Spooky action at a distance

[tomBitonti]

Physics just took a spooky turn, and just in time for Halloween:

"Quantum ‘spookiness’ passes toughest test yet"

http://www.nature.com/news/quantum-spookiness-passes-toughest-test-yet-1.18255

"Sorry, Einstein. Quantum Study Suggests ‘Spooky Action’ Is Real."

http://www.nytimes.com/2015/10/22/s...t-said-to-prove-spooky-interactions.html?_r=0

And because I couldn't resist:

https://www.youtube.com/watch?v=eqBR8knRM2w

Thx!
TomB

 

[freyar]

One thing that the NYT article gets wrong is that these measurements say quantum mechanics isn't "local," that there is "action" at a distance. Quantum mechanics obeys special relativity --- there is no communication faster than light even in these weird situations. What these experiments show is that quantum mechanics isn't "real" --- there is no meaningful way to assign values to properties of quantum systems when they aren't being observed.

 

[tomBitonti]

One thing that the NYT article gets wrong is that these measurements say quantum mechanics isn't "local," that there is "action" at a distance. Quantum mechanics obeys special relativity --- there is no communication faster than light even in these weird situations. What these experiments show is that quantum mechanics isn't "real" --- there is no meaningful way to assign values to properties of quantum systems when they aren't being observed.

I was wondering about that. The articles seem to present an idea of instantaneous action, which I didn't think was the case.

Here are some presentations that I found which provide a little more detail, but they seem to make the same implications. They do add some nice to have detail on the nature of the Bell test (but really just a beginning of an explanation):

http://hansonlab.tudelft.nl/loophole-free-bell-test/

They are a little too self congratulatory for my tastes, especially before replication.

Thx!
TomB

 

[freyar]

It's a common misconception/mis-explanation.

 

[Scott DeWar]

I was wondering about that. The articles seem to present an idea of instantaneous action, which I didn't think was the case.

Here are some presentations that I found which provide a little more detail, but they seem to make the same implications. They do add some nice to have detail on the nature of the Bell test (but really just a beginning of an explanation):

http://hansonlab.tudelft.nl/loophole-free-bell-test/

They are a little too self congratulatory for my tastes, especially before replication.

Thx!
TomB

It's a common misconception/mis-explanation.

So, am I to understand that if spooky physics is happening, it is still happening at the speed of light, or "C"? not simultaneous?

 

[Nagol]

So, am I to understand that if spooky physics is happening, it is still happening at the speed of light, or "C"? not simultaneous?

I believe it is more that no information is transferred through discovering the actual state of a previously entangled particle.

*spurious simplified explanation removed*

 

[freyar]

So, am I to understand that if spooky physics is happening, it is still happening at the speed of light, or "C"? not simultaneous?

I believe it is more that no information is transferred through discovering the actual state of a previously entangled particle.

Nagol is partly right --- two people at the different locations can't communicate using this kind of experiment, at least not without sending other information using normal (ie, slower than light speed) means. So there is no information transfer at all in this experiment, and there is certainly none faster than light.

But it seems like there is information transfer because there are correlations in measurements made that could not influence each other at less than light speed. Specifically, if the electron at location A "points up," the electron at B will always "point down." Or if A "points left," B will "point right." And that's true even if B couldn't possibly know the result at A if the correlation were due to information transfer at less than the speed of light. However, the weirdness of quantum mechanics isn't due to some kind of FTL semi-information transfer. The weirdness is in the way the state of the two electrons is set up in the first place (and the fact that it stays weird). You see, what we want to say is that the results of the experiment mean that either (1) the electrons have to know which way they "point" in advance or (2) there is FTL information transfer when the first electron is measured. Neither is true. But the electrons do know in advance that they always "point" oppositely (really, the math is a bit more specific), and any other statement about how they "point" is nonsensical until the measurement is made.

Incidentally, I kept putting "point" in quotes because I really mean to talk about electron spin, but that's a little esoteric. In a simplified sense, though, every electron's spin points in some direction (when it is measured).

 

[Umbran]

I believe it is more that no information is transferred through discovering the actual state of a previously entangled particle.

There's a problem with that statement. It assumes that the particle was in a definite state, and we just didn't know it. Instead, quantum mechanics says it isn't in a definite state until it is observed. At that time the state of the entire system (which, for entangled particles, covers a great deal of distance) resolves into one state or another.

The part of it that runs counter to our normal intuition is how the "far" portion of the system knows that the "near" portion has been observed. One would normally think that the near portion would have to communicate with the far portion in order for that far portion to know what the result of the measurement had been.

 

[freyar]

There's a problem with that statement. It assumes that the particle was in a definite state, and we just didn't know it. Instead, quantum mechanics says it isn't in a definite state until it is observed. At that time the state of the entire system (which, for entangled particles, covers a great deal of distance) resolves into one state or another.

A little more precisely, the entire system (ie, both electrons in this case), is in a definite state in quantum terms, but that state does not correspond to a definite value of any measurement for the individual electrons.

 

[Nagol]

There's a problem with that statement. It assumes that the particle was in a definite state, and we just didn't know it. Instead, quantum mechanics says it isn't in a definite state until it is observed. At that time the state of the entire system (which, for entangled particles, covers a great deal of distance) resolves into one state or another.

The part of it that runs counter to our normal intuition is how the "far" portion of the system knows that the "near" portion has been observed. One would normally think that the near portion would have to communicate with the far portion in order for that far portion to know what the result of the measurement had been.

As I envision, entangled particles become a system. We can know the internal properties of the system "the particles will assume opposite spin" -- assuming no interference to destabilise it -- but we can't predict external specifics of a part of the system "this particle will spin up" until we measure at least one part. Once we have a measurement, we can use it and the expected properties of the system to predict how other parts of the system behaved.

The only part that "feels weird" to me is Bell's Theorem. I would be more at ease if we could say "there are hidden variables that underlie the system, but we can't get to them". I guess we're just getting too close to the underlying limits of the universe simulation...