91–100 of 172 posts
http://lesswrong.com/lw/r5/the_quantum_physics_sequence/
It's kind of weird and has some asides about consciousness and what not but other than that, it gives you a really good mindset for thinking about the subject.
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…
Nobody seems to like my theory that the programmers of the simulation we're all living in were deferring procedurally generating that level of detail until it was necessary because we'd actually examined it closely. They're probably still cursing our Hubble telescope, not to mention computers with their decreasing semiconductor scales. This comment probably just triggered their simulation-awareness detector. :-) Actu…
http://arxiv.org/abs/1110.3795
[pdf] http://arxiv.org/pdf/1110.3795v1
So let's clear up some misconceptions: First, this is not a problem specific to Copenhagen or any other interpretation of QM. Second, it is not just the EPR paradox. Third, it is not the first time someone has proposed a system utilizing quantum entanglement for superluminal communication; that title goes to Karl Popper:
http://en.wikipedia.org/wiki/Poppers_experiment
Popper's experiment was a very clever way to get around the no-communication theorem. It was eventually performed, but no FLT communication could be observed [some suggest we need to keep looking]. I presume that this new paper is another clever way to avoid the NCT, but I don't have time to read it at the moment.
Earlier quoted context omitted.
Nobody seems to like my theory that the programmers of the simulation we're all living in were deferring procedurally generating that level of detail until it was necessary because we'd actually examined it closely. They're probably still cursing our Hubble telescope, not to mention computers with their decreasing semiconductor scales. This comment probably just triggered their simulation-awareness detector. :-) Actu…
Your theory reminds me of Fassbinder's 1973 film Welt am Draht ( World on a Wire ). The technical director of a simulated world project slowly realizes he lives within a larger simulation. https://en.wikipedia.org/wiki/Welt_am_Draht
This article completely ignored the Many Worlds Interpretation, which preserves all of realism, locality, and Relativity.
Can you explain how MWI is local? In the period of time before the observer is 'entangled' into the same system as the observed particles, the different possibilities can interfere with each other. If this can happen even if the entangled particles are separated by a lot of space, surely that is the same as nonlocality. Maybe my confusion is that I'm not sure a which point the universe splits. Suppose I entangle two…
Two particles are entangled and separated by a vast distance.
At some point, I conduct a measurement on the first particle, causing me to split into two different versions of myself that have measured two different states. Now, the effect of that measurement spreads outwards from the site of the measurement, so I may affect other things based on the measurement, etc.
My problem is that if a measurement is done on the other particle, long before any message from me could possibly have got there, then that measurement and the effects it has on its local environment and the effects they have are all also dependent on my measurement.
I imagine this as a wave of universe splitting spreading out from the site of my measurement and the entangled particle despite the separation.
Now, perhaps this is a nontechnical use of the word nonlocal, but I'd describe that as a nonlocal phenomenon.
This is for me the most interesting part of the whole teleportation / entanglement research. When these papers started coming out we debated the notion of 'faster than light' communication. The counter argument was that you had to move the particles apart and that was constrained by the speed of light. Then the question of "when" the state was resolved was pondered. There were two thought experiments proposed at this…
The most interesting question to me is - what happens when one of the entangled particles get annihilated. If the other one does too, instantly, then we can use that to communicate faster than light.
You may be familiar with the Schrodinger equation (HΨ = ih' dΨ/dt) or the more accurate time-dependent Dirac equation. In each of these equations is a function called the wavefunction (denoted with Ψ). This function represents the "quantum state" of your system -- in other words, all the information that exists within a system. Ψ evolves deterministically in time. You can apply an operation to this function, and when you do, you get the original function back multiplied by some value. There are different operators, each corresponding to an "observable" (the thing you measure in the lab). For example, you can measure momentum, position, energy, spin etc... and each of these observables has a different corresponding mathematical operation that you perform on Ψ to get XΨ, where X is the mean value of the observable.
Now in QM textbooks, you'll frequently see Ψ written as Ψ(r, t), where r is a position vector and t is time. r denotes the position of whatever particle constitutes your system. So what if you have a two particle system like hydrogen (proton and electron) or positronium (positron and electron)? Well, a QM textbook will write the state of your quantum system as Ψ1 * Ψ2 and completely gloss over the fact that this approximation does not apply in all situations. It is physically inaccurate to say that Ψ of two particles is two individual Ψ's multiplied together. For some systems, it is a good approximation and makes things easy to calculate, but in reality, there is really only one wavefunction Ψ and it is a function of all the particles in the universe.
So now you can see where entanglement comes in. If Ψ is a wavefunction of all extant particles, then surely there will be correlations between every measurement of Ψ that you take! Now most of the time, you can't find correlations -- too many particles are affecting too many other particles (decoherence). But if you prepare two of them together and keep outside particles from interfering with them, then you can observe the correlations between two particles no matter what the distance!
So now for the whole "information transfer" business. I said earlier that applying an operator to Ψ gives you the value of an observable -- what you measure. The weird thing though is that what you measure isn't always exactly this value. Instead, the mean value of many measurements will be this value. You can also compute the standard deviation of these measurements using Ψ, but that's about it. Nobody knows where the random "noise" in measurements comes from. So far, it seems as though our universe just has some randomness inherent to it (and we're quickly ruling out all remaining superdeterministic theories; Gerard t'Hooft seems to be a hold-out: http://physics.stackexchange.com/questions/34217/why-do-peop...)
So you can't control or predict the individual measurements to as much precision as you'd like. Sucks, huh?
Anyway, you can plot and analyze this data, and what you'll notice for two entangled particles separated by thousands of miles or more is that there are statistical correlations between the two sets of data (again, data you can't control -- if you can't control it, you can't send information with it).
Obviously, you need both sets of data to notice that there are correlations.
This article completely ignored the Many Worlds Interpretation, which preserves all of realism, locality, and Relativity.
Can you explain how MWI is local? In the period of time before the observer is 'entangled' into the same system as the observed particles, the different possibilities can interfere with each other. If this can happen even if the entangled particles are separated by a lot of space, surely that is the same as nonlocality. Maybe my confusion is that I'm not sure a which point the universe splits. Suppose I entangle two…
It isn't that the universe has split, it's that one section of the universe's wavefunction has split, or more exactly become a bimodal distribution. At both locations there are bunches of the wavefunction corresponding to both possible observations - but both locations are entangled since the two particles that touched this off were. That means that when you observe the two experiments you don't "split" into four, but only into two since they are already entangled and you only get entangled with this complex once. The information of "What's entangled with what" spread at strictly sub-light speeds, and the information of "Did it pass through the polarizing filter or not" also traveled at sub-light speeds.
This reminds me of the Ansible, a communication device allowing instant or near instant faster-than-light communication. It is seen in many science fiction works and often justified as quantum entanglement in practice. https://en.wikipedia.org/wiki/Ansible
I didn't realize that Ursula Le Guin coined that term. My first recollection of it was from Orson Scott Card and later, Dan Simmons. In any event, entanglement certainly doesn't look like it will lead to an ansible yet.