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okay welcome to arts and ideas in the air under the tent around Baltimore this
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is wondrous Wednesday where I talk about some particular topic of interest so
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I'll try to keep it brief well it's a big topic what I want to talk about
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today is called quantum non-locality so we already talked about what kind of
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quantum means it's these very small things like electrons and photons and so
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forth that you know have strange properties I talked about the double
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slit experiment where depending on the setup particle might seem like a wave
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instead of something with a definite position particles you can think of as
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just like little balls moving around and so it's kind of weird to think of a ball
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as kind of like an ocean wave right so that was bizarre now I did say that the
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resolution of that in my opinion is boming mechanics which says there's a
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wave that tells the particle how to move that's why you see wave like behavior
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and you see particle like material behavior because it's actually a
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particle it's it's a ball it's ball moving on an ocean no problem now that's
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all fine except the interesting part in the part that kind of makes physicists
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like me is involves mostly multiple particles I think there might be an
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argument for one particle where there's some weirdness going on but the easiest
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thing is kind of two particles kind of being related to each other and there's
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something going on that allows them to communicate at speeds faster than light
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now the notion of locality is that what happens here can only affect something
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over there at the speed of light or less so if if what I'm doing here like I'm
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record I'm talking in this microphone now if my voice was kind of
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instantaneously broadcast to the Andromeda galaxy so like kind of like in
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my frame of mind of now if suddenly my voice was Andromeda there that would be
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considered non-local but if I'm talking this microphone and it's broadcasting
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the thing into deep space and like a million years later or however far
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Andromeda is I don't actually know and you know my voice among traveling along
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these light waves reaches there in a million years and I was perfectly local
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that's fine okay so the idea was you know you can ask is quantum mechanics
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non-local now in standard physics the idea is that when you measure something
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it collapses to the definite value so if you measure the position of something
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it collapses to you know a definite position if you measure how fast it's
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moving before that it was just moving in this strange blend of different speeds
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or whatever but when you measure the speed it collapses to a single speed and
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so that's kind of like instant as soon as you do the measurement this thing
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happens fine good now and as it turns out when you measure the position of a
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particle the speed gets uncertain it starts varying a lot if you measure the
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speed of a particle its position gets very uncertain that's how quantum
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mechanics works in terms of the experiments that they talk about in
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measuring these things okay good now in quantum mechanics two particles can be
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kind of correlated with each other so they're the behavior of the one impacts
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the behavior of the other and so Einstein came up with this idea of two
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particles traveling in like opposite directions and their speeds were
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exactly sort of correlated and so if you you could deduce the you know the setup
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is such that if you measure the position of particle a you can you can deduce
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with the the the position of particle B is and if you measure the speed of
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particle a you can deduce the speed of particle B and so basically that is sort
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of the non-local stuff that is of question so yeah so the idea is that you
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shoot these particles out one side you you know yeah you can do a position or
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speed measurement and the other one it has to have it so that means the values
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that measurement has to happen you know faster than speed of light if you've set
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it up so that they're far enough apart that when you do this thing make this
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you have to make the decision randomly far enough away that can't that decision
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can't be propagated by the speed of light and so then that's what that's
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what happens so so he said quantum mechanics is now on local that's a
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problem unless of course the position in momentum were already known so that if
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they actually existed beforehand in some fashion then you're just kind of
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deducing what was already there and somehow then doing measurements breaks
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his stuff and so he really wanted to find a theory where you could do that
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where you could assign stuff like that now there is another kind of experiment
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along these lines that allows for really interesting well so the EPR experiment
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what it showed was that the standard quantum view leads to non-locality and
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then this is something that physicists are reluctant to really acknowledge
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because they don't really want to say that momentum and position exist and
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therefore somehow collapsing and having things happen it's I don't know it's
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kind of vague enough that they're like whatever they have something else they
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call a non-locality condition for quantum mechanics but so goes now the
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other experiment the other idea which actually was it was thought up by boom
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of boming mechanics although had nothing to do with boming mechanics it was just
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he had come up with this different idea so there are is another particle system
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where well so there's a notion of spin so if like an electron kind of spins and
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if you so you can have a magnetic field and if it spins in one direction it goes
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up and spins in a different direction it goes down and you can you know so that's
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just a thing however it can spin along different axes and so you can measure
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you know relative to those different axes and in classical physics you know
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if you're spinning and kind of pointing upwards our point pointing in one
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direction you know go up or down but if your point spinning around another one
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it wouldn't just go up or down in the same way it would go somewhere like in
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between or something depends on exactly where it's you know how it's what it's
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spinning around basically but in quantum mechanics what's found is that if you
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spin if you measure it in one direction you get up or down if you measure it in
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a different direction you also get an up and down for that so it's like it's
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spinning around all these different axes all at the same time that's the behavior
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that we see by the way the picture of it being a ball that's spinning around an
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axis is completely wrong but you know the behavior is consistent with that
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kind of model anyway so now there's a system where things can spin up I mean
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where if this particle is found to spin up then the its partner is found to
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spin down and that's true among any direction that you measure the spin
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around so if it's if it's you know whatever you find on the one you know
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the one on the other side so spin up spin down is how it goes and so that
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allows you to measure the the spin up and spin down of these separate
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particles and you know if you measure just in the one direction then you know
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you can instantly say that okay this was up over here so we know it's going to be
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down over there and that's what you always see good so there's a certain
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sense okay yeah that should be the same right you need to have something
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pre-existing somehow that determines this up and down or you need to
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communicate faster than the speed of light good good so I think that's
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probably enough for now but a man named John Stewart Bell comes into the
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picture when he realizes who and he was inspired by this by actually reading
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boming mechanics and being like oh okay that looks great but it's kind of
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non-local can we get rid of this non-local thing and I'll talk more about
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that later but his idea was oh measured along these different directions and
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then you you you see you know you get a certain statistics from it and it turns
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out that you can't actually assign some kind of underlying value scheme that
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works with the quantum mechanical results I'll talk about that next time
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but you can look it up if you like just look for Bell non-locality or Bell
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inequality or something like that EPR Bell boom you know you'll you'll find
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the good stuff anyway that's for next time thanks for listening