time travel (time travellisten)) appears frequently in popular culture, with time travel storylines appearing heavily in film, television, and literature. However, this is actually an old notion – there is an argument for it greek tragedy Oedipus Rexwritten by Sophocles more than 2,500 years ago, it is the first time travel story.
However, is time travel really possible? Given the popularity of the concept, this is a fair question. As a theoretical physicist, I find there are several possible answers to this question, and not all of them are contradictory.
The simple answer is that time travel is impossible because if it were, we’d already be doing it. Some people might argue that time travel is against the laws of physics, e.g second law of thermodynamics or relativity. There are also technical challenges: Time travel is possible but would require an enormous amount of energy.
There are also time travel paradoxes; we could – hypothetically – fix it if free will is illusory, there are many worlds, or the past can only be witnessed but not experienced. Perhaps time travel is impossible simply because time must proceed in a linear fashion and we have no control over it, or perhaps time is an illusion and time travel is irrelevant.
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The laws of physics
Since Albert Einstein’s theory of relativity, which describes the nature of time, space and gravity, is the most profound theory of time, we tend to think that time travel contradicts relativity. Unfortunately, one of Einstein’s colleagues from the Institute for Advanced Study in the United States, Kurt Gödel, created the universe where time travel is possible and the past and the future intertwine.
Actually we can design a time machinebut most (in principle) require negative energy, or negative mass, which does not appear to exist in our universe. If we drop a tennis ball with negative mass, it will fall straight up. This argument is slightly unsatisfactory because it simply involves another elusive idea that explains why we can’t travel in time in practice.
Mathematical physicist Frank Tripler came up with the concept a time machine that does not involve negative mass, but requires much more energy than is available in the universe.
Time travel is also breaking down second law of thermodynamics, which states that entropy or randomness must always increase. Time can only move in one direction. In other words, we cannot return scrambled eggs to their original shape. More specifically, by traveling back in time, one goes from the present time (a state of high entropy) to the past which should have a lower entropy.
This argument comes from British cosmologists Arthur Eddington, and it is not quite complete. The argument states that travel to the past is impossible but says nothing about time travel to the future. In practice, time traveling to the following Thursday is just as difficult as time traveling to last Thursday.
Solve the paradoxes
There is no doubt that if we were faced with a paradox if we could travel freely through time. The most famous paradox is “grandfather paradox(“grandfather paradox”): A person could hypothetically use a time machine to travel back in time and kill the grandfather before the father was conceived, thus eliminating the possibility of his own birth. Logically, we cannot be alive and not alive at the same time.
Read more:
Time travel might be possible, but only with parallel timelines
Kurt Vonnegut’s anti-war novels, Slaughterhouse-Five, published in 1969, describes how to avoid the grandfather paradox. If there were no free will, it would be impossible to kill a grandfather in the past because he was actually not killed in the past. The novel’s protagonist, Billy Pilgrim, can only travel to other points in his own worldline (the timeline he is in), but not to any other point in time and space, so it would be impossible for him to even think of kill his grandfather.
The universe a Slaughterhouse-Five consistent with everything we know. The second law of thermodynamics works very well in it and there is no conflict with relativity. However, it is inconsistent with some things we believe in, such as free will: we can observe the past, just like watching a movie, but we can’t interfere with the actions of the people in it.
Is it possible to change the real past so that we can kill our grandparents… or Hitler? There are several multiverse theories that assume that there are multiple timelines for different universes. It’s also an idea that’s been around for a long time: in novels A Christmas carol Charles Dickens’ Ebeneezer Scrooge experiences two alternate timelines, one of which leads to death and the other to happiness.
Time is a river
Roman emperor Marcus Aurelius wrote that:
“Time is like a river which consists of various events taking placeand rapid currents; for as soon as one thing is seen, it is carried away and another takes its place, and these too will be carried away.
We can imagine that time actually flows through every point in the universe, like a river around a rock. However, it is difficult to get the idea right. Flow is the rate of change: The flow of a river is the amount of water that travels a certain length in a certain amount of time. Therefore, if time is a flow, it moves at the rate of one second per second. This is not useful information.
Theoretical physicist Stephen Hawking states that “alleged chronological protection” there must be. This is a still unknown physical principle that prohibits time travel. Hawking’s concept stems from the idea that we cannot know what is happening inside black hole (a black hole) because we can’t get any information from it. However, this argument is too repetitive: simply put, we can’t travel in time because we can’t travel in time!!
Researchers are studying a more fundamental theory, in which space and time “emerged” from something else known as quantum gravity. However, this is unfortunately not yet available.
So can we travel through time? Chances are not, but we don’t know for sure.
Zalfa Imani Trijatna of the University of Indonesia translated this article from English.!
