Q&A: Black Holes

Q:
Are worm holes traversable?

A:
If a large enough wormhole existed, it would allow almost instantaneous movement to another part of the universe. Certainly, Jodie Foster was able to do it in the movie Contact and it happens routinely in other science fiction movies, TV programs and novels.

A wormhole is a hypothetical type of tunnel consisting of two entrance holes that resemble black holes. The entrance holes can be far apart, yet connected by a tube that extends through hyperspace.

The only way to keep a wormhole from collapsing immediately is to fill it with negative energy. Positive energy will not do, because in general relativity energy equals mass, and hence more gravity, which would close up the wormhole. Negative energy is permitted by quantum theory, and its effects have been observed in the laboratory.

However, when negative energy is created it must obey three conditions:

1. The longer the pulse of negative energy, the weaker the amount
2. A negative energy pulse must be followed by a positive energy pulse to balance the books
3. As the interval between the negative and positive energy pulses increases, the positive energy pulse must be larger.

So, in order to hold a wormhole open long enough for space travel, an incredible amount of negative energy would be required. For example, it has been estimated that to create a wormhole with a diameter one millionth the size of a proton, wormhole engineers would need negative energy equivalent in magnitude to the energy generated by ten billion suns in one year. As you can see, this would be a very expensive way to travel!

Further reading:
Much of the information presented here was adapted from:
L. Ford and T. Roman, "Negative Energy, Wormholes and Warp Drive" Sci. Am. Jan. 2000, p.46.
An excellent introduction to black holes and wormholes is:
K. Thorne, "Black Holes And Time Warps: Einstein's Outrageous Legacy" W.W. Norton, 1994.