Earlier quoted context omitted.
So if you check that the gloves are black they are black every time you check (axis 1). And then if you check that they have five fingers, they have five fingers every time(axis 2). So, it sounds exactly like a "gloves in a box" example, right? I'm not trying to be cheeky, I'm just pointing out that the example really does sound analogous, as stated so far.
It depends on how those states interact with each other. Lets say you can't know a gloves fingers and a gloves color at the same time, so checking number of fingers resets the color and checking color resets number of fingers. Then if you check number of fingers many times, you get the same result every time. But if you alternate checking fingers and color, you will get random results every time. Edit: Not that I'm s…
Why quantum entanglement doesn't allow faster-than-light communication (2016)
151–160 of 166 posts
Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)
#152I’ve been working on quantum computing and quantum communication for 15 years now and what I really want people to know is that entanglement is “beyond classical correlation.” Correlation which is not beyond classical is shaking up a shoebox with a pair of gloves in it, and having two people take the gloves far away from each other to then observe what hand they got. They then understand the hand the other has. There…
> Many quantum information theorists don’t even believe the wave function is “real” but just a mathematical tool for making predictions about measurement outcomes You are correct that many say this, but this is a constant source of frustration for me (a physicist who does believe the wave function is the only real thing). These physicists never seem to articulate what then is supposed to actually be “real” (under the…
Bookiping for things that happen so fast and at such a small scale that our current technological tools cannot fully capture data with enough precision and accuracy for us to make an good model of the underlying behaviour.
Imagine you put a spinning ball on top of a frozen lake on a windy day. You are going to observe the ball spin continously towards the same orientation until several gusts of wind make it spin the other way around, and this goes on and on for hours. From the measurements of the wind and current spin of the ball, you can make a model that accurately and precisely predicts the spin of the ball on the almost frictionless frozen lake.
Now imagine your spinning ball is extremely small you can't even see it or any "wind" with any tools that you currently have, but you can still measure its spin to a certain precision. Now imagine this "wind" is so strong and volatile that the tools you have sometimes takes a somewhat accurate physical snapshot of it and sometimes it just misses the gust. You take a look at the somewhat accurate measured spin and it seems to have changed without any reason, but it was just because your tooling is not accurate and precise enough to capture all the quantum gusts of wind that influence the quantum ball, so it looks like the ball is changing its spin randomly, whist in reality, we just can't precisely measure whatever is influencing the ball's spin with our current tooling. The influences are there, it's just that our tooling can't capture them precisely and accurately enough.
To combat that, we continously measure the ball's spin and we are able to figure out a pattern, not a precise one (because again, our tooling is not precise and accurate enough), but a pattern based on probability of the ball being in a specific spin state, we can even combine this with our inaccurate measurements of the quantum wind and further improve the accuracy of the probability. But never to a precise pattern, because our tooling sometimes misses certain wind states that it looks like the ball chagend spin randomly.
If we had tools that precisely and accurately measured the ball's spin and the quantum wind, we would be able to build a precise and accurate model of the spin based on those measurements. But we can't, although, we still want to make science around these inaccurate measurements, and probability based patterns are just enough for the science we want to make.
The wave function is just the result of our lack of precise and accurate measuring tools and measuring methods at this quantum scale. And for now, it's good enough for the science we want to do.
Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)
#153Earlier quoted context omitted.
> I suppose all that is left in the intuition busting, is how the probabilities don't add up as expected? Lets imagine electrons are objects in a program, then the "electron class" has a private field containing a seed value to a pseudo-random number generator (ie deterministic), and the two electrons are initialized with the same seed value. Further imagine that performing a measurement of an electron amounts to tak…
I thought the hidden variable idea was proven not to hold, though? Like, I thought that was the point? That the behavior observed can only be explained using the state of the remote measure as part of the explanation? I have not looked back at the book I read. I definitely remember it had examples that were not paired off. I'm assumingy memory is simply off.
Hidden variables, like my "electron objects", would give a linear relationship.
However what quantum mechanics predicts and what we measure in the lab is a non-linear relationship that for some angles yield stronger correlations. Hence the phrase "violating Bell's inequality".
After Bell people devised other inequalities for other experimental setups which also can be used to rule out local hidden variables. A popular example are the CHSH inequalities[1], which is easier to realize experimentally, and give a stronger disagreement with hidden variables.
I've never seen the particles not paired up, and I don't see how that would work.
The whole point is that according to quantum mechanics, the pair of entangled particles aren't two separate systems, but that they must be treated as having a single state.
Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)
#154Earlier quoted context omitted.
The "speed of light" is actually a somewhat poor common name for the limitation. It should be called the "speed of information." If the sun somehow magically disappeared, we would continue to orbit that empty space for about 8 minutes.
or the speed of causality
Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)
#155This is my two cents: Maybe entanglement is a much more 'immediately physical' phenomenon than 'spooky action at a distance'. Just guessing as a layman here: maybe entangled particles are just physically connected {along some higher dimension / some unknown process}. Spinning together (effectively switching spaces constantly) such that they are always the same state. So the undetermined measurement stems from being u…
So where did all our antimatter go… ?
Yes, this ties into this.
Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)
#156Earlier quoted context omitted.
> In order to refute this Refute what? I'm pointing out that classical (non-quantum) scratch-off lottery tickets can have the property you described. This is only thematically related to the CHSH game, and I'm rather confused as to what you're trying to say. The Wikipedia articles about the CHSH inequality are IMO quite bad. The conclusion of CHSH has approximately nothing to do with measurement angles. Here's what C…
> I'm pointing out that classical (non-quantum) scratch-off lottery tickets can have the property you described. No, if A always scratches the left, and B alternates between left and right, your classical trick of having some tickets with two winners and some with two losers won’t produce the correct win distributions for B’s choices. The CHSH game is an attempt at explaining the experiment. The core of CHSH is a for…
My proposal was intended to be independent of A and B’s strategy. As a fully worked-out example, suppose the tickets are printed like this:
With probability 42.5%: all positions win
With probability 42.5%: all positions lose
With probability 7.5%: Both of A’s options win and both of B’s options lose
With probability 7.5%: Both of A’s options lose and both of B’s options win.
This follows the rules of the game, and it has the following properties. A wins with probability 50% regardless of their strategy, as does B. And A and B get the same outcome 85% of the time.
For the CHSH inequality (following the pretty-bad Wikipedia article), each E term is the probability that A and B both win when they use the indicated strategies, which is 0.425. So S=0.85, which is well within the limit, as it should be since these are extremely boring classical tickets.
Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)
#157Earlier quoted context omitted.
Yeah, I am aware of Bell's theorem. What I am saying is that the hidden variable hypothesis is nonetheless a good mental model as a first approximation to reason about QE, say as a non-professional physicist. People get confused, especially sci-fi authors, adding to the general confusion about anything touching Quantum Physics being almost magical/limitless or unexplainable. This is a lot more pedestrian in practice.
It do not think sci-fi authors are confused, but just willing to live with inaccuracy for the sake of the story and universe building. Its like faster than light travel - you need to find some excuse to make something work. I very much doubt Ursula Le Guin thought we could build an ansible (FTL comms) any more than Larry Niven thinks the Teela Brown gene (heritable luck) is real.
It is a really tough topic to get an intuition for, though.
Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)
#158Is entanglement real or is it just that two things happen to be aligned the same way and measuring them reveals how they always were? Like if I gave two people red balls without telling them what the colour is. One takes it out and sees it is red, the other now instantly has a red ball. But they were always red. So there is no actual interaction between the balls, they were just set up in a pre-defined matching state…
What you are talking about is hidden variable theory, Bells theorem shows that it is likely not the case, so quantum entanglement is likely real. Bells theorem has been tested experimentally so we know the world works as it says, the question is just how we interpret it. https://en.wikipedia.org/wiki/Bell%27s_theorem
Also Superdeterminism might allow for Local Hidden Variables.
Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)
#159Earlier quoted context omitted.
> Many quantum information theorists don’t even believe the wave function is “real” but just a mathematical tool for making predictions about measurement outcomes You are correct that many say this, but this is a constant source of frustration for me (a physicist who does believe the wave function is the only real thing). These physicists never seem to articulate what then is supposed to actually be “real” (under the…
> bookkeeping for __what__? Bookiping for things that happen so fast and at such a small scale that our current technological tools cannot fully capture data with enough precision and accuracy for us to make an good model of the underlying behaviour. Imagine you put a spinning ball on top of a frozen lake on a windy day. You are going to observe the ball spin continously towards the same orientation until several gus…
But even if you could make some baroque version of a model like this (with the position of one ball instantaneously reacting to other far away balls perhaps and some pilot waves) invoking it still wouldn’t answer my question about ontology. Implicit in this description seems to be the existence of a separate non-quantum realm (little balls that spin, jostled by “wind”). What are these balls supposed to be made of? If not atoms (since atoms are stable by virtue of quantum mechanics, which you seek to explain), then why don’t they suffer from ultraviolet catastrophes? Hopefully you see my point.
Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)
#160This is my two cents: Maybe entanglement is a much more 'immediately physical' phenomenon than 'spooky action at a distance'. Just guessing as a layman here: maybe entangled particles are just physically connected {along some higher dimension / some unknown process}. Spinning together (effectively switching spaces constantly) such that they are always the same state. So the undetermined measurement stems from being u…
Did you know, antimatter is just time-reversed matter? So where did all our antimatter go… ? Yes, this ties into this.
https://en.wikipedia.org/wiki/CPT_symmetry
Worse, the symmetries of the Standard Model are pretty complicated, especially when one goes from the local Lorentz or Poincaré symmetries x SU(3) x SU(2) x U(1) to the global continuous symmetries that capture https://en.wikipedia.org/wiki/Custodial_symmetry, (particlularly QCD) flavour symmetry, and scale symmetry. There are some further long-range approximate symmetries too, and those get worse with spacetime curvature. These all may have to be accounted for if one is time-reversing a region of the spacetime-filling fields of the Standard Model.
> So where did all our antimatter go?
Good question. Nobody can really tell you right now. Maybe there are galaxy clusters totally dominated by antimatter, maybe the antimatter is in a different Hubble volume, maybe it all annihilated into the cosmic microwave background and other ultra-low-energy relic fields (e.g. the cosmic (anti-)neutrino background) we haven't detected or discovered yet, maybe into primordial black holes, maybe in an extension of the Standard model to extremely high energies there isn't a matter-antimatter balance in the first place. One can write down an enormous number of different theories, and relax knowing that there is presently no evidence to favour or disfavour it, provided it's compatible with the experimental and astrophysical evidence we have today.
(I do like the idea, building on an idea arising from Wheeler's one-electron universe, that anti-electrons (in this case more than one) are screened within pion condensates ("maybe they're hiding in neutrons", vaguely), because that makes the symmetries even crazier, and particle physicists deserve that).