Time Machine | Time Travel

Time travel is the idea of movement (such as by a human) between certain points in time, the same as movement between different points in space, usually using a possible device known as a time machine, in the form of a vehicle or of a doorway connecting distant points in time. Time travel is a recognized idea in (way of thinking/related to learning about how people think) and fiction, but traveling to a random point in time has a very limited support in (related to ideas about how things work or why they happen) physics, and usually only connected with (related to tiny, weird movements of atoms) mechanics or wormholes, also known as Einstein-Rosen bridges. In a more narrow sense, one-way time travel into the future via time(expanding/enlarging) is a well-understood important thing/big event within the (solid basic structures on which bigger things can be built) of special relativity and general relativity, but advancing a large amount of time is not (able to be done) with current technology.[1] The idea was touched upon in different earlier works of fiction, but was (made well-known) by H. G. Wells' 1895 novel The Time Machine, which moved the idea of time travel into the public imagination, and it remains a popular subject in science fiction.

Some very old stories show a character skipping forward in time. In Hindu very old stories, the Mahabharata talks about/says the story of King Raivata Kakudmi, who travels to heaven to meet the creator Brahma and is surprised to learn when he returns to Earth that many ages have passed.

The Buddhist Pāli Canon talks about/says the relativity of time. The Payasi Sutta tells of one of the Buddha's chief loyal students, Kumara Kassapa, who explains to the doubter Payasi that, "In the Heaven of the Thirty Three Devas, time passes at a different pace, and people live much longer. "In the period of our century; one hundred years, only a single day; twenty four hours would have passed for them."

The Japanese story of "Urashima Tarō", first described in the Nihongi tells of a young fisherman named Urashima Taro who visits an undersea palace. After three days, he returns home to his village and finds himself 300 years in the future, where he has been forgotten, hishouse is in ruins, and his family has died. 

Early science-fiction stories feature characters who sleep for years and awaken in a changed(community of people/all good people in the world). Among them L'An 2440, reve s'il en fût Jamais (1770) by Louis-Sebastien Mercier, Rip Van Winkle (1819) by Washington Irving, Looking Backward (1888) by Edward Bellamy, and When the Sleeper Awakes (1899) by H.G. Wells. Lengthy sleep, like the more familiar time machine, is used as a means of time travel in these stories.

General relativity 
Time travel to the past is probably (but not definitely) possible in certain general relativity space time geometries that allow traveling faster than the speed of light, such as (universe-related) strings, transversable wormholes, and Alcubierre drive. The explanation of general relativity does suggest a scientific basis for the possibility of backward time travel in certain unusual pictures/situations, although arguments from semi classical gravity suggest that when (related to tiny, weird movements of atoms) effects are included/combined into general relativity, these (problems in the wording of a law that lets people sneak past it) may be closed. These semi classical arguments led Selling to plan the history-related protection educated guess, suggesting that the basic laws of nature prevent time travel, but physicists can not come to a definite judgment on the issue without an explanation of (related to tiny, weird movements of atoms) seriousness to join (related to tiny, weird movements of atoms) mechanics and general relativity into a completely brought together (as one) explanation (of why something works or happens the way it does).

Special space time geometries 
The general explanation of relativity extends the special explanation (of why something works or happens the way it does) to cover gravity, illustrating it in terms of curvature in space time caused by mass-energy and the flow of speed and power. General relativity describes the universe under a system of field equations, and there exist solutions to these equations that allow what are called "closed time-like curves", and because of this time travel into the past. The first of these was (offered/suggested) by Kurt Gödel, a solution known as the Gödel metric, but his (and many others') example needs/demands the universe to have physical (features/ qualities/ traits)that it does not appear to have. Whether general relativity forbids closed time-like curves for all realistic conditions is unknown. 

Wormholes 
Main article: Wormhole 
Wormholes are a possible twisted/sick space time which are permitted by the Einstein field equations of general relativity. A proposed time-travel machine using a traversable wormhole would possibly work in the following way: One end of the wormhole is fast to some significant part of the speed of light, maybe with some advanced propulsion system, and then brought back to the point of origin. Or,/In a different way, another way is to take one entrance of the wormhole and move it to within the (related to gravity) field of an object that has higher gravity than the other entrance, and then return it to a position near the other entrance. For both of these methods, time (expanding/enlarging) causes the end of the wormhole that has been moved to have gotten old less, or become "younger", than the unmoving end as seen by an external (person who watches something); however, time connects differently through the wormhole than outside it, so that (made two or more things look the same or happen at the same time) clocks at either end of the wormhole will always remain (made two or more things look the same or happen at the same time) as seen by a (person who watches something)passing through the wormhole, no matter how the two ends move around.  This means that a (person who watches something) entering the "younger" end would exit the "older" end at a time when it was the same age as the "younger" end, effectively going back in time as seen by a(person who watches something) from the outside. One significant limitation of such a time machine is that it is only possible to go as far back in time as the first creation of the machine; basically, it is more of a path through time than it is a device that itself moves through time, and it would not allow the technology itself to be moved backward in time.