Physics Question: communicating faster than light

Given that you have two hypothetical fixed points in space that are 10 light years apart and you bridge the gap between these two points using some type of very rigid, strong and straight wire. Could you then nudge one end of the wire causing it to nudge forward simultaneously on the other end 10 light years away? If you could do this then couldn’t you theoretically communicate faster than the speed of light using some sort of morris code by tapping the wire? Just curious. If I’m way off on this it’s because I know nothing about physics… so be gentle… thanks :slight_smile:

Well, creative thought will take you far in life. Unfortunately, that Nobel prize will have to be for your next great thought.

The problem is that the strongest stiffest wire is still composed of molecues, which are mostly empty space, so compressible to a degree. The compressibility part means that the wire doesn’t move in fixed manner, but rather ripples, and that ripple takes time to get from one end to the other.

Awww shux! I was afraid that might happen… ah well, looks like it’s back to the drawing board…

Sound travels through air by pushing a bunch of molecules, which push a bunch of other molecules, which push a bunch of other molecules, etc. etc.

With your proposed idea, its basically the same thing, except faster since the molecules are denser. So, no, you wouldn’t be able to communicate FTL.

Then how about a straight row of neutrons?

Although I’d imagine that uncertainty will save relativity in this example.

Let’s do some numbers:
Using steel and assuming a 1 inch square rod, calculate the mass of a rod ten light years long, and the force needed to make it move.
Density of steel:0.286 pounds/cubic inch
Number of inches in one mile: 528012=63360 inches
Number of cubic inches in one mile of a one inch square rod: 63360
Number of miles in one light year: 186283miles/second
365246060=5873201568000 Miles
Ten light years=58732015680000 Miles
Number of cubic inches in a one inch square rod ten light years long: 3721260513484800000 cubic inches
Mass of a one inch square steel rod ten light years long: 0.286 pounds/cubic inch
3721260513484800000 cubic inches=1064280506856652800 pounds=483763866753024 tons
What did you plan to push this thing with? Blasting it with a 100megaton bomb wouldn’t even do you any good. You’d just vaporize the near end, and you still wouldn’t have enough force to move the sucker.

And what is to hold the neutrons together?
Even granted that such a “rod” would have an almost infinitesimal mass, it will still not have enough strength to withstand the force needed to move it.

Yep. And you still have to put enough oomph into the original shove to set all of the molecules from end to end in motion. See the calculations above.

In the book “The Cosmic Code” by eminent mathematician Heinz Pagels, he extensively discusses FTL communications and speculates on instant communciations at FTL speed based on quantum effects of Bell’s Inequality. It has been many years since I read the book so I cannot recall the details, but the theory is that particles that interacted at any point in time are permanently connected on the quantum level, no matter how far distant they are. Get some molecules from the same tank of gas, separate half of them into another tank, and you should be able to stimulate the molecules in one tank and then instantly measure that effect in the other tank, even if the 2 tanks were light-years apart. You can send single bits of data through this system, although it could be very low bandwidth. Hey, there’s an amusing thought, what if you could communicate at FTL speeds, but the message would always take a long time to send?

But anyway, the wire idea has some possibilites in it, albeit not in anything related to the manner you described.

Go read “The Cosmic Code.” It’s the best hard-science book targeted at nontechnical people that I ever read.

Morse code.

Zedan:“Hello, Bethlehem Steel? I need some steel.”
Bethlehem Steel"That’s what we make. How much and what form?"
Zedan:“Bar steel, one inch square. Umm, let’s see, where’s that note? Ahh, yes. 483763866753024 tons.”
Zedan:“And, uh, that’d be in one bar. Ten light years long. Can you get that to me by next Wednesday?”
Zedan:“Hello, hello? Damn. They were the last steel manufacturer on the list. Why did they all hang up on me like that?”

Sorry. Couldn’t resist.

Chas, what you’re describing basically sounds like one of the objections that Einstein had to QM. My memories are also fuzzy, but if you did a search for the Einstein-Podalski-Rosen paradox (EPR might be safer, since the chances of me actually getting the names and their spellings correct), it might tell you a bit more about this idea. But I do remember that there’s no conflict with SR here and this mechanism doesn’t actually let you transfer information FTL.

Basically, IIRC, this is because when you measure a change in your gas molecules, you have no idea if YOU are causing the change or if the change is because the person on the other end of the line did something to cause it. In other words, it’s only when you compare your observations to the person you’re talking to that actual information is exchanged.

On the usenet newsgroup, they have an old expression:

“Causality, relativity, FTL: choose any two…”