A non-mathematical introduction to the idea of Nonlocality in quantum theory

[heintron]

Why is this related to boyd rice?!

[Karlemids]

randomize.

[TaylerKnox]

You are not applying the scientific method - you are an atheist fascist without the courage to step up.

[martifingers]

A brave attempt to simplify what must be a very complex situation. Is it possible to say something about the experimental verification of this theory and at what stage in the development of quantum thoery did this occur?

[PhysicsMathCharlatan]

@martifingers

Thanks. I don't really know the history fully. But two major papers on the topic were the Einstein-Podolsky-Rosen paper (maybe 1935?) and the paper by John Bell on Bell inequalities (1960s).The PR box example discussed in the video cannot be achieved by any known physical theory, but a more restricted form of nonlocality is now regularly investigated in modern experiments, up to various controversies about statistical accuracy and possible loopholes in the experiments.

[ExcessivelyArgumen]

Or, maybe if Alice only presses A, a signal change by Bob within a ten second increment can mean one thing and its lack can mean something else. Alice doesn't have to know what signal Bob sent, just that Bob changed the signal and that change means something while its lack means something else.

[ExcessivelyArgumen]

Why not have Alice only press B and have Bob avoid sending any signals for ten seconds to say he's sad and send at least one signal within a ten second increment to say he's happy. Next ten seconds they switch. They agree on the time of day to start by postcard.

[TaterGumfries]

OK.

[TheUnhiddenBible]

Very nice video ... thanks for posting this.

[qbrute]

You've got to stop keep saying "OK?" ... it's irritating!

[PhysicsMathCharlatan]

@qbrute

you're right it is annoying. ok sorry about that. i didn't realise that i was doing it at the time ok. though ok by the end i had stopped saying it as much. hope all else is ok with the explanation however. ok won't do it again. sorry.

[bandet888]

I think what quantum theory is that It's possible for a partical to exist in two places at the same time. so when a particle does something in one location it does the exact same thing in another location at the exact same time. No comunication is needed for the particle is one and the same in two locations. Best way to look at this (although slightly different) is to picture a globe of the earth then think of sticking a piece of rod through it. When you rotate one end the other will rotate too.

[PhysicsMathCharlatan]

@bandet888

The problem with analogies such as the one you present is that two spheres that can be deliberately rotated in the same way at the same time can be used to *communicate* an instant signal. Quantum theory (including nonlocal quantum systems) cannot be used to communicate a signal instantaneously. If you want more details on the stuff described in the clip please read the paper S Popescu and D Rohrlich, Nonlocality as an axiom, Foundations of Physics, 24, 379, (1994).

[PhysicsMathCharlatan]

Just to clarify I mean that: any sphere that rotates in an identical way when another distant sphere is rotated allows information to be communicated instantaneously.

[ldl1949]

worst explanation ever..! as far as I could tell nonlocality is actually a very simple (sadly could not find if proven or not so I will call it idea) idea where two particles are connected (in some sort of way) to each other as so an action you take with one particle directly affects anther particle (""its brother"") in a far away place.

correct me if im mistaken...

[PhysicsMathCharlatan]

@ldl1949

Thanks for your comment.

While your statement cannot be called "wrong", phrases like "two particles are connected (in some sort of way)...and so an action you take with one......directly affects another" do not clearly indicate that nonlocality is all about the *statistics* of measurements.

To demonstrate it you have to show that the *statistics* are non-local. The clip was an attempt to explain what the phrase "non-local statistics" means.

[ldl1949]

@PhysicsMathCharlatan

Thanks for the response.

So as far as I understand its either I am confusing two fields (as I was referring to quantum physic's, and acording to the way people were speaking this is ""proven"" in some sort of experiment which I am trying so hard to find). or there is no experiment and all this was deduced from playing with numbers and facts on a peace of paper (which is a shame if true).

Could you help me to understand which statement is true..?

[PhysicsMathCharlatan]

@ldl1949

Nonlocality is of course a phenomenon that has to be demonstrated experimentally - see e.g. experiments performed in research groups of Gisin (Geneva) and Zeilinger (Vienna). But to show that an experiment has demonstrated nonlocality you have to do a statistical analysis of the data. The clip is an attempt to indicate (admittedly in a very cursory way) what that means.

[fridogg]

does this theory explain how hairy your arms are?

[PhysicsMathCharlatan]

@fridogg

alas not.

but there is a result known as "the hairy ball theorem" (which you may look up on wikipedia) that may have applications to other parts of the body.

[goatboooy]

it has not and may never be proved that communication across a quantum field ,between a particle and its anti particle has to follow the laws of physics...indeed their are many experiments that suggest they DO communicate instantaneously, i thought that was the premise of string theory...

[bandet888]

@goatboooy Read my other comment on this video. Our points of view are similar. Even though you say the other particle is it's brother and I say there one and the same somehow in two different locations at the same time. I think we both have the general idea.

[PhilAtremo]

Great!

[ankhaton]

Hi - I guess you know actuarian stuff -

It's very easy to prove that we do not exist.

Are you aware of that Calculation ?

The conclusiopn after the Math is that there is only one.

[randomlaughingman]

if it works then it does permit faster-than-light communication, because as soon as one parts spin is altered, the other parts are altered too. that's the point...

& i'm just saying 'if it works' to let anyone down gently, cause it works.

[PhysicsMathCharlatan]

Thanks for your interest, but that's not quite correct.

In both the specific (not believed to exist in nature) non-signalling theory discussed in the clip, and in the quantum description of entangled states (which are believed to exist in nature), nothing that Bob can choose to do can deliberately affect the statistics that Alice sees. So in both cases she cannot receive a signal from Bob. The same is true the other way round - Alice cannot signal to Bob.

[Allyredstar]

Well, it seems i know everything about that unfortunately

[randomlaughingman]

must be a different EPR then, cause the one i read up on > a decade ago is clear that it is about an atom being in > 1 part such that when one spin is altered, the other parts spins are instantaneously altered in direct relation to it.

there's no point in your eponymous bs continuing; this tech is coming very very soon, so just get over it. it exists already.

[PhysicsMathCharlatan]

EPR experiments have been done, and the technology to do them is getting better still.

However, they do not enable faster than light communication.

Suppose Alice/Bob share an EPR pair, and she measures her particle. Although her outcome tells her what Bob will get when he measures his side (if he measures in the same direction), it does not allow her to fix what his value will be, because she had no control over what outcome she got. All they know is that their outcomes are opposite.

[randomlaughingman]

they aren't quantum then are they. cause then the spin change has instantaneous results.

? do you mean they know the outcomes are opposite, but can't predict them? in terms of opposite as-in say a not gate, then you know what the result will be going soley on what you input.

[PhysicsMathCharlatan]

If you want to communicate to me, you need to be able to affect in a controlled manner something that I will observe. If Alice shares an EPR pair with Bob, and measures say, spin, on her particle, then in the usual EPR setup she will know (from her measurement outcome) exactly what Bob will get if he measures the spin in the same axis. However, she has not been able to affect it in a *controlled* way, because her *own* measurement outcome was also *random* to her - she could not control it.

[PhysicsMathCharlatan]

anyway if you know a little about quantum theory already, and want to understand more, take a look at the paper "nonlocality as an axiom", from 1994, available on the website of Sandu Popescu at bristol university. they won't let me post the link here.

[randomlaughingman]

that sounds like instead of accepting it is faster than light, you've not mentioned that part but have tried to make me look wrong by focusing on something else instead.

true, if person a can only measure but not control the state at their end then strictly speaking they aren't controlling the data - but in terms of how this system will be implemented, it's only important that the transmitted state output will be known in advance. eg a spin in any direction can represent 1 or 0 (or both or.....

[randomlaughingman]

contd........neither 1 nor 0, since this is about quantum info and quantum computers use those 4 states.)

[bobwatters]

wow im not into physics but i think i started to understand the theory u were trying to get across

great video to bad its the stupid cutie kittens and crap that get the 20million views or the world might be a little smarter place

[claymodeling1]

Great video, thanks for putting something of this quality on youtube! I am relieved to find someone talk about non-locality with referring to conciousness and cosmic mumbo-jumbo.

[phrozeninfeno]

Nice way to explain Nonlocal Theory! e= mc² ftw

[redmanghost]

haha uh