Physisisisisists needed
Say I have a perfectly inelastic, arbitrarily long string. We each hold one end, and hold the whole string taut. When I tug on one end, you can feel it instantly. We can communicate by an agreed pattern, e.g. by Morse code.

Now say that the string is very long indeed - 1 light minute. I tug on the string, and send the message "hello" - and you receive the message immediately.

Have I transmitted information faster than light? Or totally misunderstood relativity?
(ragged, Thu 27 May 2010, 0:39, 12 replies, latest was 16 years ago)

I vaguely remember Physics A-Level ...
... so I think you've managed to get the phone number of the factory just outside either Cambridge or Oxford (can't remember which) that makes smooth inclined planes, frictionless surfaces, and point masses.

If you can manufacture, purchase or otherwise come by a perfectly inelastic, arbitrarily long string, then I'm thinking that the folks who want to make space elevators (amongst many other cool things, from a scientific viewpoint) would be extremely keen to talk to you. :-)
(BrianHequator was stretching owls, on, or around, Thu 27 May 2010, 0:55, Reply)

Disregard the string theory
but imagine you've got a steel rod that's a billion miles long and a couple of metres round. We put a guy exactly a metre away from each end and move the rod back and forth to convey a message in morse code. What you're doing there is moving an object through space reasonably slowly. You may be transmitting information across a billion miles - but not in the sense that you're breaking any kind of speed records.
( Noeli overtheshoulderboulderholderthingstraplatchboobs, Thu 27 May 2010, 6:23, Reply)

I'm not sure about this.
If the rod is rigid, and a code is sent down it in morse, the code will arrive instantanly at the other end, at the rate it was sent. If at the same time, an identical code was tapped out, at the same rate, on an aldis lamp, and observed from the end of the rod, it would arrive later than the rod's message.

The whole packet of data would have travelled fater than light.

What do you think?
( Bartleby A dead man on vacation, Thu 27 May 2010, 7:37, Reply)

That's two separate definitions of 'transmission' though isn't it?
In one you're using the relationship and forces between atoms to relay data physically, in the other you're using electromagnetic waves.
( Noeli overtheshoulderboulderholderthingstraplatchboobs, Thu 27 May 2010, 8:00, Reply)

Yes, but the medium isn't the issue, the timing of the message is.
Anyway, its all theoretical bollocks. If I had an aldis lamp that worked at that distance it would have the power of a death star.

Now that would be worthwhile.
( Bartleby A dead man on vacation, Thu 27 May 2010, 8:08, Reply)

Actually, further to this
of course the nuclear forces holding atoms together cannot travel faster than light either, so the information would take the same time or fractionally less than an electromagnetic transmission anyway. Edit: and that's exactly what K2 said down there. Doh.
( Noeli overtheshoulderboulderholderthingstraplatchboobs, Thu 27 May 2010, 8:34, Reply)

Strings, rods, they're all the same
Yes, you would have instantaneous action at a distance. But such a material can't exist in practice, because on an atomic scale, the vibrations have to travel from one atom to the next. And they are prohibited from doing so any faster than the speed of light, therefore even the stiffest possible theoretical material would only transfer information at (slightly below) the speed of light.

Sorry ragged. No Nobel prize for you this year.
( K2k6 has a proper job these days, Thu 27 May 2010, 8:13, Reply)

Always practical you are.
I want a death star.
( Bartleby A dead man on vacation, Thu 27 May 2010, 8:15, Reply)

I quite like a few of the posts on here:
forums.civfanatics.com/archive/index.php/t-97813.html
( Noeli overtheshoulderboulderholderthingstraplatchboobs, Thu 27 May 2010, 8:23, Reply)

effectively you are just pushing on the atoms at one end
and they in turn transfer that force to the next atoms and so on. There's a ripple that travels down the object to move it. It's just too fast to be observed in objects under about a light-second in length.
( The Light in Chains don't touch the Pope's boner, Thu 27 May 2010, 9:52, Reply)

It's not instantaneous
If you tug one end, I don't actually feel the pull instantaneously. Your tug pulls on the fibres nearest to you, and the 'tug' propagates along the length of the string as the stretched fibres pull on the fibres behind them, in an attempt to even out the tension you've put upon the string.

Think about it this way: if you twang the string instead of tugging it, the small wave you create will propagate along the string, rather than reaching me instantaneously (of course, it will gradually get smaller, so the signal will be very small by the time it reaches me).

Doing this over a string of length 1 light minute, your message will take a very long time to reach me, if it gets there at all.
(LongJohnBaldry, Thu 27 May 2010, 9:56, Reply)

Many thanks
For all the clear explanations.

*rethinks doomsday device*
(ragged, Thu 27 May 2010, 16:53, Reply)