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Black Holes

There are two ways that a black hole may be harnessed for time travel: using it's massive gravitational field to dilate time, or, if you're lucky enough to find a rotating, Kerr hole, it could be used as a wormhole into other universes.

» Option 1: Gravitational time dilation

According to Einstein's General Theory of Relativity, time slows down when it is near supermassive gravitational fields. One could then time travel to the future by hanging around one of these babies (at a safe distance!) and then going back to Earth to find that a few thousand years have passed, while you've only aged a couple of years.

» Option 2: Kerr holes

In 1963, New Zealand mathematician Roy Kerr proposed the first realistic theory for a rotating black hole.

Y'see, in a normal, unrotating black hole, the hole consists of:

Typical diagram of a typical black hole.

Where the event horizon is the "point of no return", and the singularity is the point of oblivion. Sounds pretty scary, huh? But in a rotating, Kerr hole:

Not-so-typical diagram of a rotating Kerr hole

As you can see, the singularity here is no longer a point of oblivion, but a ring - an enterance (or an exit?) into another universe!

» Why does this happen?

When you spin a bucket of water 'round and 'round, where does the bucket want to go? Out. As the black hole/your bucket of water spins, it wants to go in a constant velocity (that is, at the same speed and in the same direction - this is Newton's first law of motion!). It wants to fly off! The centripetal force acting on it (gravity, your arm, etc) keeps the singularity/bucket from flying off.*

In this case of the rotating Kerr hole, the energy of the rotation overcomes the centripetal force (gravity) and allows the singularity to open. When this happens, the black hole can now act as a wormhole.


*Some may say that this is because of "centrifugal forces", and not centripetal forces. This is incorrect, as "centrifugal forces" don't exist.