jay@npois.UUCP (Anton Winteroak) (06/05/85)
A way to look at the long scissors experiment to demonstrate to yourself that you cannot use them to transmit information at faster than the speed of light (in a vacuum) is that one bar of the scissor can be held stationary, while the other moves. The moving bar must be waved back and forth in a way that represents the information being sent. The stresses in the bar which cause each succeeding layer of atom to sway one way or the other cannot move faster than the speed of light. Of course if you are only looking for one sweep of the blades, you can get the cross-over moving at faster than the speed of light, but you cannot send information faster than light. Not to be a spoilsport or anything, but how thick would the blades of such scissors have to be in order to keep them from breaking under the stress of the force to move them, or at least to prevent mechanical bending that far outsizes the relativistic bending? I hear that if you accelerate a meter stick made of 3 cm on a side spring steel up to 50% the speed of light, at the maximum rate that won't permenently deform it more than 1 mm, it will as far away as Venus when it gets up to speed.
mikes@AMES-NAS.ARPA (06/14/85)
From: mikes@AMES-NAS.ARPA (Peter Mikes) The fundamental problem with wery long scissors is an ~ implict assumption ~ that blade is a rigid body. a rotating rigid body -- a sweep of a blade, lead to superluminal if size is large enough. But how do you define a rigid body in a Lorentz covariant form ??
chrisa@azure.UUCP (Chris Andersen) (06/16/85)
> From: mikes@AMES-NAS.ARPA (Peter Mikes) > > The fundamental problem with wery long scissors is an ~ implict assumption ~ > that blade is a rigid body. a rotating rigid body -- a sweep of a blade, > lead to superluminal if size is large enough. But how do you define a rigid > body in a Lorentz covariant form ?? Okay, how about this for a better analogy: Have you ever been to the beach and just sat there and watched the waves? If you have you may have noticed that every now and then, two waves will come in at the same time. One will be tilted at a slight angle to the other so that they can be distinguished from each other. Like this: \\\\ //// \\\\ //// \\\\ //// \***/ //// \\\\ //// | \\\\ | V Direction of beach and waves motion The point where the stars are is the intersection of the two waves. Now the point to be made by all this is that while the speed of the waves through the water is limited to a certain value (what that is I don't know), the speed of the point of intersection can be *greater* then that limiting speed. If you extend this to two wave fronts of light at an angle greater then 0 to each other, there point of intersection is travelling greater then the speed of light.