Some of you were talking about you wanted a problem that really stretched your mind. This might not do that, but I'll try. Think about something that is in one spot, but connected to a motor and spinning. could it be possible to accelerate the outer part of the spinning object to anywhere near the speed of light? The outer part of something spinning travels faster. When most people think about time travelling and going near the speed of light, they think about travelling in a straight line. Well, despite the incredible g's, I think we would have more of a chance on the outside of a very quickly spinning object. (no the object would not have to be heavy, but maybe wide) Anybody have any comments on this? The object travelling would stay in the same general area instead of travelling way out into space. It would take a lot of energy, but about how fast do you think we could accelerate something like that? Also, would there be any way to counter the g's? Just a thought, and maybe this will get some people thinking.

-strategicman

This is apparently an old chestnut.
http://physics.hallym.ac.kr/education/faq/rigid_disk.html
It turns out that Lorentsian contraction would exert stresses on a disk rotting near the speed of lihgt that would tear it apart.

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My answer is that, in order to play this trick, it seems that you are really suggesting to apply our torque near the center where we need not move very fast at all, and that the outside will have the same angular velocity, but much greater tangential velocity by virtue of its larger radius. The problem, I think, is that we cannot assume this equality in the anqular velocity, because this disk is not perfectly rigid, definitely not rigid physically, but also not rigid in the context of relativity.

This torque is transferred from the center towards the outside. A simple way of looking at it is to say that the disk is a set of concentric rings of increasing size. The thickness is arbitrary. The point is that the inner ring can only pull the next outer ring according to relativity. My prediction is that the disk would actually start to "spiral" like a galaxy, because the relative motion of the adjacent rings does funny things as it approaches the speed of light.

If you want to be trite, you could just say that, as the mass elements on the edge approach the speed of light, the marginal increase in their kinetic energy for a given acceleration goes to infinity, and therefore the motor would have to deliver infinite power to accomplish this feat/feet/phete (sp?).

If we just consider the combination motor-disk, then I predict that they would distort into either diverging parabaloids or hyperboloids. I have not tried to derive this, it is just my first intuition. If we consider them as a motor fixed relative to the stars, and a disk that rotates in this frame, then I think it would just be the disk that would spiral in its own plane.

Here's a question that I have not yet been able to resolve. What does rotation really mean? It seems like there is at least an absolute frame of orientation implicit in the concept of rotation. I have heard of, and read about, Mach's principle, and about Newton's spinning pale of water, but I don't quite get what this is saying about the mass distribution. Do you know anything about this?