Wormholes

Space-time wormholes are hypothetical objects in German-born Jewish physicist Albert Einstein's general theory of relativity, where intense gravitational fields warp space and time to provide shortcuts from one part of our universe to another (or worse, perhaps, a route from our universe to some other universe). Physicists have not found solid experimental evidence that wormholes exist, but there are reasonably convincing theoretical arguments that strongly suggest that wormholes should be part of the theory of quantum gravity .

As theoretical objects, wormholes were invented and named in the late 1950s by American physicist John Archibald Wheeler, an early pioneer in the quest for quantum gravity. Since then they have become a standard tool in science fiction (such as in the television series Star Trek and Farscape and the novel Einstein's Bridge ), but they have also attracted a lot of serious scientific attention. Although physicists cannot conduct any experiments yet, wormholes can be used in "thought experiments" to see how solid and reliable certain theories are.

Science fiction stories make wormhole travel look relatively straightforward, if not exactly easy. The physicists' conception is more conservative and less encouraging: Naturally occurring wormholes, if they exist at all, are likely to be extremely small, about 10 septillion (10²⁵) times smaller than a typical atom. They are expected to be part of a quantum-mechanical "space-time foam" that is expected to arise at extremely short distances. Wormholes of this size are not useful for human travel, or even for sending signals.

Creating a large wormhole, or artificially enlarging a small naturally occurring wormhole, would require the manipulation of large quantities of matter—planet loads of mass. A wormhole 1 meter (about 1 yard) across would require the manipulation of objects with the mass of the planet Jupiter and the squeezing of them into a region about a meter wide. Worse, because the gravitational field of a wormhole is in some sense repulsive (one would not want a black hole to form), one would need to manipulate large quantities of what is called "exotic matter," which is basically negative energy matter with less energy than the energy of an equal volume of vacuum .

Needless to say, we do not currently have the technology needed to do this, nor is there any realistic hope of acquiring such technology in the foreseeable future. We cannot even manipulate positive masses the size of Jupiter, nor have we ever found large quantities of negative mass lying around anywhere. So realistically, the prospects for space travel using wormholes is close to zero. This will not stop physicists from investigating the subject, but one should try to not be overly enthusiastic about the chances.

Because wormholes connect distant places, and the laws of space-time physics seem to treat space and time on an almost equal footing, it has also been suggested that wormholes should be able connect distant times: If you find a wormhole, it would seem at first glance to be relatively easy to turn it into a time machine. Now this does scare the physics community; allowing time travel into physics is, to say the least, awkward. There is an idea called "chronology protection," formulated by English physicist Stephen Hawking, to the effect that quantum physics may "keep the universe safe for historians" by automatically destroying any wormhole that gets too close to forming a time machine. As Hawking put it: "there is considerable evidence in favour of [chronology protection] based on the fact that we have not been invaded by hordes of tourists from the future."

see also Cosmology (volume 2); Einstein, Albert (volume 2); Zero-Point Energy (volume 4).

Matt Visser

Bibliography

Morris, Michael S., and Kip S. Thorne. "Wormholes in Spacetime and Their Use for Interstellar Travel: A Tool for Teaching General Relativity."American Journal of Physics 56 (1988):395-412.

Thorne, Kip S. Black Holes and Time Warps: Einstein's Outrageous Legacy. New York:Norton, 1994.

Visser, Matt. Lorentzian Wormholes: From Einstein to Hawking. Reading, MA: American Institute of Physics Press, 1996.