Using entanglement is not forbidden by relativity??

[Lorentz Jr]

From the thread Sending an instantaneous signal:

 

7 hours ago, geordief said:

Suppose there was a way to look for entangled particles ...

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?

We would be  effectively setting up a walkie talkie system between the past and the present

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

 

6 hours ago, Lorentz Jr said:

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.

 

3 hours ago, swansont said:

Quote

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.

 

Could someone please do me a favor and address these misconceptions? I'm afraid I don't understand them.

By "using entanglement" I meant using entangled particles to send an instantaneous signal, as the OP had asked about (or, more speculatively, possibly using whatever process underlies entanglement sometime in the future, if such a process exists and we can learn how to use it).

 

Edited November 18, 2022 by Lorentz Jr

[Ghideon]

4 minutes ago, Lorentz Jr said:

Could someone please do me a favor and address these misconceptions?

English is not my first language but I see a possible misunderstanding; I'll give it a quick try.

5 minutes ago, Lorentz Jr said:

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

A: If the above means "Theory of relativity does not allow for entanglement. Entanglement is a speculative concept." or similar then @swansont is correct.
B: If the above means "OP in the other thread speculates about using entanglement as a method for faster than light communication. Faster than light communication is not possible according to special relativity" then that seems correct but probably ambiguously formulated. 

Comments?

[Lorentz Jr]

40 minutes ago, Ghideon said:

English is not my first language

To use something is to employ it or utilize it or take advantage of it, in order to accomplish some task or goal or objective. In the "Sending an instantaneous signal" thread, the goal in question was sending instantaneous signals.

Edited November 18, 2022 by Lorentz Jr

[swansont]

57 minutes ago, Lorentz Jr said:

From the thread Sending an instantaneous signal:

 

Could someone please do me a favor and address these misconceptions? I'm afraid I don't understand them.

By "using entanglement" I meant using entangled particles to send an instantaneous signal, as the OP had asked about (or, more speculatively, possibly using whatever process underlies entanglement sometime in the future, if such a process exists and we can learn how to use it).

 

I took the statement to mean that entanglement violates relativity. Since you’ve clarified that this is not the case, my apologies, and please disregard my comment.

[Lorentz Jr]

8 minutes ago, swansont said:

please disregard my comment.

Disregarded.  🙂

[md65536]

7 hours ago, Lorentz Jr said:

By "using entanglement" I meant using entangled particles to send an instantaneous signal, as the OP had asked about (or, more speculatively, possibly using whatever process underlies entanglement sometime in the future, if such a process exists and we can learn how to use it).

Entanglement doesn't imply or even suggest the possibility of ever sending a signal faster than light. It is consistent with relativity in that sending such a signal seems theoretically impossible.

You can interpret entanglement in such a way that some signal is sent faster than light, but you're basically adding your own "magic," something made up that hasn't been or maybe can't be experimentally observed. Magic could be something reasonable, or not, it's made up. Then if you ask, "Is magic forbidden by relativity?", the answer is probably no. Relativity has nothing to say about magic. A faster-than-light signal could break causality, which along with relativity can lead to paradoxes, so I suppose faster-than-light communication is forbidden by consistent causality plus relativity.

Besides, special relativity doesn't forbid faster-than-light particles, it forbids accelerating particles from slower than light to faster than light. We haven't seen faster particles and probably shouldn't expect them to exist. It's other parts of reality as we know it that forbid them or using them for communication.

 

Suppose you have a pair of sealed boxes each with a coin in it, and they have the property that the first time a coin is looked at, whether it's heads or tails, it's 100% certain that the first time the other coin is looked at, it will be the opposite. An equivalent device should be possible with entanglement. Say you have as many of them as you want. How would you use it to send a message from one coin holder to the far distant other, say a short message like 0 or 1 decided independently by someone else? Both coin holders can agree to a strategy beforehand. Anything anyone does to examine whether a coin is currently heads or tails counts as an observation.

If you can find a way to send a message, it's certain that this is a bad analogy for entanglement, and not that entanglement allows sending messages.

This is just an analogy, but there should be no way to force a coin to be either heads or tails without first observing what it currently is, and no way to know what's happened to the other coin, including whether it's been looked at. The weirdness here, if such a device existed, would be that you could shake both boxes, then open them to see that they're opposite, or you could shake both boxes, assume that they'd be opposite if you looked at them, and then purposefully flip one of them over, then look at them and see that they're only now opposite. This is an analogy only, and the analogy is that if you have 2 entangled particles, and you do different things to them but maintain their entanglement, they'll still maintain their entangled properties. In reality, excess manipulation will probably break the entanglement.

It's mysterious and unintuitive, but not magic.

Edited November 19, 2022 by md65536

[Lorentz Jr]

5 hours ago, md65536 said:

Entanglement doesn't imply or even suggest the possibility of ever sending a signal faster than light.

Not directly, no. But entanglement suggests the possible occurrence of FTL communication within coherent systems, and that suggests at least the conceivability of harnessing such a process in some other way.

Quote

You can interpret entanglement in such a way that some signal is sent faster than light, but you're basically adding your own "magic," something made up that hasn't been or maybe can't be experimentally observed.

Speculation isn't the same thing as magic. Lots of theoretical research introduces new concepts. An example of magic would be the relativistic explanation for time dilation in the twins paradox (or at least the only explanation I've ever seen from mainstream sources), which is attributed to the "geometry" of Minkowski space. A space with a complex metric isn't real geometry, so the idea that the physical explanation for time dilation is the spaceship's "shorter path through spacetime" is magical thinking.

 

Edited November 19, 2022 by Lorentz Jr

[md65536]

9 hours ago, Lorentz Jr said:

Not directly, no. But entanglement suggests the possible occurrence of FTL communication within coherent systems, and that suggests at least the conceivability of harnessing such a process in some other way.

Speculation isn't the same thing as magic. Lots of theoretical research introduces new concepts. An example of magic would be the relativistic explanation for time dilation in the twins paradox

"Magic" wasn't the right word for me to use, especially since we're taking it to mean opposite things. Yes, entanglement gives some the idea of FTL communication, but when you look at the details of what's actually being measured, there's nothing there to actually do it. Like a trick illusion, where you get the impression of something extra happening, but if you look closely you see it didn't. The idea can still remain, because it's based on nothing real and can continue as such regardless of real measurements. Real measurements of entanglement show correlation (or at least statistical correlation), but not necessarily communication. The geometric explanation of the twin paradox can be measured using real measurements, so I disagree that it's magical.

There are no quantum effects that have suggested any future experiment in which we would expect to see FTL communications. Speculatively, it's possible that some future experiment does show that it's possible. That speculation is effectively that there's something new that we haven't yet discovered that in some way goes against the observations and understanding we have so far.

 

[geordief]

2 hours ago, md65536 said:

Real measurements of entanglement show correlation (or at least statistical correlation

Is this true ?Have there only been statistical observations and never a one to one observation?

 

(I only ask to fill in this gap in my knowledge  and not to buttress any pov I might have....)

 

 

Edited November 19, 2022 by geordief

[Lorentz Jr]

4 hours ago, md65536 said:

when you look at the details of what's actually being measured, there's nothing there to actually do it. 

Well, I don't know. I have my own intuitive guesses about what entanglement might be, but I can't prove them. Along the lines of what you were saying, Sabine Hossenfelder has a youtube video about the delayed-choice quantum eraser, which is a version of the double-slit experiment:

 

As for relativity, you need to distinguish between the Lorentz transformations and how they're interpreted. You can't measure an interpretation.

 

1 hour ago, geordief said:

Have there only been statistical observations and never a one to one observation?

Statistical correlations compiled from individual observations. They slow down the flow rates until they can observe one particle at a time, and they have to synchronize their clocks to make sure they're not mixing up particles from different pairs. For entangled electrons, the spin correlation is -1 when the two measurements are along the same axis and 0 when they're perpendicular to each other. To test Bell's inequality, they do funky things like comparing spin measurements along axes that are diagonal to each other.

Edited November 19, 2022 by Lorentz Jr

[geordief]

1 hour ago, Lorentz Jr said:

 

 

Statistical correlations compiled from individual observations. They slow down the flow rates until they can observe one particle at a time, and they have to synchronize their clocks to make sure they're not mixing up particles from different pairs. For entangled electrons, the spin correlation is -1 when the two measurements are along the same axis and 0 when they're perpendicular to each other. To test Bell's inequality, they do funky things like comparing spin measurements along axes that are diagonal to each other.

Are the statistical correlations  what result when the individual  observations are fed into the Bell's inequality equations?

And do the individual  observations give a 100% accurate as predicted  outcome? ie each matched pair of entangled particles exhibits inverse properties for  ,for example spin?

 

(So I quite wrong in my assumption in my previous post?)

[MigL]

I remember watching the PBS Space-time video about the Quantum Eraser experiment, and not being particularly thrilled about the conclusions drawn in that video.
It would have pleased Bangstrom, I'm sure, because it suggested non-locality lead to the causality violations.

Glad to know Sabine and Sean Carroll are not thrilled with it either.

Edited November 20, 2022 by MigL

[Markus Hanke]

21 hours ago, Lorentz Jr said:

A space with a complex metric isn't real geometry

Please define what you mean by “real geometry”?

Also, the components of the metric tensor in Minkowski spacetime are real-valued, so I’m not sure what you mean by “complex metric”.

Edited November 20, 2022 by Markus Hanke

[Lorentz Jr]

4 hours ago, Markus Hanke said:

Please define what you mean by “real geometry”?

A geometry with no negative terms in the metric (and only real-valued coordinates).

I started a new thread for the topic. Thanks for asking. 🙂

Edited November 20, 2022 by Lorentz Jr

[Markus Hanke]

18 minutes ago, Lorentz Jr said:

A geometry with no negative terms in the metric

Such a metric would be isomorphic to the Euclidean one, and thus cannot give rise to Lorentz transformations, an invariant speed of light, or any other relativistic phenomenology. It’s precisely that - time and space parts of the metric having opposite signs - that yields relativity. Note that the choice of which part has which sign is arbitrary, so long as they are opposite.

[studiot]

 

1 hour ago, Markus Hanke said:

Such a metric would be isomorphic to the Euclidean one, and thus cannot give rise to Lorentz transformations, an invariant speed of light, or any other relativistic phenomenology. It’s precisely that - time and space parts of the metric having opposite signs - that yields relativity. Note that the choice of which part has which sign is arbitrary, so long as they are opposite.

Actually no.

If we use τ = ict then we get an all positive metric.

It is the squares of the space and time coordinate axes that have to be of opposite signs, not their first degrees.

Edited November 20, 2022 by studiot

[Markus Hanke]

2 hours ago, studiot said:

 

Actually no.

If we use τ = ict then we get an all positive metric.

It is the squares of the space and time coordinate axes that have to be of opposite signs, not their first degrees.

Sorry, yes. That is what I actually had in mind - I’m not used to the “ict” convention, which I haven’t seen used all too often in more modern texts.

Thanks for correcting +1

[studiot]

4 hours ago, Markus Hanke said:

Sorry, yes. That is what I actually had in mind - I’m not used to the “ict” convention, which I haven’t seen used all too often in more modern texts.

Thanks for correcting +1

Glad to help and I'm sure you have returned the favour for my bo-bos  more times than I have for yours.

We all make them.

[md65536]

21 hours ago, geordief said:

Is this true ?Have there only been statistical observations and never a one to one observation?

As far as I know (which is not much and hopefully someone else can explain or correct me), whether an experiment is measuring the distribution of many particles or a single entangled pair doesn't matter much because the results are consistent. However, even with a single observation, I think there is always an inherent randomness to them (at least where probability wave functions are involved), which makes drawing a conclusion from it probabilistic. A single photon doesn't show a diffraction pattern in a double-slit experiment, it just follows the probability distribution of the pattern.

For example say you have an experiment to see if some action maintains the entanglement of a pair of particles, or breaks it. Suppose a measured event is expected to happen 70% of the time for entangled particles, and 50% of the time for random particles. If you observe a single pair and the event happens, were they entangled, or was it random chance? If the event doesn't happen, were they not entangled, or a random entangled outlier?

 

My under-educated impression is, anything you do to make a result 100% certain ("collapsed wave function") removes the interesting effects you only see with the interaction of probability wave functions.