traviling at the speed of light?

[JediJeb]

Here is a question I have often pondered and very hypothetical. If you had a metal rod that was one light year long and you push one end of it, would it take one year for the other end to move or would it move instantly, assuming no compression of the molecules or flexing of the rod? If it moves instantly would that be considered having something travel faster than the speed of light?

 

[Barnaby W. Füi]

If you had a rod that was a light year long and pushed one end of it, nothing in that rod would be moving even close to the speed of light. That would only happen if somehow magically YOUR end of it got to the other end in one year. If you push it and the other end moves, then each atom/whatever in it is only moving the distance that you pushed - not a light year.

Say I fill up a garden hose with water, and then blow a tiny bit of air into one end. A little water will spill out of the other end, but that water did not travel the entire distance in that one push. It was already at that end, and it just got pushed out a little and fell out.

 

[RossGr]

assuming no compression of the molecules or flexing of the rod?

Unfortunately this assumption creates a nonphysical situation, no meaningful information can be learned from thought experiments which assume away the real physics of a situation.

Any movement of a REAL object is transmitted from atom to atom via electro magnetic interactions. The fastest any information can be transmitted from one end of a rod to other (no matter what the length) is at the speed of sound in that material. This of course is much slower then the speed of light.

 

[silverpig]

Originally posted by: BingBongWongFooey
If you had a rod that was a light year long and pushed one end of it, nothing in that rod would be moving even close to the speed of light. That would only happen if somehow magically YOUR end of it got to the other end in one year. If you push it and the other end moves, then each atom/whatever in it is only moving the distance that you pushed - not a light year.

Say I fill up a garden hose with water, and then blow a tiny bit of air into one end. A little water will spill out of the other end, but that water did not travel the entire distance in that one push. It was already at that end, and it just got pushed out a little and fell out.

He's trying to say that you could send information instantaneously by pushing on a rod. Instead of using a radio to signal a person 1 ly a way and have the signal take 1 yr to get there, why not use a 1 ly long rod and tap out the signal instantaneously via pushing on it? That's what he was trying to say.

This is still impossible for the reasons RossGr said. You're stuck at the speed of sound in the material, and it'd be lossy.

Stuff can travel faster than light, but it just can't carry information.

 

[ranmaniac]

Dark Helmet "Light speed is too slow, we need to go into Ludicrous speed!"

 

[Chaotic42]

Originally posted by: NeoPTLD
Can you replicate this by attaching an atomic clock on a large rotor and spinning it fast enough to achieve a linear velocity equivalent to Concorde? I don't know if this is possible realistically, so I mean in theory.

Any movement should work. If you could attach a massless clock to a photon, and then read it a billion years later, the clock wouldn't have changed at all.

Movement through spacetime, that is our 3 every-day sized spacial dimensions and one time dimension, can be thought of as a clock having a certain allowance of "speed". It can move with all of its speed through time, and none through space (it's resting). That clock is going though time as fast as possible. It can move with a little of its "speed" through space, and a lot though time, like the clock on that plane. It's moving a bit slower through time, so it says 4:38 pm while a clock on the ground would say 4:39 (Note that it would have to move pretty fast to have a 1 minute difference over a 12 hour flight, but you get the point).

The clock could move with almost all of its "speed" through space, and therefore it would have very little of its allowance to spend on movement through time. Something moving .9999999c is an example.

A massless clock can move with all of its "speed" through space, and therefore never age. A photon never ages. You can't really ask what it would be like, any more than you can ask what going 15 miles south of the South pole is like. You just can't do it.

 

[IaPuP]

Originally posted by: Skyclad1uhm1
Btw, thanks to the movement between (and in) atoms and molecules if you get close to the speed of light some energy will already be exceeding the speed.
Unless the 'internal' movement comes to a total stop.

Sorry, I gotta reply to this. You're missing the whole point of relativity. The concept that time slows down for the object (person) traveling at near the speed of light exactly compensates for the effect you describe.

According to relativity, you cannot exceed the speed of light, nor can any particles in you. The thought experiment that can demonstrate this follows:

Take a spaceship going at .99c relative to an observer and turn on the headlighs. Do the beams of the headlights shoot out away from the spaceship at 1.99c? No, the headlights move away from the ship at exactly the speed of light (c)... this is true for both the person on the ship and the observer who is stationary relative to the ship. The only way that the same thing can have the same speed when the relative speed of the observers compared to eachother is so vastly different is if the observers are experiencing a different relative "speed" of time.

most of you knew that, but i wanted to share with our fellow poster who clearly did not.

Eric