Thought Experiment I recently had

Imagine a long bar of steel, several billion kilometres long, in space.
Imagine that there was absolutely 0% stretch when a force is exerted on it.
If you were holding one side of it and I was holding the other, and I pulled on my side, you would feel the pull instantly on yours..
This is potentially over a region that would take light a recordable time to pass...
So the signal is travelling faster than light..
Right?

Feel free to rip it apart etc I would just like to know feed back

That is a tough one. Give me a minute to research...

Mr. M

Thanks..
I got bored and had just discussed with a friend light acceleration beyond the speed of light..
Was trying to think of another way to send signals...
If you have something that has absolutely no stretch then, I think, this MUST work!
Though not sure.

What signal?
You're just pulling the bar. Nothing is traveling at all except the bar when it gets pulled.

Wrong, the "bar" has a molecular structure, just like anything else. Therefore, technically speaking, the molecules would be travelling faster than the speed of light, which is insane. That is an enourmous feat to achieve for such a large group of molecules.

Mr. M

That, and that it would be a way of communicating faster than the speed of light..
If I was on one end of the universe and I pulled on this magic bar, you would feel it (in theory) straight away, if you were on the other end of the universe..
That would revolutionaize communications in outerspace, etc, as it would only really take two bars to transmit a whole message
(e.g. 1 bar represents '1', the other represents '0', and you transmit messages in binary)


Any scientists wanna help resolve this thught experiment?

[Edited on 11-3-2004 by browha]

It is definitely an excellent theory. I recommend distribution to NASA under copyright. You never know, maybe you can sell it.

Mr. M

The Superluminal Scissors

Look up some more on the topic if that isn't enough.

Sorry

yeah it seems like you would have to break the law of physics to do what you're suggesting and if you have to do that then your theory dosen't really stand up.
I like your thinking though. I'm always racking my brains over this sort of thing.

I've skim-read the link, and it's interesting..
but the issues:
1) We are not closing a pair of scissors. We are pulling directly on a material in which there can be no void, so when one molecule is pulled, every molecule in the bar is pulled..
Imagine a TIGHT peice of string. You pull on one end, the person on the other feels it
2) There isnt the aspect of 'closing' the blades, as it is a single inextensible object that is rigid and cannot stretch.. At the moment this material doesnt exist, but with polymerisation and new compounds/mixtures, I am sure it isnt too far away.

Originally posted by pantha
yeah it seems like you would have to break the law of physics to do what you're suggesting and if you have to do that then your theory dosen't really stand up.
I like your thinking though. I'm always racking my brains over this sort of thing.

Just out of interest, where does this violate the laws of physics, except possibly (unless we refine our perspective) the speed limit as such...
Light has been accelerated several thousand times faster than what it normally travels at (I'm sure you can easily find experiments of these kinds on the internnet, or people here will know about them... It certainly was discussed in an earlier thread)
Or, perhaps, if you look at it on an molecular level, there is no violation. One molecule pulls on another, which in turn pulls on another, etc.

Also, if I was to discuss this with NASA, who do I e-mail, etc?
Thanks

No, the steel bar isn�t breaking the light speed. If you pulled the bar at one end, the bar would move only as fast as you pulled it. Say 3 feet per second.

Hmmm. If you are holding this imaginary bar on one end and someone else moves it on the other, how is it traveling faster than the speed of light?

Every molecule in the bar is only traveling as far as you push it, only as fast as the speed you push it at. It's not really traveling a great distance because it is the distance. It's just moving over a little.

Very fun idea...

Here is the flaw in your concept.

You assume a perfectly rigid structure. Thats just doesn't happen in reality.

What happens is you exert a force on some of the atoms of the rod which then exert a force on the next, and the nxet, and the next, and so on. When you are talking about things on a earth scale such as a few thoushand miles this seems virtualy isntantaneous. But it isn't. The wave of force would propogate at the speed of light. Even gravity propogates at the speed of light.

In your little thought experiments you assume rigidity. So since you assume something outside of reality, you can get results outside of reality.

Originally posted by Thorfinn Skullsplitter
Hmmm. If you are holding this imaginary bar on one end and someone else moves it on the other, how is it traveling faster than the speed of light?

Every molecule in the bar is only traveling as far as you push it, only as fast as the speed you push it at. It's not really traveling a great distance because it is the distance. It's just moving over a little.

Very fun idea...

No the signal would not move faster than light speed, the forces holding the object (metal in this case) together only work at light speed. So the far end would not move instantaneously.

As each atom moves the next one doesnt move immediately, with small objects it is near enough for it not to make any difference. But with objects as massive as these the metal acts a little like rubber in that way the signal goes down the object at sub-light speeds.

Remember, at these small scales the atoms are not held together by any rigid structure as we would know it, but by electromagnetic forces. These forces only work at the speed of light.

[Edited on 11-3-2004 by Kano]

In theory, if we take it for a fact that this "infinite rigidity" steel bar could exist. Then yes, browha, your theory would be correct. However, I suggest you read the Superluminal Scissors paper in depth for it states:

"S(pecial)R(elativity) sets a theoretical upper limit to the rigidity of the material."

So according to physics as we know it, this material cannot exist. I personally dont think that anything made of conventional matter (i.e. atoms) can have infinite rigidity, but we may find some substance that behaves this way eventually.

Also; Quest, your comment about gravity propagating at light speed is debatable.

"The contribution to the Newtonian potential at a given location in space at a given instant due to a mass m is strictly a function of the distance of that mass from the given location at the same instant. In other words, if we let r[t] denote the distance from the given location to the mass particle at the time t, then the contribution of that mass to the gravitational potential V[t] at the given location at the time t is V[t] = -m/r[t]. Thus, Newtonian gravity represents instantaneous action at a distance, because the effect of changing the position of a gravitating mass is "felt" throughout the universe at the instant when the mass moves."
(as quoted from www.mathpages.com...)

browha, your theory is more of a philosophy question than a physics question. However, in your postulate, the signal being transmitted would be the movement of the distant end of the bar, so assuming this steel bar were real, this signal would indeed travel faster than the speed of light.

very interesting indeed.

-Durandal

Look. Theo object itself isn't moving at anything ear the speed of light. It is just an object floating in space...an extremely long object in space.

someone Pulling it towards should mean that at the other end the object is being pulled away from the other person at the other end basically instantly, no matter how long it was..

It allt he particles are stuck together with no strathc, bend, no other way to move...then it owuld happen as just mentioned above. If u had 2 bars opposite eahc other and moved them back and forward to discern thema s binary... 1's and 0'1, then u would be sending a signal across space faster than the speed of light...

Though if u were to send an electrical current along those bars without moving them...the signal will still take AGES to get to the other end going as fast as an electrical signal would travel, whihc is slower than the speed of light i think... (if this bar was somehow conductive)...

DaRAGE,

You dont need two bars to send a signal, a signal can be something as simple as the bar moving. Now if you want to get complex and send a data stream down the one bar, all you would have to do is alternately push/pull the bar and use those states as a NRZ(non-return to zero) means of signaling and it would be infinately faster than anything we would be able to do with light, nomatter howmany pulses a second we could send. Simply because of the instantaneous transmission. The bit-rate would be extremely slow, but the medium is instant where light would take years to cross the gap. If you would like to improve bitrate, we could go into such things as Time Division Multiplexing or Frequency Division Multiplexing.

-Durandal