What is Schrödinger's cat? Schrödinger's cat and his difficult fate

As Heisenberg explained to us, due to the uncertainty principle, the description of objects in the quantum microworld is of a different nature than the usual description of objects in the Newtonian macroworld. Instead of spatial coordinates and speed, which we are used to describing mechanical movement, for example, a ball along billiard table, in quantum mechanics, objects are described by the so-called wave function. The crest of the “wave” corresponds to the maximum probability of finding a particle in space at the moment of measurement. The movement of such a wave is described by the Schrödinger equation, which tells us how the state of a quantum system changes over time.

Now about the cat. Everyone knows that cats love to hide in boxes (). Erwin Schrödinger was also in the know. Moreover, with purely Nordic fanaticism, he used this feature in a famous thought experiment. The gist of it was that a cat was locked in a box with an infernal machine. The machine is connected through a relay to a quantum system, for example, a radioactively decaying substance. The probability of decay is known and is 50%. The infernal machine is triggered when the quantum state of the system changes (decay occurs) and the cat dies completely. If you leave the “Cat-box-hellish machine-quanta” system to itself for one hour and remember that the state of a quantum system is described in terms of probability, then it becomes clear that whether the cat is alive or not depends on this moment time, it probably won’t work, just as it won’t be possible to accurately predict the fall of a coin on heads or tails in advance. The paradox is very simple: the wave function that describes a quantum system mixes two states of a cat - it is alive and dead at the same time, just as a bound electron can be located with equal probability in any place in space equidistant from atomic nucleus. If we don't open the box, we don't know exactly how the cat is doing. Without making observations (read measurements) of an atomic nucleus, we can describe its state only by superposition (mixing) of two states: a decayed and undecayed nucleus. A cat in nuclear addiction is both alive and dead at the same time. The question is: when does a system cease to exist as a mixture of two states and choose one specific one?

The Copenhagen interpretation of the experiment tells us that the system ceases to be a mixture of states and chooses one of them at the moment when an observation occurs, which is also a measurement (the box opens). That is, the very fact of measurement changes physical reality, leading to the collapse of the wave function (the cat either becomes dead or remains alive, but ceases to be a mixture of both)! Think about it, the experiment and the measurements that accompany it change the reality around us. Personally, this fact bothers my brain much more than alcohol. The well-known Steve Hawking also has a hard time experiencing this paradox, repeating that when he hears about Schrödinger’s cat, his hand reaches out to the Browning. The severity of the reaction of the outstanding theoretical physicist is due to the fact that, in his opinion, the role of the observer in the collapse of the wave function (collapsing it into one of two probabilistic) states is greatly exaggerated.

Of course, when Professor Erwin conceived his cat-torture back in 1935, it was an ingenious way to show the imperfection of quantum mechanics. In fact, a cat cannot be alive and dead at the same time. As a result of one of the interpretations of the experiment, it became obvious that there was a contradiction between the laws of the macro-world (for example, the second law of thermodynamics - the cat is either alive or dead) and the micro-world (the cat is alive and dead at the same time).

The above is used in practice: in quantum computing and quantum cryptography. A light signal in a superposition of two states is sent through a fiber-optic cable. If attackers connect to the cable somewhere in the middle and make a signal tap there in order to eavesdrop on the transmitted information, then this will collapse the wave function (from the point of view of the Copenhagen interpretation, an observation will be made) and the light will go into one of the states. By conducting statistical tests of light at the receiving end of the cable, it will be possible to detect whether the light is in a superposition of states or has already been observed and transmitted to another point. This makes it possible to create means of communication that exclude undetectable signal interception and eavesdropping.

Another most recent interpretation of Schrödinger's thought experiment is the story of Sheldon Cooper, the hero of the series "Theory big bang" ("Big Bang Theory"), which he delivered for his less educated neighbor Penny. The point of Sheldon's story is that the concept of Schrödinger's cat can be applied to human relationships. In order to understand what is happening between a man and a woman, what kind of relationship is between them: good or bad, you just need to open the box. Until then, the relationship is both good and bad.

Despite the fact that the planetary model of the atom has proven its validity, the theory existing at that time could not fully explain all processes, which were observed in real life. It turned out that in reality, for some reason, classical Newtonian mechanics does not work at the micro level. Those. the prototype model, borrowed from real life, does not correspond to the observations of scientists of that time in the case of considering the atom instead of our solar system.

Based on this, the concept was significantly redesigned. There was such a discipline as quantum mechanics. The origins of this direction were the outstanding physicist Erwin Schrödinger.

Concept of superposition

The main principle that distinguishes the new theory is superposition principle. According to this principle, a quantum (electron, photon or proton) can be in two states at the same time. If make it easier to understand this formulation, we get a fact that is completely impossible to imagine in our minds. A quantum can be in two places at the same time.

At the time of its appearance, this theory was contradictory not only classical mechanics, but also common sense. Even now, an educated person far from physics can hardly imagine such a situation. After all, this understanding ultimately implies that he himself the reader can be here and there now. This is exactly how a person tries to imagine the transition from the macroworld to the microworld.

For a person who was accustomed to experiencing the action of Newtonian mechanics and perceiving himself at one point in space, it was extremely difficult to imagine being in two places at once. Besides, there was no theory or patterns as such during the transition from macro to micro. There was no understanding of specific numerical values and rules.

However, the instruments of that time made it possible to clearly record this “quantum dissonance”. Laboratory instruments confirmed that the formulated postulates are indeed consistent and the quantum is capable of being in two states. For example, electron gas around the nucleus of an atom was detected.

Based on this, Schrödinger formulated a famous concept that is now known as the cat theory. The purpose of this formulation was to show that in classical theory physics, a huge gap has formed that requires additional study.

Shroedinger `s cat

The thought experiment about the cat was that the cat was placed in a closed steel box. The box was equipped a device with a poisonous gas and a device with an atomic nucleus.

Based on known postulates, the nucleus of an atom may disintegrate into components within one hour, but may not disintegrate. Accordingly, the probability of this event is 50%.

If the nucleus decays, then the counter-recorder is triggered, and in response to this event a toxic substance is released from the previously described device with which the box is equipped. Those. the cat dies from poison. If this does not happen, the cat does not die accordingly. Based on a 50% chance of decay, the cat has a 50% chance of surviving.

Based on and quantum theory, an atom can be in two states at once. Those. the atom both decayed and did not decay. This means that the recorder worked, breaking the container with poison, and did not disintegrate. The cat was poisoned by poison, and the cat was not poisoned by poison at the same time.

But it is simply impossible to imagine such a picture that upon opening the box, the researcher discovered both a dead and a living cat. The cat is either alive or dead. This is the paradox of the situation. It is impossible for the viewer's consciousness to imagine a dead-alive cat.

The paradox is that the cat is an object of the macrocosm. Accordingly, to say about him that he is alive and dead, i.e. is in two states at once, similar to a quantum, will not be entirely correct.

Using this example, Schrödinger concentrated specifically on the fact that there are no clear parallels between the macro- and microworlds. Subsequent comments given by experts explain that a radiation detector-cat system should be considered, not a cat-spectator system. In a detector-cat system, only one event is likely.

Schrödinger's Cat is a famous thought experiment. It was directed by the famous Nobel laureate in the field of physics, the Austrian scientist Erwin Rudolf Joseph Alexander Schrödinger.

The essence of the experiment was as follows. IN closed chamber(box) the cat was placed. The box is equipped with a mechanism that contains a radioactive core and poisonous gas. The parameters are selected so that the probability of nuclear decay in one hour is exactly fifty percent. If the core disintegrates, the mechanism will come into action and a container with poisonous gas will open. Therefore, Schrödinger's cat will die.

According to the laws, if you do not observe the nucleus, then its states will be described by two main states - the decayed and non-decayed nuclei. And here a paradox arises: Schrödinger's cat, who is sitting in a box, can be both dead and alive at the same time. But if the box is opened, the experimenter will see only one specific state. Either “the nucleus decayed and the cat is dead,” or “the nucleus did not decay and Schrödinger’s cat is alive.”

Logically, at the exit we will have one of two things: either a living cat or a dead one. But potentially the animal is in both states at once. Schrödinger tried in this way to prove his opinion about the limitations of quantum mechanics.

According to the Copenhagen interpretation and this experiment in particular, a cat in one of its potential phases (dead-alive) acquires these properties only after an outside observer intervenes in the process. But as long as this observer is not there (this implies the presence of a specific personality who has the advantages of clarity of vision and consciousness), the cat will be in limbo “between life and death.”

The famous ancient parable that a cat walks by itself takes on new, interesting shades in the context of this experiment.

According to Everett, which differs markedly from the classical Copenhagen one, the process of observation is not considered something special. Both states that Schrödinger's cat can be in can exist in this interpretation. But they decohere with each other. This means that the unity of these states will be disrupted precisely as a result of interaction with the outside world. It is the observer who opens the box who brings discord into the cat’s state.

There is an opinion that the final word in this matter should be left to such a creature as Schrödinger’s cat. The meaning of such an opinion is the acceptance of the fact that in everything this experiment it is the animal that is the only absolutely competent observer. For example, scientists Max Tegmark, Bruno Marshall and Hans Moraven presented a modification of the above experiment, where the main point of view is the opinion of the cat. In this case, Schrödinger's cat undoubtedly survives, because only the surviving cat can observe the results. But scientist Nadav Katz published his results in which he was able to “return” the state of the particle back after changing its state. Thus, the cat’s chances of survival increase significantly.

If you are interested in an article on a topic from quantum physics, then there is a high probability that you love the TV series “The Big Bang Theory”. So, Sheldon Cooper came up with a fresh interpretation Schrödinger's thought experiment(You will find a video with this fragment at the end of the article). But to understand Sheldon's dialogue with his neighbor Penny, let's first turn to the classical interpretation. So, Schrödinger's Cat in simple words.

In this article we will look at:

Brief historical background
Description of the experiment with Schrödinger's Cat
The solution to the Schrödinger's Cat paradox

Immediately good news. During the experiment Schrödinger's cat was not harmed. Because physicist Erwin Schrödinger, one of the creators of quantum mechanics, only conducted a thought experiment.

Before diving into the description of the experiment, let's make a mini excursion into history.

At the beginning of the last century, scientists managed to look into the microworld. Despite the external similarity of the “atom-electron” model with the “Sun-Earth” model, it turned out that the familiar Newtonian laws of classical physics do not work in the microcosm. That's why it appeared new science– quantum physics and its component – quantum mechanics. All microscopic objects of the microworld were called quanta.

Attention! One of the postulates of quantum mechanics is “superposition”. It will be useful to us to understand the essence of Schrödinger's experiment.

“Superposition” is the ability of a quantum (it can be an electron, a photon, the nucleus of an atom) to be not in one, but in several states at the same time or to be in several points of space at the same time, if no one is watching him

This is difficult for us to understand, because in our world an object can only have one state, for example, being either alive or dead. And it can only be in one specific place in space. You can read about “superposition” and the stunning results of quantum physics experiments In this article.

Here is a simple illustration of the difference between the behavior of micro and macro objects. Place a ball in one of the 2 boxes. Because the ball is an object of our macro world, you will say with confidence: “The ball lies in only one of the boxes, while the second one is empty.” If instead of a ball you take an electron, then the statement that it is simultaneously in 2 boxes will be true. This is how the laws of the microworld work. Example: The electron in reality does not rotate around the nucleus of the atom, but is located at all points of the sphere around the nucleus simultaneously. In physics and chemistry, this phenomenon is called the “electron cloud”.

Summary. We realized that the behavior of a very small object and a large object are subject to different laws. The laws of quantum physics and the laws of classical physics, respectively.

But there is no science that would describe the transition from the macroworld to the microworld. So, Erwin Schrödinger described his thought experiment precisely to demonstrate the incompleteness general theory physics. He wanted Schrödinger's paradox to show that there is a science to describe large objects (classical physics) and a science to describe micro objects (quantum physics). But there is not enough science to describe the transition from quantum systems to macrosystems.

Description of the experiment with Schrödinger's Cat

Erwin Schrödinger described a thought experiment with a cat in 1935. The original version of the experiment description is presented on Wikipedia ( Schrödinger's cat Wikipedia).

Here is a version of the description of the Schrödinger's Cat experiment in simple words:

A cat was placed in a closed steel box.
The Schrödinger Box contains a device with a radioactive nucleus and poisonous gas placed in a container.
The nucleus may decay within 1 hour or not. Probability of decay – 50%.
If the nucleus decays, the Geiger counter will record this. The relay will operate and the hammer will break the gas container. Schrödinger's cat will die.
If not, then Schrödinger’s cat will be alive.

According to the law of “superposition” of quantum mechanics, at a time when we are not observing the system, the nucleus of an atom (and therefore the cat) is in 2 states simultaneously. The nucleus is in a decayed/undecayed state. And the cat is in a state of being alive/dead at the same time.

But we know for sure that if the “Schrödinger box” is opened, then the cat can only be in one of the states:

if the nucleus does not decay, our cat is alive
if the nucleus decays, the cat is dead

The paradox of the experiment is that according to quantum physics: before opening the box the cat is both alive and dead at the same time, but according to the laws of physics of our world, this is impossible. Cat can be in one specific state - being alive or being dead. There is no mixed state “the cat is alive/dead” at the same time.

Before you get the answer, watch this wonderful video illustration of the paradox of the Schrödinger's cat experiment (less than 2 minutes):

The solution to the Schrödinger's Cat paradox - the Copenhagen interpretation

Now the solution. Pay attention to the special mystery of quantum mechanics - observer paradox. An object of the microworld (in our case, the core) is in several states simultaneously only while we are not observing the system.

For example, the famous experiment with 2 slits and an observer. When a beam of electrons was directed onto an opaque plate with 2 vertical slits, the electrons painted a “wave pattern” on the screen behind the plate—vertical alternating dark and light stripes. But when the experimenters wanted to “see” how electrons fly through the slits and installed an “observer” on the side of the screen, the electrons drew not a “wave pattern” on the screen, but 2 vertical stripes. Those. behaved not like waves, but like particles.

It seems that quantum particles themselves decide what state they should take at the moment they are “measured.”

Based on this, the modern Copenhagen explanation (interpretation) of the “Schrödinger’s Cat” phenomenon sounds like this:

While no one is observing the “cat-core” system, the nucleus is in a decayed/undecayed state at the same time. But it is a mistake to say that the cat is alive/dead at the same time. Why? Yes, because quantum phenomena are not observed in macrosystems. It would be more correct to talk not about the “cat-core” system, but about the “core-detector (Geiger counter)” system.

The nucleus selects one of the states (decayed/undecayed) at the moment of observation (or measurement). But this choice does not occur at the moment when the experimenter opens the box (the opening of the box occurs in the macroworld, very far from the world of the nucleus). The nucleus selects its state at the moment it hits the detector. The fact is that the system is not described enough in the experiment.

Thus, the Copenhagen interpretation of the Schrödinger's Cat paradox denies that until the moment the box was opened, Schrödinger's Cat was in a state of superposition - it was in the state of a living/dead cat at the same time. A cat in the macrocosm can and does exist in only one state.

Summary. Schrödinger did not fully describe the experiment. It is not correct (more precisely, it is impossible to connect) macroscopic and quantum systems. Quantum laws do not apply in our macrosystems. In this experiment, it is not “cat-core” that interacts, but “cat-detector-core”. The cat is from the macrocosm, and the “detector-core” system is from the microcosm. And only in your own quantum world the core can be in 2 states at the same time. This occurs before the nucleus is measured or interacts with the detector. But a cat in its macrocosm can and does exist in only one state. That's why, It’s only at first glance that it seems that the cat’s “alive or dead” state is determined at the moment the box is opened. In fact, its fate is determined at the moment the detector interacts with the nucleus.

Final summary. The state of the “detector-nucleus-cat” system is NOT associated with the person – the observer of the box, but with the detector – the observer of the nucleus.

Phew. My brain almost started boiling! But how nice it is to understand the solution to the paradox yourself! As in the old student joke about the teacher: “While I was telling it, I understood it!”

Sheldon's interpretation of Schrödinger's Cat paradox

Now you can sit back and listen to Sheldon's latest interpretation of Schrödinger's thought experiment. The essence of his interpretation is that it can be applied in relationships between people. To understand a good relationship between a man and a woman or bad - you need to open the box (go on a date). And before that they were both good and bad at the same time.

Well, how do you like this “cute experiment”? Nowadays, Schrödinger would get a lot of punishment from animal rights activists for such brutal thought experiments with a cat. Or maybe it wasn’t a cat, but Schrödinger’s Cat?! Poor girl, she suffered enough from this Schrödinger (((

See you in the next publications!

I wish everyone have a good day and have a nice evening!

P.S. Share your thoughts in the comments. And ask questions.

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Surely you have heard more than once that there is such a phenomenon as “Schrödinger’s Cat”. But if you are not a physicist, then most likely you have only a vague idea of what kind of cat this is and why it is needed.

« Shroedinger `s cat" - this is the name of the famous thought experiment of the famous Austrian theoretical physicist Erwin Schrödinger, who is also a laureate Nobel Prize. With the help of this fictitious experiment, the scientist wanted to show the incompleteness of quantum mechanics in the transition from subatomic systems to macroscopic systems.

This article is an attempt to explain in simple words the essence of Schrödinger’s theory about the cat and quantum mechanics, so that it is accessible to a person who does not have a higher education technical education. The article will also present various interpretations of the experiment, including those from the TV series “The Big Bang Theory.”

Description of the experiment

Erwin Schrödinger's original article was published in 1935. In it, the experiment was described using or even personifying:

You can also construct cases in which there is quite a burlesque. Let some cat be locked in a steel chamber with the following diabolical machine (which should be regardless of the cat's intervention): inside a Geiger counter there is a tiny amount of radioactive substance, so small that only one atom can decay in an hour, but with the same probability may not disintegrate; if this happens, the reading tube is discharged and the relay is activated, releasing the hammer, which breaks the flask with hydrocyanic acid.

If we leave this entire system to itself for an hour, then we can say that the cat will be alive after this time, as long as the atom does not disintegrate. The very first disintegration of the atom would poison the cat. The psi-function of the system as a whole will express this by mixing or smearing a living and a dead cat (pardon the expression) in equal parts. It is typical in such cases that the uncertainty initially limited atomic world, is converted into macroscopic uncertainty, which can be eliminated by direct observation. This prevents us from naively accepting the “blur model” as reflecting reality. This in itself does not mean anything unclear or contradictory. There's a difference between a blurry or out-of-focus photo and a photo of clouds or fog.

In other words:

There is a box and a cat. The box contains a mechanism containing a radioactive atomic nucleus and a container of poisonous gas. The experimental parameters were selected so that the probability of nuclear decay in 1 hour is 50%. If the nucleus disintegrates, a container of gas opens and the cat dies. If the nucleus does not decay, the cat remains alive and well.
We close the cat in a box, wait an hour and ask the question: is the cat alive or dead?
Quantum mechanics seems to tell us that the atomic nucleus (and therefore the cat) is in all possible states simultaneously (see quantum superposition). Before we open the box, the cat-core system is in the state “the nucleus has decayed, the cat is dead” with a probability of 50% and in the state “the nucleus has not decayed, the cat is alive” with a probability of 50%. It turns out that the cat sitting in the box is both alive and dead at the same time.
According to the modern Copenhagen interpretation, the cat is alive/dead without any intermediate states. And the choice of the decay state of the nucleus occurs not at the moment of opening the box, but even when the nucleus enters the detector. Because the reduction of the wave function of the “cat-detector-nucleus” system is not associated with the human observer of the box, but is associated with the detector-observer of the nucleus.

Explanation in simple words

According to quantum mechanics, if the nucleus of an atom is not observed, then its state is described by a mixture of two states - a decayed nucleus and an undecayed nucleus, therefore, a cat sitting in a box and personifying the nucleus of an atom is both alive and dead at the same time. If the box is opened, then the experimenter can see only one specific state - “the nucleus has decayed, the cat is dead” or “the nucleus has not decayed, the cat is alive.”

The essence in human language: Schrödinger's experiment showed that, from the point of view of quantum mechanics, the cat is both alive and dead, which cannot be. Therefore, quantum mechanics has significant flaws.

The question is: when does a system cease to exist as a mixture of two states and choose one specific one? The purpose of the experiment is to show that quantum mechanics is incomplete without some rules that indicate under what conditions the wave function collapses, and the cat either becomes dead or remains alive, but ceases to be a mixture of both. Since it is clear that a cat must be either alive or dead (there is no state intermediate between life and death), this will be similar for the atomic nucleus. It must be either decayed or undecayed (Wikipedia).

Video from The Big Bang Theory

Another more recent interpretation of Schrödinger's thought experiment is a story that Big Bang Theory character Sheldon Cooper told his less educated neighbor Penny. The point of Sheldon's story is that the concept of Schrödinger's cat can be applied to human relationships. In order to understand what is happening between a man and a woman, what kind of relationship is between them: good or bad, you just need to open the box. Until then, the relationship is both good and bad.

Below is a video clip of this Big Bang Theory exchange between Sheldon and Penia.

Did the cat remain alive as a result of the experiment?

For those who did not read the article carefully, but are still worried about the cat - good news: Don't worry, according to our data, the result of a thought experiment by a crazy Austrian physicist

NO CAT WAS HURT