Does 'virtual photons' obey 'c'?

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Offline yor_on

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Does 'virtual photons' obey 'c'?
« on: 29/07/2012 12:27:13 »
?
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Offline JP

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Re: Does 'virtual photons' obey 'c'?
« Reply #1 on: 30/07/2012 13:10:59 »
No.  If a particle lives for a short time, it can exceed the speed of light (a consequence of the uncertainty principle).  However, this isn't a problem for special relativity, which says that information can't travel faster than the speed of light.  No one has been able to devise an experiment in which information goes faster than the speed of light. 

(The details of the virtual particle case are beyond me, but you can check Baez for them: http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html.  It does seem to be similar to entanglement where something seems to move faster than light, but no information is gained until the 2 distant observers compare notes.)

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Offline McQueen

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Re: Does 'virtual photons' obey 'c'?
« Reply #2 on: 31/07/2012 13:16:25 »
If Information cannot move faster than c , what about  quantum computing ? It seems to work on the principle of FTL interactions, or am I mistaken?
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Offline yor_on

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Re: Does 'virtual photons' obey 'c'?
« Reply #3 on: 31/07/2012 13:46:34 »
JP "However, this isn't a problem for special relativity, which says that information can't travel faster than the speed of light."

Virtual photons are force carriers in mains stream descriptions, so they better carry 'information' as I think. If they don't they're rather 'worthless' to me, ahem :) And I guess that's what McQueen asks about too, in another way. And there we lift up 'interactions' which is a very interesting point to make.
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Offline yor_on

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Re: Does 'virtual photons' obey 'c'?
« Reply #4 on: 31/07/2012 13:55:10 »
And yeah, to me it's all about 'fields' JP :) Which I don't understand btw ::))
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Offline imatfaal

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Re: Does 'virtual photons' obey 'c'?
« Reply #5 on: 31/07/2012 14:26:32 »
Quantum computing relies on strange mathematical results from the application of superposition - and has been demonstrated at a very low level; however, I do not know where there is any FTL communication in quantum computing.  Entangled particles do not allow communication of data faster than light anyway

 
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Offline yor_on

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Re: Does 'virtual photons' obey 'c'?
« Reply #6 on: 31/07/2012 18:08:39 »
Let me put it another way, why seems 'virtual photons' the preferred  main stream definition? What exactly is better with that as compared to indeterminism?
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Offline Geezer

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Re: Does 'virtual photons' obey 'c'?
« Reply #7 on: 31/07/2012 21:10:38 »
If Information cannot move faster than c , what about  quantum computing ? It seems to work on the principle of FTL interactions, or am I mistaken?

It's just a way of doing a lot of things in parallel. That's where the speed advantage comes from. No FTL required.
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Offline yor_on

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Re: Does 'virtual photons' obey 'c'?
« Reply #8 on: 01/08/2012 15:53:16 »
Now, if 'c' was a result of the room existing, as that could be a interpretation of SpaceTime, how can 'entanglements' correlations exist over macroscopically large distances? Are we inside something 'more', or 'outside' it, as some bubble/dimensions/degrees of freedom, cut off?

What exactly makes us think we are 'cut off' if so, considering a entanglement again?
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Offline yor_on

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Re: Does 'virtual photons' obey 'c'?
« Reply #9 on: 09/08/2012 13:30:38 »
The thing I'm wondering about is why radiations constant define information for us. It's almost as if the whole universe was some superposition in where 'c' is the constant making it 'real'. Another thing is the way LorentzFitzGerald contractions are complementary to time dilations, which they must be as far as I understand. To assume a 'seamless universe', the same for us all we need something not 'observer dependent', and there you have lights speed in a vacuum.
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Offline yor_on

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Re: Does 'virtual photons' obey 'c'?
« Reply #10 on: 10/08/2012 03:17:01 »
This one is subtle, either you assume that 'c' is a universally seamless constant, but it isn't, although, it really is :) it's very tricky thing from a 'seamless universe/perspective' in that it always is locally defined, but never the less also always found to be the same in all local experiments. One can argue whether this only is valid for SR, or for relativity as a whole, but to me that is relativity, with gravity/accelerations.

So 'c' will always be a local definition, although still valid for all 'frames of reference' and so a 'universally local constant', as I think of it.
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Offline McQueen

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Re: Does 'virtual photons' obey 'c'?
« Reply #11 on: 12/08/2012 07:56:01 »
Geezer,

It's just a way of doing a lot of things in parallel. That's where the speed advantage comes from. No FTL required.

If what you say were really true, it would be a wonderful simplification, unfortunately one of the tenets of QM is that on the atomic scale, particles can be in two places at once. Surely that indicates some kind of FTL interaction ?  OR if it doesn't it should.
« Last Edit: 12/08/2012 08:04:35 by McQueen »
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Offline McQueen

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Re: Does 'virtual photons' obey 'c'?
« Reply #12 on: 12/08/2012 08:03:42 »
Imaatfaal,
Apparently Quantum computing had found practical applications as far back as 2004 http://www.quantum.at/research/quantum-cryptography/quantum-secured-bank-transfer.html one wonders why there has been no great leap forward after this.
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Offline evan_au

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Re: Does 'virtual photons' obey 'c'?
« Reply #13 on: 12/08/2012 11:29:15 »
If you can entangle two photons heading in opposite directions, then quantum entanglement might allow you to communicate instantly at a distance - but only between two points which can be reached at or below the speed of light from the original point of entanglement.

In a sense, this would allow quantum communication at twice the speed of light...  but this is still a very new field, so it's not clear what is truly possible.

I am sure that many stock brokers would love to shave a few milliseconds off the transmission time between two stock exchanges, so they can profit from small differences in the buy and sell prices between the different stock exchanges!

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Offline imatfaal

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Re: Does 'virtual photons' obey 'c'?
« Reply #14 on: 14/08/2012 12:34:06 »
If you can entangle two photons heading in opposite directions, then quantum entanglement might allow you to communicate instantly at a distance - but only between two points which can be reached at or below the speed of light from the original point of entanglement.

In a sense, this would allow quantum communication at twice the speed of light...  but this is still a very new field, so it's not clear what is truly possible.

I am sure that many stock brokers would love to shave a few milliseconds off the transmission time between two stock exchanges, so they can profit from small differences in the buy and sell prices between the different stock exchanges!

But you cannot communicate ftl - it is interesting and magical but not communications.  You know the state of your measured signal photon and thus you can tell the state of the the entangled idler photon - but that state was set when you entangled them!  And thus any communication was at light speed.  You cannot cannot manipulate one photon and observe the other one wiggle.
There’s no sense in being precise when you don’t even know what you’re talking about.  John Von Neumann

At the surface, we may appear as intellects, helpful people, friendly staff or protectors of the interwebs. Deep down inside, we're all trolls. CaptainPanic @ sf.n