Sunday, July 4, 2010

Making Gravity

We all know that when you're in space, particularly during planetary orbit, you tend to float around. After all, you are technically in free fall. This is what we see whenever we get live video from astronauts on the space station. Yet when we see people aboard various space ships in science fiction film and TV, be it the Enterprise, Millenium Falcon, or Serenity, they are usually seen with their feet planted firmly on the floor. We then have to assume that there is some sort of artificial gravity being generated throughout the ship. However, that is not as easy to dismiss as one would hope. This entry is dedicated to the impossible ubiquity of artificial gravity.

There are four fundamental forces in the universe that we know of so far. Only two of these are directly felt by us humans, namely, gravity and electromagnetism. There is also one more way to create a so-called "fictitious" force very similar to gravity which is to accelerate yourself in some direction. So how might we go about creating artificial gravity given what we know today? Probably the only practical method would be to use the acceleration technique in its centrifugal form. In other words, spin the cabin of the space ship around at a speed that creates an equivalent gravitational acceleration at the appropriate distance from the center where the astronauts are located. In this case, "up" would be toward the center of the rotation. This is exactly the method employed in the ships featured in 2001: A Space Odyssey and its sequel. It is also the method proposed by Stanford in 1975 for a viable space colony. Even this would present some issues since any attempt to move toward the center of the rotation would make you lighter and moving away would make you heavier. Also, for small radii, you'd have to deal with the coreolis effect. Of course, we know that is not the method used in most popular sci-fi ships.

We could not accelerate the ship in the same direction for very long, so that is out of the question. We're left with electromagnetism. The problem in this case is that the human body is not statically charged or magnetic, so it doesn't generally respond to EM fields. Occasionally, I have seen an attempt to fit magnetic shoes to astronauts and claim that it simulates gravity, but that is not really the case. Walking would be awkward since you'd have to keep at least one foot flat on the ground at all times. Non-magnetic objects like hair, clothing, food, and water would still float around, as would your upper body which could lean in any direction without falling to the floor. Most sci-fi shows do not try to attempt such an explanation. I suppose we could get creative and try to alter the human body in some way so as to make it respond to EM fields, but I haven't seen that one tried yet.

So if there is no known way that the laws of physics can currently support what we see on the screen, it is the responsibility of the writers to come up with some relatively convincing way for us to suspend our disbelief. In this case, you can't just say we have some new technology that just works because it is not a matter of technology. Simulating gravity is squarely a physics problem, and most of the time there is no attempt to explain it to audiences.

To make matters even worse, if a space ship undergoes any acceleration, it must still be felt inside the ship. Given the speeds that we are supposed to believe are being reached in short periods of time in order to travel huge distances, the number of g's involved would immediately kill you in the real world. Most film and TV shows will have the crew knocked around a bit from time to time, but it usually reflects very small changes in acceleration. It was always amusing to see the Enterprise crew sway from side to side while the ship was supposed be changing its speed by a factor of c (speed of light) every few seconds or so.

Oh well. I guess after this long we have to let it slide, as long as people sit up and notice when a writer actually makes a successful attempt to handle the problem.

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