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Sending an instantaneous signal


geordief
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(wasn't sure in which sub forum  to put this one)

I have been trying to follow (some of) the ongoing entanglement topic and this has occurred to me.

 

Suppose there was a way to look for entangled particles (coming from deep space)  that showed a pattern indicating that they were created  deliberately  ,could that be an indication someone was sending a message from the location of the "twins" of the particles we had just  encountered ?

 

Could we answer by locating the source of the  signalling and  then finding a source of entangled particles midway between us and them and encoding them?(they would reach us and our interlocutors at the same time)

 

.......In theory (if the technology advanced to make it a practical proposition)

 

We would be  effectively setting up a walkie talkie system between the past and the present ,so we might have to stand well clear!!!:)

 

Have there been other attempts(in theory)  to do this? (I know that no signal can be sent directly from one location to the other  by "conventional" means.

 

Even if this worked for a distance of 1 light milli  milli milli milli second it would show the potential for inter civilization communication....so has it been definitively shown that this cannot happen (obviously we can never prove a negative -if I got that right)

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You 'look for' particles by detecting, or interacting with, them.
You have, then, detrmined the state of its entangled partner; wherever it might be.
( although momentum conservation laws would give an indication of directio of travel )

But, once detectedd, how would you even know you are dealing with a member of an entangled pair ?

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48 minutes ago, geordief said:

Suppose there was a way to look for entangled particles (coming from deep space)  that showed a pattern indicating that they were created  deliberately  ,could that be an indication someone was sending a message from the location of the "twins" of the particles we had just  encountered ?

Have there been other attempts(in theory)  to do this?

What kind of source generated a signal and how long the signal took to reach Earth are different questions. Specifically identifying entangled particles is very, very speculative. I don't think anyone has searched for anything like that, although I suppose you could ask the people at SETI....

Using entanglement is also speculative. It's forbidden by relativity, and even quantum mechanics doesn't allow incoherent systems to violate that rule. Faster-than-light communication would require (a) that entanglement does indeed involve such communication between particles (which is still a controversial subject), and (b) that there's an as-yet-unkown way to get around the rules. The short answer is no, no one has the slightest idea of whether or how that could possibly be done.

Edited by Lorentz Jr
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46 minutes ago, MigL said:

You 'look for' particles by detecting, or interacting with, them.
You have, then, detrmined the state of its entangled partner; wherever it might be.
( although momentum conservation laws would give an indication of directio of travel )

But, once detectedd, how would you even know you are dealing with a member of an entangled pair ?

If there was an encoded message in the (stream of) particles that  said anything at all (esp "hi,my name is hjuigr. I am your entanglement  partner .How can I help you?") it might be an indication that there was a (stream of) particles out there with an encoder tapping away.

 

I mean the message could be anything  but it could be some kind of a language primer

 


)

Quite apart from the specific nature of this OP I am trying to understand the topic of entanglement  on the round.

 

I wonder whether what I understand to be the random nature of the result of any interaction  would act to prevent any such "stream" or encoding to be established in the first place?

 

I mean ,yes, I imagine anyone could encode a message using a stream of entangled particles but would the message be irredemably  lost  because of the random nature of the phenomenon (I am fishing for replies.Even as OP I am not qualified to suggest an opinion

Edited by geordief
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2 hours ago, Lorentz Jr said:

Using entanglement is also speculative. It's forbidden by relativity

No, it’s not. If you wish to discuss it, open your own thread on entanglement, so your misconceptions can be addressed.

3 hours ago, geordief said:

Suppose there was a way to look for entangled particles (coming from deep space)  that showed a pattern indicating that they were created  deliberately  ,could that be an indication someone was sending a message from the location of the "twins" of the particles we had just  encountered ?

Entangled particles are in undetermined states until detected, so how is anything “encoded”?

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20 minutes ago, swansont said:

No, it’s not. If you wish to discuss it, open your own thread on entanglement, so your misconceptions can be addressed.

Entangled particles are in undetermined states until detected, so how is anything “encoded”?

I was imagining that the time intervals btw particles could be encoded.(or  similar methods)

It would be enough to know that a stream of entangled particles was "incoming" and that something about the stream  was ordered in some way.

 

If there was a way of knowing that a group of particles had been entangled   then we might be able to read off the order in which they had been entangled. 

The individual  readouts  could be irrelevant. 

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If you sit at one place and take spin measurements on a particle (say a photon,) being completely clueless about whether that particle comes from an entangled pair, or triplet, etc., you wouldn't know. There's hardly anything you would be able to say about other parts of the universe it's just disentangled from.

One particle is... well, one particle. You measure its spin --after that, it becomes disentangled from whatever it was entangled with before --as @MigL said. Suppose it gives +1 in the direction you set your polariser at.

What can you say from that? Practically nothing. +1: That's all your information.

Just one piece of data from a measurement doesn't tell you anything much about where it came from. If you take care not to do anything that changes the spin, it will produce +1 again and again. So, sure, you can say something about this photon now.

If, OTOH, you measure spins for a stream of particles all identically prepared in the same entangled state, you would see a sequence now. It could go like:

+1, +1, -1, +1, -1, +1, -1, -1, -1, +1, +1, -1, +1, +1...

So what? What can you tell from that? You can call upon Zeilinger himself, if you wish, to interpret your data. You can tell nothing from that. Not yet. It's just a random sequence of binary code.

But, if you can arrange to communicate --by the usual, sub-luminal channels-- with someone far away in the Andromeda galaxy measuring the partner particles making up the identically-entangled pairs, now, and not before, you would be able to tell something, if you're lucky. If you both have chosen the same polarisation direction for your respective polarisers, you would find something funny: They're exactly anti-correlated each and every time. When your particle reads "+1", the other one reads "-1", and viceversa.

But if you set your polarisers in a non-parallel way, there's not even the slightest amount of correlation.

That's a big wow! on my part. It's strange, weird, seems magic --if you don't understand QM. But still doesn't allow you to send any signals in and of itself. As I said in the other thread, concerning quantum teleportation:

Quote

but to complete the quantum teleportation, classical information needs to be sent from sender to receiver. Because classical information needs to be sent, quantum teleportation cannot occur faster than the speed of light.

https://en.wikipedia.org/wiki/Quantum_teleportation

However, and most importantly, even if, after having gone through all that trouble, you find the perfect anti-correlation, your local stream of data (the sequence of +1, +1, -1, +1, -1, +1, -1, -1, -1, +1, +1, -1, +1, +1..., etc.) is still a random, nonsense, totally-garbage noise of +1's and -1's. What do you wanna do with that for the purposes of communication?

See my point?

Do you want to communicate with the Andromeda galaxy with photon spins somehow coding a message? Fine. Here's one particular way you could go about doing that.

You take a sufficient power of 2, eg, 27=128

You can code 128 characters with this. More than enough for all to represent the different characters in the English language, lower case and capitals, plus Arabic numerals, spaces, punctuation, and a bunch of special symbols.

It could go like,

Space ->  0000000

Dot -> 0000001

a -> 0000010

etc.

Now you can prepare your photons to "mean something." It would --it would have to-- look like a pre-determined, precise sequence of zeros and ones. Importantly, you have to filter the sequence so that each photon is +1 (stand-in for 1) or -1 (stand-in for 0) to be precisely at the place it has to be to constitute your message.

I think the idea is clear enough at this point. You can't do that with the output of an entangled state. A random string of 0's and 1's is not a message. And it's not, no matter what direction you set your polarisers in.

Sending a random sequence is not a message, no matter how non-classically structured these strings of noise are. Even though they are.

All my previous comments go without even starting to consider the problem of keeping quantum coherence through interstellar space all the way from here to the Andromeda galaxy, with interstellar dust, asteroid rings, cosmic rays knocking off my photons, etc. I don't envy the engineer whose task was to guarantee something like that.

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2 hours ago, joigus said:

If you sit at one place and take spin measurements on a particle (say a photon,) being completely clueless about whether that particle comes from an entangled pair, or triplet, etc., you wouldn't know. There's hardly anything you would be able to say about other parts of the universe it's just disentangled from.

One particle is... well, one particle. You measure its spin --after that, it becomes disentangled from whatever it was entangled with before --as @MigL said. Suppose it gives +1 in the direction you set your polariser at.

What can you say from that? Practically nothing. +1: That's all your information.

Just one piece of data from a measurement doesn't tell you anything much about where it came from. If you take care not to do anything that changes the spin, it will produce +1 again and again. So, sure, you can say something about this photon now.

If, OTOH, you measure spins for a stream of particles all identically prepared in the same entangled state, you would see a sequence now. It could go like:

+1, +1, -1, +1, -1, +1, -1, -1, -1, +1, +1, -1, +1, +1...

So what? What can you tell from that? You can call upon Zeilinger himself, if you wish, to interpret your data. You can tell nothing from that. Not yet. It's just a random sequence of binary code.

But, if you can arrange to communicate --by the usual, sub-luminal channels-- with someone far away in the Andromeda galaxy measuring the partner particles making up the identically-entangled pairs, now, and not before, you would be able to tell something, if you're lucky. If you both have chosen the same polarisation direction for your respective polarisers, you would find something funny: They're exactly anti-correlated each and every time. When your particle reads "+1", the other one reads "-1", and viceversa.

But if you set your polarisers in a non-parallel way, there's not even the slightest amount of correlation.

That's a big wow! on my part. It's strange, weird, seems magic --if you don't understand QM. But still doesn't allow you to send any signals in and of itself. As I said in the other thread, concerning quantum teleportation:

https://en.wikipedia.org/wiki/Quantum_teleportation

However, and most importantly, even if, after having gone through all that trouble, you find the perfect anti-correlation, your local stream of data (the sequence of +1, +1, -1, +1, -1, +1, -1, -1, -1, +1, +1, -1, +1, +1..., etc.) is still a random, nonsense, totally-garbage noise of +1's and -1's. What do you wanna do with that for the purposes of communication?

See my point?

Do you want to communicate with the Andromeda galaxy with photon spins somehow coding a message? Fine. Here's one particular way you could go about doing that.

You take a sufficient power of 2, eg, 27=128

You can code 128 characters with this. More than enough for all to represent the different characters in the English language, lower case and capitals, plus Arabic numerals, spaces, punctuation, and a bunch of special symbols.

It could go like,

Space ->  0000000

Dot -> 0000001

a -> 0000010

etc.

Now you can prepare your photons to "mean something." It would --it would have to-- look like a pre-determined, precise sequence of zeros and ones. Importantly, you have to filter the sequence so that each photon is +1 (stand-in for 1) or -1 (stand-in for 0) to be precisely at the place it has to be to constitute your message.

I think the idea is clear enough at this point. You can't do that with the output of an entangled state. A random string of 0's and 1's is not a message. And it's not, no matter what direction you set your polarisers in.

Sending a random sequence is not a message, no matter how non-classically structured these strings of noise are. Even though they are.

All my previous comments go without even starting to consider the problem of keeping quantum coherence through interstellar space all the way from here to the Andromeda galaxy, with interstellar dust, asteroid rings, cosmic rays knocking off my photons, etc. I don't envy the engineer whose task was to guarantee something like that.

So the sender cannot ensure the the particles are what he or she intends  without breaking the entanglement?

Is that the crux?

 

They must be random for him to send them  and so the best that can be arrived at is a mirror image of a random stream?

 

But what about spacing the time intervals  btw the pulses?

Would that be information that the sender could control which would not be random but intended?

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9 minutes ago, geordief said:

So the sender cannot ensure the the particles are what he or she intends  without breaking the entanglement?

Exactly. If you measure a particle's spin along a particular direction, that spin is no longer entangled to any other spin in the universe. You have just set up a qubit to 0 or 1, as people in quantum computing say.

32 minutes ago, geordief said:

But what about spacing the time intervals  btw the pulses?

Would that be information that the sender could control which would not be random but intended?

Well, sure, of course. You could also send electrons and positrons, one after the other. Or whatever other code, or use the frequencies and positions, like we do for a TV set. But then it's not information contained in the spin. It's in other variables. And they would be subject to subluminal speed limits and causality. Like anything else. Is that helpful?

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34 minutes ago, joigus said:

 

Well, sure, of course. You could also send electrons and positrons, one after the other. Or whatever other code, or use the frequencies and positions, like we do for a TV set. But then it's not information contained in the spin. It's in other variables. And they would be subject to subluminal speed limits and causality. Like anything else. Is that helpful?

Yes,thanks. I didn't think of that.

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