Quantum entanglement shows that reality can't be local • Hacker News Board

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

#71

Post by Osmium » Tue, Oct 30, 2012, 8:29 PM UTC

hasenj wrote: post #64

Osmium wrote: post #36

Earlier quoted context omitted.

"If B has property ~k, then we've proven that B had an internal state before we performed the measurement." This part is the flaw in the logic. That doesn't prove that B has an internal state. All it proves is that, in some sense, B's state is related to A (assuming you repeat the experiment until you reach statistical significance). Entanglement is nothing more than saying one particle is connected, in some sense, t…

Why not choose the mundane and least astonishing explanation? If an object A is moving (with a known momentum) and hits a stationary object B, we can measure the momentum of either A or B and instantly know the momentum of the other object without having to measure it. The two objects are somehow "connected"; their state (momentum) is "entangled". Why is quantum entanglement different?

Because that momentum transfer is mediated by a fundamental force, typically the electromagnetic force. Entanglement is a property of the particle, and is not mediated by a force: the collapse of the wavefunction of one particle doesn't /cause/ the collapse of the other, rather they both collapse simultaneously.

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

#72

Post by numbsafari » Tue, Oct 30, 2012, 8:30 PM UTC

Anderkent wrote: post #13

Osmium wrote: post #7

Earlier quoted context omitted.

"Hidden variables" have been proven to not be a satisfactory explanation for quantum mechanical effects for some time now. http://en.wikipedia.org/wiki/Bell%27s_theorem Though, I should add, what makes this paper interesting is that they try and find loophole around Bell's theorem. This would be a big deal if true.

Local hidden variables. Bell's theorem does not address non-local variables.

So Satan was the angel that made reality work by using global variables. He was cast out by god for violating the coding standard. All the evil you see in the world is the result of errors caused by the use of global variables and a lack of sufficient testing prior to release that was the result of an unreasonable schedule that was pulled out of God's ass simply because he wanted to prove he could make the angels ship something in six days.

We need an update to Time Bandits.

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

#73

Post by btilly » Tue, Oct 30, 2012, 8:32 PM UTC

Osmium wrote: post #38

MBlume wrote: post #27

Earlier quoted context omitted.

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.

Could you expand on this a little more? I'm not quite sure I follow.

The many world's interpretation is based on the assumption that both the observed system and the observer is modeled by a wavefunction. In that case observation is entanglement, which seems weird to us, but which makes perfect logical sense.

Other interpretations of quantum mechanics start with the assumption that the world is fundamentally like our naive experience leads us to think of it as. Therefore when we observe something, we couldn't really be thrown into a superposition of states, each of which observed a different thing and which cannot meaningfully interact due to quantum mechanical principles. If we can't be thrown into such a superposition, then there must be some sort of underlying reality, or quantum collapse, or other weirdness that is not explained by QM.

All of the weirdness of interpretations other than many worlds can be understood as the conflict between how they would like to understand the world (there is a reality that happened), and how quantum mechanics described things.

All of the weirdness of the many worlds interpretation can be understood as, "We can't perceive the process of quantum superposition, so it seems really, really weird to us."

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

#74

Post by btilly » Tue, Oct 30, 2012, 8:33 PM UTC

powertower wrote: post #68

I'm starting to believe that we confuse the mathematics of quantum mechanics with being the actual underlining physical phenomena , to the point where we start to believe that "wave function collapse" are real, rather than just a way of looking at something via probabilities; or being the models, or abstractions, or the artifacts of the maths involved.

Take that one step farther and you'll arrive at the conclusion that if we take QM seriously, then there is never a collapse, and the many worlds interpretation is a logical consequence.

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

#75

Post by joe_the_user » Tue, Oct 30, 2012, 8:36 PM UTC

Ok, as far as I can tell, this all just a rehash of EPR paradox and the weirdness of the Copenhagen interpretation of QM. The many worlds interpretation resolves everything with full locality. http://en.wikipedia.org/wiki/Many-worlds_interpretation

Just consider, if I take a black marble and a white in hand, shake them up and put them in two boxes so I don't know which marble is in which box and put the two boxes on two sides of the world. Then, when I open one box, I instantly learn the state of the marble in the other. The information is "transmitted" to me "faster than the speed of light" but all because the actual switch event happened in the past. Now, as far as I can, QM entanglement is pretty much the same thing as these boxes. The only weird thing is that the standard interpretation (not the standard theory since it is not necessary for any meaningful measurement), the standard interpretation is that in QM, the equivalent of our marble switch happens when the final measurement happens.

There's nothing in any of this research that involves any concrete evidence whatsoever that faster-than-light information transmittal happens, (feel free to counter-references that), but as far as I've read, all the "transmittal" is "transmittal" the sense of above.

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

#76

Post by lnanek2 » Tue, Oct 30, 2012, 8:40 PM UTC

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…

In the usual experiment used, if the two electron spin detectors for the two entagled particles are tilted the same, they'll get opposite results always. But if you tilt them differently, however, you no longer get results that are exactly opposite each other all the time. Therefore the electrons are in a superposition until they hit the detectors. It isn't decided yet what they will be.

Keep in mind we're working with quantized values. Spin is always completely up or down, no matter what angle you measure it from. Measuring it at that angle locks it down, but tilting another detector in the chain after means you go back to a non-linear probability calculated by quantum mechanics (cosine of the angle in this case) to if it is up or down again at the new tilt and locks it down to that new tilt. There isn't any pre-determined value the electrons can be set to beforehand that matches the observed number that deflect in the detectors up or down at all measurement angles.

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

#77

Post by btilly » Tue, Oct 30, 2012, 8:41 PM UTC

cs702 wrote: post #44

I've always found classical Newtonian physics, the Special Theory of Relativity, and (to a lesser extent) the General Theory of Relativity to be understandable at an intuitive level, but quantum phenomena just baffles me, even when I think I "understand" it. PS. IvoDankolov: I find it difficult or impossible to think intuitively about quantum phenomena.

Let me make it worse.

Ever heard of chaotic systems? Any dynamic system that shows extreme sensitivity to initial conditions is chaotic. For instance smoke curling from a cigarette, planetary orbits over time, weather, water dripping from a tap - all of these show extreme sensitivity to initial conditions.

Here is the fun thing. In quantum mechanics everything evolves linearly. Therefore extreme sensitivity to initial conditions is entirely impossible. We only think that we observe that. Yet the world is full of cases where we can demonstrate such sensitivity!

See http://www.iqc.ca/publications/tutorials/chaos.pdf for some of the attempts to reconcile observed classical facts with what we think are true quantum truths.

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

#78

Post by kybernetikos » Tue, Oct 30, 2012, 8:45 PM UTC

joe_the_user wrote: post #75

Ok, as far as I can tell, this all just a rehash of EPR paradox and the weirdness of the Copenhagen interpretation of QM. The many worlds interpretation resolves everything with full locality. http://en.wikipedia.org/wiki/Many-worlds_interpretation Just consider, if I take a black marble and a white in hand, shake them up and put them in two boxes so I don't know which marble is in which box and put the two boxes on…

Could you explain why your example isn't just a hidden variable explanation, which as we know from measurements of Bell's Inequality ( http://en.wikipedia.org/wiki/Bell%27s_theorem ), cannot result in a theory compatible with both locality and the predictions of quantum mechanics.

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

#79

Post by mtrimpe » Tue, Oct 30, 2012, 8:46 PM UTC

joe_the_user wrote: post #75

Ok, as far as I can tell, this all just a rehash of EPR paradox and the weirdness of the Copenhagen interpretation of QM. The many worlds interpretation resolves everything with full locality. http://en.wikipedia.org/wiki/Many-worlds_interpretation Just consider, if I take a black marble and a white in hand, shake them up and put them in two boxes so I don't know which marble is in which box and put the two boxes on…

This Google Talk from last year provides an argument and interpretation of this that's fairly understandable with a programmer's mindset:

http://www.youtube.com/watch?v=dEaecUuEqfc&sns=em

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

#80

Post by ZenoArrow » Tue, Oct 30, 2012, 8:48 PM UTC

Usual disclaimers: I am not a scientist and my knowledge of quantum mechanics is very minimal.

However... "Repeated experiments have verified that this works even when the measurements are performed more quickly than light could travel between the sites of measurement"

What interests me at this stage is not 'why' entanglement works, but rather how it can be used. The article indicates that repeated experiments have verified it appears to be a real process, where actions on one particle can influence another particle (seemingly) no matter how far away, so why can't we use it for communication? To use a simple example, if I encode data as movement in the 'sender' particle, and the movement can be monitored in the 'receiver' particle, then you can have a system for sending messages.

Seems to me the need to control the internal state of the particles to communicate may be unnecessary. Perhaps to explore further, can anyone here the types of measurable phenomena that have been seen to be mirrored in entangled particles (the ones you know of, anyway)? Would particle spin be one example? Thanks!