Time is one of the greatest mysteries of the universe. The river of time carries us all without exception, regardless of our desire and even against our will.
Each of us at some point has thought about the strange and mysterious nature of time and how much time differs from space. If in space we can easily move in any direction, then why is everything different in time? Each of us thought about what awaits humanity after us. The individual's age is limited, but we are all terribly interested in everything that happens in the future, after us.
Time travel poses many challenges, both technical and social. Larry Dwyer raises all kinds of moral, legal and ethical questions; he says: “Should the time traveler be charged if he beat himself, only the younger one (or vice versa)? If the time traveler commits murder and hides in the past, should he be tried in the past for a crime he has yet to commit? If he gets married in the past, can he be judged for bigamy, if the other wife is to be born, say, five thousand years later?"
But perhaps the most intractable problems are the logical paradoxes that arise with time travel. What happens, for example, if we kill our parents before we are born? This is logically impossible, so a paradox turns out - sometimes it is called the “grandfather's paradox”.
There are three ways to resolve these paradoxes. First, it is possible that when you return to the past, you will simply have to go through the same thing again, thereby restoring history in its former form. In this case, you are deprived of free will and are forced to repeat the past in the form in which it was realized once. In this situation, it turns out that if you go into the past in order to pass on the secret of time travel to yourself, then this means that this is how everything should have happened: the secret of time travel was indeed delivered from the future. This is fate. (I must say, it remains unclear where the original idea came from.)
Second option. You have free will and, accordingly, you can change the past, but within limited limits. Your free will works as long as you don't create temporary paradoxes. As soon as you try to kill your parents before you are born, the mysterious power will not let you pull the trigger. This position is defended by the Russian physicist Igor Novikov. (He argues this as follows. For example, there is a law of nature that prevents us from walking on the ceiling, although we may want to. Why not assume that there is a law that will prevent us from killing our parents before we are born? unknown force will not let us pull the trigger.)
Finally, the third option. The universe splits in two. The people you killed are exactly like your parents, but in fact they are not, since you are already in a parallel universe. This seems to be the case with quantum theory.
All the paradoxes of time can be resolved. If you killed your parents before you were born, it simply means that you killed people who are not really your parents - although genetically identical to them, they have the same personality and the same memories.
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The idea of multiple worlds solves at least one major problem of time travel. For the physicist, the number one problem with time travel (besides looking for negative energy) is that the effects of radiation will accumulate, and one of two things will happen: either you fall dead when you try to enter a car, or the wormhole will collapse. when you walk through it. These radiation effects will accumulate because any radiation that hits the time portal will travel to the past; there this radiation will come out and will roam the Universe until today, when the time comes for it to re-enter the portal. Since radiation can enter the portal an infinite number of times, inside the portal it can reach incredibly high levels - enough to kill anyonewho gets there. But if we talk about the version with "multiple worlds", then this problem will be solved by itself. The radiation that has entered the time machine is indeed sent to the past, but enters a new universe; it cannot enter the time portal again and again and again. This means that there is an infinite number of universes, each cycle has its own, and in each cycle only one photon of radiation penetrates into the time portal - and not infinitely many.and in each cycle only one photon of radiation penetrates into the portal of time - not infinitely many.and in each cycle only one photon of radiation penetrates into the portal of time - not infinitely many.
In 1997, when three physicists finally managed to prove that Hawking's intention to ban time travel once and for all was incorrect in principle, the controversial issues were slightly cleared up. Bernard Kay, Marek Radzikowski, and Robert Wald have shown that time travel does not contradict any known physical laws, except for one point. When it comes to time travel, all problems are concentrated on the event horizon (located near the entrance to the wormhole). But this horizon is the very place where, according to modern ideas, Einstein's theory gives way to quantum effects. The problem is that in trying to calculate the radiation effects at the entrance to the time machine, we are forced to use a theory that combines Einstein's general theory of relativity and the quantum theory of radiation. But,no matter how we naively try to combine these two theories, the result is inconclusive; in some places the answer is endless, which makes no sense.
Here comes the time of the so-called theory of everything. All the problems of wormhole travel that plague physicists (for example, the stability of a wormhole, life-threatening radiation, the collapse of a wormhole when trying to get through it) is concentrated on the event horizon - exactly where Einstein's theory loses its meaning.
Thus, the key to understanding time travel is understanding the physics of the event horizon - which can only be described and explained by a theory of everything. This is why most physicists at the moment agree that the only way to solve the issue of time travel is to develop a complete theory of gravity and space-time.
A theory of everything should combine the four fundamental physical interactions of the universe and allow us to mathematically calculate what happens when we enter a time machine. Only a theory of everything could successfully calculate the radiation effects created by a wormhole and clarify the question of how stable a wormhole will be when a person enters a time machine. But even after creating such a theory, we may have to wait several centuries or even longer before the first time machine can experimentally test its conclusions.