Wormholes could be the key to time travel
Wormholes are one way that physicists have imagined traveling into the past. But if something gets there, is it physically possible to change anything?
Wormholes, once considered mere science fiction, have captivated physicists as a potential means of time travel. Albert Einstein's theories of special and general relativity opened the door to the possibility of traveling both into the future and potentially the past. One of the most intriguing solutions to this problem came from Kurt Gödel, who, as a gift to Einstein, proposed a model in 1949 that allowed for timelike curves.
These curves would enable an object to travel into the past and return to its original point in time.
However, Gödel's model was deemed unrealistic due to its basis in a universe with a negative cosmological constant and particles moving like a liquid. In 1988, Kip Thorne and his colleagues discovered traversable wormholes, which could also support time travel within realistic models of the universe. This discovery reignited interest in the subject and led to the formulation of the self-consistency principle by Russian physicist Igor Dmitriyevich Novikov.
According to Novikov, time travelers could influence the past but could not change it, preventing paradoxes such as the grandfather paradox.
Thorne and his students developed a model to support this principle, illustrating how a ball rolling through a wormhole and colliding with its future self would prevent the ball from entering the wormhole in the first place. They found that for every initial condition, there was a solution in which the ball did not prevent its future self from entering the wormhole, strengthening their hypothesis that self-consistent solutions for time travel were possible.
However, this hypothesis was not entirely proven, as it depended on the assumption that the ball was in a superposition of all consistent possibilities at the moment it exited the wormhole, meaning it could take all possible paths simultaneously. This solution was accepted by some physicists but rejected by Stephen Hawking, who proposed the chronology protection conjecture.
This conjecture suggests that physical laws in a yet-to-be-defined fundamental theory would prevent macroscopic objects from traveling backward in time, keeping the universe safe for historians.
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