Wormholes and Warpdrives

For years science fiction writers have come up with methods to tie interstellar empires together. Although these semi scientific methods of travel are as varied as the stories that accompany them, they all must be quick and cheap means of transportation. It is difficult to even imagine a society that extends outside the solar without some means of travel faster than light. While light moves at 300,000,000 m/s, those speeds would be far too slow to effectively tie civilizations in different solar systems together. A second problem with sub-light speeds is time dilation. When traveling at speeds that are a significant percentage of the speed of light, time slows down compared to those on Earth. This would present a problem to those that travel between two solar systems as years or decades would have passed before they even reach their destination although for them it might seem much shorter a journey. On the other hand, technologies that would allow for faster than light speeds are currently predicted to be impossible. Along with time dilation the mass of an object speeding up increases as that speed approaches 300,000,000 m/s. In short, the energy to send a spaceship to another star at the speed of light is infinite. There are only two proposed methods that could circumvent this cosmic speed limit and make a vast interstellar civilization possible.

The first of these is the wormhole. This idea was first formulated by Einstein and Nathan Rosen. They realized that a solution to the equations of general relativity allows for the existence of "bridges" in the spacetime continuum.
These could connect any two points in a spacetime whether it be another solar system thousands of lightyears away, a time in the distance past, or even another universe. In theory, the use of wormholes for space travel is simple. While no spaceship can move over a given distance faster than the speed of light, a wormhole could be used to decrease the actual distance traveled to another point in space. In other words, while still moving slower than light a space traveler could reach a distant star first by taking a massive short cut.

Unfortunately, simplicity ends there. While wormholes would be perfect for interstellar travel in theory in reality wormholes are very unstable. Any matter or energy that entered the wormhole would cause it to collapse. To solve this problem, exotic matter is required. Exotic matter put simply is a material with negative mass. As such it is repelled instead of attracted by gravity. The covering of the throat of a wormhole with such a material would cause the wormhole to stabilize. The only known way to create a negative mass is by use of the Casimir effect. A mysterious force in of itself the Casimir effect causes two metallic plates to repel each other when place in a vacuum. Although this force falls off very quickly with distance, it is powerful enough to apply a force equal to that of our atmosphere at 10 nm.

The second proposed method for faster than light travel is more similar to that found in Star Trek or Star Wars. Known as the Alcubierre warp drive, this method of travel would circumvent the speed of light entirely by keeping a spacecraft immobile. By manipulation of spacetime itself a warp drive would propel a ship forward at arbitrarily large speeds. By contracting spacetime ahead and expanding it behind a ship, it is theoretically possibly to create a spacetime bubble which would move the spaceship forward. Such a warp drive would require both exotic and normal matter in order to bend spacetime. Alcubierre's drive is similar in concept to a moving walkway. Although the speed that a person can walk down the walkway is limited just as the speed of a spaceship is limited by the speed of light, the rate at which a person can get to their destination is much greater due to the additional speed that the walkway imparts. The downside of the Alcubierre drive is that the walkway must be constructed before it can be used. Since the ship moving inside the spacetime bubble is moving faster than the speed of light outside of the bubble it is impossible for the pilot of the ship change course or end the journey of his ship. A road which the bubble will follow is necessary to control, accelerate, and decelerate any starship. Another objection to the use of this theory is the massive amount of energy needed to create such a bubble. Even by the most conservative estimates, it will take on the order of 6 x 10^30 kg of matter and at least a few milligrams of negative mass to create a spacetime bubble big enough to transport a small starship across the galaxy. While this may seem like a vast amount, some have predicted that it will take more energy to shape such a bubble than is currently contained within the universe.



http://www.daviddarling.info/encyclopedia/W/wormhole.html

http://en.wikipedia.org/wiki/Casimir_effect

http://en.wikipedia.org/wiki/Wormhole

http://en.wikipedia.org/wiki/Alcubierre_drive

http://en.wikipedia.org/wiki/Krasnikov_Tube

http://www.zamandayolculuk.com/cetinbal/warpDrivesx.htm