# Data can't move faster than the speed of light?

1. Sep 17, 2006

### jhokie

Data can't move faster than the speed of light??

Okay, so I've heard this basic concept several times in physics texts... so if someone could explain how this simple example I'm giving doesn't debunk it that'd be awesome.

Imagine you had a seesaw constructed in outer space. Let's imagine that seesaw is very long. Say, 100 billion miles long.

Would it not be possible to instantly tap out morse code using this seesaw, thus circumventing the supposed limitation that data can't be transmitted faster than the speed of light?

D 0 - Bell
x
x
x
0 - Fulcrum } 100 billion miles
x
x
x
x

Move this end to strike bell, tapping out morse code 100 billion miles away, instantly.

Now, I know constructing this object in space wouldn't be feasible or even remotely possible, but my point is the concept.

Why couldn't this work, allowing faster than light data transmission? Thanks for any responses.

2. Sep 17, 2006

### chroot

Staff Emeritus
The mechanical motion, which is essentially a "sound wave," propagates through the material at the speed of sound. When you tap one end of your rod, the other end won't move for a very, very long time.

In fact, the speed of sound in solids is generally many orders of magnitude slower than the speed of light, so your 100 billion mile rod wouldn't be very useful at all.

- Warren

3. Sep 17, 2006

### jhokie

But if the rod was made to be stiff (would not bend at all), then would pushing, or swinging one end of it not cause the other end to move instantly?

4. Sep 17, 2006

### chroot

Staff Emeritus
If you could make a perfectly rigid rod, then yes, the speed of sound in that rod would be infinite, and you would receive the Nobel prize for discovering a limitation of the theory of relativity.

On the other hand, you're not going to find a perfectly rigid material in this Universe, so the theory of relativity is safe and sound.

- Warren

5. Sep 17, 2006

### jhokie

As another alternative, if for example if you used a very long and taut rope, couldn't you just pull on one end of it, and then reset it on the other end, tapping out data like that?

Would a pulling motion on a taut rope not be transmitted instantly? That would be something that could be testable in real world situations. If someone wanted to contstruct a tube with a rope in it say 50 miles or so long, experiements would be doable.

I'm not trying to just pointlessly debate this, but it's somehthing I really want to understand.

6. Sep 17, 2006

### chroot

Staff Emeritus
Again, there's no perfectly rigid material, so you can't make a perfectly rigid rope which does not stretch. When you pull on the end of a real rope, you stretch part of it. That stretch is propagated down the rope by a longitudinal wave, which travels at the speed of sound.

- Warren

7. Sep 17, 2006

### rcgldr

I remember something about "paired" electrons where one seems to respond to a reaction by the other electron faster than the speed of light? Is this just the equivalent of an urban legend?

8. Sep 17, 2006

### chroot

Staff Emeritus
You're talking about quantum entanglement. The collapse of such an entangled pair does indeed occur instantaneously, but you cannot use quantum entanglement to transmit information at all, much less faster than light.

- Warren

9. Sep 17, 2006

### Labguy

No matter of any type (rope, wire, wood, diamond, etc.) can transmit any information at all faster than c. In fact, many believe that electricity travels through a wire at c, but it doesn't. This is because any conductive material has resistence which slows the flow of electrons to <c. That is why G. Westinghouse won out over T. Edison in promoting AC current instead of DC current as Edison proposed.

Your rope is going to stretch, and the far end won't move for a very long time.

10. Sep 17, 2006

### chroot

Staff Emeritus
Electrons practically crawl through wires, on the order of centimeters per second.

Even more telling, changes in the electric field also generally propagate slower than c. In empty space, disturbances in the electric field propagate exactly at c, but, when surrounded by dielectric matter, changes in the electric field propagate at less than c.

- Warren

11. Sep 17, 2006

### moose

Just remember that atoms don't touch each other. They interact with each other.

12. Sep 18, 2006

### octelcogopod

This might be a little stupid of a question, but why is everyone so certain nothing can move faster than the speed of light?

I mean it seems like scientists are pretty rigid when it comes to this topic, and I wonder why.. Simply because we haven't observed something which can, or?

13. Sep 18, 2006

### Gelsamel Epsilon

If 2 superposed (lets say spin-wise) particles set so that one is always opposite spin wise to the other. When one is measured and collapses would not the other collapse despite it's position in space?

14. Sep 18, 2006

### Chaos' lil bro Order

What about a light house that has a rotating light. IF the shore on the opposite end of the lake was sufficiently far, couldn't the light emitted from this lighthouse skim along the distant shore at speeds over C?

Clearly the light emitted from the light house never exceeds C, but what about the light racing along the coast of the distant shore?

15. Sep 18, 2006

### Tomsk

Yes that would travel greater than c, but you can't use it to communicate from one end of the shore to the other. Likewise shadows can move faster than c, but you can't pass information with them. Although, I don't actually know what 'information' is, strictly. I'm sure it doesn't violate causality though. ;)

16. Sep 18, 2006

### ZapperZ

Staff Emeritus
You can't just come up with something like this, of course. There has to be an impetus, and this is where you need to read up on, of all things, HISTORY.

Einstein came up with the postulates of SR because he was working on a major problem of 19th Century physics - the non-covariant of Maxwell electromagnetic equations. When he made the postulates, and we incorporate that into the Lorentz equation, we noticed that it solved this problem. We then TEST the postulates and their CONSEQUENCES and found that they verify with experimental evidence. This part is crucial because experimental evidence is what compels us to accept anything to be valid.

So it has nothing to do with being "rigid". It has everything to do with how we accept an idea to be valid. Nothing is accepted in physics until it has ample empirical verifications. We continue to test to what extent Einstein's postulates are valid. However, until such cases where we have a clear indication of when and where it fails, any claim that it doesn't work is simply speculation with no empirical support. You might as well come up with whatever you like and that will be no different. That is not how physics is, and should be, done.

Zz.

17. Sep 18, 2006