General Relativity predicts that wormholes could connect two distant parts of the universe in a way that could be traversed instantaneously, or nearly so. Given that Special Relativity had previously demonstrated that traveling faster than light would be the equivalent of traveling in time, this raises the question of whether wormholes could also allow us to travel through time. A new exploration of the topic argues the answer is yes, at least in certain circumstances.
Wormholes remain very much a theoretical phenomenon. We’ve never knowingly observed one, although last year a paper concluded that at the angle we are seeing it, we can’t tell if M87* is a black hole or a wormhole. Such is their importance and fascination, however, that physicists devote a great deal of energy to trying to work out what wormholes would be like if they do exist.
The latest effort focuses on a specific type of wormhole called a ring wormhole, which unlike “standard” wormholes have no matter within them, making passage through much less hazardous. They do, however, have a thin shell of matter around one of the mouths. The paper calculates that such a wormhole would produce “closed timelike curves” in spacetime, meaning objects traveling the curve would end up at the same time as they started. “This process inevitably transforms such a traversable ring wormhole into a time machine,” the paper concludes. By this, they mean that it would be possible to travel through the wormhole in one direction, return in the other, and emerge at a time earlier than the first entry.
One of the key features of General Relativity is that space can be shaped, for example by powerful gravitational fields. The idea is usually represented by having a two-dimensional stretchy material warped by a large weight. Things might get so distorted, physicists have argued, that two points in space come quite close to each other in an additional dimension while being a long way apart by means of ordinary travel. This led to the concept of the Einstein-Rosen bridge, more popularly known as a wormhole, proposing the two points could be joined.
After considering whether wormholes can exist, the next most important question is whether it is possible to survive passing through. Follow-ups include whether it is possible to send messages back about what is found (yes according to one paper, but only if you’re quick).
If the fabric of the cosmos is the spacetime continuum, as relativity proposes, then using a wormhole to cross between two points may also be traveling in time.
The new paper bases itself on previous modeling of traversable wormholes, and considers one in a weak gravitational field, undisturbed by a nearby star or planet. The authors conclude that when such a wormhole first forms it will not function as a time machine, but will inevitably become one later.
The time it takes for this to occur is approximately equal to RLc/GM where R and M are the radius and mass of the thin shell, L is the distance between the two mouths, and G is the Gravitational constant. There’s not much you can do about G, but if you want your time machine soon, increase the radius of the shell, while reducing its mass. Once you have your time machine, waiting will be irrelevant of course, but until then it’s probably as painful as for the rest of us.
Maybe there is a space-faring species with a proverb that translates to “a watched wormhole never turns into a time machine.”