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Faster than the speed of light?
Posted: 16 October 2007 02:11 PM   [ Ignore ]   [ # 16 ]
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Even if you could warn the people on earth, what are they going to do, start up their backup generators?

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Posted: 16 October 2007 05:11 PM   [ Ignore ]   [ # 17 ]
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dougsmith - 16 October 2007 01:19 PM

Sorry, you’ve lost me there. And color me skeptical, since I don’t believe faster-than-light communication is possible.

How fast are these “gamma photons” moving along the pencil? Aren’t they moving at the speed of light? If so, then the “signal” (of motion) will travel down the pencil at the speed of light.

They are, indeed, moving at c.  However, they are generated whenever an electrostatic interaction occurs between charged particles, travel subatomically small distances and are being simultaneously generated down the length of the pencil (at lots of point interactions and in all directions.  Hence, the earth end of the pencil moves with the George end of the pencil.  There is no gap, during which George’s end of the pencil has written one metre of text and the other end hasn’t actually moved because it’s waiting for a wave to travel down the length of the pencil.  This is because george moving his end doesn’t create a photon of gamma radiation which then has to wait for the next atom along it to the same before the next one can do the same.  It does the same at the same time because it too is moving relative to the next atom along. and therefore simultaneously interacting electrostatically with that one and the one before it.  Theoretically, faster than light communication is possible in the way George described.  Practically there are problems; not least, those of sitting on the sun and holding and controlling a pencil that stretches all the way to the earth.

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Posted: 16 October 2007 05:16 PM   [ Ignore ]   [ # 18 ]
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narwhol - 16 October 2007 05:11 PM

They are, indeed, moving at c.  However, they are generated whenever an electrostatic interaction occurs between charged particles, travel subatomically small distances and are being simultaneously generated down the length of the pencil (at lots of point interactions and in all directions.  Hence, the earth end of the pencil moves with the George end of the pencil.  There is no gap, during which George’s end of the pencil has written one metre of text and the other end hasn’t actually moved because it’s waiting for a wave to travel down the length of the pencil.  This is because george moving his end doesn’t create a photon of gamma radiation which then has to wait for the next atom along it to the same before the next one can do the same.  It does the same at the same time because it too is moving relative to the next atom along. and therefore simultaneously interacting electrostatically with that one and the one before it.  Theoretically, faster than light communication is possible in the way George described.  Practically there are problems; not least, those of sitting on the sun and holding and controlling a pencil that stretches all the way to the earth.

Again, you’ve lost me.

Firstly, and this must be stressed, no material is so rigid as to be able to move the way you describe.

Secondly, if the photons transmitting the electromagnetic interactions between the atoms are moving at the speed of light, there is no way for the far end to be moving simultaneously with the near end. The information of motion wouldn’t have reached the far end, as the photons can only move at the speed of light.

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Posted: 16 October 2007 05:36 PM   [ Ignore ]   [ # 19 ]
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... and I should add that materials—even quite rigid ones—deform under pressure so slowly one can watch the pressure waves. E.g., the Tacoma Narrows bridge disaster, involved a steel and concrete suspension bridge. These pressure waves propagate quite slowly across the material, certainly nowhere near the speed of light, I’d venture even slower than the speed of sound. Now, the speed of these pressure waves may have been determined by the resonant frequency of the bridge. But that said, if you were to pick up the near end of this bridge with your finger, the far side wouldn’t move immediately. Indeed, likely the steel would stretch and the far side wouldn’t move at all.

It may be that the assumption of perfect rigidity leads to other physical impossibilities.

[ Edited: 16 October 2007 05:38 PM by dougsmith ]
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Posted: 16 October 2007 05:40 PM   [ Ignore ]   [ # 20 ]
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Sorry to pull rank, but I am a physicist.  You seem to be labouring undera delusion about the way materials are held together.  They are mostly empty space, interspersed with particles. nucleus, which is tiny, is made of up and down quarks held together by the strong electromagnetic force in the form of gluons.  This has an overall positive charge.  Outside that, you have a comparatively vast empty space in which there are probabilistic density functions of electrons (a “particle” of the lepton family).  The nucleus and the electrons attract each other when they move (and therefore cut flux) within each other’s fields.  This generates a photon (electromagnetic “particle”) of gamma frequency that transmits energy corresponding in quantity to the work done by the field.  Outside of these atoms there are other atoms.  These have instantaneous pockets of local disproportionate charge density distributed over their “surfaces” that change as their electron density translocates.  When the charges of these two instantaneously charges atoms move relative to each other within each other’s fields (thereby cutting flux lines), this generates an electromagnetic “particle”, a photon of gamma frequency and energy equal to the work done by or against the field depending upon whether the charge density pockets are of like or unlike polarities.  You seem to thinnk that a photon has to travel the whole length of the pencil in order to transmit the work George does on his end (of the pencil!) to the tip.  This doesn’t happen.  Photons are transmitting forces between all pairs of neighbouring atoms throughout the pencil all of the time.  There is no step-wise generation of photons effect that needs to take time to travel down the length of the pencil, and there is no wave that travels the length of the pencil other than flexural effects of wobble (only of significant amplitude around the middle sections of the pencil anyway) that would have no bearing on the speed of writing the message anyway, but may make George’s handwriting a little bit more untidy.  The flexural strength of the material would have no bearing on the speed of communication of the message.

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Posted: 16 October 2007 06:07 PM   [ Ignore ]   [ # 21 ]
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narwhol,
If that is true, why then isn’t the speed of sound transmitted through rigid materials not infinite?

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Posted: 16 October 2007 06:15 PM   [ Ignore ]   [ # 22 ]
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Because sound is a compression wave that has to propagate, whereas the writing isn’t.  The writing is a controlled set of forces that does not require a wavelike motion through the rigid material, but rather requires the material itself to move as a whole. Which materials do, unless a snapping force is exerted on it.

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Posted: 16 October 2007 06:31 PM   [ Ignore ]   [ # 23 ]
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Certainly, I assume you are a physicist; however nothing I said depended on any denial of the belief that, as you put it, materials “are mostly empty space, interspersed with particles.” I am indeed interested in the specifics of what occurs between the various atoms in the solid—as I say, my understanding is that the interactions within the material were electromagnetic. This appears from your description to be correct. Electromagnetic forces are transferred by photons, which move at the speed of light.

So far we seem to be agreeing with my take on things. Now, you then say

You seem to thinnk that a photon has to travel the whole length of the pencil in order to transmit the work George does on his end (of the pencil!) to the tip.  This doesn’t happen.

Fair enough, but I never claimed that there was any single photon traveling the entire distance. What I was after was something more like this:

Photons are transmitting forces between all pairs of neighbouring atoms throughout the pencil all of the time.

That is, that there was a transfer of energy from one atom to the next in the material, transferred by photons, which travel at the speed of light. So the crucial part of your explanation is this:

  There is no step-wise generation of photons effect that needs to take time to travel down the length of the pencil ...

“no step-wise generation of photons”. But then how is the motion-energy transferred?

Do you do materials science? Are you accounting for effects of rigidity? Because unless you are talking about some perfected material, your claim is patently impossible. No material is so rigid as to move simultaneously along a distance of 93 million miles.

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Posted: 16 October 2007 06:32 PM   [ Ignore ]   [ # 24 ]
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Suppose the pencil is spring mounted so that yelling (quite loud) at my end of the pencil caused it move to and fro.  With your explanation, wouldn’t the far end of the pencil move at the same time and reproduce my sound wave?  How is this not sound travelling infinitely fast?

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Posted: 16 October 2007 06:34 PM   [ Ignore ]   [ # 25 ]
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the PC apeman - 16 October 2007 06:32 PM

Suppose the pencil is spring mounted so that yelling (quite loud) at my end of the pencil caused it move to and fro.  With your explanation, wouldn’t the far end of the pencil move at the same time and reproduce my sound wave?  How is this not sound travelling infinitely fast?

Yes, exactly.

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Posted: 16 October 2007 06:54 PM   [ Ignore ]   [ # 26 ]
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no exactly.  Sound waves are not what is moving the pencil in the example (And we are talking vibration if they were, but they’re not and neither are we).  However, to dougs point, rigidity is not important here.  The middle of the pencil can sway in the solar breeze for all anyone cares provided the ends are fixed (by george choosing sufficient pressure with which to push down and suitable tribological properties of the paper used), but no resutant work is being done in holding the pencil together and this is a contiuous processes, but provided sufficient work is done to move the pencil from George’s end and the ends are fixed as mentioned before, the only thing that possibly can result from this is that the whole pencil is translated in the direction of the force, including the unperturbed position about which any fexural vibration is occuring.  Thus, the whole thing, which is staying together as one piece can only move in the direction of the force and since the other end is fixed wrt any flexural red herrings you’ve introduced, it moves with George’s end, without delay.  The exchange particles are continually being produced and resonating, and only over infinitessimally distances and are there throughout, rather than acting sequentially or within any time lag. because they are simultaneous.  If they weren’t you’d have one half of the pencil leaving the other half behind.  Can you not see that that is ludicrous?

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Posted: 16 October 2007 07:11 PM   [ Ignore ]   [ # 27 ]
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narwhol - 16 October 2007 06:54 PM

no exactly.  Sound waves are not what is moving the pencil in the example (And we are talking vibration if they were, but they’re not and neither are we).

You’ll have to do better than that if you wish to convince me.  What is being compressed when sound is being transmitted through a material if not the material itself?  Why is the material not equally compressed when equally moved by hand?

If they weren’t you’d have one half of the pencil leaving the other half behind.  Can you not see that that is ludicrous?

Not really.  Isn’t this what hardness/elasticity is all about?

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Posted: 16 October 2007 07:26 PM   [ Ignore ]   [ # 28 ]
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Not that I particularly care about convicing you, but no sound will not compress the material itself since the compressions are balanced and by rarefactions. and this is a damped and lossy form of energy transmission. whereas using a force to translate an object sideways is not.

as to whether I am a materials physicist, yes I am presently a tribologist (mostly I’m a senior manager involved more in commercial matters, but I have two labs I can go to to have a play whenever the urge takes me).  In the past, I have published papers in J. Mater Sci, Mater res. bull., Advanced Mater., and a chapter in one of the “Recent research advances in materials science” textbooks.

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Posted: 16 October 2007 07:47 PM   [ Ignore ]   [ # 29 ]
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narwhol - 16 October 2007 07:26 PM

Not that I particularly care about convicing you, but no sound will not compress the material itself since the compressions are balanced and by rarefactions. and this is a damped and lossy form of energy transmission. whereas using a force to translate an object sideways is not.

Well then let’s change the scenario a bit.  Suppose at the far end of the pencil there is a paper tape moving past the pencil tip.  My “writing” is consists of me pushing and pulling the pencil against the tape so as to produce Morse code.  If I code somewhere in the range of 500 to 5,000 dots and dashes per second, is there any delay at the far end?  If I understand you correctly, yes.  But it I were to move the pencil side-to-side, that handwriting motion would manifest at the far end without delay.  Is that it?

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Posted: 16 October 2007 07:54 PM   [ Ignore ]   [ # 30 ]
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No.  How could there be a delay?  I know I said sideways motion, but I just meant translational motion.  If you chose to call two of the faces of the long edge of the pencil fron and back, the up and down movement would now be a sideways movement.  What I meant was translating the pencil as a whole object from one place to another as opposed to particles within it transmitting energy as a longitudinal wave, which is lossy and slow.

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