Brian Greene at the 2023 Aspen Ideas Festival

foreign good afternoon thank you Walter hi I'm Brian Green professor of physics and Mathematics Columbia University co-founder of the world Science Festival and there has deservedly been a lot of discussion at the ideas Festival about Ai and so I thought I would just quickly share my own recent experience because I wanted to begin here on a on a lighter note so I did what most of us would do in the post November 2022 World would I consulted with chat GPT I asked chat to write me a joke of course a physics joke and because I'd be delivering it I asked chat to write it in the style of Brian Greene here's what chat came up with why did the photon go to the doctor answer because it was feeling lightheaded not bad not great hold your applause on that so so I asked Chad I said can you come up with something more clever something more creative and chat replied of course I can come up with something more creative and clever but you asked me to write in the style of Brian Greene now in that little joke was the word Photon right and the photon is a notion that achieves its most refined articulation in a description of the universe called quantum mechanics and we are now in the 100th anniversary year or really decade of the discovery of quantum mechanics and it's still a hugely active field the 2022 Nobel Prize in physics was awarded to three researchers in the arena of quantum mechanics so what I'd like to do in the brief time that we have here this afternoon is just take us on a tour of where we are what the state of the art is in our understanding of quantum mechanics now what is quantum mechanics the best way to answer that question is by comparison to the earlier description of the universe called classical mechanics and briefly put in the 1700s and the 1800s we were able to discern patterns in the motion of objects and we were able to articulate those patterns in the rigorous language of mathematics and with the language of mathematics we could make predictions for how things move for instance how a ball would bounce or how a wheel would Spin and travel or how a object going through space would follow a particular trajectory but here's the thing as we push their understanding beyond the macro world into the Micro World the world of photons and electrons we found that the earlier ideas gave wrong predictions and we were forced through a series of experiments and ideas to change our Paradigm from predicting what will happen to giving a probabilistic prediction of what may happen and if you don't remember anything else from the remarks I'm giving here today Beyond quantum mechanics being a theory that is based on a probabilistic framework you will have really gotten the essence of the transition into the quantum world now let me just try to give you a feel for why science was forced to this probabilistic description and there's a simple little experiment that captures the heart of the reasoning it's called the double slit experiment and it goes like this so imagine now we have a little gun that's firing pellets BBs at a barrier with two openings two slits you would expect that those BBS that go through the left opening will land and abandon the left and those that go through the right opening will land on a band on the right side and indeed if you did this experiment this is exactly what you would find good now let's make one change dial down the size of the pellets the BBS make them smaller and smaller make them as small as a photon or an electron now our intuition would tell us that the size of the projectile shouldn't matter and so you would expect exactly the same kind of pattern those that go through the opening on the left land and abandon the left side those that go through the right opening will land unband on the right but if you do this experiment this is not the pattern you find instead if you do this experiment with photons or electrons you find a pattern that looks like this now notice it's not random but it's not the pattern we expect based on our everyday experience as say the electrons go through the best we can say is that a fraction of a time they land on the far left and a fraction of the time on the band next to that and so forth now these are particles that are being fired in exactly the same way yet they land in a variety of distinct positions so the best we can do is describe the motion in terms of the probability of the electron Landing in one location or another and that's what gives rise to this probabilistic description now Albert Einstein right the Great Master of understanding the universe he resisted this idea of probabilities in a metaphorical poetic language where he said he could not believe that God plays dice with the universe now Niels Bohr in a retort that has less Fame responded by saying Einstein stop telling God what to do and indeed this probabilistic predictions are ones that we hold dear in our understanding of physics but you might ask yourself why did Einstein so resist this probabilistic approach to the world because after all we hear probabilities all the time weather reports casinos flipping a coin but those probabilities are fundamentally different from the probabilities of quantum mechanics because those probabilities emerge because of a lack of detail a lack of full understanding right if you knew everything about every molecule in the atmosphere its position where it's been where it's going you would be able to determine whether or not it is going to rain you wouldn't need probabilistic forecasts but because we don't have access to all of that information we have to resort to this idea of likelihoods or probabilities the probabilities of quantum mechanics are different they are foundational probabilities not because of a lack of complete information it's because at Rock Bottom according to these ideas the world is governed by a game of chance second reason why Einstein resisted this idea it went against the grain of his understanding of how the world works it's because when we say a coin has a 50 chance of heads or tails we know what that means it's going to land either heads or tails nothing in between but in quantum mechanics when we say an electron has a 50 chance of being here or there before we actually look according to the most conventional interpretation of the theory the electron is hovering in a mixture of being at those two locations that is so weird that Einstein resisted it now you might say if you were talking to Albert Einstein I said look you know we don't experience electrons in everyday life so just imagine that that's how things behave way down there and that somehow when you get up to the big world we don't encounter this sort of hazy fuzzy reality that holds in the micro world and in a famous thought experiment that everybody has heard of Aaron Schrodinger showed that that notion that somehow probabilities could be sequestered in the micro world and not infect the macro world he showed that could not be true how do you do that well you imagine they have a cat in a box if the electrons on the left hand side the cat lives but if the electrons on the right some poison is released and the cat dies now he says what if that electron is in a fuzzy mixture half on the left and half on the right would that mean the cat is in a fuzzy mixture of being alive and dead now that is such a weird idea a cat being a mixture of being alive and dead that this gives some feel for why Einstein resisted this so why would we physicists accept quantum mechanics the answer is it's not just pictures we have mathematics mathematics makes predictions that predictions are borne out by experiment now every time that I've been on this very stage in the past and I turned to mathematics I never did it alone I always did it with two particular very special helpers Elkin Sophia come up here one second so here on this t-shirt is the standard model of particle physics Sophia what is that symbol meant to describe I hate field yes and this term over here what is that man a Hicks potential I Hate's potential thank you very much we're back by Command Performance can I have my two helpers Alec and Sophia what equations do we have right here Einstein field equation what do we have over here short Shield solution right and now for the I suspect the final time that I will ever be able to convince them to do this Alec and Sophia all right so Sophia tell me what you have on your shirt right there Schrodinger's equation for the evolution of the quantum wave function perfect allocate what's on your shirt here this is feynman's sum over history's approach revealing how awaited some of all possible trajectories yields the quantum probability thank you both very much now the point is using that mathematics we can make very detailed predictions for things like the properties of particles so electrons have a property known as the electron Magnetic Moment experiment you don't need to know exactly what that means it's like a little tiny magnet when you measure that magnetic property this is the number you get when you use that mathematics to calculate that number here's what you get breathtaking agreement between Theory and observation and beyond that once you can describe the micro rule but that kind of precision you can control it you can manipulate it giving rise ultimately to the integrated circuit which is why we have all of the powerful technological devices that we walk around with in everyday life in fact 35 percent of the gross national product relies in this way on quantum mechanics and actually I went back to check that 35 percent just to have the source you know I went to you know NPR to the New York Times and unfortunately I'm the source of the 35 percent and I have to tell I've never done the calculation so it's a totally made up number but you get the idea you get the idea that a great deal of what we produce relies upon quantum physics but Einstein still even with the evidence that was available in his time could not accept that this was the full story and in 1935 he writes a paper trying to expose a flaw in quantum mechanics and that flaw has to do with something called quantum entanglement let me just quickly describe for you what Einstein found in the mathematics of quantum mechanics and I'll describe it in a little example every particle in the universe it turns out it spins at one particular rate either in One Direction or the other and we have some language that we use if it's spinning in this way we wrap our fingers around and we say that it is spinning up if it's spinning the opposite we say it's spinning down okay now just as an electron can be partially here and partially there a particle can be partially spinning up and partially spinning down and it only acquires a definite spin when we measure it so here it's up and down measure it we find it to be down now that's weird that reality can exist in this fuzzy Haze of multiple possibilities that only resolves itself upon measurement but I want you to accept this because it's true and I want to go much further here is what Einstein found he said look you could have two particles in this fuzzy mixture of up and down and you could then separate those particles as widely as you would like you can then go over to say the particle on the left and measure it three two one measure causing it to snap out of the haze and exactly that moment the other particle also snaps out of the haze even though you have done nothing to it another version imagine we have them in this fuzzy mixture you go over this time to the particle on the right hand side three two one you measure it it snaps out of the haze and the particle on the left also does Einstein called this spooky spooky action at a distance you do something here and it affects something over there and although I frame this in a laboratory setting it can be anywhere in space across the entire universe if you like these entangled particles according to the math of quantum mechanics you measure one let's say I measure the one on the right hand side snaps out of the haze similarly the particle on the left does as well Einstein said nobody in their right mind could accept that this is how the world works decade after decade scientists developed the mathematics further developed the experimental techniques further and showed that this is not a flaw of quantum mechanics it's a feature of quantum mechanics and indeed the 2022 Nobel Prize was awarded to these three individuals for all the work that they did establishing that this spookiness this quantum entanglement is Real is how the universe actually works in moreover especially the gentleman on the right hand side Anton zeilinger show that you can do stuff with this you can teleport objects particles from one location to another right so imagine that we have two entangled particles one says in New York the other is in Paris and imagine you want to teleport a third particle the red particle from New York to Paris here's how you can do it you take that red particle and you bring it into an association you let it meld in some very specific way with the entangled particle in New York that imprints the Key properties of the red particle on the particle in New York and through entanglement those properties are instantaneously imprinted on the particle in Paris and then through an appropriate measurement in New York you can tell the person in Paris exactly what to do to pull out those properties yielding an identical version of the red particle now in Paris and in fact the act of undertaking this quantum teleportation destroys the particles back in New York so the only remaining version of the red particle is indeed the one in Paris and this is real this is not hypothetical in fact Anton zeilinger not only is a very clever physicist he knows the life that he likes to lead he has his experiment for teleportation set up in the Canary Islands La Palma Tenerife 90 miles apart he routinely teleports particles between one location and another now the coda to this story which of course is one that continues to be developed is this in 1935 Einstein wrote another paper having nothing to do with quantum mechanics having to do instead with the general theory of relativity the theory of warps and Curves in the fabric of space and time and in this paper which is with one of the colleagues in the entanglement paper Nathan Rosen they showed that there might be things called wormholes right this is a familiar idea from anybody who watches some science fiction what is the idea that if space can warp and curve you can have shortcuts going from one location in space to another location through a kind of tunnel a wormhole like tunnel from one location to another and in this particular imagery anyone who's following the news and has noted that the feds have approved the first ever congestion pricing in New York City will recognize this would be a beautiful way to not enter Midtown Manhattan and be subject to that particular toll but putting that application to the side Einstein had no idea that there might be any connection to this notion of entanglement and what's happening now right at the Forefront of understanding is this work that really Finds Its origins in string theory and other cutting-edge developments have shown that there is a deep connection between wormholes which connect one location to another with entanglement that connects a particle at one location to another this is a work of Juan malda Cena Lenny suskind and this may very well be the key to realizing long-standing dream of Einstein's of finding a unified theory which in the modern language would meld together our understanding of the laws of the small quantum mechanics with our understanding of the laws of the large the general theory of relativity so I certainly look forward to Future years coming back and describing where this goes but I want to finish with one mystery a profound mystery that no Quantum physicist no physicist at all has given us any insight into which is this how could it be I mean seriously think about it how could it be that Tom wamscans could possibly ascend to the throne of way star Rocco to answer that mystery I will now see the stage next discussion Katie Kirk and Brian Cox thank you very much [Applause]

Channel: The Aspen Institute

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Length: 22min 0sec (1320 seconds)

Published: Wed Jun 28 2023