Documentary: How Physicists Proved The Universe Isn't Locally Real - Nobel Prize in Physics

23 Oct 2022 #nobelprize #Einstein #entanglement

Alain Aspect, John Clauser and Anton Zeilinger conducted ground breaking experiments using entangled quantum states, where two particles behave like a single unit even when they are separated. Their results have cleared the way for new technology based upon quantum information.
0:00 The 2022 Physics Nobel Prize 0:51 Is the Universe Real? 1:58 Einstein's Problem with Quantum Mechanics 5:09 The Hunt for Quantum Proof 7:37 The First Successful Experiment 11:06 So What?

The 2022 Physics Nobel Prize

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on October 4th our land aspect John

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clauser and Anton zeilinger were awarded

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the Nobel Prize in physics for proving

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that the Universe isn't locally real

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what I love about this story is that

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it's a story of quite literally some of

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the smartest people who have ever lived

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being confused and how ultimately

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Einstein was proven wrong which doesn't

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really happen all that often that idea

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of locally real is made up of two

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concepts locality is the idea that

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things are only affected by their local

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environment you can't flick a switch in

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another galaxy hundreds of light years

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away and instantly see the results here

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because nothing not even information can

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travel faster than light realness though

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is much harder to explain and that is

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the focus of the Nobel Prize

Is the Universe Real?

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foreign

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close to the beginning around the 1930s

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where there were two paradigms two ways

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of thinking about the physics of small

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things like particles atoms electrons

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photons Etc the view of Einstein and

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many others was that the universe is

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real the particles atoms and electrons

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have definite properties that are

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inherent to them regardless of if they

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are being measured essentially the if a

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tree falls in the forest and no one is

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around to hear it it does in fact make a

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noise and then there was a counter group

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The anti-realists championed by people

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like Bohr as well as many others the

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particles have properties that haven't

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really made up their minds until you

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actually go out and measure them that

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they exist in a wave function of

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possible States and only when you

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actually take a measurement do they

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really make up their minds the famous

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example here is that of Schrodinger's

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cat that is both alive and dead until

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you look in the box and then ultimately

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you go to prison foreign

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[Music]

Einstein's Problem with Quantum Mechanics

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culminated in a famous paper called the

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epr paper where Einstein podolki and

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Rosen put forward a thought experiment

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that they thought perfectly highlighted

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the quantum mechanics at best was

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incomplete and at worst may be totally

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wrong their thought experiment focused

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on an idea in quantum mechanics called

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entanglement that the property of two

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particles can be inherently related

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their line of reasoning for their

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thought experiment started with well we

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know that energy is conserved things

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don't suddenly start moving in a

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direction unless someone or something

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pushes or pulls them neither also do

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they suddenly start spinning rotating

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jumping up and down or doing anything

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else unless someone else is directly

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affecting them number two if we start

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with a small quantum mechanical particle

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that isn't spinning moving or doing

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anything else let's imagine that

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particle spontaneously breaks into two

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if we look at one one of those pieces it

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breaks into and find that it's moving to

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the right we know instantly that the

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other particle must be moving to the

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left to conserve momentum or if we had

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looked at it and found that it was

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spinning one way maybe clockwise we

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would know instantly that the other

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particle must be spinning

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counterclockwise to conserve angular

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momentum you'd be confused if you looked

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at this system and saw both particles

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suddenly moving to the right your

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intuition would tell you that some

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outside force maybe must have hit them

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or for the same reason though may be

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less intuitively because most people

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don't think about angular momentum or

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spin you'd be equally surprised if you

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saw both particles rotating in the same

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direction you'd assume that something

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must have hit them and caused them both

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to start spinning step 3 quantum

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mechanics here says these states are

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impossible to know before you go out and

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measure them if you separated these

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particles light years apart and measured

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one say and found that it was spinning

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clockwise you'd know instantly even if

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that particle was a universal way a that

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its counterpart must be spinning

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counterclockwise but how could this be

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if they really only take on a definite

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value when you measure them and the

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other one always needs to be the

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opposite of what you've measured then

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the particle that you did measure would

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need to instantaneously communicate to

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its partner and tell it to adopt the

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opposite value permanently Einstein

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argued that this was impossible because

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it would have violated locality and

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meant that information had traveled

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instantly faster than the speed of light

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to tell the other particle to collapse

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its wave function and make up its mind

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which way it was spinning instead he

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argued it must have made up his mind at

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the very beginning when it was created

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we just didn't know it or we weren't

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smart enough yet to find a good way of

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measuring it he called this unknown

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knowledge hidden variables and said that

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this was the piece in quantum mechanics

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that was yet to be completed and for

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around 30 years physicists really kind

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of split into two groups either they

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sided with Einstein or they sided with

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cool mostly because no one had really

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come up with a good theoretical or

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experimental counter argument to

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Einstein's epr paper

The Hunt for Quantum Proof

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that was until about 1964 when John Bell

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an Irish physicist on sabbatical from

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working at CERN started to do some more

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theoretical work of his own these Works

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which were later called Bell's theorem

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or Bell's inequalities of which there

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are many different forms but the

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underlying idea is to try and get the

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universe to pick a side tell us whether

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those hidden variables and Einstein's

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right or tell us whether truly there is

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a wave function and that quantum

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mechanics is real now this hinges a lot

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on what happens to Quantum objects when

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you actually go out and measure them so

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let me introduce you to the idea for a

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particle of light called a photon

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photons have a property called

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polarization which describes which way

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the wave of light is oscillating through

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space either vertically or horizontally

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or potentially somewhere in between if

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you wanted to measure which state a

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photon was in you would put it through a

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polarizer that lets through either

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vertical light in one orientation or it

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will only let through Horizon gentle

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light in another orientation but then at

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least your detector which you place

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behind that polarizer knows what sort of

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light it's detecting if you fired in

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randomly polarized light some of it

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vertical some of it horizontal some of

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it in between by placing a vertical

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polarizer first then a horizontal

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polarizer after you would expect

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correctly to see that no light reached

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your detector because all polarization

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angles had been blocked you can see this

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effect when using polarizing films which

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are the same stuff you find on a pair of

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polarizing Sunglasses by orienting two

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polarizing films at 90 degrees to each

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other you see no light emerges through

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them what is interesting here is that if

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you place a third polarizer between

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these two you suddenly and I think quite

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counter-intuitively start to see more

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light this is because fundamentally

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measuring a particle changes its state

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allowing light to slip through the final

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polarizer where usually it wouldn't be

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able to so you start to see more light

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than you would otherwise expect so let's

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jump back though into the story at this

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point in history Belle's work was still

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more Theory and thought experiment than

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anything else and that classically is

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the problem with theoreticians if you

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look at them from a distance it just

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looks like a wizard trying to have an

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argument with you

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[Music]

The First Successful Experiment

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physicists really needed to find a way

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of actually completing an experimental

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measurement

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one of the early and most elegant and

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now heavily evidenced extensions of

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Belle's theorem work is the chsh

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inequality by John clauser the Nobel

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Prize winner that we're talking about

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here Michael Horn Abner shimini and

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Richard Holt and their work here makes

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this theorem that Bell developed

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actually experimentally testable the

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scenario the describe is similar to what

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we've talked about before two entangled

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photons are sent in opposite directions

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to Two observers Alice and Bob both Bob

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and Alice get a polarizer to play with

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into their setup that helps them

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determine which polarization the light

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is actually in and finally Alice and or

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Bob at random are told to rotate their

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polarizers over time and record where

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the photons arrive successfully or not

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at their detectors what we're interested

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in doing here is counting how frequently

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that Alice and Bob agree on whether

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they've seen or not seen a photon

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if Alice and Bob perfectly anti-aligned

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their polarizers then they should always

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both either see a photon or neither one

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should see a photon they should always

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agree on whether photons arrived or

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photons didn't arrive

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if however Alice and Bob both align

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their polarizers either Alice should see

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a photon and Bob shouldn't see one or

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Bob should see a photon and Alice

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shouldn't see one the interesting part

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happens at angles between these

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positions if the universe is real and

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photons are truly independent Alice and

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Bob's rate of agreement should linearly

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move between full agreement and full

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disagreement

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if however the universe is not real we

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should expect to see a higher rate of

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coincidence than otherwise expected just

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like in our three polarizer setup except

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now our polarizers are on the other side

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of the Universe from each other and the

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same Photon isn't going through both or

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is it this can only be true if the

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particles are really still connected to

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let each other know which polarization

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state to be in so that measurement on

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one truly does affect measurement on the

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other and in 1972 it was John clauser

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who built the first experimental setup

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capable of conducting this measurement

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in the paper that he released that year

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this was the figure that he displayed

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exactly matching the prediction of

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quantum mechanics proving that the

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Universe isn't locally real that

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Einstein's deterministic view was

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incorrect and a story from this point

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goes I'm not sure if it really happened

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or not that excited by proving the

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result clauser runs into Richard

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feynman's office to tell him the news

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and in classic Feynman fashion Feynman

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throws him out of his office for ever

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doubting quantum mechanics and tells him

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good now get on with some real physics

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the other Nobel Prize recipients Elaine

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aspect and Anton Zollinger closed

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important loopholes that remained within

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this experiment as well as showing that

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quantum entanglement can be transferred

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to other particles in a process called

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quantum teleportation all this to say

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that without a doubt the universe showed

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itself to be Stranger Than even Einstein

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had imagined

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[Music]

So What?

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all of these phenomena are really the

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backbone of what is driving the modern

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Quantum Computing Revolution the idea

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that at some point in the hopefully near

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future quantum computers will outperform

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classical computers because they have

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this inherent baked in advantage that

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down at their core their particles that

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run them are communicating to each other

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while this doesn't prove and I can

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absolutely forgive anyone for on first

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hearing thinking it that people can now

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communicate faster than light although

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it would be possible to derive some fast

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and light communication that

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unfortunately is where the field pretty

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unanimously says no this is ultimately

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because the core to this phenomenon is

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inherent Randomness at the source of

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that Photon or entangled particle

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generation and then also at those

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measurement Points each Photon will

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either make it or not make it through a

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polarizer each Photon will either be

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created in some combination of states

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that ultimately those combination of

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states will be impossible to know until

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measured there's no way of loading

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information onto that Communication

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channel and as a result there is no way

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of violating Einstein's fundamental

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contribution which is that the speed of

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light is a fundamental limit in the

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universe that absolutely stands correct

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and I think with Keith Einstein

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reasonably happy

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[Music]

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thank you

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foreign

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[Music]