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Author Topic: What is the maximum speed of information?  (Read 20505 times)

Offline lightarrow

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What is the maximum speed of information?
« Reply #25 on: 13/01/2011 20:19:37 »
Of course if I am wrong and I may well be then none of the above would work!  :o
Correct  :)
 

Offline Geezer

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« Reply #26 on: 13/01/2011 20:42:34 »
Of course if I am wrong and I may well be then none of the above would work!  :o
Correct  :)

Ah yes, but if you were to send a continuous stream of entangled particles from A to B and C, you could use a sort of Morse Code that was based on whether you measured them or not - maybe?
 

Offline QuantumClue

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« Reply #27 on: 13/01/2011 21:56:29 »
Geezer

You asked how tunneling entered the discussion early on. That was me.

The reason why something tunnels, as I am sure you may be aware, is because some kind of ''hill'' stands between an efficient trajectory of a particle. The hill is a steep potential, and it costs less energy to tunnel this barrier rather than travel the whole deal. In much the same sense, a high potential is created when talking about information sharing over very large distances. To avoid the trouble of contradicting SR postulates, it may be best to imagine information being forced to tunnel large distances, rather than allowing it to travel it at superluminal speeds.
 

Offline Geezer

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« Reply #28 on: 13/01/2011 22:05:49 »
Geezer

You asked how tunneling entered the discussion early on. That was me.

The reason why something tunnels, as I am sure you may be aware, is because some kind of ''hill'' stands between an efficient trajectory of a particle. The hill is a steep potential, and it costs less energy to tunnel this barrier rather than travel the whole deal. In much the same sense, a high potential is created when talking about information sharing over very large distances. To avoid the trouble of contradicting SR postulates, it may be best to imagine information being forced to tunnel large distances, rather than allowing it to travel it at superluminal speeds.

Thanks QC. Yes, that does make sense and it might well explain what's going on, not that I can understand it or anything!
 

Offline QuantumClue

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« Reply #29 on: 13/01/2011 22:24:56 »
Of course, this depends if our universe really does have a description of nonlocality. To be honest, I'm not even sure how to visualize something complex like nonlocality. Surely however, if nonlocality exists, it is not safe to call the universe purely nonlocal in nature. In all reasoning, the universe must be local and nonlocal depending on what circumstances of a system is brought to attention. Locality cannot simply die as a true definition of certain systems in light of a nonlocal attribute.
 

Offline JP

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« Reply #30 on: 14/01/2011 01:40:51 »
There were some experiments done by a fellow named Gunther Nimtz on the speed of tunneling photons.  He claims to have seen them moving faster than light, but it's a bit controversial at the moment, since no one's reproduced it, and obviously this kind of claim has to be checked very carefully.
 

Offline yor_on

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« Reply #31 on: 14/01/2011 01:52:57 »
But you can easily send information using two entangled particles!!  You just have to have the language sorted out before you attempt anything. 

Ok lets say one wiggle is a 0 and two wiggles is a 1.   Using this technique you would have binary code. 

From what I understand, if one of these particles is made to rotate clockwise then the other entangled particle will have to be rotating the opposite way. 

Of course if I am wrong and I may well be then none of the above would work!  :o

The problem is how to make the code make sense :)

You could possibly send entangled photons like we've done in some experiments, but first you will have to send the decoder, and that you will need to do at under light speed. It would not be smart to send that by the same entanglements. The other restriction is in one photons spin per 'bit of information' and you will need a lot of those to tell which letter you mean. so assuming that you sent someone away he will need to store an awful lot of entangled photons for an awful long time before needing them, as he moves under light speed. On the other hand you then have solved the 'decoder' problem as you gave it to him before he left your planet.

The other way is to send 'entangled photons' on their own, then they will move at 'c' but not faster to whatever destination. And you still need to send a 'code book'. The third way is to assume that all light might be entangled some way? Then I think someone would have used it already to give us improbable spins when measuring. That would be one way to 'communicate' even if not making 'sense' as we have no 'codebook'.
=

Another thing, when measuring a spin you can't know before how it will fall out for you. That the opposite spin gets created doesn't mean that you would know which type of spin it was. Assume then a order of photons in a row where the information depend on which photon change spin for you, at what position in that row, at that star. But how would you ever know that one of them had changed 'spin'? Without measuring them?

And when you do you destroy it. The spin I mean, you 'set' it as you measure.
« Last Edit: 14/01/2011 02:07:56 by yor_on »
 

Offline Geezer

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« Reply #32 on: 14/01/2011 06:24:28 »

You could possibly send entangled photons like we've done in some experiments, but first you will have to send the decoder, and that you will need to do at under light speed. It would not be smart to send that by the same entanglements. The other restriction is in one photons spin per 'bit of information' and you will need a lot of those to tell which letter you mean. so assuming that you sent someone away he will need to store an awful lot of entangled photons for an awful long time before needing them, as he moves under light speed. On the other hand you then have solved the 'decoder' problem as you gave it to him before he left your planet.

The other way is to send 'entangled photons' on their own, then they will move at 'c' but not faster to whatever destination. And you still need to send a 'code book'. The third way is to assume that all light might be entangled some way? Then I think someone would have used it already to give us improbable spins when measuring. That would be one way to 'communicate' even if not making 'sense' as we have no 'codebook'.
=

Another thing, when measuring a spin you can't know before how it will fall out for you. That the opposite spin gets created doesn't mean that you would know which type of spin it was. Assume then a order of photons in a row where the information depend on which photon change spin for you, at what position in that row, at that star. But how would you ever know that one of them had changed 'spin'? Without measuring them?

And when you do you destroy it. The spin I mean, you 'set' it as you measure.

I've really no idea if this would work, but I suspect the only option is to have two "stores" of entangled photons at both ends. You sort of have to take them with you, otherwise it could be a bit pointless.

Then, assuming you can figure out some method of encoding a message (which may well be impossible), you have the problem that the store is finite, so once you've depleted the store, you can no longer communicate until you get a "refill" at, or less than, light speed.
 

Offline JP

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« Reply #33 on: 14/01/2011 06:56:02 »
It's a bit beyond me to come up with a general proof that entanglement can't send information faster than light.  I don't know if anyone can do that, actually.  I do know that every attempt to come up with an FTL-transfer scheme based on entanglement apparently fails to actually send information until a classical channel is opened up.

If someone wants to take a stab at proposing a method for an FTL information transfer based on entanglement, maybe we can show why it can't work...
 

Offline Geezer

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« Reply #34 on: 14/01/2011 07:40:11 »
It's a bit beyond me to come up with a general proof that entanglement can't send information faster than light.  I don't know if anyone can do that, actually.  I do know that every attempt to come up with an FTL-transfer scheme based on entanglement apparently fails to actually send information until a classical channel is opened up.

If someone wants to take a stab at proposing a method for an FTL information transfer based on entanglement, maybe we can show why it can't work...

Good idea. Let's see if this can survive for a couple of picoseconds:

Assuming you and I have very large photon stores, as previously mentioned, if you are reading your store at the same time as I am - nope! That's not going to work.

The problem seems to be that, as we can't know what the sequence is in advance, we can only prove that we were "communicating" by comparing our results after the fact. Is that about right?

Or, it's as if we both have an envelope that contains the same random number. I can alter your random number when I read my copy, but, because you cannot know what the original number was, you have no way of knowing whether I changed it or not.
 

Offline Geezer

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« Reply #35 on: 14/01/2011 08:11:44 »
Soooo, if that's true and we have multiple envelopes containing numbers that actually have some sort of statistical bias, that would allow me to read my envelopes in a way that either increased, or decreased, that bias, which you should be able to detect as a form of Morse Code.

However, if it's not possible to create envelopes with biased numbers, it's not going to work. 
 

Offline JP

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« Reply #36 on: 14/01/2011 08:33:24 »
Exactly!  The random-envelope situation is the exact problem with the simple setup for sending information via entanglements.  The numbers I read appear random, regardless of what you've done.  It's only when you send some light-speed information that I know whether you've measured or not.

I don't think there's a way to create bias with measurements alone--at least I can't think of a simple way to do it, and I presume if there was, someone would have come up with it already.
 

Offline JP

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« Reply #37 on: 14/01/2011 08:37:09 »
But the random-envelope case also shows a really good use of quantum entanglement: cryptography.  If I want to send you a coded message, I first need to come up with a secure key and send it to you.  If I sent you a bunch of entangled particles, then I measure them, I'm determining a random key that we both will agree on. (The actual algorithms are more complicated, since they involve ways of detecting eavesdropping, which effects the quantum statistics between entangled particles.)
 

Offline yor_on

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« Reply #38 on: 14/01/2011 10:13:03 »
JP when you let a photon into a condense, 'stopping it'? Do one set the spin then too? Or can I look at that as something not interfering with the photons superposition?

Myself i have this feeling that as soon as one 'touch it' in any way the spin must be set, no matter if you measure it or not. On the third hand that would mean that  I've now 'interacted' with it, without destroying it, if so? Nah, It gotta be superpositioned even after you slowed it down. Or I will have to rethink what an 'interaction' means.
 

Offline JP

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« Reply #39 on: 14/01/2011 11:03:37 »
Usually "slowing it down" implies not destroying the superposition. 
 

Offline QuantumClue

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« Reply #40 on: 14/01/2011 16:49:15 »
There were some experiments done by a fellow named Gunther Nimtz on the speed of tunneling photons.  He claims to have seen them moving faster than light, but it's a bit controversial at the moment, since no one's reproduced it, and obviously this kind of claim has to be checked very carefully.

Fascinating.
 

Offline Airthumbs

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« Reply #41 on: 14/01/2011 20:57:36 »
Ok, so instead of rotating the entangled particles why not make one of them positive, this would mean the other has to be negative? 

And then instead of using just a pair of entangled particles to try and transmit, you could use literally millions of them allowing complex transmission and receivers. 

Has anyone discovered what exactly is the information that passes between the two entangled particles?  Something is transmitted and whatever that is moves significantly faster then the speed of light.  You might even say that the speed is infinite?  So maybe the maximum speed of information in this context is infinity? What I find fascinating is that there appears to be some kind of force capable of traversing the entire universe instantaneously!

If there is a way to identify exactly what this is and investigate it then we might have a way to talk to the stars  ;D
You can tunnel, dig, fold, or even worm your way through space so why not just ignore it all together, something does!
 

Offline QuantumClue

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« Reply #42 on: 14/01/2011 21:16:10 »
Ok, so instead of rotating the entangled particles why not make one of them positive, this would mean the other has to be negative? 

And then instead of using just a pair of entangled particles to try and transmit, you could use literally millions of them allowing complex transmission and receivers. 

Has anyone discovered what exactly is the information that passes between the two entangled particles?  Something is transmitted and whatever that is moves significantly faster then the speed of light.  You might even say that the speed is infinite?  So maybe the maximum speed of information in this context is infinity? What I find fascinating is that there appears to be some kind of force capable of traversing the entire universe instantaneously!

If there is a way to identify exactly what this is and investigate it then we might have a way to talk to the stars  ;D
You can tunnel, dig, fold, or even worm your way through space so why not just ignore it all together, something does!

Well, we just don't know do we :)

It's probably a safe bet to say that whatever it is, it is not a physical transaction. Whatever it is, Bells Theorem has, and I qoute:

''In conjunction with the experiments verifying the quantum mechanical predictions of Bell-type systems, Bell's theorem demonstrates that certain quantum effects travel faster than light and therefore restricts the class of tenable hidden variable theories to the nonlocal variety.''

http://en.wikipedia.org/wiki/Bell's_theorem
 

Offline Geezer

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« Reply #43 on: 14/01/2011 21:19:16 »
Ok, so instead of rotating the entangled particles why not make one of them positive, this would mean the other has to be negative?

Sadly, it would not make any difference. The root of the problem is that you can't influence the "direction" of the entanglement during the entanglement process. You are creating a random number when what you really want to do is create a nonrandom number, but that's not possible.

Think of it this way. You need a way to load the dice. Unfortunately, you can't ever get you hands on them. Not only that, you can't even look at them in advance, so you have no prior knowledge of the random number that was generated.
 

Offline Geezer

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« Reply #44 on: 14/01/2011 21:36:02 »
Wait a minute!

If we didn't know what the random number was in the first place, how do we know all this measuring palaver is doing a dang thing?
 

Offline imatfaal

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« Reply #45 on: 14/01/2011 21:45:29 »
Because even though you have separated in space the entangled particles continue to produce the same interference/random number/measurement.  Per the experiment you posted yesterday - the photons interfered although geographically remote to an extent that any communication between them would have to be superluminal.  the entangled photons caused the same macroscopic events to occur - and to show that no lightspeed particle had conveyed a signal from one to the other - the two sites were placed far enough apart that both macroscopic events would have completed before any lightspeed particle/information would have time to bridge the gap.   
 

Offline Geezer

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« Reply #46 on: 15/01/2011 00:30:49 »
Thanks Matthew. That's not what I was concerned about. I'll have to read up on the measuring process again. I suspect I'll find the answer there.

What I'm wondering is, could the pair be "fooling" us into thinking that they are interacting superluminally as a result of our measuring when they are actually ignoring us, so to speak. If we knew a state before we measured it, we would know for sure, but we can't do that. I'm sure there's a good answer though.
 

Offline QuantumClue

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« Reply #47 on: 15/01/2011 01:55:49 »
Geezer

I cannot help but read this last one as invoking perhaps some kind of determinism, is this what you are hinting at?
 

Offline Geezer

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« Reply #48 on: 15/01/2011 02:47:55 »
Geezer

I cannot help but read this last one as invoking perhaps some kind of determinism, is this what you are hinting at?

I wouldn't really know ;D but I don't think that's what I mean to imply. I'm wondering if there could be some sneaky false assumption in the logic, although I can't imagine how that would get past so many clever scientists. I asked the question more because I don't fully understand it myself than as a direct challenge to the experiment.

However, as you bring it up, if there was some sort of determinism at play, would the experiment point to that as a possible explanation?


 

Offline JP

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« Reply #49 on: 15/01/2011 03:42:51 »
Geezer, check this post and the one I make following it.  It's a description of the unique statistics of entanglement in one case.  It might help clear things up.  Then again, it might not.  :)

There are also more general proofs (Bell's inequalities) that quantum entanglement generates unique statistics that can't be generated by "hidden variables," i.e. that the numbers aren't set up with local variables that let them decide to agree without having to communicate something to each other instantly.  If you Google for tests of Bell's inequality, you'll find plenty of experiments testing this and finding that entanglement is not generated by hidden variables.
 

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What is the maximum speed of information?
« Reply #49 on: 15/01/2011 03:42:51 »

 

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