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?

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Last week I explained how Albert Einstein’s special theory of relativity makes time travel into the future possible—and how varied solutions to his general theory of relativity open the door to traveling into the past. One of the most memorable solutions comes from a brilliant friend and colleague of Einstein whom I’ve written about in this newsletter before ( here and here ): Kurt Gödel.

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In 1949, as a birthday present for Einstein, Gödel developed a solution that would permit timelike curves. As mentioned in the last newsletter, if you were to travel along these curves, you would start at one point in spacetime, move into the past and ultimately end up back at your temporal starting point.

The universe described by Gödel’s solution was bizarre, however. It consisted of dustlike particles that moved like a liquid in a spacetime with a negative cosmological constant. He specifically designed it this way to make travel into the past possible.

This led physicists to assume that timelike curves were a kooky artifact of unrealistic solutions to general relativity. But in 1988 future Nobel laureate Kip Thorne and his colleagues found a new kind of solution to Einstein’s field equations: traversable wormholes, which would allow time travel in realistic models of the universe. This rekindled scientists’ interest in time travel.

The possible existence of closed timelike curves raises many questions. Consider one posed in French writer René Barjavel’s 1944 novel Future Times Three : What if a person travels into the past and causes the death of their grandfather before he could father any children? In that case, the time traveler cannot exist, creating a paradox.