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Author Topic: Can we communicate faster than light speed?  (Read 6764 times)

Offline pirunner

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Can we communicate faster than light speed?
« on: 31/05/2008 10:45:50 »
JAMES WOLZ  asked the Naked Scientists:

Chris,
 
I love the show and listen to it every week on my runs! This week's show on Mars, even though astronomy is not my favourite subject, got me thinking about two things that I hope you can answer for me.
   
First of all, someone mentioned on the show that if the sun went out today we would still have a few million years before we would actually run out of light. I understand this phenomenon, but what about if we looked directly at the sun? Would there still be a burning bright orb that was brighter that the rest of the sky, would we not see it as a concentrated light source anymore, or would it just be a big black hole in the sky?
   
Next, as I was listening to another science show for here in the states, the host said what I thought was a terribly wrong statement. He first talked about hos it takes something like 17 minutes for our communications signals to reach Mars and vice versa. This is true and makes perfect sense, based on the speed of light.

Then, however, he went on to say, in a hopeful kind of tone, that we would eventually be able to cut down this time to the point where there would be almost no time delay and we could control robots simultaneously with their actions.

Now, I'm pretty sure this would mean that these signals would have to be traveling faster than the speed of light, which is definitely impossible. Am I right?
   
Thanks for any help you can give me, and thanks for the show!
   
  Kevin
  17 y.o.
  Chicago, Illinois

What do you think?


 

Offline lightarrow

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Can we communicate faster than light speed?
« Reply #1 on: 31/05/2008 12:47:20 »
If you heat in a flame a piece of iron so that it becomes bright, it doesn't immediately stop emitting light after you take it out of the flame. If the piece of iron is bigger, it keeps emitting light for a longer time. In the case of the sun, since its mass is incomparable bigger, it would keep emitting light for much more time (of course slowly decreasing the intensity and the peak frequency). If you have understood this, there isn't much more to add. Sincerely, I don't know what do you mean to ask with: "what about if we looked directly at the sun?" Where is the difference?
Quote
Next, as I was listening to another science show for here in the states, the host said what I thought was a terribly wrong statement. He first talked about hos it takes something like 17 minutes for our communications signals to reach Mars and vice versa. This is true and makes perfect sense, based on the speed of light.

Then, however, he went on to say, in a hopeful kind of tone, that we would eventually be able to cut down this time to the point where there would be almost no time delay and we could control robots simultaneously with their actions.
Don't see how.
 

Offline LeeE

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Can we communicate faster than light speed?
« Reply #2 on: 31/05/2008 16:25:43 »
I haven't listened to the show but I'm not at all sure that the statement about there being light for a few million years is correct, or is at least, a little misleading.  Presumably, when they referred to the Sun going "out" they were saying that if the fusion process in the core stopped now there would be enough residual heat in the Sun's mass to keep it glowing but this doesn't seem to take into account the fact that the core fusion process stops the sun from collapsing under it's own gravity.  The scenario seems to actually match what will happen when the Sun has eventually burnt most of it's fuel and reached the end of it's life on the Main Sequence.  Yes, there will still be light, but the Earth will have been swallowed by the Sun as it goes through it's red-giant phase.

Faster than light communication may be possible through quantum entanglement, albeit, not directly through the entangled particles themselves.
 

Offline chris

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Can we communicate faster than light speed?
« Reply #3 on: 31/05/2008 17:41:15 »
What was meant by the statement was that if fusion stopped abruptly in the Sun, but it otherwise remained the same, the photons that had already been produced would continue to spill out for another million years or so because that's roughly (theoretically) how long they take, on average, to escape and then  begin their journey to Earth.

Chris
 

Offline lightarrow

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Can we communicate faster than light speed?
« Reply #4 on: 31/05/2008 19:46:38 »
Faster than light communication may be possible through quantum entanglement, albeit, not directly through the entangled particles themselves.
No, faster than light communication doesn't exist nor it could be possible in that way.
 

Offline DoctorBeaver

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Can we communicate faster than light speed?
« Reply #5 on: 31/05/2008 21:14:57 »
Faster than light communication may be possible through quantum entanglement, albeit, not directly through the entangled particles themselves.
No, faster than light communication doesn't exist nor it could be possible in that way.

Alberto - It feels wrong contradicting someone whose knowledge of physics is far greater than mine, but everything I've read on this subject says that if you interfere with an entangled particle its partner feels the effect instantaneously .
 

Offline lightarrow

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« Reply #6 on: 01/06/2008 12:43:14 »
Faster than light communication may be possible through quantum entanglement, albeit, not directly through the entangled particles themselves.
No, faster than light communication doesn't exist nor it could be possible in that way.

Alberto - It feels wrong contradicting someone whose knowledge of physics is far greater than mine, but everything I've read on this subject says that if you interfere with an entangled particle its partner feels the effect instantaneously .

Yes but it's wrong to deduce from this the possibility of FTL (faster than light) communication. It was proven, and well known from physicists, that it's impossible to use this effect to transmit FTL information.

Let me make an analogy: we have two points A and B on the Moon, 1000 km apart; between them there are many mirrors, equally spaced; with a powerful and very collimated laser I send a beam of light on A, then I move the laser quickly, in 1 ms = 0.001 s, towards B. Light to A will arrive in L/c seconds (L = Earth-Moon distance) and light to B will arrive in 0.001 + L/c seconds; so, someone looking only at the flashes of light from the mirrors on the Moon will see these flashes moving from A to B in 0.001 seconds. Should he conclude that a signal were moving at v = s/t = 1000km/0.001s = 1,000,000 km/s ? (c = 300,000 km/s). No, because you can't use that effect to send information from A to B.

With entanglement it's something analog to it.
 

Offline DoctorBeaver

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Can we communicate faster than light speed?
« Reply #7 on: 01/06/2008 16:22:50 »
Alberto - I understand all that. But if you have 2 entangled particles and poke 1 of them, the other will react instantaneously. The fact that particle A has been poked will be communicated instantaneously to particle B.

However, is it actually instantaneous, or just too short a time for us to measure? I don't know if this is feasible, but what if entanglement acts via a compactified dimension of Planck-scale size? The communication would then take place not instantaneously, but in the time it takes for light to traverse the compactified dimension. FTL communication would not actually be acheived, so no physical laws are broken; but the time taken would be too small for us to measure and so would appear instantaneous.

For argument's sake, let's say that is how entanglement works. Would it be possible to utilise entanglement to transmit a kind of photonic binary code via a Planck-scale size dimension?

Gawd - I get some really dumb ideas!  [:I]
 

Offline syhprum

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Can we communicate faster than light speed?
« Reply #8 on: 01/06/2008 17:12:55 »
Light arrow/Doc

This of course is an example of phase velocity where the limit of "C" does not apply,
a homely example would be waves coming into the beach at a very flat angle the point where the wave break will move very rapidly sideways at a much greater speed than that of the incoming wave but this phenomena is no good for communication.
 

Offline graham.d

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Can we communicate faster than light speed?
« Reply #9 on: 01/06/2008 18:16:06 »
Quantum Entanglement does not enable FTL communication. The measurement of the state of a particle in one position will cause a collapse of the wave function and determine the state of the particle in another position that was entangled with it, but no data is transmitted. Interestingly, FTL information transport can occur over very short distances. Feynman pointed out that there is a probability amplitude for a photon to be travelling at less than or greater than the speed of light although the average is as you would expect.
 

Offline LeeE

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Can we communicate faster than light speed?
« Reply #10 on: 01/06/2008 19:13:19 »
What was meant by the statement was that if fusion stopped abruptly in the Sun, but it otherwise remained the same, the photons that had already been produced would continue to spill out for another million years or so because that's roughly (theoretically) how long they take, on average, to escape and then  begin their journey to Earth.

Chris

Ah - I see, but if fusion stopped abruptly in the Sun, it would not otherwise remain the same.
 

Offline DoctorBeaver

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Can we communicate faster than light speed?
« Reply #11 on: 01/06/2008 20:18:26 »
The measurement of the state of a particle in one position will cause a collapse of the wave function and determine the state of the particle in another position that was entangled with it...

Can you not determine the state (or a particular value) of the first particle by measuring the state of the second?
 

Offline LeeE

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Can we communicate faster than light speed?
« Reply #12 on: 01/06/2008 20:22:59 »
Faster than light communication may be possible through quantum entanglement, albeit, not directly through the entangled particles themselves.
No, faster than light communication doesn't exist nor it could be possible in that way.

Hmm... I didn't say that it was possible, only that it may be possible, and I did say that it was not possible directly through the entangled particles.

It is not possible to communicate directly through the entangled particles because it is not possible to set the particles to a specified state, which is then conveyed by the entanglement.  However, it is possible to use quantum entanglement to communicate if a parallel classiscal channel is also used.  This may seem to defeat the entire purpose of it all but it is only necessary to send a single bit of information via the classical channel to validate, or invalidate a potentially unlimited amount of data via the entanglement channel.

For example, Alice wishes to send 'n' bits of information to Bob.  To do so, she resolves 'n' qubits.  If the pattern of the resolved qubits matches what she wants to send, she transmits '1' via the classical channel and the transmission is done.  However, if the pattern does not match, she transmits a '0', meaning that the data is invalid, and a new set of 'n' qubits must be used for a second attempt.

So in this example, although a classical channel is required, it is only for validation and not for the communication of the data itself.

I think that it may be possible to devise statistically based protocols that do not need a classical channel, although they will probably always incorporate a degree of error and would require huge numbers of qubits.  Such a 'lossy' protocol might be something akin to the JPEG picture compression format, where the original data is not preserved in the copy but the larger meaning of the original data is.
 

Offline LeeE

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Can we communicate faster than light speed?
« Reply #13 on: 01/06/2008 20:30:11 »
DrB, you can determine the state, and therefore know what the other person will see, but you can't set the state to a required value.  In this respect, the state can be used to decide an action to be taken, and people at both ends of the entanglement will know what action has been taken without the need for a classical channel, but neither end can choose what action is taken.
 

Offline DoctorBeaver

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Can we communicate faster than light speed?
« Reply #14 on: 01/06/2008 20:33:24 »
DrB, you can determine the state, and therefore know what the other person will see, but you can't set the state to a required value.  In this respect, the state can be used to decide an action to be taken, and people at both ends of the entanglement will know what action has been taken without the need for a classical channel, but neither end can choose what action is taken.


If you start with enough, couldn't you find some that are in the state you want? Ah, of course, determining what state they are in will collapse the waveform. Hmmm...
 

Offline qazibasit

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Can we communicate faster than light speed?
« Reply #15 on: 13/06/2008 14:33:05 »
i dont think so. coz then u have to communicate in  the form of light waves instead of sound waves which means ur larynx is producing light :). second even if it is the cause and u put a light wave reciever bypassing the ear and the vibrating tympanic membrane still the nerves will take a time of 240 km/hrs. so ultimately u will lag a little with in terms of light is too much.
 

Offline DoctorBeaver

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Can we communicate faster than light speed?
« Reply #16 on: 14/06/2008 05:25:50 »
i dont think so. coz then u have to communicate in  the form of light waves instead of sound waves which means ur larynx is producing light :). second even if it is the cause and u put a light wave reciever bypassing the ear and the vibrating tympanic membrane still the nerves will take a time of 240 km/hrs. so ultimately u will lag a little with in terms of light is too much.

We already communicate using light. Writing, film, photos, sign language, body language, etc all use light as the medium. In those cases it is our eyes that perceive the comunication rather than our ears.
 

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Can we communicate faster than light speed?
« Reply #16 on: 14/06/2008 05:25:50 »

 

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