Although a quantum theory of gravity has immediate practical application there is one budding area of physics devoted to a novel application of quantum physics: time travel. Oddly enough, Einstein's equations admit the possibility of time travel. But it may take the full power of the unified field theory to calculate whether it's really possible or not. Back in 1949, Einstein's next door neighbor at the Institute for Advance Study, the great mathematician Kurt Goedel, demonstrated Einstein's own equations allowed for time travel. If the universe rotated, and you went around the universe, you could arrive back before you left!

In his memoirs, Einstein pointed out that Goedel's solution could be dismissed on "physical grounds." Our universe expands, it doesn't rotate. But this leaves open the possibility that if the universe rotated, then time travel would be common place!

Since then, literally hundreds of solutions of Einstein's equations have been found which yield time travel solutions. They include:

An infinite, spinning cylinder. This allows for time travel if one travels around the cylinder.

Cosmic strings. They allow for time travel if the cosmic strings collide.

A spinning black hole. This collapses into a spinning ring (not a point), so anyone falling through the ring might actually fall through a wormhole (the Einstein-Rosen Bridge) which, like Alice's Looking Glass, connects two different regions of space and time.

Negative matter. If enough negative matter were to be found,then it might open up a wormhole large enough so that a trip through time wouldn't be any more jarring than a ride on an airplane.

Negative energy. Similarly, an intense concentration of negative energy can also open up a wormhole. A crude version of "warp drive" can be obtained if one stretches the space in front of you and compress the space behind you via negative energy.

A Theory of Everything may also help explain the sticky paradoxes found in time travel stories,such as the grandfather paradox (what happens if you kill your ancestors before you are born). Because the entire universe must be quantized, it’s possible the universe splits in half when you alter the past. The "river of time" forks into two different rivers.

If you go back in time to save President Kennedy from being assassinated, you will only save someone else's President Kennedy. Your own past cannot be changed.

But don't expect any amateur inventor to announce the invention of a time machine anytime soon. Negative matter has never been seen (it falls up, not down) and you need a fantastic amount of both negative and positive energy, called the Planck energy (which is a quadrillion times larger than the energy of the LHC). When Michael J. Fox jumped into his plutonium-fired De Lorean car in ‘Back to the Future’, we can calculate that his plutonium power source does not have enough energy to open a hole in space-time. Even if we could buld one the stability of these time machines is in question. We don't know if they will be stable enough to transport us safely back in time.

Outlook

At present, superstring theory has emerged from being a fringe theory of physics to becoming one of the dominant areas of research, generating tens of thousands of papers. The pace of research is feverish. Edward Witten of the Institute of Advanced Study, one of the principle researchers in string theory, recently made another discovery, that there might even be a hidden eleventh dimension. But the truth is that no one is smart enough to completely solve the theory and settle intriguing theoretical questions about what happened before the Big Bang and if time travel is possible

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