Many people have heard this expression, but perhaps not everyone understands even its simplified meaning. Let's try to figure it out without complicated theories and formulas.
"Schrödinger's cat" is the name of the famous thought experiment of the famous Austrian theoretical physicist Erwin Schrödinger, who is also a Nobel Prize winner. With this fictional experience, the scientist wanted to show the incompleteness of quantum mechanics in the transition from subatomic systems to macroscopic systems.
Erwin Schrödinger's original article was published in 1935. Here's a quote:
You can also construct cases in which burlesque is enough. Let some cat be locked in a steel chamber along with the following devilish machine (which should be independent of the cat's intervention): inside the Geiger counter 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 triggered, releasing the hammer, which breaks the cone with hydrocyanic acid.
If you 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 decay of the atom does not occur. The very first decay of an atom would have poisoned the cat. The psi-function of the system as a whole will express this by mixing or smearing a living and a dead cat (sorry for the expression) in equal parts. Typical in such cases is that the uncertainty, initially limited to the atomic world, is transformed into macroscopic uncertainty, which can be eliminated by direct observation. This prevents us from naively accepting the "blur model" as reflecting reality. In itself, this does not mean anything unclear or contradictory. There is 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 with a poisonous gas. The parameters of the experiment were selected so that the probability of nuclear decay in 1 hour is 50%. If the nucleus disintegrates, a container with 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 ourselves: is the cat alive or dead?
- Quantum mechanics, as it were, tells us that the atomic nucleus (and therefore the cat) is in all possible states simultaneously (see quantum superposition). Before we opened the box, the “cat-core” system is in the state “the nucleus 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 state of nuclear decay occurs not when the box is opened, but also 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.
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According to quantum mechanics, if no observation is made over the nucleus of an atom, then its state is described by the mixing of two states - a disintegrated nucleus and an unresolved 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 of human language: Schrödinger's experiment showed that, from the point of view of quantum mechanics, a cat is both alive and dead, which cannot be. Hence, quantum mechanics has significant flaws.
The question is: when does the 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 the same for the atomic nucleus. It must be either disintegrated or non-disintegrated (Wikipedia).
Another most recent interpretation of Schrödinger's thought experiment is the story of Sheldon Cooper, the hero of the series Big Bang Theory, which he recited for Penny's less educated neighbor. The essence of Sheldon's story is that the concept of Schrödinger's cat can be applied in relationships between people. In order to understand what is happening between a man and a woman, what kind of relationship between them: good or bad, you just need to open the box. Before that, relationships are both good and bad.
Below is a video of this Big Bang Theory dialogue between Sheldon and Singing.
Schrödinger's illustration is the best example for describing the main paradox of quantum physics: according to its laws, particles such as electrons, photons and even atoms exist in two states at the same time ("living" and "dead", if you remember the long-suffering cat). These states are called superpositions.
American physicist Art Hobson from the University of Arkansas (Arkansas State University) offered his own solution to this paradox.
“Measurements in quantum physics are based on the operation of certain macroscopic devices, such as the Geiger counter, which determine the quantum state of microscopic systems - atoms, photons and electrons. Quantum theory implies that if you connect a microscopic system (particle) to a certain macroscopic device that distinguishes between two different states of the system, then the device (Geiger counter, for example) will go into a state of quantum entanglement and will also be in two superpositions simultaneously. However, it is impossible to observe this phenomenon directly, which makes it unacceptable,”says the physicist.
Hobson says that in Schrödinger's paradox, the cat plays the role of a macroscopic instrument, a Geiger counter attached to a radioactive nucleus, to determine the decay state or "non-decay" of that nucleus. In this case, a live cat will be an indicator of "non-decay", and a dead cat is an indicator of decay. But according to quantum theory, the cat, like the nucleus, must be in two superpositions of life and death.
Instead, according to the physicist, the quantum state of the cat must be entangled with the state of the atom, which means that they are in "non-local connection" with each other. That is, if the state of one of the entangled objects suddenly changes to the opposite, then the state of its pair will change in exactly the same way, no matter how far from each other they are. In doing so, Hobson refers to experimental confirmation of this quantum theory.
“The most interesting thing in the theory of quantum entanglement is that the change in the state of both particles occurs instantly: no light or electromagnetic signal would have time to transfer information from one system to another. Thus, we can say that this is one object, divided into two parts by space, no matter how great the distance between them,”explains Hobson.
Schrödinger's cat is no longer alive and dead at the same time. He is dead if decay occurs, and alive if decay never occurs.
We add that similar options for solving this paradox were proposed by three more groups of scientists over the past thirty years, but they were not taken seriously and remained unnoticed in wide scientific circles. Hobson notes that solving the paradoxes of quantum mechanics, even theoretical ones, is absolutely necessary for its deep understanding.
You can read more about the physicist's work in his article, which was published in the journal Physical Review A.
Schrödinger.
But more recently, THEORETICS EXPLAINED HOW GRAVITY KILLS SCHRODINGER'S CAT, but this is already more difficult …
As a rule, physicists explain the phenomenon that superposition is possible in the world of particles, but not possible with cats or other macro-objects, interference from the environment. When a quantum object passes through a field or interacts with random particles, it immediately assumes only one state - as if it were measured. This is how the superposition is destroyed, as scientists believed.
But even if in some way it became possible to isolate a macro-object in a state of superposition from interactions with other particles and fields, then sooner or later it would still assume a single state. At least this is true for the processes occurring on the surface of the Earth.
“Somewhere in interstellar space, maybe a cat would have a chance to maintain quantum coherence, but on Earth or near any planet this is extremely unlikely. And the reason for this is gravity,”explains the lead author of the new study, Igor Pikovski of the Harvard-Smithsonian Center for Astrophysics.
Pikovsky and his colleagues at the University of Vienna argue that gravity has a destructive effect on quantum superpositions of macroobjects, and therefore we do not observe such phenomena in the macrocosm. The basic concept of the new hypothesis, by the way, is summarized in the feature film Interstellar.
Einstein's general theory of relativity states that an extremely massive object will bend spacetime near it. Considering the situation at a finer level, we can say that for a molecule placed near the surface of the Earth, time will go somewhat slower than for the one in the orbit of our planet.
Due to the influence of gravity on space-time, a molecule that has come under this influence will experience a deflection in its position. And this, in turn, should affect its internal energy - vibrations of particles in a molecule, which change over time. If a molecule were introduced into a state of a quantum superposition of two locations, then the relationship between position and internal energy would soon force the molecule to "choose" only one of the two positions in space.
“In most cases, the phenomenon of decoherence is associated with external influence, but in this case, the internal vibration of particles interacts with the movement of the molecule itself,” explains Pikovsky.
This effect has not yet been observed, since other sources of decoherence, such as magnetic fields, heat radiation and vibrations, are usually much stronger, and cause the destruction of quantum systems long before gravity does. But experimenters are trying to test the hypothesis stated.
Markus Arndt, an experimental physicist at the University of Vienna, is conducting experiments to observe quantum superposition in macroscopic objects. It sends small molecules into the interferometer, effectively giving the particle a “choice” which path to take. From the point of view of classical mechanics, a molecule can go only one way, but a quantum molecule can go through two paths at once, interfering with itself and creating a characteristic wavy pattern.
A similar setup can also be used to test the ability of gravity to destroy quantum systems. To do this, it will be necessary to compare the vertical and horizontal interferometers: in the first, the superposition should soon disappear due to time dilation at different "heights" of the path, while in the second, the quantum superposition may persist.