# Physics question

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This came to mind a little while ago and I'm trying to find out if it's theoretically possible or not, but am not getting a clear answer anywhere.

Say you have two entangled particles. One is put into a spaceship on orbit, the other is on Earth. Then, you use a giant laser or some other means to propel the spacecraft in orbit to very close to light speed. At that point, the spacecraft is traveling through time very quickly due to time dilation. From the ship's perspective, it would've traveled much farther through time. Through the entangled particle on Earth, would you be able to use this to 'see' into the future (or interact with the distant future), or is something missing here?

Edited by Clockwork13

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1 hour ago, Clockwork13 said:

Through the entangled particle on Earth, would you be able to use this to 'see' into the future (or interact with the distant future), or is something missing here?

You are missing something.

Entangled particles cannot pass information back and forth. They just happen to both be in the same state at the same time. If you force your particle to be in a specific state it's not quantum anymore, and observing the other particle will return either state (and then set your particle to that state, if I know my quantum particles correctly which I may not).

And I'm pretty sure though not 100% sure that all these interactions occur to the two particles at the same absolute time. IE if your particle is traveling significantly quickly enough to go through time twice as fast as mine, then my observations and changes to my particle will just cause your particle to change states twice as fast.

Edited by 5thHorseman

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10 hours ago, Clockwork13 said:

Say you have two entangled particles. One is put into a spaceship on orbit, the other is on Earth. Then, you use a giant laser or some other means to propel the spacecraft in orbit to very close to light speed. At that point, the spacecraft is traveling through time very quickly due to time dilation. From the ship's perspective, it would've traveled much farther through time. Through the entangled particle on Earth, would you be able to use this to 'see' into the future (or interact with the distant future), or is something missing here?

As @5thHorseman said, you can't use quantum entanglement for communication, because even though the particles "communicate" with each other in a probabilistic sense, they cannot be used to pass information to an observer. However, we don't really know how time dilation (whether from inertial acceleration or gravity) affects quantum entanglement. There's ongoing research to tackle exactly that.

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10 hours ago, 5thHorseman said:

You are missing something.

Entangled particles cannot pass information back and forth. They just happen to both be in the same state at the same time. If you force your particle to be in a specific state it's not quantum anymore, and observing the other particle will return either state (and then set your particle to that state, if I know my quantum particles correctly which I may not).

And I'm pretty sure though not 100% sure that all these interactions occur to the two particles at the same absolute time. IE if your particle is traveling significantly quickly enough to go through time twice as fast as mine, then my observations and changes to my particle will just cause your particle to change states twice as fast.

Forcing untangle them as I understand, if not you could use this to communicate.
Take 100 tangled particle pairs. Send one pair to mars, at one set time you force all 100 to the same spin, at the same time check the spin on mars.
you have now transferred an bit of data.

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11 minutes ago, magnemoe said:

Forcing untangle them as I understand, if not you could use this to communicate.
Take 100 tangled particle pairs. Send one pair to mars, at one set time you force all 100 to the same spin, at the same time check the spin on mars.
you have now transferred an bit of data.

When you force them to the same spin, you break entanglement.

Entangled bits are great for communicating private keys, as you can know what the other guy has and verify that no one else can know(because if it got intercepted en-route, you would not have received it).  But all of the actual communications (outside of the shared secret) still takes place  over conventional channels, including the check-sums to verify which q-bits each party has on-hand.

But you cannot control what message the other person gets, it will just be a random assortments of ones and zeroes that happens to match the assortment of ones and zeroes(possibly inverted, I forget) as what would be gotten if you measured the other set of entangled bits.  You cannot even tell if you were the first to measure, or if they other guy measured first

I believe there is actually a mathematical proof that it is impossible to communicate with quantum entanglement.(I vaguely remember the proof showing that communicating over quantum entanglement is the same as time-travel, so if you can do one, you can do the other)

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If gravitons exist, can they be entangled?

If so, should a graviton from a black hole bring info about its entangled counterpart inside the event horizon?
(Say, if they appeared one by one as a pair in Planck length radial distance from each other).

Edited by kerbiloid

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1 hour ago, kerbiloid said:

If gravitons exist, can they be entangled?

If so, should a graviton from a black hole bring info about its entangled counterpart inside the event horizon?
(Say, if they appeared one by one as a pair in Planck length radial distance from each other).

Yes to the first question. No to the second, as entangled particles cannot be used to transmit information.

Note that if you destroy one of the entangled particles, you collapse the wavefunction.

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26 minutes ago, sevenperforce said:

No to the second, as entangled particles cannot be used to transmit information.

Note that if you destroy one of the entangled particles, you collapse the wavefunction.

But if they are entangled, they do just by being at opposite side of the event horizon.
If we "see" this entangled graviton, we know the another one's state. Let it stay unchanged, no problem.
Aren't we not able to get information from a black hole?

Edited by kerbiloid

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1 hour ago, kerbiloid said:

But if they are entangled, they do just by being at opposite side of the event horizon.
If we "see" this entangled graviton, we know the another one's state. Let it stay unchanged, no problem.
Aren't we not able to get information from a black hole?

You’re not getting information from the black hole; merely the state they were in before entering it. And if they’re still entangled or not.

You have two notes of paper, both with the letter “A” on them. You toss one of them over the event horizon. “The black hole nows contains a note with the letter ‘A’ on it.” Does that mean you funneled information out of the black hole?

Edited by Kerbart

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13 minutes ago, Kerbart said:

Does that mean you funneled information out of the black hole?

I don't know.

As before dropping the note I didn't have information if there is the note inside, after dropping it (if presume it's indestructible) I know it is, so there is 1 bit of information between my two states, and I should presume that I have gotten 1 bit of information relative to my state before the dropping.
Also I should presume that if this note disappeared here, then I got -1 bit of information about its presence here. as now I don't know if it is here, I can't see it.
In both cases it looks like I received +/-1 bit of information.

Edited by kerbiloid

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37 minutes ago, kerbiloid said:

I don't know.

As before dropping the note I didn't have information if there is the note inside, after dropping it (if presume it's indestructible) I know it is, so there is 1 bit of information between my two states, and I should presume that I have gotten 1 bit of information relative to my state before the dropping.
Also I should presume that if this note disappeared here, then I got -1 bit of information about its presence here. as now I don't know if it is here, I can't see it.
In both cases it looks like I received +/-1 bit of information.

Quantum entanglement only produces the "weird spooky action at a distance" effect if you assume wavefunction collapse by the observer. It doesn't cause paradoxes in our ordinary experience.

Consider the following.

You place a quarter into a special machine. The machine has a mechanism which will slice the quarter exactly in half lengthwise, so one disc will be the "heads" disc and one disc will be the "tails" disc, and then drops each half into a separate box. The two boxes are unmarked, and you do not know which box holds which disc. The "slice" is such that the two halves weigh exactly the same, so you cannot do anything to determine which is which.

These boxes are now "entangled". If you open one box and get tails, you know the other box has the heads, and vice versa. This is true regardless of the locations of the boxes. If you put one box in London and one box in New York City and open the one in New York City to see that it is tails, you know instantly that the box in London is heads. You can put one box on Earth and one box in space, one box on Earth and one box on the moon, one box on Mars and one box on Alpha Centauri, and the same relationship will hold true: you can gain information about the distant quarter instantaneously, simply by observing the quarter in the box you have. Similarly, a distant observer can gain information about your quarter instantaneously simply by observing the quarter in her box.

There's nothing spooky here at all. No information is moving faster than the speed of light. It's not a paradox.

What gets weird, however, is when we enter the world of quantum mechanics, where you can have an object in an "uncollapsed" wavefunction: the dead-and-alive cat of the Schrodinger's Cat thought experiment. You can have situations where two particles were produced in the same experiment and both have equal probability of having one value or another. It can be proven both mathematically and by actual experiment that it is not just an issue of uncertainty; both particles actually have both possible values until observed, at which point the wavefunction "collapses" into a state where one particle has one value and the other one has the corresponding one. And thus we have the weird situation where you "collapse" the distant particle instantly by observing the near one, in which it feels like information is moving faster than light. But you still cannot use this to transmit information.

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I like to think of it as, quantum entangled particles have the same random number seed. Observing one tells you what the other is only because they're the same random numbers.

No it's not a perfect analogy but hey it's quantum physics I'm doing my best

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Probably containing one particle in a box on a spaceship and accelerating that box will collapse the wavefunction and break entanglement.

There is no way of knowing when wave functions collapse.If they collapse before being observed, we don't know when.

If we count the observation of the particles as two events.  And the two events are simultaneous in some reference frame.  This does not mean they are simultaneous in all reference frames.  Only the space-time interval between the events is the same in all reference frames.

Edited by farmerben

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27 minutes ago, farmerben said:

Probably containing one particle in a box on a spaceship and accelerating that box will collapse the wavefunction and break entanglement.

There is no way of knowing when wave functions collapse.If they collapse before being observed, we don't know when.

It would not break entanglement. Only opening the box would break entanglement. If you have only one box, you do not know whether the wavefunction has collapsed because you do not know whether the other box has been opened, but if you know that both boxes remain unopened then you know the wavefunction has not collapsed.

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29 minutes ago, sevenperforce said:

t if you know that both boxes remain unopened then you know the wavefunction has not collapsed.

How do you know that?

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4 hours ago, farmerben said:

How do you know that?

Because that is the nature of quantum entanglement under the Copenhagen interpretation of quantum mechanics.

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I.e. it is as correct as the Copenhagen interpretation is.

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17 minutes ago, kerbiloid said:

I.e. it is as correct as the Copenhagen interpretation is.

Precisely.

The "weird action at a distance" behavior commonly associated with entangled particles is solely the result of applying the Copenhagen interpretation of uncollapsed superposed states. If you take the many-worlds hypothesis, for example, you end up "splitting the universe" whenever you open either box.

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3 minutes ago, sevenperforce said:

If you take the many-worlds hypothesis, for example, you end up "splitting the universe" whenever you open either box.

What looks lovely in the many-worlds: the Cat can always stay alive.

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13 minutes ago, kerbiloid said:

What looks lovely in the many-worlds: the Cat can always stay alive.

Seeing how many cats its around I belive its true.

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11 hours ago, sevenperforce said:

if you know that both boxes remain unopened then you know the wavefunction has not collapsed.

I'm not sure that Bohr or Heisenberg ever made quite that strong a claim.  Even if some people do say that, what is their argument?

A weaker claim is that a large set of events or interactions could cause wave function collapse and everything that could be described as observation is within that set.  Accelerating the box for a long spaceflight probably is too, as we have changed the momentum and energy of the particle in a precise way.

Quantum computing deals with decoherence as the biggest problem.  Even in situations which can preserve complex entanglements, they break down more often than not.

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