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Old 04-12-2010, 04:47 PM   #1
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Default Physics question

...not a question with a definite answer per se, but more of an interesting point to debate!

Let's say I've got a solid, completely non elastic rod that stretches from here to the moon. Bob is on the moon and awaiting instructions, I'm at ground control telling him what to do. I communicate with him by moving the rod backwards and forwards using morse code. A forward shove is a dot, a backwards shove is a dash. (The method of communication doesn't really matter, it's more the fact this rod could be used for communication.)

So, I shove this rod back and forth a few times and Bob immediately gets the instructions at the other end, and starts walking around.

Sounds theoretically sound to me.

However (here's the big but) Bob received those signals instantaneously, as soon as I shoved it, the other end on the moon also moved.

Traditionally, using radio waves travelling at the speed of light, it'd take a couple of seconds for the instructions to reach the moon.

SO the big question - have I just communicated with Bob faster than the speed of light?
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Old 04-12-2010, 05:00 PM   #2
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Default Re: Physics question

Interesting. If that was at all possible; I'm guessing, yes
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Old 04-12-2010, 06:09 PM   #3
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Default Re: Physics question

Only as fast as you can do Morse code. lol.
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Old 04-13-2010, 01:12 AM   #4
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Default Re: Physics question

Electrical Signals in a medium only move as fast as the speed of light at the best of efficiency so there wouldn't be a way to communicate instantaneously between the moon and mission control.
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Old 04-13-2010, 01:18 AM   #5
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Default Re: Physics question

no because the rod only had to travel a few inches back and forth, it was already at the moon and mission control at the same time, one end at mission control, one on moon. so unless you moved the rod super fast, it doesnt matter.

thats like sayin if i poke somebody next to me i did it at the speed of light. lol.
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Old 04-13-2010, 01:23 AM   #6
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ok nm, i see what your talking about.

but, no, that still wouldnt be at the speed of light.
due to the rod having to bend and fluctuate, even IF it was a super solid carbon filament material.
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Old 04-13-2010, 01:54 AM   #7
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Default Re: Physics question

Quote:
Originally Posted by sniperviper21 View Post
ok nm, i see what your talking about.

but, no, that still wouldnt be at the speed of light.
due to the rod having to bend and fluctuate, even IF it was a super solid carbon filament material.
but for arguments sake, lets just say this rod was made of a non bendable material. doesnt matter. because the rod is already in 2 places at once. it only needs to travel a few inches back and forth even though the rod is 230,000 miles long to begin with lmao
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Old 04-13-2010, 02:47 AM   #8
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Default Re: Physics question

talking physics, nothing is absolute, so nothing is non bendable.
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Old 04-13-2010, 06:01 AM   #9
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Default Re: Physics question

I just thought about it as braking the rod down into segments. The first segment (where your hands are holding) moves a few inches, so does the segment after, and all the way up, and they all move at the same time

(as long as the pole was light enough to hold and move obviously)

..................

To be honest if i had a pole that big i'd be doing other things with it..


Note: Technically you did communicate with him faster than the speed of light, as he would recieve the message instantly (well a movement instantly.. then you have to process the movement etc, where as sound or light could communicate that message in a simpler output) .. but the stick itself isnt moving fast.
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Old 04-13-2010, 06:04 AM   #10
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Default Re: Physics question

I find this an interesting question.

the conditions set down are good, completely solid, non elastic, so we're ignoring bending and flexing.

in theory the answer is yes, you communicate faster than the speed of light.

in practice, it seems as though it should be impossible,

I'm guessing that the real problem is that it's impossible because if you push on one end or the rod all the molecules in the rod also have to move, you've not pushing the rod, you're pushing the atoms at the end of the rod, which in turn are pushing other atoms, so you actually send a wave of compression up the rod rather than moving it as a solid object.

in practise, with the materials that we have today this is impossible.

but in theory, the completely solid, non elastic rod that doesn't bend or flex.
it seems like it should be possible...


I guess the question here is, can a force be transmitted faster than the speed of light? we're asking if electromagnetic radiation can travel faster that a molecule can transmit a compressive force...

the principal being that you're sending a really simple 1 bit of information with a push, and that 1 bit gets there very quickly because the rod is solid, faster than the few minutes it would take radiation to get there.

but the wave of compression still has to travel up the rod, we don't know how long that takes, (because we don't have this infinitely stiff material).

we're not talking about the rod moving faster than light though, it's just got to be able to move backwards and forwards at a rate of a couple of shoves a second and it beats radio communication to the moon.

I guess the answer is, in principal, if you add some conditions that are impossible to meet, yes. you can communicate faster with a solid medium than using radio transmissions,
in practice, it's probably going to be impossible.
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