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Wormholes are hypothetical shortcuts through space-time that could allow for faster-than-light travel, but in reality, movement through a wormhole would be at normal speed through folded space. They are popular in science fiction, but probably don’t exist as they would require negative matter and would detach almost instantly. If they did exist, they could function as time machines, but the causality-breaking properties would be prohibited by cosmic censorship. More research on wormholes would require a quantum theory of gravity.
A wormhole is a hypothetical space-time topology, a “shortcut” that would allow to travel between two points at speeds apparently higher than light. The name comes from the spacetime analogy to the surface of an apple, where a wormhole is a tunnel through the apple. In reality, movement through a wormhole would not be faster than light, but rather moving at normal speed through folded space.
Wormholes are popular in science fiction because they allow characters to travel great distances in short periods of time. In real life, wormholes probably don’t exist, as they would require negative matter, an exotic substance that has never been observed and whose existence is not predicted by the Standard Model of particle physics. Mathematical models of the wormhole’s space-times show that it would “detach” almost instantly. Also, a wormhole would have to be extremely small: most models show wormholes with openings smaller than an atomic nucleus.
Wormholes have also been called Schwarzschild wormholes or Einstein-Rosen bridges, in the context of earlier mathematical analyses. An Einstein-Rosen bridge would have a black hole at both entrances, meaning that once a theoretical traveler entered the wormhole, he would have crossed an event horizon and been stuck in the middle.
If wormholes could exist, they could also function as time machines. According to Einstein’s theory of relativity, time passes more slowly for a highly accelerated body. If one end of a wormhole were accelerated to approach the speed of light while the other was stationary, a traveler entering the stationary hole would emerge from the accelerated hole in the past. This type of wormhole would be called a closed time curve or timehole.
Physicist Stephen Hawking has proposed that the causality breaking properties of such wormholes would be physically prohibited by a form of cosmic censorship. This is because time travel would cause seemingly unsolvable paradoxes, such as a case where someone goes back in time to kill their previous self. Learning more about the theoretical properties of a wormhole would require a quantum theory of gravity, which hasn’t been developed yet.
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