Is it possible to travel time?

Time travel is a situation in which we can travel to any place in the universe in the least amount of time, which we have to travel at the speed of light. Time travel is therefore the concept of moving between a few points at a time, corresponding to the movement between different points in space by an object or person, using an imaginary device commonly known as a time machine.

History of the concept of time travel

Time travel is a widely recognized concept in philosophy and fiction, which was popular only among scientists before 1895. But after that in 1895, the idea of ​​time machine was first popularized by the HG Wells novel " The Time Machine " among the common people.

Time travel, according to Japanese story

The Japanese story, "Urashima Taro" also describes time travel, in which a young fisherman named Urshima Taro goes to a palace under the sea, and after three days when he returns to his village home, he finds himself in the future 300 years ahead, 300 years have passed in his village, where he has been forgotten, his house is in ruins, and his family has died.

Time travel, according to physics

Developed in 1905, the special theory of relativity suggests that, time passes at different rates for those who are growing relative to each other - although the effect only becomes larger. When you travel at the speed of light.

The special and general relativity suggests that, suitable geometries of space-time or specific types of motion in space may allow time and future travel.

Many people in the scientific community believe that the chances of traveling past time are very low. It also states that, any theory that will allow time travel will also give rise to potential problems of one reason or the other. A modern example of a problem associated with this is " grandfather paradox ". The grandfather paradox says that, what if someone travels and goes to a time where he kills his grandfather before his father is born?

Some physicists, such as Novikov and Deutsch have suggested that these types of temporal contradictions can be avoided through the Novikov self-consistency theory or through a change of interpretation of the many-worlds interpretation.

General relativity

General relativity states that, if a person returns to Earth after traveling at the speed of light in a spacecraft, only a few years will pass on the spacecraft, but many years must have passed on Earth. This is known as "twins paradox". Because a traveler will find himself much younger in age than his twin after making such a journey.

Time travel in the past was theoretically possible in general relativity and some space-time geometries, which allow light to travel at speeds, such as cosmic strings, transversal wormholes, and Alcubierre drives.

The theory of general relativity suggests a scientific basis for the possibility of past time travel in some unusual scenarios, although semiclassical gravity arguments suggest that when quantum effects are included in general relativity, Then these flaws may be closed. These semiquantitative arguments prompted Stephen Hawking to formulate chronological conservation hypotheses, stating that the basic laws of nature prevent time travel, but physicists have yet to get into quantum mechanics and the theory of quantum gravity to join general One cannot make definitive decisions on relativity in a fully integrated theory without this issue.

Different space-time geometries

The theory of general relativity describes the universe under a system of field equations that determine the distance function of the metric or space-time. Exact solutions to these equations exist, including closed time-like curves, which are world lines that intersect themselves. Due to world lines, some point in the future is also in its past, a situation that can be described as time travel. Such a solution was first proposed by Kurt Gödel, a solution known as the Gödel metric, but his (and other ') solution requires the physical characteristics of the universe, which does not seem to be the case. Such as lack of rotation and Hubble expansion. Whether general relativity decreases like closed time for all relative conditions is still being researched.

Wormholes

Wormholes are an imaginary warped space-time allowed by Einstein's field equations of general relativity. Some scientists believe that time travel is possible using a traversable wormhole.

Anyone wanting to get a glimpse of the future has only one problem - to come back. This would mean traveling faster than light - and this is not possible. But it can be found in general relativity, Einstein's theory of gravity that unites space and time as "space-time", which decreases in the presence of mass. This allows for the possibility of a wormhole - a kind of tunnel through space-time that connects otherwise very distant parts of the universe.

If the "mouth" of the wormhole is moving relative to each other, crossing the bridge between different points in space will also take a passenger to a different point in the time in which he or she started the time travel. .

However, it would still be impossible to go back and forth from the point at which the wormhole would have formed, limiting travel options to some extent - explaining why we had not yet encountered any visitors from the future.

If a natural wormhole was formed in the Big Bang, it may be possible to travel to a limited number of points in the past and in the distant universe.

Quantum physics

More limited still, theoretical work by Caltech's Kip Thorne has suggested using a partial integration of general relativity with quantum physics that any wormhole that allows time travel collapses as soon as it is created. That is, the wormhole does not last long.

Grandfather paradox

However, Thorne resolved an obvious issue that could arise due to time travel (within the range of general relativity). " Grandfather paradox " involves going back in time and killing one's own or one's grandfather before accidentally or intentionally imagining his or her father - that is, stopping his or her own birth, thereby going back in time and having a It becomes impossible to kill the grandfather of. Thorne found that for a point mass crossing a wormhole, no initial condition creates such a contradiction.

Conclusion

Time travel is the idea of ​​going back in time in the past or going forward in the future. Time travel is not possible in the modern era yet, but it is used a lot in fictional stories.

Sources

Black holes, Wormholes and Time Travel, a Royal Society Lecture

Time Travel and Modern Physics at the Stanford Encyclopedia of Philosophy

Time Travel at the Internet Encyclopedia of Philosophy