In 1949, the German mathematician Kurt Gödel, having solved the equations of the gravitational field obtained by Einstein, theoretically proved the possibility of time travel. Almost seventy years later, American and Canadian scientists have built a mathematical model for this. And last spring, the quantum computer returned a split second.
New dimension - new opportunities
At the beginning of the twentieth century, physicists began to consider time as an equal dimension along with the three already known: up and down, right and left, and back and forth. As a result, a concept of the space-time continuum appeared in science and a different view of the laws of nature was formed - the special and general theory of relativity (SRT and GRT). SRT considered only straight and uniformly moving objects, GRT - situations when bodies were accelerated or turned to the side.
It was for general relativity in 1915 that Einstein, together with the German mathematician Hilbert, derived a system of equations for the gravitational field that connects space-time with the properties of the matter filling it. Thirty years later, Gödel solved these equations by representing matter as uniformly distributed rotating dust particles. When he proposed to consider galaxies as these particles, he got a model of a rotating Universe.
In it, light is involved in rotational motion, which means that objects are able to move along trajectories that are closed not only in space, but also in time. In other words, traveling through the universe, you can return to the past. The probability of the existence of such trajectories (they are called closed timelike curves) is determined by other versions of solutions of the gravitational field equations - the "Tipler cylinder" obtained in 1974 and "passable wormholes."
Through space and time
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British physicist Roger Penrose assumed that closed timelike curves must cross the event horizon - an imaginary boundary in space-time. On the one side of the border there are points of space-time about which something can be learned, on the other - nothing is known. The person is outside this event horizon. Therefore, he is unable to notice the violation of the principle of causality in closed timelike curves.
According to Stephen Hawking, an attempt to create such curves must necessarily end with the appearance of a black hole. As a result, for the observer, a naked singularity - a point at which an infinitely distant future or past is visible - turns out to be closed by the events of black holes. Even if a person gets to this point, he will not be able to tell anyone about it. To do this, you need to get out of the black hole, which is completely out of the question.
However, scientists have found a way, while theoretical, to get around these limitations. American and Canadian physicists have developed a mathematical model of a time machine that allows you to move along closed time-like curves at superluminal speed. Moreover, in search of these curves, it is not necessary to get inside black holes, the authors of the work note.
The direction of time on the surface of space-time looks like a curvature that intensifies when approaching a black hole - there is evidence that time in its immediate vicinity is slowing down. Scientists have described the possibility of a circular curvature for passengers in a time machine outside the black hole. This circle sends them to the past.
The time machine itself is a bubble. People who find themselves inside it move into the past and future along the resulting closed curve, and then return to their starting point. At the same time, an external observer will see two versions of passengers: for one, time flows normally, and for the other, in the opposite direction.
True, such a time machine is still a purely speculative construct. The material from which it could be made has not yet been invented.
A split second ago
In March of this year, scientists from Russia, the United States and Switzerland demonstrated that time travel is possible in practice, but only at the quantum level. They created such a state of the system, which itself developed in the opposite direction - from chaos to order, that is, it violated the second law of thermodynamics, which states that over time the chaos of the Universe (in scientific terms, entropy) steadily grows, which means that time moves only in one direction: from the past to the future.
First, physicists theoretically showed that an electron in empty space is capable of spontaneously moving into the past, that is, returning to the state in which it was a few moments ago. However, such an event, according to calculations, can occur only once during the entire existence of the Universe. In this case, it will be possible to go back only 0.06 nanoseconds.
Then they tried to carry out this operation in an experiment using a cloud quantum computer. In one case, two were combined, in the other, three qubits - elementary computational modules and memory cells of quantum machines. We filled them with some set of numbers and began to manipulate the contents so that the level of chaos in this quantum system grew rapidly. When the entropy reached a certain level, another program took over the control of the qubits and transferred them to such a state that further evolution went towards order rather than chaos. As a result, the qubits were momentarily in their original state. In other words, they returned to the past.
However, this trick was not always successful: in about 80 percent of cases with two qubits, and only in half with three. According to the authors of the study, failures are associated with errors in the operation of the quantum computer itself, and not with some unexplained reasons. This means more efficient algorithms for travel to the past can be created.
Alfiya Enikeeva