Author Topic: Entangled particle deep space communication  (Read 6278 times)

Offline PeterAlt

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Entangled particle deep space communication
« on: 07/10/2014 04:51 pm »
Just wondering if the method of using entangled particles for spacecraft communication has been considered? Advantages would be instantaneous data for deep space probes and the elimination of gigantic dish networks.

Offline ddunham

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Re: Entangled particle deep space communication
« Reply #1 on: 07/10/2014 05:29 pm »
What method is this that you speak of?  There is no known way to use entangled particles to communicate information at faster-than-light speeds.


Offline strangequark

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Re: Entangled particle deep space communication
« Reply #2 on: 07/10/2014 05:49 pm »
Like ddunham said. This is one of those recurring ideas that pops up now and again. There's formal proofs showing that entanglement does not allow FTL transmission of information (look up the "no-communication theorem"). It's not engineering impossible, it's physics impossible (which is much harder to overcome).
« Last Edit: 07/10/2014 05:54 pm by strangequark »

Offline PeterAlt

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Re: Entangled particle deep space communication
« Reply #3 on: 07/10/2014 06:33 pm »
They're launching an entangled particle experiment. I don't know the mission, but I'll look it up. Basically, the entangled particle's "mate" on Earth would reverse its spin and detectors monitoring the one on the satellite experiment would see if the other one (on the satellite) reverses its spin as well, as expected. If so, in theory, it may be possible to use entangled particles to instantly send digital data (the change in spin could translate into bits).

Offline Jim

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Re: Entangled particle deep space communication
« Reply #4 on: 07/10/2014 06:40 pm »
They're launching an entangled particle experiment. I don't know the mission, but I'll look it up. Basically, the entangled particle's "mate" on Earth would reverse its spin and detectors monitoring the one on the satellite experiment would see if the other one (on the satellite) reverses its spin as well, as expected. If so, in theory, it may be possible to use entangled particles to instantly send digital data (the change in spin could translate into bits).

it is a proposal and not a firm mission or even experiment.

Offline ChrisWilson68

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Re: Entangled particle deep space communication
« Reply #5 on: 07/10/2014 06:54 pm »
They're launching an entangled particle experiment. I don't know the mission, but I'll look it up. Basically, the entangled particle's "mate" on Earth would reverse its spin and detectors monitoring the one on the satellite experiment would see if the other one (on the satellite) reverses its spin as well, as expected. If so, in theory, it may be possible to use entangled particles to instantly send digital data (the change in spin could translate into bits).

Again, as others have said upthread, this is wrong.

There are some things in Quantum Theory that are very strange, in that they go counter to our intuition.  This is one of them.  You'd think that if entanglement causes an instant change in one particle when the other is handled in some way, that could be used for instantaneous communication, but that is not the case.  As was said upthread, the very theory that says there's an instantaneous change has as a mathematically provable result that you can't get faster-than-light communication using it.

Very unintuitive, but true.

Offline rklaehn

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Re: Entangled particle deep space communication
« Reply #6 on: 07/10/2014 07:01 pm »
They're launching an entangled particle experiment. I don't know the mission, but I'll look it up. Basically, the entangled particle's "mate" on Earth would reverse its spin and detectors monitoring the one on the satellite experiment would see if the other one (on the satellite) reverses its spin as well, as expected. If so, in theory, it may be possible to use entangled particles to instantly send digital data (the change in spin could translate into bits).

It is impossible to transfer information with superluminal velocity using quantum entanglement. See http://en.wikipedia.org/wiki/No-communication_theorem.

Offline JasonAW3

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Re: Entangled particle deep space communication
« Reply #7 on: 07/10/2014 07:42 pm »
There's still some debate as to whether or not information can be transmitted via entangled particles, but my guess is that if information can be transmitted over a large distance, the information would be so scrambled as to be incoherent.

It MAY be possible to creat such a system that works AT light speed, but so far as we can tell, not faster than light.
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Offline ChrisWilson68

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Re: Entangled particle deep space communication
« Reply #8 on: 07/10/2014 07:50 pm »
There's still some debate as to whether or not information can be transmitted via entangled particles, but my guess is that if information can be transmitted over a large distance, the information would be so scrambled as to be incoherent.

It MAY be possible to creat such a system that works AT light speed, but so far as we can tell, not faster than light.

There's only "debate" about it in the sense that there's debate right here in this forum among amateurs.

There's no debate among people who actually understand Quantum Theory.  Quantum Theory unambiguously says classical information cannot be transmitted through entanglement.  You need a side-channel to transmit some classical information to make use of the entangled information.  It's a simple mathematical consequence.  Debating it is like debating whether pi is rational.

Quantum Theory could, of course, be wrong.  But entanglement is a consequence of Quantum Theory, so any experiments that show the effects of entanglement don't put Quantum Theory in doubt.  So entanglement won't get you faster-than-light communication.  It doesn't even actually give communication you can use at all.  If you want that, it has to come from some new, unknown physics beyond Quantum Theory, and that's not entanglement.

Offline RanulfC

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Re: Entangled particle deep space communication
« Reply #9 on: 07/10/2014 08:02 pm »
You should be Ok as long as you can avoid Imperial Entanglements....

(sombody had to do it :) )

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Offline Stormbringer

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Re: Entangled particle deep space communication
« Reply #10 on: 07/10/2014 11:36 pm »
i would not give up on the ansible just yet. there might be some way to do it with wormholes or perhaps FTL particles are more than just a mathematical artifact. who knows? i don't think any thing has ever been achieved by people who said that that particular thing cannot be achieved. so keep dreaming!
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Offline A_M_Swallow

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Re: Entangled particle deep space communication
« Reply #11 on: 07/11/2014 02:22 am »
I have no problem believing that information is sent between the two entangled particles at the speed of light - a speed limit is a speed limit.  However saying that entangled particles cannot be used to transfer information does not make sense - entanglement must mean something.

Have a look at what is going down the side channel.  Can this information be sent say 2 years in advance?

If made to work transmission by entanglement would be a low power point to point data transmission method.

Offline QuantumG

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Re: Entangled particle deep space communication
« Reply #12 on: 07/11/2014 02:47 am »
Please, if you don't understand physics, pick up a textbook.
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Offline Nilof

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Re: Entangled particle deep space communication
« Reply #13 on: 07/11/2014 03:04 am »
There is no "message" being sent between the two particles, only correlation of measurements made on them.

To make an analogy, imagine that you had a pair of gloves and two identical boxes. Let's say that I put one glove in each box, and randomly select one and give it to you before you go on an interstellar trip. For both me and you, opening the box will reveal a right hand or a left handed glove randomly. Furthermore, you'll know instantly whether I have a right handed or left handed glove. But it would be ridiculous to suggest that this implies that a FTL message is actually sent between the two gloves when you open the box.

Instead, using your knowledge that the correlation exists you are essentially making a measurement on your past lightcone and deducing that the box i took had the glove with the other handedness, and everything you encounter in your future will have to be consistent with that.

In QM this is most easily understood by using the density matrix formulation. The fact that information can't be transferred corresponds to the fact that partial trace operations commute with each other and with block diagonal unitary transformations.
« Last Edit: 07/11/2014 03:57 am by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline A_M_Swallow

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Re: Entangled particle deep space communication
« Reply #14 on: 07/11/2014 03:42 am »
There is no "message" being sent between the two particles, only correlation of measurements made on them.

To make an analogy, imagine that you had a pair of gloves and two identical boxes. Let's say that I put one glove in each box, and randomly select one and give it to you before you go on an interstellar trip. For both me and you, opening the box will reveal a right hand or a left handed glove randomly. Furthermore, you'll know instantly whether I have a right handed or left handed glove. But it would be ridiculous to suggest that this implies that a FTL message is actually sent between the two gloves when you open the box.
{snip}

What you are saying is that I cannot force Gi to be a left hand glove.

Offline Nilof

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Re: Entangled particle deep space communication
« Reply #15 on: 07/11/2014 03:58 am »
What you are saying is that I cannot force Gi to be a left hand glove.

Yes. You can use the correlation to your advantage for say making one-time pads for scamgraphy, but you can't use it to transfer information.
« Last Edit: 07/11/2014 03:59 am by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Nascent Ascent

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Re: Entangled particle deep space communication
« Reply #16 on: 07/11/2014 04:22 am »
There's still some debate as to whether or not information can be transmitted via entangled particles, but my guess is that if information can be transmitted over a large distance, the information would be so scrambled as to be incoherent.

It MAY be possible to creat such a system that works AT light speed, but so far as we can tell, not faster than light.

There's only "debate" about it in the sense that there's debate right here in this forum among amateurs.

There's no debate among people who actually understand Quantum Theory....

No one really understands Quantum theory.

Online Lar

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Re: Entangled particle deep space communication
« Reply #17 on: 07/11/2014 04:29 am »
No one really understands Quantum theory.

OK, between that pretty accurate summation of the thread so far, and the less than collegial atmosphere, I think we're done for now. Locked.
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