Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: EvilHomer15 on 26/02/2011 05:08:19

Title: Can information of movement travel faster than light?
Post by: EvilHomer15 on 26/02/2011 05:08:19

This is purely a theoretical question:

Say you make a 1 light year long stick.
You push one end of the stick 1 meter over a duration of 1 second,
does this push make the other end of the stick move one meter immediately, and therefore the information of the push break the speed of light?

Title: Can information of movement travel faster than light?
Post by: Geezer on 26/02/2011 06:42:00

Good question!

I seem to remember we beat this one to death some time ago. I'll try to find the thread, but, as you may have already surmised, the answer is no.

Title: Can information of movement travel faster than light?
Post by: yor_on on 26/02/2011 10:17:37

The 'information' about you moving the stick is seen to transfer at the speed of sound in that stick, much as a shock wave does. If you assume a perfectly rigid stick though I'm not sure. It falls back to what you see as motion too. Assume that the perfectly rigid stick moves 'instantly' in its whole length, no shock wave needed. To do so it would either have to surpass the speed of light in a vacuum, or we have found a 'new' way of 'moving' faster than light. Any which way the idea falls on its complicatedness. A infinitely rigid stick is nowhere to be found, and the mass needed for constructing one, say a light year long, is daunting to say the least. Also you would need to overcome that mass moving it, which should make it quite impossible.
==

If it would work I'm sure we would find something restricting us from using it as a Morse code. That's one of SpaceTimes big tenets, no 'information' can ever be faster than the speed of light in a vacuum. But I don't know, assume a Lockheed SR-71 Blackbird moving through the air, at what speed are its shock waves transmitted through its body, relative whom? The pilot, the guy on the ground?
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'complicity' and 'complicated' has the same root (17th century (in the sense ‘combine, entangle, intertwine’): from Latin complicat- 'folded together', from the verb complicare, from com- 'together' + plicare 'to fold')

So, I keep mixing them. Yes, I'm old, although not that old :)

Title: Can information of movement travel faster than light?
Post by: lightarrow on 26/02/2011 13:05:24

Quote from: yor_on on 26/02/2011 10:17:37

The 'information' about you moving the stick is seen to transfer at the speed of sound in that stick, much as a shock wave does.

Exact.

Quote

If you assume a perfectly rigid stick though I'm not sure.

But such an object cannot exist, for the speed of sound cannot (as any other physical speeds) be greater than light speed.