Quote:
Originally posted by redlemon
MuadDib, let me try again, because you (and others) aren't getting the point of the original question. Grab a pair of scissors. Open them partway. Put a pencil in between the blades as close to the handles as you can. Now open the scissors further, and see that you can put the pencil in further. That is the "point" Jaseca is talking about.
Now take out the pencil and close the scissors slowly. Notice that the "moving point" moves faster than the tips of the blades. Extrapolate to light speed. Explain.
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You are assuming the scissor baldes are rigid.
Rigid bodies don't exist.
Therefore, your pencil will travel only at the speed of light, as that is the maximum speed with which the "signal" of you closing the scisoors can propagate along the baldes.
If you want to visualise it, you must think of the blades as being made of a "rubber" substance.
Think of this situation.
You have a rigid meter stick, and you hold it a milimeter away from a button. you can push the stick into the button in one milisecond.
In other words, you can send a signal from point A to B, a meter apart in one milisecond.
Now what happens when you increase the length of the stick?
Surely you could send a signal from A to B in one milsecond, for an arbitrarily large distance?
Well no...because the signal still has to propagate down the length of the stick.
So if you start to push on the stick at end A, end B will only start to move correspondingly at a time no less than (A-B)/c...i.e. the signal won't travel faster than c.
To visualise it, think of picking up a piece of string and flicking it, so that you create a wave in it, and observe the wave traveling down the piece of string.
The same thing happens with the stick...which you cannot visualise as a uniform rigid body...but instead as a mass of atoms, all bound by elctomagnetic attractions (which cannot exceed c).
Here's a way, where you can actually make "something" move faster tha the speed of light.
Take a very powerful laser pointer.
Point it on the surface of the moon.
Bring the dot over the the far left side of the moons surface.
Now really quickly point your laser pointer a few degrees right.
It will take you only a tiny fraction of a milisecond to move your laser pointer, from right to left, yet the "dot" will have to travel, in that same length of time, a very large distance.
To some one on the moon, they will see a red dot very quickly move from one point on the surafce to another...so fast in fact that it is seen as going faster than the speed of light.
I will leave it up to yourself to see how this does not break relativity.