Faster-Than-Light Travel 3

-from A Wrinkle in Time

Faster-than-light travel is the travel through space faster than the travel of light. An important note is that an actual speed exceeding that of the speed of light is not necessary for faster-than-light travel; in fact, most techniques for traveling faster than light do not involve exceeding C, the speed of light. The first technique is the Cherenkov Effect. The Cherenkov Effect is the fact that light moves slower in a medium such as air, water, or glass than in a vacuum like space. This means that it is possible to outpace light in such a medium without surpassing C, as C only applies for light in a vacuum. A shadow or light spot can change faster than light if the light beam projecting them is far enough away and is moved. In a rocket moving at close to the speed of light, time on their ship would slow down according to special relativity, causing the calculation of speed over time (velocity) relative to the passengers of the rocket to be faster than light. However, as light is not actually travelling at the speed of light C in the first scenario, no information or objects are able to be transmitted in the second scenario, and the rocket does not exceed the speed of light to an outside observer no witnessing the slowing of time in the third scenario, none of these are considered true faster-than-light travel. Most methods of theoretical faster-than-light travel feature the same flaws as these.

Other theoretical methods of faster-than-light travel run into different flaws. The first is universal expansion. The expansion of the universe moves objects inside it, allowing objects to be pulled in opposite directions in such a way that a third party observer would see the distance between them increasing at a speed faster than that of light. However, the objects themselves would not register velocities above those at light. This is generally not considered true faster-than-light travel, however, as it does not allow any object to actually travel across the galaxy faster than light could, and instead only allows faster-than-light travel in relation to a cosmic reference frame. There are other supposed instances of faster-than-light travel using reference frames, such as the speed in which the moon orbits over one’s head as one rotates with the Earth, but these run into the problem that space and time alone are relative. The object itself, such as the moon, would not actually experience itself outpacing light; the observer on Earth is just considering himself at rest when in fact he is the one moving with the rotation of the Earth. Neither of these examples work as a usable faster-than-light travel mechanism.

There are actual methods of travelling faster-than-light, however. The first is through the use of wormholes. A wormhole in space-time artificially shortens the distance in space-time an object must travel to reach its destination, allowing it to travel between two points faster than light would in a straight path through the normal configuration of space-time. The book A Wrinkle in Time describes such motion as a tesseract, where space-time is folded to allow distant points to touch each other. However, the energy requirements for holding open such a wormhole make such a feat impractical and possible unachievable outside theoretical speculation. Another method for achieving faster-than-light travel is the warp drive. Popularized in Star Trek, this method would warp space-time in such a way that the object would actually be pushed through space at a speed faster than light. The object would reside inside a stable bubble of space-time to prevent the space-time warping required for such motion to harm the transmitted passengers or information. Mexican physicist Miguel Alcubierre actually determined a theoretical method for achieving such travel in 1994 by contracting spacetime in front of a vessel and expanding space-time behind it to create a wave of space-time that the vessel rides on to exceed light speed. The process ran into the problem that it would require energy usage equivalent to the mass of jupiter, but Harold White, a physicist at NASA, discovered a way to reduce the energy requirements to the equivalent of the mass of Voyager 1 by altering the shape of the spacecraft, and theorized that it would be possible to decrease the requirements even more by oscillating the warpage of space-time. NASA is currently working on developing such a spacecraft. However, such travel requires the violation of certain energy rules. Also, the spacecraft is inside a space-time bubble for the duration of the faster-than-light travel, so the entire trajectory must be planned out  beforehand, a process that may itself require faster-than-light travel. These issues, among others, have made some scientists doubt that a warp drive can ever be plausibly created. Many others see these problems as surmountable, and much progress has been made in the last couple of decades. That being said, both of these methods of faster-than-light travel only outpace light because they use a different method of travel through space-time; if the same circumstances of travel were applied to light as to the beneficiaries of these methods instead of comparing the methods to light traveling through normal space-time, light would outspeed them. In this way even the most promising methods of faster-than-light travel cannot be said to be truly travelling faster than light.

In fact, true faster-than-light travel -- travel that would beat light in a straight-up race in normal space, is theoretically impossible. Special relativity states that the combined motion through space-time is equal to the speed of light. When one is at rest in space, one moves through time at the speed of light, and when one moves through space at the speed of light, one is at rest in time. Therefore, moving in space faster than the speed of light would require moving backwards in time to maintain the balance. This leads to the Grandfather Paradox. If one could travel back in time, then they could meet and kill their grandfather, preventing themselves ever having been born. But if they had never been born, they never could have traveled back in time to kill their grandfather. This paradox is widely used to disprove time travel to the past. However, it therefore could also be said to disprove faster-than-light travel. So although there are many techniques to create the appearance of travelling faster than light, and some even to give the practical effects of travelling faster than light, actual faster-than-light travel can be written off.

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