Thought experiment time!

[R1Geezer]

Faster than light communication?
Imagine you had a hose pipe 1million miles long and it was completely full of marbles along it's length all touching each other now if I put another marble in one end one would pop out of the other end. Ignoring for this exercise limiting factors like force needed to press the marble in and flexibility in the hose etc etc. Would the marble at the end pop out instantly? if so would that constitute faster than light communication?

[squarebear]

Yes it would come out instantly.
How would it communicate though? It wouldn't be the same marble?

This is also very basically how electricity works. People assume it's faster than light but is in fact very, very slow.

[Gromit]

No, it would mean you'd lost your marbles.

[R1Geezer]

well it's essentially transmitting something faster than light I guess whether that's communication I'm not sure.

[Teddio]

The marble wouldn't come out instantly. A force would have to be transmitted over a distance of 1 million miles. The force in question is the electromagnetic force of repulsion between the electron clouds around the atoms making up each marble. The force carrier is the virtual photon (the exchange particle) which is limited to the speed of light.

[squarebear]

But it's not transmitting anything. It's a completely separate marble.

[R1Geezer]

but square bear electricity works like this as you explained above. You could communicate in morse code this way for example by varying the frequency of marble pressing. However Teddio has explain very well why we could not exceed light speed transmission.

[jake-the-peg]

For the best bet for faster than light communication you should consider quantum entangled particles.

Such as in the CPR paradox (look it up it'll blow your mind)

Whilst there are reasons why we can't currently use it, I'm not sure I'd entirely rule out this from being possible.

However there are possible consequences relating to time travel which could be messy

[Clanad]

However, there's a dispute as to the instantness of Mr. Geezer's proposal and it's readily demonstrable in a simple desktop toy. I'm sure I'm not the only one who's been fascinated by the heavy, inch sized metal marbles suspended one after the other by string from a frame on someone's desk. One pulls one of the end marbles back and releases it to strike those in the row. As this occurs, the one at the other end of the row then, demonstrating the laws of inertia, flies away from the row without any of the intermediate marbles being disturbed (apparently). You'd notice a minute but measurable lag in the time the end marble is released and the time the other end marble flies off. Compound this by a million such marbles and one sees the time neccessary for the end marble to exit the pipe to be exponentially greater... not only missing the mark as related to the speed of light, but probably taking several months if not years (I haven't done the math)...

[Tweed]

'Electricity is slow'. No it's not. If you're tracking a particular electron it may take a while for that electron to travel a distance but the current flow is certainly not slow.

[fo3nix]

Speed of light limit deals with transfer of information. In your thought experiment, no information is being transferred.

Look up the difference between group and phase velocity (one is confined by rules of speed of light, other isn't, guess which one yours is).

[R1Geezer]

as I explained above information could be transmitted this way, morse code for example.

[BillyBB]

You can look at it several ways.
A theoretical 'Newtons Cradle' one million miles long where the marbles do not move, this would still be limited to the speed of the shockwave in your marble - about 5500meters per second. So about three minutes where nothing visibly moves.
Or a million mile long rod of glass that you push 3/4" - Ignoring the force need to move it (and the fact that the movement would be absorbed and take minutes to transmit) the whole thing would still travel only at the speed of your finger.
Even with marbles cut from diamond it's 83 seconds.

[Bert]

BillyBB is nearly right (in my opinion). This thought experiment does not need to be marbles in a tube, it can be a solid length of anything. Squarebear is wrong and Teddio is right. fo3nix is wrong too. Information is being passed. Clanad used the word 'exponentially' without giving it much thought. It would take just twice as long for the 'signal' to get through 10 marbles as it would take to get through 5 marbles. If you have a metre rule made of wood (or anything else), and you push one end, you think the other end moves instantaneously, but it doesn't. The other end can only move when the pressure wave from your push reaches the other end. The signal travels at the speed of sound (in wood), which is very fast, but nowhere near the speed of light. Electricity is slow, in the sense that the electron cloud consists of electrons moving relatively slowly, but, when you apply a potential difference across the ends of a conductor, the signal (a current) flows almost instantaneously. I don't know how fast the signal will go, but it won't go as fast as the speed of light in vacuo. I guess it will go at the speed of light in the material, though it is hard to imagine light travelling along a wire. BillyBB is right when he says that the whole thing will travel at the speed of your finger, i.e. the far end of the rod will travel as fast as your finger moves, but there will be a delay before the other end moves equal to the length of the rod divided by the speed of sound in the material the rod is made of.