Titans of Science: Paul Davies

0:11Hello,

0:16welcome to the Naked Scientist podcast, the programme that brings you the biggest breakthroughs in science, technology and medicine. I'm Chris Smith and this week we are delving into the science that Einstein dubbed spooky action at a distance. It is the quantum realm and my guest is the award-winning physicist and science populariser Paul Davies.

0:45Titans of Science is all about showcasing science superstars making huge breakthroughs and giant leaps forward in their scientific realms and this episode is no exception except that the subject matter demands this time that we turn that telescope around to consider the extremely strange effects that kick in when physics shrinks down to the atomic scale. We are, of course, taking a tour through the world of quantum mechanics, and our guide is the physicist, writer and broadcaster Paul Davies. Now, more about him in a second, but first to give you a flavour for why the subject he studies even baffled Einstein.

1:26Consider this. If you take a strip of paper and cut two vertical slits in it, side by side, and shine light through them, Like waves washing into the entrances of a harbour, behind each slit you see a pattern of rings. And where those rings overlap and the waves either add together or cancel out, you see bright or dark patches respectively. So what happens if, instead of doing this with light waves, you instead use particles, like electrons or even whole atoms? Well, logic says that a particle would have to go through one or the other slit. It can't be in two places at once, so you wouldn't get that same pattern.

2:09But you do. In other words, the atom or the electron must have gone through both slits at the same time, mustn't it? Yes, I warned you this was weird, but stay with me because it gets weirder still. because if you measure which slit the particle went through, it was either just one or the other. And as soon as you turn that detector on to tell you that, the pattern vanishes. The particle knows you're watching it. Welcome to the world of quantum mechanics, a world inhabited by Arizona State University physicist Paul Davies. Paul was born in Finchley, North London, on the 22nd of April 1946. He attended Woodhouse Grammar School and read physics at University College London.

2:58From there, his career took him to Cambridge, to Adelaide and Sydney, and latterly, Arizona State University. Along the way, he has probed the origins of the universe, the quantum properties of black hole, and even the nature of time. Paul's written dozens of acclaimed science books. He's produced and presented hugely popular programmes for the BBC and other broadcasters, and his contributions to scientific research and communication have also been globally recognised. He's the recipient of the Templeton Prize, which has also been bestowed upon the likes of Mother Teresa, Dame Jane Goodall and even the Dalai Lama, with whom Paul has worked in the past.

3:34And if that's not enough, Paul even has an asteroid named after him. I'm with him now at the BBC's new broadcasting house in London, not far from where it all began. Welcome to Titans of Science. Thank you very much. It's a pleasure to be back in London, where I come from. Well, tell us a bit about that intro and getting into science then. How did the story begin? Very simple. It began in Charing Cross Hospital. I was born a physicist. I never wanted to do anything else. As a child, I was always fascinated by things unseen, looking up at the sky and imagining what might lie beyond what I could see, and then invisible fields, and anything that was sort of outside of the everyday experience, fascinated me.

4:17And I suppose that's one reason I became interested in quantum physics. We can't see the weird goings-on down at the atomic level. Who lured you into the quantum realm, though? When you started getting into science at a higher level, usually when you talk to scientists, there's somebody that really pulled them in. So who was that then for you? I don't think there was a specific lecturer at University College London. We of course had to learn quantum mechanics I think in years two and three. I found it inspirational but mystifying. It took a while to wrap my head around it but I finally did and it really became an important part of my research.

5:00Niels Bohr allegedly said if you're not baffled by it you didn't understand it. Well, you know, quantum mechanics is one of these peculiar things that it's the most successful scientific theory in history. And so it explains so much. In fact, the nature of matter all the way from subatomic particles up to stars. And it's given us dazzling technology, things like the laser transistor and superconductors and MRI machines and quantum dots, high definition televisions. You know, all these things around us are consequences of quantum physics. And yet, deep down, when you actually take a look at it, it doesn't seem to make any sense.

5:36It describes a world in which there isn't like a single reality out there. We tend to think, look around us, see tables and chairs, that they really exist independently of us observing them. But when you get down to the atomic level, all that dissolves away. And it's simply not possible to say that a particle like an electron or even a whole atom really is in a certain place or it really is moving with a certain speed. you can look and see and then what you find is an atom at a place or an atom with a speed but it's not that our observations reveal or unveil a pre-existing reality they somehow create that reality through the act of observations very mystical I'm sounding very mystical aren't I but that is the standard so-called Copenhagen interpretation of quantum mechanics due to Niels Bohr and a lot of my colleagues just don't like that at all and so this is a placeholder for some deeper way of trying to understand what is really going on in the subatomic realm, the quantum realm.

6:36Where did the field actually come from? How did scientists realise there had to be something there that we need to delve into? In other words, when did it get started? Well, the word quantum was coined by Max Planck, and he was investigating the nature of heat radiation. There was a puzzle in the late 19th century about if you have something like a kiln or an oven, it's got heat radiation trapped within it and that has a certain spectrum and nobody could quite understand the shape of that spectrum. It didn't seem to fit with the nature of electromagnetic waves. The other puzzle are atoms. We take atoms for granted these days but in the 19th century they were still very hypothetical.

7:18Nobody had ever seen an atom but when the electron was discovered and After all, everyone's familiar with electricity. Normal matter is not electrically charged, and so they have to be positive particles. And now we have this model of the atom with a sort of positively charged nucleus, electrons whizzing around it, and that's like a sort of planetary model. The big problem there is that when electrons accelerate, they emit radiation, electromagnetic radiation. That's how you get radio waves. You jiggle electrons up and down in antennae. There's probably one on the roof here. And that's how you transmit radio waves.

7:52So when an electron goes round and round in an atom, it ought to be blasting out very high frequency radiation for all it's worth. And then it would go into a death spiral. It would spiral into the nucleus and the atom would collapse in very short order. Clearly atoms don't collapse. And so the stability of the atom was another big problem. And all of this fell into place when quantum mechanics was developed 100 years ago this year. What sort of seminal experiments began to be done to show what people said was an extremely weird sector of science? For me, the starting point of the serious putting together of this quantum mechanics were the experiments with what we might call matter waves.

8:34So it was understood that light and other electromagnetic radiation are waves, but it looked, and this was Einstein's idea, looked that under certain circumstances it could behave more like particles and we now talk about photons like little particles of light so is it a wave is it a particle nobody could quite make up their minds but then the same thing happened in the 1920s with matter waves so firing electrons or now you can do it even with whole atoms they have a wave-like character but surely an electron is a little particle and yet why does it behave sometimes like a wave and so this was the starting point, trying to understand what were these matter waves?

9:12How could you interpret them? Because they're not like waves of stuff sloshing around. And the answer came in the mid 1920s. These waves, I liken them to crime waves. We talk about a crime wave passing through a city. You don't mean there's some criminality stuff sloshing about. What you mean is that there's an increased probability of a crime being committed. And that's the way we interpret the matter waves. Where the matter wave is strong, there is a greater chance that you will find the particle to be located if you look, if you do a measurement. And so that interpretation of matter waves really set the scene because now it was possible to explain the stability of atoms because the waves, the electron waves, wrap around the atom in certain shapes and patterns, a bit like musical instruments.

9:58There are only certain notes that can be played in an instrument. So it's almost like the harmony that is taking place around the atom of these electron waves and that explains all the energy levels and explains all the observations of spectra and other things so it all fell into place. One of the things we did when I was doing physics at school was to shine light waves through slits and you could see that they form patterns of rings and if you put the light waves through two slits you see an overlapping pattern of rings where you get light patches and dark patches and are you saying that matter particles because i'm comfortable that how a light wave would do that are you saying then if you did the same experiment with electrons particles i'd similarly see a pattern of rings then and and light and dark patches that's absolutely right what you don't see is light and dark patches what you you can do is count the electrons where they arrive on an image screen and they build up a pattern in a speckled sort of way each electron hits at a certain place and when you have enough speckles you see a pattern just like the you do with light we call it an interference pattern because the waves going through one slit interfere with those going through the other slit now that seems straightforward if we just think in terms of waves but now what happens if you fire just one electron at a time because that experiment's been done hasn't it we've actually got to the stage where you can say well i'll send one electron through at a time because the hypothesis would be if it's a particle it can only be in one place at a time if it's a wave it can go through both slits so if I fire just one I should just see one spot in one place.

11:35Right you're exactly right and you can do the experiment and you do fire them one at a time and you do get a spot in one place and so a single spot doesn't tell you anything but when you've got a million spots one at a time that accumulated pattern shows the interference fringes and you might think well why can't I just station some little device near the slits and figure out which slit it's going through because surely it can only go through one and not both and if you do that the pattern goes away. So the electron knows you're watching? Yes sort of it does seem very creepy and you can do it with photons as well and and with photons it's even more spectacular because you can send a photon through a slit system like that and then through a crystal that makes the one photon split into two and one of these photons can go to the image screen where are going to record the pattern the other can go off to Albania or somewhere and you can do a measurement on the Albanian photon that tells you which slit the photon went through and when you do that when you choose to make that measurement you don't see the pattern so hang on a minute I shine light through a slit and I put a crystal behind that splits the original photon into two so I've got two new photons one that goes to the screen I'm watching one that goes to a detector if I get a nice pattern as though there was no detector there no no crystal there like the normal experiment the minute i turn the detector on it goes away well you have to interpret this very carefully it's not the minute you turn the detector on it's when you have recorded that information when you go back and sit down with your accomplice in the lab saying show me the results of your counting on the image screen you see that there is a correlation and that on the occasions when you got the information about which slit the photon went through it doesn't contribute to the pattern and vice versa and it's even more creepy than that because there's something called the the quantum eraser experiment where what you do is you get the information and potentially it's available to you but then you erase it before you can inspect it and under those circumstances the interference pattern remains these experiments have been done this is It's not just some mystical mumbo-jumbo I'm talking about.

13:53There's real physics, and not only real physics, but physics which is now used in technology, because all of this stuff that we're talking about, and often a lot of it goes under the term entanglement, because the photon over here is entangled with a photon over there. This entanglement is the basis of a lot of what I call quantum 2.0, things like quantum computing and teleportation and the quantum internet, quantum cryptography uses this entanglement as a resource to be exploited so that you can monetize the weirdness of quantum physics which initially of course was only investigated just to try and settle arguments about what is really going on in the quantum realm but Einstein was skeptical wasn't he he dubbed this spooky action at a distance it was the photon knowing that you're measuring its counterpart and therefore erasing the information the pattern he was uncomfortable with that yeah Einstein didn't like quantum mechanics right from the outset god does not play dice with the universe was a famous quote because what we're talking about here is results which are probabilistic I mentioned that earlier these are statistical results and and and he He never liked the idea that nature is not fully determined down at the microscopic level.

15:14So he dreamt up an experiment in 1935, which we would now call entanglement, with two photons or two electrons, doesn't matter, that fly apart. And then you have two physicists, you know, Alice and Bob, they're usually called, and they can perform measurements independently on their respective photons. but the key thing is they can change their minds at the last minute. So, you know, Alice and Bob might say, well, we'll measure the momentum of each particle and we'll compare or we'll measure the position or something like that and we'll compare. But Alice might say, no, I've changed my mind and I'll measure something else.

15:50And Einstein, he was of the opinion that that only made sense if the particles already possessed definite values of those quantities. but according to Niels Bohr particles do not possess properties in advance of you measuring them it's not fair to say that when you do the measurement you're simply uncovering what already exists somehow you bring it into being and Einstein hated that idea and he called it spooky action at a distance but the final point about this sort of Alice and Bob and opposite sides of the lab is those experiments have been done and in the 1980s and Einstein got it wrong it is in fact the case that the properties of the particles what you choose to measure are brought into existence by the act of measurement and they're not already there from the get-go when the particles fly apart from the common center so somehow the experiment or the the measurement is bringing into being the reality of these separated particles it seems a bit like telepathy and some people mistakenly think you can send information faster than light that way you can't do that.

16:56But there is a correlation between these separated events that cannot be explained by saying that these particles had really existed in well-defined states prior to being measured. Schrödinger's cat was another way of illustrating the weirdness of quantum mechanics by saying, well, it's all very well down at the level of atoms and photons and so on. But at what point when you consider larger and larger objects, do these quantum effects go away? And Schrödinger had this idea of incarcerating a cat in a box i should say for cat lovers this is a thought experiment only i'm told that schrodinger did have a cat when he was living in oxford called milton and the plan was you put the cat in the box and there's a radioactive source and a file of cyanide and a 50 chance that say after one minute the the source has decayed and triggered the hammer that smashed the cyanide and kills the cat but if you seal the box if you consider it a sort of totally isolated system, you have to conclude the cat is both alive and dead.

17:57At the same time, with a 50 % probability, it's in a hybrid, it's an amalgam of alternative realities. You open the box and see, and then the quantum state collapses into either one or the other. But in the absence of the observation, it's an amalgam of both. And that just is a way of illustrating that surely somewhere between atom and cat, this theory breaks down. And yet, Many of my colleagues think it doesn't break down. They think it applies to the universe as a whole and that the only way of making sense of Schrodinger's cat is to suppose that there are two universes, one with a live cat and one with a dead cat.

18:33The Naked Scientist podcast is produced in association with Spitfire, cost-effective voice, internet and IP engineering services for UK businesses. Find out how Spitfire can empower your company at spitfire.co.uk. Music in the programme is sponsored by Epidemic Sound, perfect music for audio and video productions. This is the Naked Scientist podcast with me, Chris Smith. And today, Titans of Science is back and I'm joined by the acclaimed physicist and writer, Paul Davies. Did I read somewhere that the Chinese did an experiment where they did what Alice and Bob, the thought experiment, dreamt up by Einstein, set out to test.

19:15and they were sending particles or basically influencing things over a thousand kilometers apart so you you do the experiment and you've got a particle that's a thousand kilometers apart from another one and effectively they both change at the same time so the only way they could do that is if information traveled between the two faster than light which we know can't happen so there must be something else connecting these two particles even when they're a universe apart from each other that's right so you're referring to entanglement or in this case teleportation that is sending a bit or in quantum mechanics we call it a qubit of information from the ground up to a satellite that's a thousandths of kilometers there's no way that you can use this to send information faster than light it is correlation not causation and that's a really important distinction so you can you can sit down afterwards and say look at my results look at your results they're correlated there's a linkage between them but you because of the uncertainty in quantum mechanics you can't say i will choose to find this result and then i know you've got that result you can't do that all you can do is to say well it's weird yes what you found what i found are linked in this way that would be impossible if these particles really possessed well-defined properties prior to them being measured and so this is called teleportation and it's done by using entangled states and it will be the basis of a future quantum internet where you want to have a quantum computer coupled to another quantum computer and you want them to share a task and you have to somehow get the qubits from the one to the other without degrading them.

20:54This quantum teleportation which has been demonstrated it can really happen. The Chinese have done it and others have done it. That would be the basis of shunting that information around. All this is to come in the dazzling new technology of quantum 2.0. What is a quantum computer then? And why is it better potentially than what we already have? Right. So what we already have, that standard digital computer, is really just a whole lot of gates or switches, you know, on or off, one or zero. With a quantum computer, you make use of the fact that there isn't a single reality, but blended alternative realities.

21:28If you toss a coin, the coin will surely either be heads or tails. But a quantum coin can be in a blended superposition of all possible heads and tails. A little bit of heads and a lot of tails and all the way through to a lot of heads and a little bit of tails. And so you can have all of those things at once and then you can entangle them. You can have 100 coins in a state where all of those things are correlated. And that gives you exponentially more power to process information than you can with a conventional supercomputer. And this is realisable. This is a tractable thing. we can do this?

22:03Well, just last week, the company Continuum claimed they have now got the world's fastest computer. They have been to see me at Arizona State University. We have problems that we need a quantum computer for. Not the only company. Google is famously working on quantum computing. And there are claims and counterclaims who's got the best, who's got the fastest. We're not quite at the point now where you can say that you can go in a shop and buy a quantum computer that can outperform the world's fastest supercomputer. But if you believe the hype, you know, within maybe 10 years, that may be the state of affairs.

22:40It's good news if what you want to do is rapid modelling of climate or drug design, financial markets, all sorts of applications where you need more speed. But there's a flip side to that, which is that it's been shown if you have a quantum computer, a lot of the codes which people have used for their email messages and their financial transactions and spying and so on can be cracked by a quantum computer. So if you've got one, that coding system, that encryption is vulnerable. So there's a scramble among obviously government agencies, but companies as well to quantum proof their communications from here on.

23:18But everything up to now is vulnerable. And the folklore says that there are some bad actors vacuuming up vast amounts of data. So when they get their hands on a quantum computer one day, they can now get into all that stuff. And so those embarrassing love letters that you wrote to your biology teacher, or that dubious financial transaction in Panama and so on, you know, it'll all be out there on the internet for everyone to read. But can we not use the power of quantum to do even better encryption in a way that people won't be able to unpick? That's exactly right. So the flip side of being able to crack encryption is that quantum encryption, using quantum mechanics to do the encryption, is completely safe because you're encrypting not just by some sort of clever bit of mathematics, but a law of nature itself.

24:07And that's because when you make a measurement of something, you don't just unveil a pre-existing quantity. You start out with the quantum state is an amalgam of a vast number of different possible states of affairs. And then when you do a measurement, and you project out one of them. And that step is irreversible and you can't go back. So it's a tamper proof. A law of nature is protecting your encryption. You've devoted quite a lot of your time to looking at quantum gravity. What's the question there that the quantum realm applies in gravity? Right. So I've said that quantum mechanics is the most successful scientific theory ever.

24:46It displays the nature of matter all the way from subatomic particles up to stars, blah, blah, blah. gives us all this technology. Surely this is, you know, the miracle cure-all that will unify all of physics. But unfortunately, when you apply it to gravitation, you run into a problem. If you just sit down and try and do the same thing as you do for the electromagnetic field, you end up with gobbledygook, you get nonsense. And this has been a fundamental problem in theoretical physics for decades. Some of my colleagues have devoted their entire career to trying to produce a quantum theory of gravitation that would pass muster and then you'd have gravitons playing the role for gravitation that photons play for electromagnetism nobody's ever seen a graviton it would be very hard to detect it so it's hard to have any experimental constraint on this but just theoretically just trying to come up with a mathematical theory that consistently describes how gravitation and quantum mechanics fit together has proved incredibly tough so it's a work in progress.

25:48What do you do to relax Paul because it's we've had a wonderful conversation it's amazing the pace your brain works at is awe-inspiring but how on earth do you turn it off? I suppose the short answer is I play something called pickleball it's taken the United States by storm it's an extraordinary game it's particularly good when you get old because it's very forgiving and it's a type of social game that you can get better at and so it's a challenge but because it's always played in a in a sort of social environment it's actually a very good thing there was an article in the new yorker can pickleball save american democracy and i think that that says it all you're 78 78 79 and and still going strong at arizona state university so you're continuing to do research and everything there no plans to to slow down from time to time I talk about retirement and my wife vetoes any mention of the R word.

26:45And I'm involved in a lot of projects. I'm going back to Arizona next week. I'm going to be teaching quantum 2.0 to undergraduates next semester. So now it's all systems go. And I don't know, there must come a point when I will quit or drop dead on the job. I mean, that's probably a better way to go. you have met the dalai lama that's quite something to have done in your career yeah i've done two events for the dalai lama the first was in london and he spoke about the concept of time in eastern philosophy and i spoke about the concept of time in fundamental physics and then we did another one in canberra where we were talking about consciousness and you know dualism and different theories of consciousness so uh yes you know he's got a soft spot for theoretical physics and uh and he's a lovely individual and so i greatly enjoyed those occasions i didn't have him down as a quantum mechanicist though oh no he's he's very much uh into quantum mechanics uh and so uh because in some ways the relationship between the part and the whole uh which quantum mechanics uh unearths the the fact that when you uh do do a measurement i've been talking about measuring a position of a atom or something like that you have a big chunk of measuring apparatus but somehow that big chunk of stuff is projecting out the reality at the micro level but the big chunk of stuff's made of atoms anyway and so somehow this looping between the the large and the small the parts and the whole is much more subtle than it would be in sort of standard reductionistic western thinking so much more amenable to eastern thought so i think fits very very well into buddhist philosophy and talking of big chunks of stuff this asteroid the paul davies asteroid where'd that come from i wish i could point in the sky to where it is as we sit here it's in the it's a main belt asteroid so it's not going to hit the earth i think won't hit the earth goes around and around how did it come to be named after me you may be wondering well in the early days uh there wasn't very much uh interest in tracking down these asteroids they do hit the earth from time to time they can cause damage and the threat from these killer asteroids hadn't been quantified when I began getting interested in this subject about 40 years ago.

29:07And I was part of a small group of people campaigning for more research funding to be put into tracking them down and trying to understand what they're made of and what their orbits are. My real interest, I might say, in this is that if a large comet or asteroid hits the Earth, it splashes material all around the solar system, some of that material can go to Mars and cocooned in these Earth rocks could be microbes that would land on Mars and make a living there and vice versa. Mars rocks come to Earth and if there was ever life on Mars it would be brought to Earth in this impact ejector and so that's the reason I got into this in the early 1990s and as a result of that a friend of mine very kindly proposed my name for an asteroid so there we are you can look it up.

29:56Have you actually seen any pictures of it uh well i wish i could say yes but you know asteroids are such small things and so far away that's a little dot of light and so um uh would be nice to think it has a smiley face or something but uh no uh just just a little dot in the sky our titan of science this week that's paul davies with a whistle stop tour of the world of quantum mechanics and what the future holds for the quantum realm that's all we've got for today do join us on friday though when we'll bring you the latest on a new strain of monkeypox virus that's circulating including in the uk and the science behind the winter blues a big thanks meanwhile to all of you who are helping us out with our running costs by making very generous donations and some of you send us lovely comments to go with those thank you we read all of them and we do write back to you if you'd like to support the program because you appreciate what we do for you each week please help us out it's at nakedscientist.com forward slash donate.

30:53You can also leave us a review on your favourite podcasting platform or follow us on Instagram, LinkedIn and X. And of course, if you don't already, do subscribe to the programme wherever you get your podcasts. The Naked Scientist is supported by Rolls-Royce. I'm Chris Smith and from all of us here at the team, thank you for listening and until next time, goodbye.

31:20Thank you.