The previous article describes the double-slit experiment, the paradoxical results of which show that the electron, without observing it, passes through two slits simultaneously. To put it somewhat more scientific, we can say that before observing (fixing the electron passing through one or the other slit), the electron is in a superposition of two states: the passage through one slit (the first state) and the passage through the other slit (the second state). The electron is characterized by a set of states, each excludes the other with a classical point of view. As soon as observing the electron as a point particle takes place, it immediately becomes like that, a particle of matter. In this case, the superposition collapses, allowing you to watch one of the states the superposition consisted of before observing.

One of the important controversial issues of quantum physics is this: Is there such a phenomenon as a superposition for the macroscopic world?

To transfer this quantum paradox in the macrocosm, Erwin Schrodinger came up with the following thought experiment, which is known as "Schrödinger's cat".

A cat, a radioactive atom and a container with poisonous gas are placed together in a closed box. Radioactive decay of an atom is subject to quantum mechanics probability law. When the atom in the box decays, it causes, with a simple mechanism, the container of poisonous gas to be destroyed, and the cat, sadly, dies. Thus, the experiment converts the state of the microsystem to the state of macrosystem, or, in other words, the macrosystem (the cat in the box) reflects the state of the microsystem (the atom).

Over time, much more than a half-decay period, decay of the atom will definitely occur, so in this case, a "non-decayed" atom goes into the state of a "decayed" atom. At any point in time before, we can not say whether or not the atom has decayed. From the perspective of quantum physics, its state is described as a superposition of the "dacayed" and "non-decayed" atom, so the atom is "simultaneously" decayed and non-decayed. But this means that the cat, sitting in the box, is alive and dead at the same time! When the experimenter opens the box, he must see only one of the possible states: "the atom has decayed, the cat is dead" or "the atom has not decayed, the cat is alive". So it will, of course. However, quantum mechanics forces us to believe that, before opening the box, the system is in a superposition of a live and dead cat, and at the time of opening the box, the observation will take place which will manifest one of the states of the cat. From the standpoint of quantum mechanics, this situation is analogous to the situation in double-split experiment, where witnessing an electron destroys the superposition making the electron a classical point particle.

Erwin Schrodinger introduced this experiment in order to show that quantum theory, in his opinion, was not complete, because no one had ever seen "live-and-dead" cats, and could not even imagine them. But in any case, it was necessary to somehow interpret those quantum paradoxes.

The opinions of scientists was so different that they have not come to an agreement even today. Currently, two main interpretations of quantum mechanics are popular among the scientists.

Copenhagen interpretation

This is the most admitted interpretation to date. It argues that at the time of measurement (observation) of a quantum system the superposition of states "jumps" into one of the states accordingly to the probabilities of those states. In other words, the system ceases to be a mixture of states, and selects one of them at the time of measuring. Thus, talking about the state of the cat before the measurement takes place has no meaning, because the state does not exist. Only the measurement itself makes the cat live or dead.

Many-worlds interpretation

Supporters of many-worlds interpretation do not try to ascribe "magical" properties to the time of observing. However, the findings, obtained in this case, is even more interesting. According to them, every possible outcome of the experiment is manifested in various states. Since these states must somewhere exist and can not coexist within the same space-time, they exist in different universes. In the case of the Schrödinger cat, before opening the box we have a superposition of just two universes, one of which has a decayed atom and a dead cat, the other has a non-decayed atom and a live cat. After opening the box, there is a "choice" of one of the universes in which we observe one particular state of the system. Note that this is not science fiction. Physicists are talking about that.

Despite the fact that the interpretations desribed above was formed as two more or less certain models of the universe, they still have a lot of "noise". For example, physicists do not fully agree what exactly "observing" is, and when the superposition of quantum system's states collapses. Strictly speaking, any interpretation of quantum mechanics goes beyond the scope of the scientific method (it's philosophy), because what happens with the system before observing can not be tested experimentally (for an experiment is observing).

However, let's be philosophical. Philosophy does not forbid us to interpret quantum mechanics and to reflect on the structure of the universe without conducting experiments. It is definitely possible to say that our traditional notions of the world, with its principled predictability, fatality, total causality, are collapsing. The essence of these ideas is that if we knew all the coordinates and momentums of all particles in the universe, we could predict the future with absolute accuracy. In the bright, clear world, the particles move along their tracks in certain directions, each one has a definite mass and velocity, each one exists in reality and "acts" by itself, regardless of whether or not it is being observed by someone. If all the scientists and observers looking at the world die, the world will not change. It is objective. It exists by itself. It is absolute. It is physically possible to distinguish between good and bad. One cause generates one effect. In this world there is truth. Let's continue by the quote from the book by Robert A. Wilson "Quantum Psychology":

"One deep reality" also implies the idea of the universe as a simple two-layer formation, consisting of "external manifestations" and a "fundamental reality" - of a mask and face hiding behind the mask. But modern researches show that at different tool magnification there are indefinitely long series of "external manifestations". Science finds no single "substance" or "deep reality" which would lie at the basis of all the various external manifestations recorded by different classes of instruments.

Indeed, based on the old considerations of objective reality, how can we explain the results of double-slit experiment? What is "objective reality" in case it behaves differently depending on how we record it? What physically is a mysterious superposition of two mutually exclusive states? There are no clear and widely accepted answers to these questions yet.