Black Holes

While writers have produced some great ideas for time machines over the years, a real-life time machine has yet to be built. Most theories of time travel don't rely on machines at all. Instead, time travel will likely be done by way of natural phenomena that will transport us instantly from one point in time to another. These space phenomena, which we are not even sure exist, include:

• Rotating black holes
• Wormholes
• Cosmic strings

Photo courtesy NASA

When stars that are more than four times the mass of our sun reach the end of their life and have burned up all of their fuel, they collapse under the pressure of their own weight. This implosion creates "black holes," which have gravitational fields so strong that even light cannot escape. Anything that comes in contact with a black hole's event horizon will be sucked in. The event horizon is the boundary of a black hole at which nothing can escape.

You can think of the shape of a black hole as similar to an ice cream cone. It is large on top and tapers into a point, called a singularity. At the singularity, the laws of physics cease to exist and all matter is crushed beyond recognition. This kind of non-rotating black hole is called a Schwarzschild black hole, named after the German astronomer Karl Schwarzschild.

Another type of black hole, called a Kerr hole, is also theoretically possible. Kerr holes are rotating black holes that could be used as portals for time travel or travel to parallel universes. In 1963, New Zealand mathematician Roy Kerr proposed the first realistic theory for a rotating black hole. In his theory, dying stars would collapse into a rotating ring of neutrons that would produce sufficient centrifugal force to prevent the formation of a singularity. Since the black hole would not have a singularity, Kerr believed it would be safe to enter it without being crushed by the infinite gravitational force at its center.

If Kerr holes do exist, it might be possible to pass through them and exit out of a "white" hole. A white hole would have the reverse action of a black hole. So, instead of pulling everything into its gravitational force, it would use some sort of exotic matter with negative energy to push everything out and away from it. These white holes would be our way to enter other times or other worlds.

Given the little we know about black holes, Kerr holes may possibly exist. However, physicist Kip Thorne of the California Institute of Technology believes that the laws of physics prevent such a formation. He says there is no such way to enter and exit a black hole, and that anything attempting to enter a black hole will be sucked in and destroyed before it even reaches the singularity.

We'll take a look at some other space phenomena in the following sections.