5 ms·
My understanding: 2 entangled particles are 2 particles whose states are unknown, except that they are linked: e.g. 2 electrons which have opposite spins, or 2
by armchairhacker 4y ago
My understanding:
2 entangled particles are 2 particles whose states are unknown, except that they are linked: e.g. 2 electrons which have opposite spins, or 2 photons which have opposite polarization. So when you measure one particle, you instantly know the state of the other even if it's light-years away (this is not FTL communication as you can't communicate this information FTL).
It's sort of like putting an "up-spin" and "down-spin" electron in a box, having someone shift around the boxes behind your back, putting the boxes far away from each other, and then opening one: before you open the box you have no idea what either box contains, after you open one you know both including the far away one.
Except it's not the same as putting an "up-spin" and "down-spin" electron in a box, because of Bell's Theorem (https://en.wikipedia.org/wiki/Bell%27s_theorem#Theorem https://en.wikipedia.org/wiki/Bell%27s_theorem#Theorem). Electrons' spin is actually determined when you measure them: you can measure up/down, but also left/right or any other 3D direction. And if you measure both electrons at a slightly different angle, their measurements probabilistically correlate in a way which means the electrons never really had any true internal "spin" (hidden variable) until you measured one of them. The fact that measuring one electron changes the others' "spin" faster than light seemingly violates the principle of locality.
The part which confuses me in the article is that, once you measure an entangled particle, they are no longer entangled. So I figure in order for this clock to be feasible you would either need an unbelievable amount of entangled atoms, you'd need to instantaneously re-entangle, or you'd need to use a "standard" atomic clock and only break entanglement after a certain number of ticks, to re-synchronize.
- nomel 4y agoI'm a dummy. Why does this make them "linked"? If I have two legos, always put them in opposite orientations, then walk away with a random one, being careful to not change its orientation, are the two legos "linked"? When I look down at the one in my hand, I will know the other ones orientation. How is the different with entangled particles? Is "entangled" just a way to say "still related because it's undisturbed"?
- drexlspivey 4y agoUsing your analogy, you don’t put the legos in opposite orientation and walk away with one, it’s more like the two legos keep spinning and you walk away with one and you stop it from spinning and instantaneously the other one stops in the opposite direction.
- wruza 4y agoWhat does “instantaneously” mean if we (afaiu) can’t even have “simultaneously” in general?
- drdeca 4y agoAiui, it doesn’t at all matter which one is measured “first”, or if the two measurements are spacelike separated such that which one is first depends on frame of reference. Whenever the two measurements are made, they will be correlated in a certain way. You cannot communicate information from one to the other via how you choose to measure them, but you can in some cases coordinate on how your actions are correlated by choosing how to measure based on some info learned on one side. So, if the direction along which A chooses to measure the spin depends on something A learned after A and B went far away from each-other, this can’t change the probabilities of B getting a result of 0 or 1, but it can change the probabilities of things like “A and B both get 1” or “A gets 1 and B gets 0”, etc. , even though not in a way that changes how likely it is for A to get 1, nor how likely for B to get 1. This could conceivably be useful if uh, how useful it is for both parties to do something vs only one party doing it, changes based on the info, I guess?
- b112 4y agoAll that pops into my head here, is that in this case, the two particles, when twinned, are actually the same particle... simply at different time references. This behaviour makes zero sense to me otherwise. That makes me think that all particles are actually the same particle, and we're only observing them at different time references. The twinning only objectifies that, so as observers, we are viewing them at time references which allow for known state. Yes, this has a gazillion holes in it. edit: to add to this, there is no reason to infer that because things are separated by distance, they are not the same thing. The universe does not have to play nice, to ensure that humanly derived, evolved logic thinks that things make sense from a classical perspective. If all electrons, for example, are the same electron? Just observed at different time references and locations? Then things such as entanglement make more sense. edit2: What I mean by 'the same particle', is that theoretically all matter in the universe was one ball of whatever prior to the big bang. Everything already is one particle, prior to diffusion and differentiation due to cooling. Thus, every electron in the universe was at one point in time the same, single thing. Therefore, they are the same thing. If time does not exist, it means that this electron here, and over there, can be the same electron, for it can spend <unlimited time> here, and then <unlimited time> there, while at the same moment co-spanning the same time reference as we view it. OK, I'll shut up now, because this is gibberish.
- graycat 4y agoFrom all I can tell about what physicists mean, their use of correlation is inappropriate. It appears that their math of correlation is correct for the math of correlation, all independent of any connections with physics. But from all I can tell, what physics they are really talking about is lack of independence. Two random independent random variables have correlation zero. But correlation zero does not mean independent. So, if physicists keep using correlation and find correlation zero, sorry, but there can still be dependence. So, net, in short, for what physics is considering in the real world, they want to know if two measurements, each a random variable, are independent or not, not have zero correlation or not.
- VerminOctopus1 4y agoYep, it must be all of quantum physicists collectively misusing a word, and not you misunderstanding something. The hubris is unreal.