018). "How does a phenomenal number of atoms, governed by quantum physics, give rise to the world we see around us?" 

Is Schrödinger's cat real? 

Schrödinger's cat cut to the heart of what was bizarre about Bohr's interpretation of reality: the lack of a clear dividing line between the quantum and everyday realms. While most people think it provides an example in support of particles lacking clearly-defined properties until they are measured, Schrödinger's original intention was the exact opposite—to show that such an idea was nonsensical. Yet, for many decades, physicists largely ignored this problem, moving on to other quandaries. 

But starting in the 1970s, researchers were able to show that quantum particles can be created in states that always correspond to one another — so if one shows an "up" orientation, the other will be "down" — a phenomenon that Schrödinger called entanglement. Such work has been used to underpin the emerging field of quantum computing , which promises to produce calculating machines that are far faster than current technologies. 

In 2010, physicists also managed to create a real-world version of Schrödinger's cat , albeit in a way that doesn't involve felicide (aka, kitty murder). University of California, Santa Barbara, scientists built a resonator, basically a tiny tuning fork, the size of the pixel on a computer screen. They put it into a superposition in which it was both oscillating and not oscillating at the same time, showing that relatively large objects can occupy bizarre quantum states.

More-recent experiments have put groups of up to 2,000 atoms in two different places at the same time , further blurring the dividing line between the microscopic and macroscopic. In 2019, researchers at the University of Glasgow even managed to take a photo of entangled photons using a special camera that snapped a picture whenever a photon showed up with its entangled partner. 

While physicists and philosophers have yet to agree on how to think about the quantum world, Schrödinger's insights have produced many fruitful research avenues and are likely to continue doing so for the foreseeable future. 

Additional resources: 

• Read how one physicist reconciles the conundrum of Schrödinger's cat, from The Conversation . 
• Learn more about the basics of quantum mechanics from Stanford University .
• Watch "The Real Meaning of Schrödinger's Cat," from Ask A Spaceman, with Paul Sutter . 

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Adam Mann is a freelance journalist with over a decade of experience, specializing in astronomy and physics stories. He has a bachelor's degree in astrophysics from UC Berkeley. His work has appeared in the New Yorker, New York Times, National Geographic, Wall Street Journal, Wired, Nature, Science, and many other places. He lives in Oakland, California, where he enjoys riding his bike. 

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Schrödinger’s cat

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Schrödinger’s cat , thought experiment designed by theoretical physicist Erwin Schrödinger in 1935 as an objection to the reigning Copenhagen interpretation of quantum mechanics .

Often considered as central to quantum physics as Isaac Newton ’s laws of motion are to classical physics, the Schrödinger equation , which he had devised in 1926, is essentially a wave equation that describes the form of probability waves (or wave functions ) that govern the motion of small particles and how these waves change over time. Solutions to the equation take the form of wave functions that can only be related to the probable occurrence of physical events. Schrödinger used the equation to predict the qualities of a hydrogen atom , and the equation remains a fundamental building block of quantum mechanics.

However, Schrödinger himself was displeased with how the equation came to be interpreted, namely, the Copenhagen interpretation (so called because its main proponent , Niels Bohr , lived in that city). Unlike Newton’s equations of motion, which provided concrete answers to questions of the universe, the Copenhagen interpretation of Schrödinger’s equation depended on the more abstract notion of probability. Instead of precise locations and quantities, quantum mechanics could only produce results no more concrete than the probability of an electron existing in a certain spot after a certain amount of time.

Schrödinger felt that while quantum mechanics was valid in describing the blurriness of the subatomic world, applying quantum mechanics indiscriminately led to strange consequences, writing in his paper “The Present Situation in Quantum Mechanics” (1935):

One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays , but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts.

Schrödinger’s cat argues that, in the Copenhagen interpretation, until an observer opens the box and reveals the cat’s fate, the cat is both alive and dead—a state described as a “superposition.” Schrödinger thought that the cat being both alive and dead was “quite ridiculous” and intended his thought experiment to challenge other scientists’ suppositions about quantum mechanics. However, scientists have since been able to place particles such as ions and photons in superposed states. French physicist Serge Haroche and American physicist David Wineland won the 2012 Nobel Prize for Physics for their work in devising experiments to create such “Schrödinger cat states,” in which particles can be observed as simultaneously being in two different states.

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Schrödinger’s cat

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Devised in 1935 by the Austrian physicist Erwin Schrödinger, this thought experiment was designed to shine a spotlight on the difficulty with interpreting quantum theory .

Quantum theory is very strange. It says that an object like a particle or an atom that adheres to quantum rules doesn’t have a reality that can be pinned down until it is measured. Until then, its properties, such as momentum, are encoded in a mathematical object known as a wave function that essentially says: if you make a measurement, here are a range of possible outcomes. The inevitable question that arose as the theory developed was: what, then, is the thing doing before that?

The most prominent answer in the 1930s came from the Copenhagen interpretation , developed in the Danish city by luminaries of quantum theory, Niels Bohr and Werner Heisenberg . This says that there really is no definitive reality before the measurement, and the object is in an undefined state known as a superposition.

Schrödinger’s thought experiment probed how this plays out when a quantum object is coupled to something more familiar. He imagined a box containing a radioactive atom, a vial of poison and a cat. Governed by quantum rules, the radioactive atom can either decay or not at any given moment. There’s no telling when the moment will come, but when it does decay, it breaks the vial, releases the poison and kills the cat.

If the Copenhagen interpretation is correct, then before any measurement has occurred, the atom, and so also the cat, are in a superposition of being decayed/dead and not decayed/alive. The absurdity of speaking of a simultaneously living and dead moggie was supposed to show that the Copenhagen interpretation must be lacking something.

The experiment played an important part in spurring other ways of thinking about quantum theory, including the many worlds interpretation, which says that the different possible realities of a quantum object crystallise into different parallel universes at the point of measurement.

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These days the thought experiment has taken on a kind of cult status. There are Schrödinger’s cat T-shirts, memes and hundreds of articles on the subject. In 2018, scientists published a more complicated variant of the thought experiment that appears to show that all existing interpretations of quantum theory are incomplete .

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Schrödinger's Cat

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Two worlds "splitting off"- one where the cat is alive and one where the cat is dead. Taken from [MWI].

Schrödinger's cat is a thought experiment designed to show how certain interpretations of quantum mechanics lead to counterintuitive results.

In the experiment, a cat is placed inside a box with a vial of poisonous gas. A mallet is set up such that it breaks the vial of gas if a particular radioactive atom decays, killing the cat. Since the radioactive decay is a quantum system, whether the cat lives or dies is determined by quantum mechanical behavior. This leads to the conclusion that before the box is opened, the cat is simultaneously alive and dead.

Erwin Schrödinger originally proposed the idea as an absurd example showing that the Copenhagen Interpretation of quantum mechanics - the most popular philosophical interpretation at the time - could not possibly be true [1]. However, it has lived on as a thought experiment fueling both physical theories and the popular imagination.

Quantum States and Superposition

The many-worlds interpretation.

The two main ideas behind quantum theory are the idea of quantized , or discrete, states, and the idea of superposition.

A physical system is defined by the set of possible states in which it can be observed . For instance, an electron can be observed either in a spin up state or in a spin down state, but never a combination of the two. Similarly, a particle emitted in radioactive decay is observed to be either emitted or not emitted, never partway emitted. However, particles prepared in identical ways will not always be observed to have the same state. Identical uranium atoms will decay or not decay at random times, though the more time has passed, the more likely the atom is to decay. The state of the system will change such that it becomes more likely to decay.

To determine how states change over time, the idea of a superposition of states is required. A superposition is a vector addition of two states. Quantum states can be in any superposition of the observable states in the system. For instance, an electron can be in a state that is 50% spin up and 50% spin down. As time passes, the electron may change states, perhaps smoothly oscillating between 100% spin up and 100% spin down, passing through the 50/50 state at each time. The Schrödinger equation , the analog of Newton's laws for quantum mechanics, describes exactly how the electron will transition between these different superpositions of states.

But this seems to be at odds with the previous statement. How can a system be an a superposition of states if it can only ever be observed in one state? The Copenhagen interpretation of quantum mechanics holds that when an observer observes a system, it "collapses" from a superposition of multiple states down to a single state in a probabilistic way. This is distinct from the smooth changes in superposition that happen due to the Schrödinger equation.

When Schrödinger's cat is observed, it is either alive or dead. But when it isn't, it is in a superposition of alive and dead.

Technical note: the space of valid states is the set of complex vectors with an eigenbasis given by the observable states and magnitude 1. For linear combinations of eigenvectors, the probability of observing each component of the state vector is given by the magnitude of the coefficient of that component. Linear algebra is important for a deep understanding of quantum mechanics: most results come directly from the properties of operators on complex vector spaces.

The collapse interpretation has an issue, though. Instead of just you observing a cat in a box, imagine putting yourself and the cat in a room and having your friend wait outside the room. You run the experiment, open the box, record your observations, and only then have your friend open the room and see what your observations were. From your perspective, the cat is in a superposition of alive and dead until you open the box, at which point a collapse occurs. You are then in the definite state of having seen the cat, a state which persists until your friend opens the door. But from your friend's perspective, up until they open the door, you are still in a superposition of having seen the cat dead and having seen it alive.

Even worse, this setup can be repeated again and again, such that every new observer is placed in a larger room. Observer \(n\) always thinks that the state has collapsed before observer \(n + 1\). The idea that different observers will disagree on the state of reality in this experiment is problematic.

The many-worlds interpretation of quantum mechanics solves this problem by rejecting the idea of collapse entirely. It instead claims that there is always a superposition of two "world-branches," one where the cat is dead and one where the cat is alive. When you open the box, there is now a superposition of two worlds with two versions of you. In one world, the cat is alive and you see the cat is alive. In the other world, the cat is dead and you see the cat is dead.

[1] Schrödinger, Erwin; Translated by Trimmer, John. The Present Situation in Quantum Mechanics. Proceedings of the American Philosophical Society . Retrieved on 7 Mar 2016 from http://www.tuhh.de/rzt/rzt/it/QM/cat.html

[flickr] Flickr user chwalker01. Retrieved on 7 Mar 2016 from https://www.flickr.com/photos/31690139@N02/2965956885

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Erwin Schrödinger and the Schrödinger's Cat Thought Experiment

Nobel Prize winning physicist who shaped quantum mechanics

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Erwin Rudolf Josef Alexander Schrödinger (born on August 12, 1887 in Vienna, Austria) was a physicist who conducted groundbreaking work in quantum mechanics , a field which studies how energy and matter behave at very small length scales. In 1926, Schrödinger developed an equation that predicted where an electron would be located in an atom. In 1933, he received a Nobel Prize for this work, along with physicist Paul Dirac .

Fast Facts: Erwin Schrödinger

• Full Name: Erwin Rudolf Josef Alexander Schrödinger
• Known For: Physicist who developed the Schrödinger equation, which signified a great stride for quantum mechanics. Also developed the thought experiment known as “Schrödinger’s Cat.”
• Born: August 12, 1887 in Vienna, Austria
• Died: January 4, 1961 in Vienna, Austria
• Parents: Rudolf and Georgine Schrödinger
• Spouse: Annemarie Bertel
• Child : Ruth Georgie Erica (b. 1934)
• Education : University of Vienna
• Awards : with quantum theorist, Paul A.M. Dirac awarded 1933 Nobel Prize in Physics.
• Publications : What Is Life? (1944), Nature and the Greeks  (1954), and My View of the World  (1961).

Schrödinger may be more popularly known for “ Schrödinger’s Cat ,” a thought experiment he devised in 1935 to illustrate problems with a common interpretation of quantum mechanics.

Early Years and Education

Schrödinger was the only child of Rudolf Schrödinger – a linoleum and oilcloth factory worker who had inherited the business from his father – and Georgine, the daughter of a chemistry professor of Rudolf’s. Schrödinger’s upbringing emphasized cultural appreciation and advancement in both science and art.

Schrödinger was educated by a tutor and by his father at home. At the age of 11, he entered the Akademische Gymnasium in Vienna, a school focused on classical education and training in physics and mathematics. There, he enjoyed learning classical languages, foreign poetry, physics, and mathematics, but hated memorizing what he termed “incidental” dates and facts.

Schrödinger continued his studies at the University of Vienna, which he entered in 1906. He earned his PhD in physics in 1910 under the guidance of Friedrich Hasenöhrl, whom Schrödinger considered to be one of his greatest intellectual influences. Hasenöhrl was a student of physicist Ludwig Boltzmann, a renowned scientist known for his work in statistical mechanics .

After Schrödinger received his PhD, he worked as an assistant to Franz Exner, another student of Boltzmann’s, until being drafted at the beginning of World War I .

Career Beginnings

In 1920, Schrödinger married Annemarie Bertel and moved with her to Jena, Germany to work as the assistant of physicist Max Wien. From there, he became faculty at a number of universities over a short period of time, first becoming a junior professor in Stuttgart, then a full professor at Breslau, before joining the University of Zurich as a professor in 1921. Schrödinger’s subsequent six years at Zurich were some of the most important in his professional career.

At the University of Zurich, Schrödinger developed a theory that significantly advanced the understanding of quantum physics. He published a series of papers – about one per month – on wave mechanics. In particular, the first paper, “ Quantization as an Eigenvalue Problem ," introduced what would become known as the Schrödinger equation , now a central part of quantum mechanics. Schrödinger was awarded the Nobel Prize for this discovery in 1933.

Schrödinger’s Equation

Schrödinger's equation mathematically described the "wavelike" nature of systems governed by quantum mechanics. With this equation, Schrödinger provided a way to not only study the behaviors of these systems, but also to predict how they behave. Though there was much initial debate about what Schrödinger’s equation meant, scientists eventually interpreted it as the probability of finding an electron somewhere in space.

Schrödinger’s Cat

Schrödinger formulated this thought experiment in response to the Copenhagen interpretation of quantum mechanics, which states that a particle described by quantum mechanics exists in all possible states at the same time, until it is observed and is forced to choose one state. Here's an example: consider a light that can light up either red or green. When we are not looking at the light, we assume that it is both red and green. However, when we look at it, the light must force itself to be either red or green, and that is the color we see.

Schrödinger did not agree with this interpretation. He created a different thought experiment, called Schrödinger's Cat, to illustrate his concerns. In the Schrödinger's Cat experiment, a cat is placed inside a sealed box with a radioactive substance and a poisonous gas. If the radioactive substance decayed, it would release the gas and kill the cat. If not, the cat would be alive.

Because we do not know whether the cat is alive or dead, it is considered both alive and dead until someone opens the box and sees for themselves what the state of the cat is. Thus, simply by looking into the box, someone has magically made the cat alive or dead even though that is impossible.

Influences on Schrödinger’s Work

Schrödinger did not leave much information about the scientists and theories that influenced his own work. However, historians have pieced together some of those influences, which include:

• Louis de Broglie , a physicist, introduced the concept of “ matter waves." Schrödinger had read de Broglie’s thesis as well as a footnote written by Albert Einstein , which spoke positively about de Broglie’s work. Schrödinger was also asked to discuss de Broglie’s work at a seminar hosted by both the University of Zurich and another university, ETH Zurich.
• Boltzmann. Schrödinger considered Boltzmann’s statistical approach to physics his “first love in science,” and much of his scientific education followed in the tradition of Boltzmann.
• Schrödinger’s previous work on the quantum theory of gases, which studied gases from the perspective of quantum mechanics. In one of his papers on the quantum theory of gases, “On Einstein’s Gas Theory,” Schrödinger applied de Broglie’s theory on matter waves to help explain the behavior of gases.

Later Career and Death

In 1933, the same year he won the Nobel Prize, Schrödinger resigned his professorship at the University of Berlin, which he had joined in 1927, in response to the Nazi takeover of Germany and the dismissal of Jewish scientists. He subsequently moved to England, and later to Austria. However, in 1938, Hitler invaded Austria, forcing Schrödinger, now an established anti-Nazi, to flee to Rome.

In 1939, Schrödinger moved to Dublin, Ireland, where he remained until his return to Vienna in 1956. Schrödinger died of tuberculosis on January 4, 1961 in Vienna, the city where he was born. He was 73 years old.

• Fischer E. We are all aspects of one single being: An introduction to Erwin Schrödinger. Soc Res , 1984; 51 (3): 809-835.
• Heitler W. “ Erwin Schrödinger, 1887-1961. ” Biogr Mem Fellows Royal Soc , 1961; 7 : 221-228.
• Masters B. “ Erwin Schrödinger’s path to wave mechanics. ” Opt Photonics News , 2014; 25 (2): 32-39.
• Moore W. Schrödinger: Life and thought. Cambridge University Press; 1989.
• Schrödinger: Centenary celebration of a polymath. Ed. Clive Kilmister, Cambridge University Press; 1987.
• Schrödinger E. “ Quantisierung als Eigenwertproblem, erste Mitteilung. ” Ann. Phys. , 1926; 79 : 361-376.
• Teresi D. The lone ranger of quantum mechanics. The New York Times website. https://www.nytimes.com/1990/01/07/books/the-lone-ranger-of-quantum-mechanics.html . 1990.
• Biography of Physicist Paul Dirac
• Biography of Brian Cox
• Biographical Profile of Niels Bohr
• Joseph Henry, First Secretary of the Smithsonian Institution
• Heinrich Hertz, Scientist Who Proved Existence of Electromagnetic Waves
• Biography of Hans Bethe
• Biography of John Bardeen, Nobel Prize-Winning Physicist
• Michio Kaku Biography
• Biography of William Shockley, American Physicist and Inventor
• Life and Work of Gustav Kirchhoff, Physicist
• Life of Léon Foucault, Physicist Who Measured the Speed of Light
• Leo Szilard, Creator of Manhattan Project, Opposed Use of Atomic Bomb
• Biography of Christian Doppler, Mathematician and Physicist
• Biography of Stephen Hawking, Physicist and Cosmologist
• Niels Bohr Institute
• The Life and Work of Albert Einstein

What did Schrodinger's Cat experiment prove?

Category: Physics      Published: July 30, 2013     Updated: November 27, 2023

By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and Associate Professor of Physics at West Texas A&M University

"Schrodinger's Cat" was not a real experiment and therefore did not scientifically prove anything. Schrodinger's Cat is not even part of any scientific theory. Schrodinger's Cat was simply a teaching tool that Schrodinger used to illustrate how some people were misinterpreting quantum theory. Schrodinger constructed his imaginary experiment with the cat to demonstrate that simple misinterpretations of quantum theory can lead to absurd results which do not match the real world. Unfortunately, many popularizers of science in our day have embraced the absurdity of Schrodinger's Cat and claim that this is how the world really works.

In quantum theory, quantum particles can exist in a superposition of states at the same time and collapse down to a single state upon interaction with other particles. Some scientists at the time that quantum theory was being developed (1930's) drifted from science into the realm of philosophy, and stated that quantum particles only collapse to a single state when viewed by a conscious observer. Schrodinger found this concept absurd and devised his thought experiment to make plain the absurd yet logical outcome of such claims.

In Schrodinger's imaginary experiment, you place a cat in a box with a tiny bit of radioactive substance. When the radioactive substance decays, it triggers a Geiger counter which causes a poison or explosion to be released that kills the cat. Now, the decay of the radioactive substance is governed by the laws of quantum mechanics. This means that the atom starts in a combined state of "going to decay" and "not going to decay". If we apply the observer-driven idea to this case, there is no conscious observer present (everything is in a sealed box), so the whole system stays as a combination of the two possibilities. The cat ends up both dead and alive at the same time. Because the existence of a cat that is both dead and alive at the same time is absurd and does not happen in the real world, this thought experiment shows that wavefunction collapses are not just driven by conscious observers.

Einstein saw the same problem with the observer-driven idea and congratulated Schrodinger for his clever illustration, saying, "this interpretation is, however, refuted, most elegantly by your system of radioactive atom + Geiger counter + amplifier + charge of gun powder + cat in a box, in which the psi-function of the system contains the cat both alive and blown to bits. Is the state of the cat to be created only when a physicist investigates the situation at some definite time?"

Since that time, there has been ample evidence that wavefunction collapse is not driven by conscious observers alone. In fact, every interaction a quantum particle makes can collapse its state. Careful analysis reveals that the Schrodinger Cat "experiment" would play out in the real world as follows: as soon as the radioactive atom interacts with the Geiger counter, it collapses from its non-decayed/decayed state into one definite state. The Geiger counter gets definitely triggered and the cat gets definitely killed. Or the Geiger counter gets definitely not triggered and the cat is definitely alive. But both don't happen.

Roger Penrose, a Nobel Prize winner and one of the most brilliant physicists of the last sixty years, wrote about Schrodinger's Cat in his book The Road to Reality as follows: "So the cat is both dead and alive at the same time! Of course such a situation is an absurdity for the behavior of a cat-sized object in the actual physical world as we experience it... There is a 50% chance that the cat will be [definitely] killed and a 50% chance that it will [definitely] remain alive. This is the physically correct answer, where 'physically' refers to the behavior of the world that we actually experience." Penrose goes on to explain that any physical theory or philosophical interpretation of quantum physics that leads to the cat being both dead and alive at the same time must be a faulty theory or interpretation, because that is not what happens in the real world.

Despite that fact that the Schrodinger's Cat story is not a real experiment, does not prove anything, does not match physical reality, and was intentionally designed to be absurd, this line of thinking does indeed lead to a meaningful question. Why does the cat in this setup not end up in a state of dead and alive at the same time in the real world? In other words, why does a measurement collapse a quantum object from a superposition of states to a single definite state? This question has not yet been fully answered by quantum physics. This is known as the "measurement problem" of quantum physics. Note that the measurement of a quantum object in a superposition of states collapsing down the object to a definite single state is very well predicted by the mathematics of quantum physics. Therefore, the "measurement problem" is more a problem of philosophical interpretation and incomplete scientific explanation, than a problem of the theory being incorrect.

In summary, quantum state collapse is not driven just by conscious observers. Unfortunately, many popular science writers in our day continue to propagate the misconception that a quantum state (and therefore reality itself) is determined by conscious observers. They use this erroneous claim as a springboard into unsubstantial and non-scientific discussions about the nature of reality, consciousness, and even Eastern mysticism. To them, Schrodinger's Cat is not an embarrassing indication that their claims are wrong, but proof that the world is as absurd as they claim. Such authors either misunderstand Schrodinger's Cat, or intentionally misrepresent it to sell books.

Topics: Schrodinger's Cat , observation , quantum , superposition , wavefunction collapse

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Schrödinger's cat: a thought experiment in quantum mechanics - chad orzel.

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Austrian physicist Erwin Schrödinger, one of the founders of quantum mechanics, posed this famous question: If you put a cat in a sealed box with a device that has a 50% chance of killing the cat in the next hour, what will be the state of the cat when that time is up? Chad Orzel investigates this thought experiment.

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What Is Schrödinger’s Cat?

Schrödinger’s Cat is a famous thought experiment that illustrates a paradox of quantum superposition. Here’s how it works.

Schrödinger’s Cat is a thought experiment devised by the Austrian physicist Erwin Schrödinger, which he designed to illustrate a paradox of quantum superposition wherein a hypothetical cat may be considered both alive and dead simultaneously because its fate is linked to a random event that may (or may not) occur.

What Is Schrödinger’s Cat in Simple Terms?

Schrödinger’s Cat, as a thought experiment, states that if you seal a cat in a box with something that can eventually kill it, you won’t know if the cat is alive or dead until you open the box. So, until you open the box and observe the cat, the cat is simultaneously dead and alive. 

How Does Schrödinger’s Cat Work?

We often use Schrödinger’s thought experiment to explain the concept of superposition . The experiment states that a hypothetical cat is locked in a box with some radioactive substance controlling a vial of poison. When the substance decays, it triggers a Geiger counter that causes the poison to be released, thereby killing the cat. 

Since the box is locked, and we on the outside don’t know whether or not the radioactive substance has decayed and released the poison, we can’t tell if the cat is dead or alive. So, until we open the box to know for sure, the cat is both dead and alive. Mathematically speaking, there’s a 50 percent chance the cat is dead and a 50 percent chance the cat is alive. 

More From Built In’s Tech Dictionary What Is Superposition?

How Is Schrödinger’s Cat Both Alive and Dead?

In quantum mechanics terms, the cat’s ability to be in an ambiguous state of both alive and dead until it’s observed (i.e. when someone opens the box) is referred to as quantum indeterminacy or the observer’s paradox . The paradox states that an event or an experiment’s observer affects its outcome. In this case, whomever is performing this hypothetical experiment can affect whether the cat remains in an unknown state or they can open the box and know if the cat is dead or alive with 100 percent certainty.

The experiment also points out when the resolution of possibilities occurs. The experiment is intended to make people ask themselves if it was logical for the observation to trigger the answer. After all, wouldn’t the cat be either dead or alive even if we never open the box? 

Schrödinger’s Cat and the Role of the Observer

In quantum mechanics, the observer (the person conducting the experiment) has a role in the results of the experiment. In this case, we are unaware of the cat’s state until the observer opens the box. Until the observer opens the box, the cat exists in a superposition state; that is, the cat is both alive and dead. Only by opening the box and looking at what’s inside (i.e., observing it) is the cat’s state confirmed to be one of the two states. This is called The Copenhagen interpretation of quantum mechanics, which basically explains that a quantum system exists in all of its possible states at the same time. Only when we make an observation can we confirm the true state of the system.

More Quantum Reading From Built In Experts Why Do Quantum Objects Keep Getting Weirder?

Why Do We Use Schrödinger’s Cat?

We still use this thought experiment today to explain quantum physics concepts in an easy-to-understand way. Some people also use Schrödinger’s Cat to talk more philosophically about how the thought experiment can be extended to other situations in life. For example, let’s say you meet your friend for a night out and you’re both unsure about what to have for dinner; until you reach an agreement or one of you decides for the group, the possible food option is “every option that can exist where you and your friend are.” Looking at things from this perspective has led many people to think of everything in life as “quantum” because until the future is here, it technically (according to Schrödinger ) exists in a state of superposition of all possible scenarios.

Frequently Asked Questions

What is schrödinger's cat in simple terms.

Schrödinger’s Cat is a famous thought experiment that demonstrates the idea in quantum physics that tiny particles can be in two states at once until they’re observed. It asks you to imagine a cat in a box with a mechanism that might kill it. Until you look inside, the cat is both alive and dead at the same time.

Is Schrödinger’s Cat a metaphor?

Schrödinger’s Cat is a thought experiment and is also considered a metaphor or a paradox.

Is Schrödinger’s Cat literal?

Schrödinger’s Cat is not meant to be taken literally, but as a thought experiment designed to show the counterintuitive idea of quantum superposition.

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©Lorenzo Ranieri Tenti

Why Schrödinger's Cat is still the most controversial thought experiment in science

Nearly a century after its formulation, the paradox remains hotly debated among researchers.

Dr Katie Mack

One of the most important tools in the theoretical physicist’s toolkit is the thought experiment. If you study relativity, quantum mechanics , or any area of physics applying to environments or situations in which you cannot (or should not) place yourself, you’ll find that you spend a lot more time working through imaginary scenarios than setting up instruments or taking measurements.

Unlike physical experiments, thought experiments are not about collecting data, but rather about posing an imaginary question and working through an ‘if/then’ logical sequence to explore what the theory really means.

Asking “what has to happen if the theory is true?” is invaluable for developing intuition and anticipating new applications. In some cases, a thought experiment can reveal the deep philosophical implications of a theory, or even present what appears to be an unsolvable paradox.

Probably the most famous of all physics thought experiments is that of Schrödinger’s Cat – both because it involves (purely hypothetical!) carnage, and because its implications for the nature of reality in a quantum world continue to challenge students and theorists everywhere.

The basic – again, purely hypothetical – experimental setup is this. Imagine you have a radioactive material in which there is a 50 per cent chance of a nuclear decay in some specified amount of time (let’s say, one hour).

You put this material in a box along with a small glass vial of poison and a device that will break the vial if a radioactive decay is detected. Then, you put a live cat in the box, close the lid, wait an hour, and then open the box once again.

Based on this setup, it’s straightforward to deduce that since the chance the atom decays and triggers the poison is 50 per cent, half the time you do the experiment, you should find a living cat, and half the time, you should find a dead one, assuming you’re not re-using the same cat each time.

But when Erwin Schrödinger described the thought experiment to Albert Einstein in 1935, he did so to highlight an apparent consequence of quantum theory that seemed to both scientists to be complete nonsense: the idea that before you open the box, the cat is both alive and dead at the same time.

Ultimately, it comes down to the principle of uncertainty in quantum mechanics. Unlike classical mechanics (the kind of physics that applies to our everyday experiences), in quantum mechanics, there seems to be a fundamental uncertainty built into the nature of reality.

When you flip a coin (a classical event), it’s only “random” because you’re not keeping careful enough track of all the motions and forces involved. If you could measure absolutely everything, you could predict the outcome every time – it’s deterministic.

But in the quantum mechanical version of a coin flip, the radioactive decay, nothing you measure can possibly tell you the outcome before it occurs. As far as an outside observer is concerned, until the measurement of the quantum coin flip occurs, the system will act like it’s in both states at once: the atom is both decayed and not decayed, in what we call a superposition.

Superposition is a real phenomenon in quantum mechanics, and sometimes we can even use it to our advantage. Quantum computing is built on the idea that a quantum computer bit (or qubit), instead of being just one or zero, can be in a superposition of one and zero, massively increasing the computer’s ability to do many complex calculations at once.

In the case of Schrödinger’s Cat, the apparently absurd conclusion that the cat is both alive and dead comes from considering the whole apparatus – the atom, the trigger device, and the poison vial, and the cat – to be a single quantum system, each element of which exists in a superposition.

The atom is decayed and not, the device is triggered and dormant, the vial is broken and intact, and the cat is therefore simultaneously dead and alive, until the moment the box is opened.

Whether this conclusion is actually absurd is an open question. What both Schrödinger and Einstein concluded was that true, fundamental uncertainty simply cannot apply to the real, macroscopic, world. These days, most physicists accept that uncertainty is real, at least for subatomic particles, but how that uncertainty 'collapses' when a measurement is made remains up for debate.

In one interpretation, any measurement that’s performed fundamentally alters reality – though it is usually argued that the trigger device, or, at least, the cat itself, provides a measurement for that purpose. In another interpretation, called Many Worlds, the entire Universe duplicates itself every time a quantum coin is flipped, and the measurement simply tells you whether you’re in the dead-cat or alive-cat universe from now on.

While we can’t say how long it will take before we fully understand what’s really going on in the black box of quantum superposition, applications of quantum theory are already bringing us incredible technological advances, like quantum computers. And in the meantime, clever thought experiments allow us to follow our curiosity, without running the risk of killing any cats.

Read more about quantum physics:

• The parallel worlds of quantum mechanics
• Dead and alive: why it's time to rethink quantum physics
• The quest for quantum gravity: why being wrong is essential to science

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Schrödinger's cat explained

In 1935, E. Schrödinger proposed his well-known cat thought experiment suggesting, but not explaining, how a measurement transforms the probable states of an atom into the actual state of a cat (alive or dead). Rather than applying quantum mechanics (the previous approach usually taken), I offer an out-of-the-box, logically consistent explanation using metrology (the science of physical measurement).

In formal quantum mechanics, an atom (or other entity) is in a superposition, or probabilistic combination of all possible states. In this widely accepted view, each state is possible and no state is actual until a measurement occurs. How does a measurement change multiple probable states into one actual state? E. Schrödinger's tongue-in-cheek thought experiment explores this by proposing a comparison of an atom's quantum superposition to the physical measurement of a cat's state.

The following is all the information Schrödinger provided on his thought experiment: "One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following diabolical device (which must be secured against direct interference by the cat): In a Geiger counter, there is a tiny bit of radioactive substance, so small that perhaps in the course of one hour, one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges, and through a relay releases a hammer which shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if, meanwhile, no atom has decayed. The first atomic decay would have poisoned it. The ψ function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts."

Schrödinger's experiment first appears to contrast the two distributions, the probabilistic time distribution of an atom's state and a cat's binary state (alive or dead) by correlating two observations (measurements): an atom's decay and a cat's death. In fact, by virtue of the apparatus, the actual time of each cat's death is a fixed time after the time of an atom's decay (due to the "diabolical device"). Schrödinger proposed the mean time of each of these equal but time-shifted distributions as one hour. With a mean time of one hour the maximum extent of every cat's actual time of death, distribution is estimated to be two hours.

Next, Schrödinger proposed one observation of the cat's state by a human at one hour. This is a one-time observation of a third distribution, the observed state of one cat over time. This may be compared with the cat's actual state (second distribution). This comparison is more interesting, as it appears to describe the measurement of a cat's state.

L. Euler defines all measurements as relative: "It is not possible to determine or measure one quantity other than by assuming that another quantity of the same type is known and determining the ratio between the quantity being measured and that quantity." The accuracy of each human observation of a cat is adjusted by calibration that correlates the measuring apparatus intervals (in this experiment, the time between observations) to a time reference (e.g., one second). This time reference is a non-local intermediate required to maintain Euler's relative quantity ratios.

The third distribution of each cat's observed time of death is correlated both to the actual time of death and to how often the human observes the cat (i.e., the time between human observations). In Schrödinger's experiment this time between observations is given as one hour. Then the accuracy of this one observation is +/- one hour relative to any possible cat's actual time of death (about a two-hour span).

When the times proposed (both one hour) are applied, the third distribution of the time between observations is uncorrelated to the first distribution of the atom's decay time. This occurs because the accuracy +/- one hour of the time between observations is close to as wide as an atom's decay distribution (two hours). This thought experiment, as presented, is two equal but time-shifted distributions of the atom's decay and cat's actual death (one ψ function) and one uncorrelated human observation (a different function). However, this experiment has drawn interest for 85 years because physical reality does not allow for the cat's state to be a superposition. What is missing?

The first human observation of a dead cat after an observation of life is measured in time relative to the beginning of the experiment (alive cat). These observations of the time of death identify that the distribution over multiple experiments is correlated with the ψ function of an atom's probabilities and that the state of each cat is binary. The actual time of death and the observed time of death are different. Because the observed time of death is also correlated to the time between observations and the time reference defined.

Consider the experiment when the observer (or measuring apparatus) counts the number of times the cat is examined. These observations result in a sequence of alive states ended by one dead state during the about two-hour maximum time to complete one experiment. Counting this sequence of alive observation generates a magnitude, but not a measurement correlated to a physical reference as Euler requires. Such a measurement requires defining and controlling the time between observations, which requires the calibration of the observer/measuring apparatus to a time reference.

As an example in Schrödinger's experiment, calibration would be setting and maintaining the time between observations to 10s (s = second, the time reference). Then the maximum variation of the observed time of death correlated to the actual time of death is +/-10s (i.e., accuracy). The count of observations is uncorrelated to any reference, and therefore not a relative measurement as Euler defined. Applying calibration, this count changes into a sum of the counted time between observations, where each time between observations is correlated to a time reference (second).

Calibration is required to observe a cat's time of death (i.e., a relative measurement). Schrödinger was correct—there is one ψ function of both the atom and the actual cat's state. But there is also a relative measurement including calibration to a reference which produces the observed cat's state. A relative measurement, which is physical reality, exists only when the second function occurs. Since quantum mechanics does not treat a reference, it cannot represent a relative measurement. Without a relative measurement, the most we can see are the probabilities of a superposition.

This story is part of Science X Dialog , where researchers can report findings from their published research articles. Visit this page for information about ScienceX Dialog and how to participate.

L. Euler, Elements of Algebra, Chapter I, Article I, #3. Third edition, Longman, Hurst, Rees, Orme and Co., London England, 1822. www.google.com/books/edition/E … &printsec=frontcover

K. Krechmer, Relative Measurement Theory, The unification of experimental and theoretical measurements, Measurement, Volume 116, February 2018, pages 77-82. www.sciencedirect.com/science/ … ii/S0263224117306887

Bio: Ken Krechmer ([email protected]) studies and teaches Isology at the University of Colorado, Boulder, CO, USA. Isology is the interdisciplinary study of references, standards and standardization. He also studies the formal application of references in quantum mechanics. He was Program Chair, or co-Chair, of several Standards and Innovation in Information Technology (SIIT) conferences. In 2012, he received first prize, and in 2006, received a joint second prize in the IEC Centenary Challenge paper competition. In 1995 and 2000, he won first prize at the World Standards Day paper competition. From 1990 to 2002, he was the founding technical editor of Communications Standards Review. He has also been secretary of TIA TR-29 (facsimile standards) and a U.S. delegate to ITU-T Study Group 8 (fax), 14 (previous modem standards), 15 (xDSL) and 16 (modem, video, conferencing) meetings. He is a Senior Member of the IEEE and a Member of The Society for Standards Professionals.

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schrodinger's cat experiment puzzle [duplicate]

In Schrodinger experiment, the cat is both alive and dead until an observer opens the box to observe the radioactive decay - but why isn't the cat itself an observer?

• heisenberg-uncertainty-principle

• $\begingroup$ Well, it is probably sleeping, so... (It is not a real experiment. It is a thought experiment. No actual cats were harmed while thinking about it.) $\endgroup$ –  Jon Custer Commented Jul 3, 2019 at 13:05
• $\begingroup$ Hmmm - well if an observer is asleep.... or half awake I think that raises a whole lot of other ponderables, such as what counts as an observer $\endgroup$ –  nickoftime Commented Jul 3, 2019 at 13:26
• $\begingroup$ the silence is deafening - does a human observer count more than an animal observer- the thought experiment is lacking something, perhaps he didn't attribute animals with observational powers in which case what makes the human observer different? $\endgroup$ –  nickoftime Commented Jul 3, 2019 at 18:30
• $\begingroup$ The concept of an 'observer' in quantum mechanics is fuzzy at best, and more philosophical than anything else. Don't get hung up on it, focus on the physics. $\endgroup$ –  Jon Custer Commented Jul 3, 2019 at 18:54

2 Answers 2

Max Born, a famous physicist of the pre-war years, said that the wave function doesn't describe a physical system but merely describes our knowledge of it. A number of other physicists at the time agreed with him, and there is reason to believe that Schrodinger himself agreed too. This resolves the paradox of Schrodinger's cat. Of course the cat is an observer and knows if it is alive, but the cat's awareness doesn't count, it is the awareness of the human observers that matters. The cat in the box is either alive or dead, not a superposition of the two.

Because the cat itself is the point of observation, which is being observed by the observer. Its significance lies in that observation which is being done while keeping the point of observation free from the observation.

Not the answer you're looking for? Browse other questions tagged heisenberg-uncertainty-principle or ask your own question .

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Schrödingers Katze

Was ist Schrödingers Katze eigentlich genau und was soll sie erklären? Das erfährst du in diesem Beitrag. Hier geht’s direkt zum Video!

Schrödingers Katze einfach erklärt

Das gedankenexperiment, hintergrund des experiments, doppelspalt-experiment.

Der Physiker Erwin Schrödinger erfand im Jahr 1935 das Gedankenexperiment, welches du bis heute unter dem Namen ‚Schrödingers Katze‘ kennst. Es ist ein paradoxes Gedankenexperiment  aus der Quantenphysik und   soll die Zustände von Atomen veranschaulichen.

In dem Experiment befindet sich eine Katze in einer Kiste . Zusätzlich ist auch eine Vorrichtung mit einem radioaktiven , chemischen Element und einer Giftampulle eingebaut. Sobald das radioaktive Material in dieser Apparatur zerfällt, wird das Gift freigesetzt und die Katze stirbt.

Das Problem besteht nun darin, dass die radioaktive Substanz in der ersten Stunde nur mit einer Wahrscheinlichkeit von 50 Prozent zerfällt. Dadurch ist nicht sicher, dass das Gift zu der Zeit bereits freigesetzt wurde und die Katze gestorben ist. Vor dem Öffnen der Kiste, wird die Katze deshalb als tot und lebendig angesehen.

Das Gedankenexperiment soll die quantenmechanischen Zustände von Atomen in der makroskopischen, also greifbaren, Welt veranschaulichen.

Stelle dir dafür folgendes vor: Eine Katze befindet sich in einer geschlossenen, undurchsichtigen Kiste. Mit ihr steht auch ein Apparat mit einer radioaktiven Substanz, einem Detektor, einem Hammer und einer Giftampulle in der Kiste. Von der radioaktiven Substanz ist dabei nur eine bestimmte, geringe Menge vorhanden. Auf diese Weise ist die Wahrscheinlichkeit dafür, dass ein Atom innerhalb einer Stunde zerfällt genauso groß wie die Wahrscheinlichkeit, dass kein Atom zerfällt. Sobald jedoch ein Atom des radioaktiven Elements zerfällt, startet eine Kettenreaktion . Der Detektor registriert nämlich den Zerfall und bewegt den Hammer. Dadurch wird die Giftampulle zerbrochen und die Katze stirbt.

Ob der Fall eingetreten ist oder nicht, lässt sich aber erst beurteilen, wenn die Kiste geöffnet wird, also eine ‚Messung‘ durchgeführt wurde. Die Atome sind zu dem Zeitpunkt vor der Öffnung also gleichzeitig zerfallen und nicht zerfallen  und die Katze gilt gleichzeitig als tot und lebendig.

In der Quantenmechanik gibt es Zwischenzustände . Du nennst sie auch überlagerte Zustände. Die Atomkerne einer radioaktiven Substanz können diesen Zustand haben. Das liegt daran, dass ihr Zerfall ein quantenmechanischer Prozess ist — somit kann er zu einer gewissen Wahrscheinlichkeit in einem bestimmten Zeitraum stattfinden, muss dies aber nicht. Ob ein Atomkern zerfallen ist oder nicht, kann dann erst bei einer Messung herausgefunden werden.

Wie unsere Alltagserfahrung zeigt, können Menschen und Tiere diesen Zwischenzustand allerdings nicht haben, sie sind entweder tot oder lebendig .

Merke : Das Gedankenexperiment ‚Schrödingers Katze‘ soll also zeigen, dass quantenmechanische Vorgänge und Zustände nicht direkt auf das alltägliche System übertragbar sind.

Das Doppelspalt-Experiment gilt als eines der Schlüsselexperimente für die Quantenmechanik. Unter anderem hat es uns geholfen zu verstehen, dass Elektronen nicht einfach Teilchen sind, sondern auch Eigenschaften haben, die du bei Wellen finden kannst.

Schau dir als nächstes unser Video zum Doppelspaltexperiment an und finde heraus, woran du das erkennst!

Beliebte Inhalte aus dem Bereich Quantenphysik

• Schrödinger Gleichung Dauer: 04:19
• Quantenzahlen Dauer: 04:52
• Heisenbergsche Unschärferelation Dauer: 04:59

Weitere Inhalte: Quantenphysik

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Schrödingers Katze – Gedankenexperiment in 3 Schritten einfach erklärt! | Quantenphysik

Aktualisiert: 16. Feb.

Schrödingers Katze ist vielleicht das bekannteste Sinnbild der Quantenphysik. Doch was genau steckt dahinter? Dieser Beitrag führt dich Schritt für Schritt durch das skurrile Gedankenexperiment und erklärt dir, warum Schrödingers Katze gleichzeitig tot und lebendig ist.

Im Jahr 1935 präsentierte der österreichische Physiker Erwin Schrödinger ein theoretisches Experiment im Bereich der Quantenphysik – bekannt unter dem Titel „Schrödingers Katze“. Das Ziel: Zu zeigen, dass die Zustände der Atome im Bereich der Quantenmechanik nicht einfach in unseren Alltag (von der mikroskopischen in die makroskopische Welt) übertragen werden können. Mit anderen Worten: Quantenphysik lässt sich nicht einfach in unserer „realen Welt“ demonstrieren. Doch beginnen wir ganz am Anfang:

Schrödingers Katze: Das Gedankenexperiment einfach erklärt

An dieser Stelle führt dich der Beitrag Schritt für Schritt durch die Ausgangssituation und zeigt dir, warum das Experiment mit Schrödingers Katze so außergewöhnlich ist:

1. Eine Kiste voller skurriler Dinge

In einer Kiste befinden sich:

Eine radioaktive Substanz

Ein Geigerzähler (misst radioaktiven Zerfall)

Eine Ampulle mit Gift (Blausäure)

Wichtig: Die Menge der radioaktiven Substanz ist dabei exakt so gewählt, dass die Wahrscheinlichkeit, dass ein Atom zerfällt, genauso groß ist, wie die Wahrscheinlichkeit, dass es nicht zerfällt. Schrödinger selbst nannte diese Kiste „die Höllenmaschine“.

2. Eine tödliche Kettenreaktion

Sobald jedoch ein Atom der radioaktiven Substanz zerfällt, beginnt eine tödliche Kettenreaktion. Der Geigerzähler in der Kiste registriert den radioaktiven Zerfall und bewegt dadurch den Hammer. Dieser zerbricht die Gift-Ampulle und die Katze stirbt.

3. Schrödingers Katze ist tot und lebendig zugleich

Solange die Kiste verschlossen bleibt, sind die Atome des radioaktiven Materials laut Quantenmechanik gleichzeitig zerfallen und nicht zerfallen. Sie befinden sich in einem sogenannten „überlagerten Zustand“ – genauso wie die Katze. Sie ist zu 50 Prozent tot und zu 50 Prozent lebendig. Quantenmechanisch ausgedrückt: Sie befindet sich in der „Superposition“ beider Zustände.

Nach den Gesetzen der Quantenmechanik lässt sich der Zustand erst dann genau erkennen, wenn das System mit seiner Umwelt interagiert, also eine „Messung“ durchgeführt wird. In diesem Fall: Wenn jemand die Kiste öffnet, um nachzuschauen. Die quantenmechanische Superposition führt nämlich dazu, dass die Teilchen einen eindeutigen Zustand annehmen. Im Gedankenexperiment: Also die radioaktiven Atome entweder zerfallen oder nicht.

Auch interessant für dich: „Symptome radioaktiver Strahlung: Folgen von Radioaktivität auf den menschlichen Körper“

Merke: Solange die Kiste mit Schrödingers Katze nicht geöffnet wurde, existieren beide Zustände zeitgleich. Die Katze ist tot und lebendig. Sobald die Kiste geöffnet wird, nimmt die Katze einen der beiden Zustände an – sie lebt oder stirbt.

„Bildlich gesprochen ist das wie bei einem Würfel, bei dem man aus Erfahrung weiß, dass eine der sechs Zahlen oben liegt. Solange man jedoch nicht nachgeschaut hat, findet laut Quantenmechanik eine Überlagerung der sechs Zustände statt. Erst in dem Moment, in dem man nachschaut, findet eine Messung statt, der Würfel entscheidet sich und das Ergebnis ist eine eindeutige Zahl.“ – Prof. Dr. Erich Runge (Technische Universität Ilmenau) zu Schrödingers Katze

Schrödingers Katze: Das Paradoxon des Physik-Experiments

Der Widerspruch besteht darin, dass gemäß unserer Alltagserfahrung kein Tier in ein und demselben Moment lebendig und tot sein kann. In der Welt der Quantenphysik sind diese bizarren Situationen jedoch üblich.

Das Gedankenexperiment mit Schrödingers Katze soll zeigen, dass sich Vorgänge aus der Quantenmechanik nicht einfach und direkt auf unseren Alltag übertragen lassen. Quantenobjekte wie Photonen und Elektronen können gleichzeitig mehrere Zustände annehmen, wie auch folgendes Experiment zeigt:

Das Doppelspalt-Experiment: Eine „reale“ Version von Schrödingers Katze

Der überlagerte Zustand lässt sich gut am sogenannten Doppelspalt-Experiment demonstrieren. Ein Photon kann nämlich durch zwei Spalten gleichzeitig durchdringen – also an zwei Orten sein. Wenn man jedoch eine Messung vornimmt – sich also anschauen möchte, wie das Photon durch beide Spalten läuft (vgl. die Kiste mit Schrödingers Katze öffnen) – wird das Photon dazu gezwungen einen bestimmten Spalt zu wählen. Das Experiment verläuft also anders, als erhofft. Hier ein kurzes Video zum Doppelspalt-Experiment:

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Quellen bzw. weiterführende Links:

(1) Welt der Physik: „Schrödingers Katze“

(2) LEIFIphysik: „Schrödingers Katze – ein Gedankenexperiment“

(3) StudySmarter: „Schrödingers Katze“

(4) chemie.de: „Schrödingers Katze“

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Breaking open the AI black box, team finds key chemistry for solar energy and beyond

Artificial intelligence is a powerful tool for researchers, but with a significant limitation: The inability to explain how it came to its decisions, a problem known as the “AI black box.” By combining AI with automated chemical synthesis and experimental validation, an interdisciplinary team of researchers at the University of Illinois Urbana-Champaign has opened up the black box to find the chemical principles that AI relied on to improve molecules for harvesting solar energy. 

The result produced light-harvesting molecules four times more stable than the starting point, as well as crucial new insights into what makes them stable — a chemical question that has stymied materials development.

The interdisciplinary team of researchers was co-led by U. of I.  chemistry  professor  Martin Burke ,  chemical and biomolecular engineering  professor  Ying Diao , chemistry professor  Nicholas Jackson  and  materials science and engineering  professor  Charles Schroeder , in collaboration with along with University of Toronto chemistry professor Alán Aspuru-Guzik. They published their results in the journal Nature.

“New AI tools have incredible power. But if you try to open the hood and understand what they’re doing, you’re usually left with nothing of use,” Jackson said. “For chemistry, this can be very frustrating. AI can help us optimize a molecule, but it can’t tell us why that’s the optimum — what are the important properties, structures and functions? Through our process, we identified what gives these molecules greater photostability. We turned the AI black box into a transparent glass globe.”

The researchers were motivated by the question of how to improve organic solar cells, which are based on thin, flexible materials, as opposed to the rigid, heavy, silicon-based panels that now dot rooftops and fields. 

“What has been hindering commercialization of organic photovoltaics is problems with stability. High-performance materials degrade when exposed to light, which is not what you want in a solar cell,” said Diao. “They can be made and installed in ways not possible with silicon and can convert heat and infrared light to energy as well, but the stability has been a problem since the 1980s.”

The Illinois method, called “closed-loop transfer,” begins with an AI-guided optimization protocol called closed-loop experimentation. The researchers asked the AI to optimize the photostability of light-harvesting molecules, Schroeder said. The AI algorithm provided suggestions about what kinds of chemicals to synthesize and explore in multiple rounds of closed-loop synthesis and experimental characterization. After each round, the new data were incorporated back into the model, which then provided improved suggestions, with each round moving closer to the desired outcome.

The researchers produced 30 new chemical candidates over five rounds of closed-loop experimentation, thanks to building block-like chemistry and automated synthesis pioneered by Burke’s group. The work was done at the Molecule Maker Lab housed in the  Beckman Institute for Advanced Science and Technology  at the U. of I.  

“The modular chemistry approach beautifully complements the closed-loop experiment. The AI algorithm requests new data with maximized learning potential, and the automated molecule synthesis platform can generate the new required compounds very quickly. Those compounds are then tested, the data goes back into the model, and the model gets smarter — again and again,” said Burke, who also is a professor in the  Carle Illinois College of Medicine . “Until now, we’ve been largely focused on structure. Our automated modular synthesis now has graduated to the realm of exploring function.”

Instead of simply ending the query with the final products singled out by the AI, as in a typical AI-led campaign, the closed-loop transfer process further sought to uncover the hidden rules that made the new molecules more stable.

As the closed-loop experiment ran, another set of algorithms was continuously looking at the molecules made, developing models of chemical features predictive of stability in light, Jackson said. Once the experiment concluded, the models provided new lab-testable hypotheses. 

“We're using AI to generate hypotheses that we can validate to then spark new human-driven campaigns of discovery,” Jackson said. “Now that we have some physical descriptors of what makes molecules photostable, that makes the screening process for new chemical candidates dramatically simpler than blindly searching around chemical space.” 

To test their hypothesis about photostability, the researchers investigated three structurally different light-harvesting molecules with the chemical property they identified — a particular high-energy region — and confirmed that choosing the proper solvents made the molecules up to four times more light-stable.

“This is a proof of principle for what can be done. We’re confident we can address other material systems, and the possibilities are only limited by our imagination. Eventually, we envision an interface where researchers can input a chemical function they want and the AI will generate hypotheses to test,” Schroeder said. “This work could only happen with a multidisciplinary team, and the people, resources and facilities we have at Illinois, and our collaborator in Toronto. Five groups came together to generate new scientific insight that would not have been possible with any one of the sub teams working in isolation.”

This work was supported by the  Molecule Maker Lab Institute , an AI Research Institutes program supported by the U.S. National Science Foundation under grant 2019897. 

Editor’s note :   

To reach Nick Jackson, email  [email protected] . To reach Martin Burke, email  [email protected] .  

The paper, “Closed-loop transfer enables AI to yield chemical knowledge,” is available  online . 

DOI: 10.1038/s41586-024-07892-1

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Sigourney weaver accepts lifetime achievement golden lion at venice film festival opening ceremony: “i want to roar”, breaking news.

Channel 4 Considering Extra Welfare Measures In True Crime Production As Report Into John Balson Death Set To Publish In “Weeks Not Months” – Edinburgh

By Max Goldbart

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The report into the tragic death of John Balson will publish in “weeks not months,” Ian Katz has said, as he revealed Channel 4 is considering rolling out additional welfare measures in true crime production.

Balson committed suicide in May after working on true crime series In The Footsteps of Killers for several months and experiencing vestibular migraine disorder. There has since been an industry outpouring along with calls for improved welfare measures, and a Guardian investigation into his death put Balson back into the news agenda last week.

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“We have created specific protections for people dealing with horrific imagery and I am open to if we need similar measures in true crime,” he said. “It would be acknowledging the stress and impact of what looking at lots of upsetting imagery and testimony can take. With Gaza imagery we are aware how much people are exposed, but we need to know more than we currently know [in true crime].”

In order to gain a better understanding, the independent report into Balson’s death from legal firm Reynolds Porter Chamberlain will publish in “weeks not months,” Katz said, and the channel will take learnings from there. Balson’s family will be briefed on the learnings from the investigation but it will not necessarily be made public. An inquest into his death is yet to take place.

“Whatever that report says we are very alive to the issues around overwork of freelancers on productions,” Katz added. “There has been lots of discussion and some of that has been triggered by John’s death.”

Communication problems

Elsewhere during a wide-ranging session, Katz acknowledged he would “think hardest about communication” with the indie sector the next time the network lands itself in financial bother.

Reflecting today and responding to a question from Deadline, he said “some people said I communicated too much, some said too little and I think I didn’t get it quite right.”

“Some people feel last year I gave the impression that things were going to be better than they were say three, six months down the line from Edinburgh,” she added. “We were all looking at the same projections for the ad market and it didn’t quite come.”

Next time, he would “think hardest about communication and making sure we were transparent all the way through” with production companies, Katz added.

Speaking earlier this week, Katz said the ad market is “wheezing” back into life and that Channel 4’s spend for the first six months of this year will be the same as the year before Covid-19. He declined to give a figure on how many shows and how much money was spent in H1 2024. “But what I can say is there is still significant opportunity in the key genres we need to drive streaming viewing,” he added.

“Illusory” IP

Katz also used his session to raise concerns that British IP could wane if the broadcasters stop taking risks, coming after MacTaggart lecturer James Graham challenged British TV gatekeepers to create “new universes.”

He said the UK is too reliant on U.S. IP, which has become a serious issue this year as U.S. buyers spend less amid market contraction.

“There is a wider problem here in that the buoyancy we thought there was in the UK film and TV industry was to an extent illusory because it was based on U.S. money and IP, and sat in the U.S.,” he explained. “So it’s more important than ever that we invest in original British ideas and stories.”

Channel 4 also used the session to unveil a new Dan Reed-helmed doc series on the recent UK riots, while showing a clip of upcoming series Go Back To Where You Came From, a social experiment format in which Brits experience the reality of crossing perilous refugee routes to the UK.

Alisa Pomeroy, who runs factual entertainment and docs for Channel 4, said it is important to “confront these opinions” as she rejected criticism of the network giving a platform to people with anti-immigration views.

She added: “The Overton window of what you say in public has changed and I think it’s really important to confront these opinions rather than pushing them away from the mainstream media where they metastasise on social media and you get things like the riots that happened three weeks ago.”

Pomeroy pointed out that the original version of the format from a decade ago is now part of the Australian school curriculum. “Every Australian chooses between writing essays on Shakespeare, Orwell or watching Go Back To Where You Came From ,” she added.

Katz and his commissioners were speaking on the Thursday of the Edinburgh TV Festival .

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Title: self-supervised topic taxonomy discovery in the box embedding space.

Abstract: Topic taxonomy discovery aims at uncovering topics of different abstraction levels and constructing hierarchical relations between them. Unfortunately, most of prior work can hardly model semantic scopes of words and topics by holding the Euclidean embedding space assumption. What's worse, they infer asymmetric hierarchical relations by symmetric distances between topic embeddings. As a result, existing methods suffer from problems of low-quality topics at high abstraction levels and inaccurate hierarchical relations. To alleviate these problems, this paper develops a Box embedding-based Topic Model (BoxTM) that maps words and topics into the box embedding space, where the asymmetric metric is defined to properly infer hierarchical relations among topics. Additionally, our BoxTM explicitly infers upper-level topics based on correlation between specific topics through recursive clustering on topic boxes. Finally, extensive experiments validate high-quality of the topic taxonomy learned by BoxTM.

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