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Quantum entanglement shows that reality can't be local

arstechnica.com

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Re: Quantum entanglement shows that reality can't be local

#21

Post by IvoDankolov »

Osmium wrote: post #9
fixermark wrote: post #4

One thing I've never understood about interpretation of quantum entanglement experiments: Based on what I've learned of these experiments, it seems to me that the least mind-bending interpretation is that the entanglement event results in two particles that have some complementary property k (i.e. one particle has k and the other has ~k) and which one of the two, k or ~k, is had by one of the particles is unknowable…

"However, both particles have the property from their inception, and so no faster-than-light or non-local interpretation should be needed." This is incorrect, both particles have a superposition of k and ~k (to use your terminology). It is not the case that when the wavefunction collapses, we just suddenly find out the "internal state" of the particle. This "internal state" simply does not exist until the wavefunctio…

But when you "collapse the wavefunction" and "create" the internal state of the particle, do you also create the internal state of the other one that is entangled to it? Do you create it instantaneously?

You see, the problem is not whether you can transfer information in human readable form (though if you could that would certainly be a huge problem with relativity!), but whether any effect that propagates faster than the speed of light exists.

You'll have a hard time explaining that in the frame of wavefunction collapse, I think.

Re: Quantum entanglement shows that reality can't be local

#22

Post by spuz »

Osmium wrote: post #9
fixermark wrote: post #4

One thing I've never understood about interpretation of quantum entanglement experiments: Based on what I've learned of these experiments, it seems to me that the least mind-bending interpretation is that the entanglement event results in two particles that have some complementary property k (i.e. one particle has k and the other has ~k) and which one of the two, k or ~k, is had by one of the particles is unknowable…

"However, both particles have the property from their inception, and so no faster-than-light or non-local interpretation should be needed." This is incorrect, both particles have a superposition of k and ~k (to use your terminology). It is not the case that when the wavefunction collapses, we just suddenly find out the "internal state" of the particle. This "internal state" simply does not exist until the wavefunctio…

> both particles have a superposition of k and ~k (to use your terminology). ... This "internal state" simply does not exist until the wavefunction collapse has occurred.

What would the implications be if particles did have an internal state?

Re: Quantum entanglement shows that reality can't be local

#24

Post by MBlume »

ecliptic wrote: post #20

If you were able to construct a rigid beam 25 million miles long wouldn't you be able to transmit data (push a button) on the other end faster than the speed of light?

Nope. Pushing on the end of the beam sends a pressure wave through the beam. The button gets pushed when the wave reaches the other end. Wave travels significantly slower than light.

Re: Quantum entanglement shows that reality can't be local

#25

Post by nessus42 »

ecliptic wrote: post #20

If you were able to construct a rigid beam 25 million miles long wouldn't you be able to transmit data (push a button) on the other end faster than the speed of light?

Relativity says that you can't construct a rigid beam 25 million miles long.

Re: Quantum entanglement shows that reality can't be local

#27

Post by MBlume »

nessus42 wrote: post #23

This article completely ignored the Many Worlds Interpretation, which preserves all of realism, locality, and Relativity.

Yeah. It shouldn't be that surprising that when you arbitrarily assume that part of the wavefunction magically disappears sometimes, you get weird results like non-locality.

Re: Quantum entanglement shows that reality can't be local

#28

Post by Osmium »

iliis wrote: post #15
Osmium wrote: post #9

Earlier quoted context omitted.

"However, both particles have the property from their inception, and so no faster-than-light or non-local interpretation should be needed." This is incorrect, both particles have a superposition of k and ~k (to use your terminology). It is not the case that when the wavefunction collapses, we just suddenly find out the "internal state" of the particle. This "internal state" simply does not exist until the wavefunctio…

Even with such a preshared rule book you wouldn't get any FTL communication. You could crate a pair of random number generators this way which will always give the same result. Certainly useful for cryptographic purposes but sadly not direct communication.

Agreed; that's what I was trying to say. Perhaps it's disingenuous to frame the problem in this way (that is, talking about rule books and the like), but I was just trying to make it more relatable to normal human experience.

Re: Quantum entanglement shows that reality can't be local

#29

Post by hasenj »

fixermark wrote: post #4

One thing I've never understood about interpretation of quantum entanglement experiments: Based on what I've learned of these experiments, it seems to me that the least mind-bending interpretation is that the entanglement event results in two particles that have some complementary property k (i.e. one particle has k and the other has ~k) and which one of the two, k or ~k, is had by one of the particles is unknowable…

I agree with you. And further more, wouldn't entanglement itself be some sort of evidence that the particle does have an internal state even before being observed?

For instance, I could phrase things like this:

- Let particles A and B get into an entangled state

- Measure the state of particle A, see that it has property k.

- Predict that B has property ~k even though it's not being measured yet.

- Measure B. If B has property ~k, then we've proven that B had an internal state before we performed the measurement.

From all the "popular" description of "quantum entanglement", I don't see anything in it that's significantly different from things like, say, the preservation of momentum in Newtonian physics.

Of course, I must be missing something, but I don't know what is that thing yet.

Re: Quantum entanglement shows that reality can't be local

#30

Post by MBlume »

nessus42 wrote: post #25
ecliptic wrote: post #20

If you were able to construct a rigid beam 25 million miles long wouldn't you be able to transmit data (push a button) on the other end faster than the speed of light?

Relativity says that you can't construct a rigid beam 25 million miles long.

I think that's going a little too far. If you can construct a "rigid beam" five feet long, I see no way that relativity countermands a "rigid beam" 25 million miles long. It's just that "rigid" doesn't mean what grandparent thinks it means -- info still travels through the beam via pressure waves.
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