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06-07-2009, 09:19 PM
Hi all, an idea just came into my head and I cannot figure out the answer:

Assume a pole sitting in space. The pole is one light year long.
There are two people standing at either end of the pole, one shines a torch at the other, the light from that torch would take 1 year to reach the other person.
Now what happens if one of the people pushes the pole slightly, would the movement be transferred instantly to the other end?

bob_doe_nz
06-07-2009, 09:23 PM
I'd say no.

As an example, take a small chain about a metre or so in length.

Now lay it on the floor and with one end, wriggle it left and right. Watch as the other end takes time to move left, then right.

06-07-2009, 09:26 PM
A chain is not rigid, the material I'm talking about is.

Metla
06-07-2009, 09:28 PM
Interesting.

I'd say yes.

pine-o-cleen
06-07-2009, 09:34 PM
So would I. I'd also say who thinks of these things!?

bob_doe_nz
06-07-2009, 09:35 PM
A chain is not rigid, the material I'm talking about is.

Ahh. Right. I'm still saying no.

R2x1
06-07-2009, 09:55 PM
Depending how you time it, it would be relatively instant. ;)
And if it wasn't - how would you know?

Jen
06-07-2009, 09:56 PM
I'd say no.

Plenty of ideas if you google this same question though ...

Ofthesea
06-07-2009, 10:00 PM
I'd say you can't really be sure until you try it out

beeswax34
06-07-2009, 10:18 PM
I'd say yes.

R2x1
06-07-2009, 10:37 PM
Nothing is incompressible, (And I am assuming you are not making the pole of nothing ;) ) and nothing is inextensible either. Since the material it is made of has mass, it has inertia. Any deflection at the driven end is going to have to manoeuvre a rather long and whippy stick without the least bending. Since a light year even in leagues is a distance approaching infinity in practical terms, there is a very strong chance that the inherent self damping will have removed the disturbance long before it has propagated to the other end. Even if we go for an ideal absolutely inflexible pole, the propagation of displacement in a solid is not likely to be at the speed of light, but more likely at the speed of sound in that substance. (That is how sound is transmitted after all.)
It would be a most odd substance that has a speed of sound equal to the speed of light. (At least, it is for this long after the big bang.)

qazwsxokmijn
06-07-2009, 10:51 PM
I think the real question is whether or not there is something with enough power to move said pole?

R2x1
06-07-2009, 10:56 PM
And somewhere to sit the said power source. (Archimedes found this out.)

Deane F
06-07-2009, 10:58 PM
It's a thought experiment - and like the rest of science, it takes place in an imaginary universe in which there are no engineers or engineering considerations...

somebody
06-07-2009, 11:14 PM
Now what happens if one of the people pushes the pole slightly

Due to the mass of the pole, and the fact that space is a vacuum, if you push the pole, you will move yourself backwards, and the pole will remain stationary (not completely, but it will move so little that it doesn't count).

--Wolf--
06-07-2009, 11:24 PM
Way to ruin everything ^

Metla
06-07-2009, 11:25 PM
Crash a planet into the ****er. She will move.

Sweep
06-07-2009, 11:27 PM
That is one very long pole you have.

For example if the Sun we live under went out for some reason we would not know for some 8 minutes.

Light travels at some 186,000 miles per second if my memory has not failed me.

The proposal says that the two people are in space so I guess I can assume that either end of the said pole is only anchored by the body weight of the two people involved. A chain is not rigid as was pointed out and neither is a pole for that matter and I know this for a fact having been involved in laying pipes for town water. Now I do know that a pole is different to a pipe but if we take a crowbar and use it as a lever it usually bends (the crowbar) that is. Pipes bend as well.

My view is that the reaction at the other end of the pole will not be felt at all ever in any event if one person pushed the pole.

This as the speed of a push does not exceed the speed of light.
In fact man or woman if you like has not ever made anything that exceeds the speed of light to date as far as I am aware.

For example if I drop my end of a pole or pipe it is highly likely that my mate on the other end will see that before he feels it.

R2x1 has a relevant point in so far if you and I are there and manage to get back it will take me at least 1/2 a light year to get back from my end of the pole and you as well.

Unless you want to bring immortality into the equation who is going to say the experiment was successful?

vinref
06-07-2009, 11:33 PM
Hi all, an idea just came into my head and I cannot figure out the answer:

Assume a pole sitting in space. The pole is one light year long.
There are two people standing at either end of the pole, one shines a torch at the other, the light from that torch would take 1 year to reach the other person.
Now what happens if one of the people pushes the pole slightly, would the movement be transferred instantly to the other end?

No.

The atomic structure of the pole would permit some deformation and stretching, however slight, giving rise to a pressure wave. This wave cannot travel faster than the speed of light.

As an aside, it is said that the expansion of the universe at the Big Bang was "faster" than the speed of light.

Metla
06-07-2009, 11:34 PM
Jesus is faster then the speed of light.

FACT.

Sweep
06-07-2009, 11:40 PM
Due to the mass of the pole, and the fact that space is a vacuum, if you push the pole, you will move yourself backwards, and the pole will remain stationary (not completely, but it will move so little that it doesn't count).

Called inertia I think.

And the mass of the pole counts here too in so far as a pole that long depending on diameter will possibly weigh as much as our Moon and we already assume that our Moon actually affects tides.

Hmmm.....

Lunatics. Is that like Pole(itics) :eek:

Rob99
07-07-2009, 12:35 AM
Chuck Noris could push the pole and turn the torch on at the same time, he would then be able to go to the other end to feel the pole move before the light got there.

FACT.

R2x1
07-07-2009, 08:24 AM
Chuck Noris could push the pole and turn the torch on at the same time, he would then be able to go to the other end to feel the pole move before the light got there.

FACT.
Of courser, the light could not approach until he commanded it.
Alas, while he was swapping ends, Chuck would find that Metla had cut the pole into firewood lengths and had it stacked for sale

Richard
07-07-2009, 10:01 AM
The pole isn't supported by a treadmill by any chance is it?

nofam
07-07-2009, 10:06 AM
Of courser, the light could not approach until he commanded it.
Alas, while he was swapping ends, Chuck would find that Metla had cut the pole into firewood lengths and had it stacked for sale

And then the Weathewhakawi iwi would appear and claim Customary Title over the pole, sell it for millions, buy many, many BMW's for the extended family, mis-manage the left-over money, and them blame Chuck & Metla for oppressing them.

:o

johcar
07-07-2009, 10:39 AM
And then the Weathewhakawi iwi would appear and claim Customary Title over the pole, sell it for millions, buy many, many BMW's for the extended family, mis-manage the left-over money, and them blame Chuck & Metla for oppressing them.

:o

... and then the children of the Weathewhakawi iwi, years down the track, would repeat the whole process and get yet more 'reparations' based on the same arguments.

Winston001
07-07-2009, 11:21 AM
No.

The atomic structure of the pole would permit some deformation and stretching, however slight, giving rise to a pressure wave. This wave cannot travel faster than the speed of light.

As an aside, it is said that the expansion of the universe at the Big Bang was "faster" than the speed of light.

Good thought experiment Adam. I'm with Vin. The wave cannot move faster than light - in fact it will be slower.

What about if you switched your torch on and started walking down the pole - would the light from your torch be moving faster than the speed of light? ;)

Gobe1
07-07-2009, 11:59 AM
Good thought experiment Adam. I'm with Vin. The wave cannot move faster than light - in fact it will be slower.

What about if you switched your torch on and started walking down the pole - would the light from your torch be moving faster than the speed of light? ;)

So he would feel it but it would not happen instantly, and it would take longer than a year.... Wheres Stephen Hawking when you need him.

the_bogan
07-07-2009, 12:01 PM
Why use a Polish person?

spaceman8815
07-07-2009, 01:19 PM
You need relativity to explain this, since information cannot travel faster than the speed of light then the force at the other end of the pole would not occur until this information is transfered to it, thus in the reference frame of the universe the pole would seem to bend into a horse shoe shape, but in the rest frame of the pole space would seem to bend around you.
This kind of science is called action-at-a-distance (http://en.wikipedia.org/wiki/Action_at_a_distance_%28physics%29).

Gobe1
07-07-2009, 01:54 PM
Interesting stuff, as in the light from the sun takes 8 minutes to get here (as ealier stated by one of the posters?) But if the sun suddenly moved would we feel the gravitation shift immediatley... Same as the polish theory, but the pipe neednt be 1 light year long to prove

sroby
07-07-2009, 01:54 PM
Bush science 101
You need to think about what you are actually doing with the push. It isnt a giant hand that grips the full length of the pole. You are apply force to the atoms at your end only, pushing them towards the neighbouring atoms, which then apply that force the their neighbouring atoms etc etc etc
:help:

sroby
07-07-2009, 02:06 PM
Interesting stuff, as in the light from the sun takes 8 minutes to get here (as ealier stated by one of the posters?) But if the sun suddenly moved would we feel the gravitation shift immediatley... Same as the polish theory, but the pipe neednt be 1 light year long to prove

Gravitational effects DO NOT travel faster then the speed of light.
Also, time is relative, not constant so if we want to be tricky we could say the
light takes a fraction of a second to get here based on time as seen by the photons. Or are we measuring time from the time light take from its creation in the middle of the sun:then its much longer than 8 minutes.

spaceman8815
07-07-2009, 02:23 PM
What about if you switched your torch on and started walking down the pole - would the light from your torch be moving faster than the speed of light? ;)

No the light remains at the speed of light in every reference frame. but the light waves wavelength would decrease by the Doppler effect (http://en.wikipedia.org/wiki/Doppler_effect), getting a slightly higher frequency. which is how the cops measure your speed with their radars.

vinref
07-07-2009, 09:55 PM
You need relativity to explain this, since information cannot travel faster than the speed of light then the force at the other end of the pole would not occur until this information is transfered to it, thus in the reference frame of the universe the pole would seem to bend into a horse shoe shape, but in the rest frame of the pole space would seem to bend around you.
This kind of science is called action-at-a-distance (http://en.wikipedia.org/wiki/Action_at_a_distance_%28physics%29).

Action-at-a-distance has nothing to do with this. The pole is a one-piece, continuous object. Action-at-a-distance would be used to try to explain something like the force between two discrete objects (i.e., gravity).

Jayess64
07-07-2009, 10:17 PM
Hi all, an idea just came into my head and I cannot figure out the answer:

Assume a pole sitting in space. The pole is one light year long.
There are two people standing at either end of the pole, one shines a torch at the other, the light from that torch would take 1 year to reach the other person.
Now what happens if one of the people pushes the pole slightly, would the movement be transferred instantly to the other end?

A couple of posters just about got it. When you push one end of the pole you create a pressure wave which will travel at the speed of sound appropriate to the material of the pole. Relativity, speed of light etc. don't come into it.

More interesting, what happens when the wave reaches the other end?

R2x1
07-07-2009, 11:21 PM
When the wave reaches the other end, it reflects and snaps the pole. The ends are now poles apart and the experiment will need to be repeated with a larger budget. 25 NCEA credits for demonstrating this effect.

beeswax34
08-07-2009, 02:13 AM
When the wave reaches the other end, it reflects and snaps the pole. The ends are now poles apart and the experiment will need to be repeated with a larger budget. 25 NCEA credits for demonstrating this effect.

Pfft, I could get that many by just picking up rubbish at school.

somebody
08-07-2009, 09:16 AM
The point is, since the people and the pole are in space (i.e. a vacuum), one person pushing on the pole as described by the OP will not move the pole - he/she will simply push themselves backwards.

Take a computer chair with wheels, sit on it outside, and push against your house. Do you move, or does the house move? If your house doesn't move, then why bother figuring out what happens at the other end?

R2x1
08-07-2009, 09:31 AM
Pfft, I could get that many by just picking up rubbish at school.
It appears that for many, rubbish is the only thing they pick up at school. ;)

Richard
08-07-2009, 10:03 AM
It appears that for many, rubbish is the only thing they pick up at school. ;)

Very good!:):)

Paul.Cov
08-07-2009, 07:58 PM
5 pages of replies... and I've not bothered to read beyond page 1.

The answer however is no, the impulse applied to the object would not be instantly transferred to the other end.

Point one - the mass to be moved in any physical object with a length equivalent to 1 light year would be incredible.
You could belt the end of it so hard that it moves a foot and splinters, but that impulse would be transmitted in a wave of compression (and some recoil).
Gotta remember - atoms in a molecule do not touch each other - they float with respect to each other, with some degree of equilibrium. The wave of compression would be somewhat absorbed, and delayed by the interation between atoms. Light remains the fastest, with the advantage of travelling in the lightest medium.

However, a quantum 'entangled' pair of atoms is believed to achieve what you're after. Problem is, entangled pairs have to be made together (in the same place), and then seperated... so you'd have to have some device carry them a light year before they can be used to instantly communicate across that light year distance.

E.T. won't be phoning home just yet.