#119 Jim Al-Khalili - The Strange World of Quantum Physics

0:00The NFL is back and FanDuel's got everything you need to play your game. From same game parlays to live betting. Right now, new customers bet$5 and get$300 in bonus bets if you win. 21 plus and present in Iowa. Must be first online real money wager. $5 deposit required. Bonus issued is non-withdrawable bonus bets that expire seven days after receipt. Restrictions apply. See full terms at fanduel.com slash sportsbook. Gambling problem? Call 1-800-BETS-OFF. Jim Al-Khalili, welcome to the show. Jim Al - Pleasure to be here. Once upon a time, when doing a lecture at the Royal Institution, you spoke about the famous double split experiment, this strange quantum phenomenon whereby something sort of appears to, light appears to act as a wave and a particle at the same time.

0:49And you issued a challenge. You said, now, if anybody thinks that they can offer a commonsensical explanation for this kind of thing, then do send me an email. How did that work out for you? I wish I hadn't done that. I'd forgotten that I wasn't just talking to the 300 or 400 people in the audience at the Royal Institution. But obviously, it gets recorded and goes out on their YouTube channel. To this day, I mean, that's about 10 years ago now. To this day, I receive, on average, one or two emails a week from people saying, I've solved the two slits mystery. You know, where's my Nobel Prize? No, we've tried that.

1:26There's a lot that's strange about quantum mechanics. Maybe we'll get into a few more of those things later on. But the American, the great American physicist Richard Feynman said that the two slit experiment is sort of encompasses the central mystery of quantum mechanics. that we know that if when you send light through two slits and you get interference patterns, light and dark fringes, what's weird is that sending particles, indeed even entire atoms through, you get the same wave-like behavior when you send particles through. So I went through in this lecture, I went through how come, you know, quantum mechanics is this wonderful, powerful theory that has revolutionized the world.

2:12uh helped our understanding of the subatomic world and yet at its heart there's this counterintuitive idea manifesting in this two-slit experiment that we still can't explain properly yeah yeah so quantum mechanics is stereotypically thought of as the sort of weird spooky kind of creepy uh leaves room for new ages to get in and say there's all kinds of you know this could explain telepathy and this and that. There was certainly a time when we start discovering these strange quantum phenomena and we think, this is completely inexplicable. It still has that reputation today, but it's been a hundred years.

2:51Is it still legitimate to say, as Richard Feynman also famously said, anyone who thinks they understand quantum mechanics doesn't understand quantum mechanics. Is it still true to say that it is just weird and creepy and spooky? Not all physicists and indeed chemists who also use quantum mechanics would agree on this. I would say yes, it is as mysterious as it's ever been. The fact is, it's also been such a powerful mathematical theory. It's helped us invent all sorts of things, you know, developing, understanding semiconductors, developing microchips and computers and smartphones and lasers and so on.

3:30it works and it tells us how the atomic and subatomic world behaves. But at its heart, it is still mysterious. And we do not yet have an agreed upon explanation of how. It's the only theory in all of science that seems to have got away with not requiring a narrative, an interpretation to explain the mathematical formalism. We have half a dozen or more different ways of explaining it. And you might say, well, so what? Because it hasn't stopped us doing the science, hasn't stopped us understanding the world. But at its heart, physicists and philosophers, I think, should still be worrying about this.

4:13Yeah. Well, people often talk about interpretations of quantum mechanics, the Copenhagen interpretation, the many worlds interpretation, whatever. You don't hear people talk about different interpretations of gravitational theory in the same way. Why not? Like, what's going on with that? Because we do have a single interpretation. I mean, when we think about Einstein developing relativity theory, his special theory in 1905, the mathematics for that was pretty much sorted out. People like Lorentz and Poincaré had already developed the equations. What they didn't have was the correct interpretation.

4:53What is this telling us about reality? Einstein comes along, he doesn't come up with new mathematics. He comes up with the correct interpretation, the narrative, the explanation of what this theory is telling us about the world. You know, that nothing can go faster than light, that time and space must be unified into 4D space-time. And Einstein is then credited with relativity theory. It's the interpretation, the explanation that's important. No other theory is like quantum mechanics, where the maths works, describes the subatomic world tells us about how atoms fit together and electrons fit orbit around the atomic nucleus and so on but we have these half a dozen or more different ways of explaining what's going on and we can't agree on which one's right yeah well it's the difference between like a mathematical model that like predicts outcomes and i hesitate to use the word explains but you know let's say describes uh the various activities of subatomic particles that is a separate question from the ontology what is the stuff like people will will commonly think about you know particles being in two places at once and being here and there at the same time and and and that's probably some kind of confusion between our mathematical models which sort of act as though you know a particle is in two places at once whether it actually is or not is a totally different question and i think you and i probably both agree that it's it's not actually in two places at once but it's like our mathematics describes it as such because it's useful so does the quantum physicist of the modern era have much at all to say scientifically beyond their like philosophical hunches and interpretation of the data do they have anything like scientific to say about what is actually going on more so now than a generation or two or three ago sure i mean certainly when i started as a PhD student in the 80s, it was very much the case that, look, quantum mechanics is a mathematical theory.

6:57It works. If you want to do philosophy, go and do philosophy. But a physicist uses it. So this is the Copenhagen view. Sometimes it's simplified into the shut up and calculate interpretation. It works. Don't worry. You're a pretty little head about how and why. We can't say, Copenhagen view says we can't say anything more about the quantum world beyond what we can measure and observe. What's going on behind the curtain before we look, we have nothing to say about it. Not that it doesn't so much exist, but we have nothing to say about it. I was always uncomfortable about that. And I felt somehow, you know, not that I was out on a limb, but it wasn't the prevailing attitude to worry.

7:38I think something must be going on. You mentioned, you know, the you know, there is something, some objective reality out there that wasn't even regarded as, as, you know, cut and dried. You know, the quantum mechanics just tells us what we, you know, the results are making predictions about the results of measurements. Most physicists today, I would say, maybe not my generation, but younger than me, are a bit more concerned. There is something going on. I want to understand what it is. That should be the job of the physicist. As John Bell famously said, the job of the physicist is to understand the world, contra Niels Bohr, who in one of your books you sort of blame for this functionalist view of science to some degree.

8:24Which is a shame, because I mean, Niels Bohr's a great hero of mine. But yeah, I mean, if Niels Bohr and John Bell, I'm siding with Bell. Yeah, because they have this conversation, which I've been talking about so much recently, about what science actually does. And in fairness, I am more in line with the view that science is functional, that it only describes and doesn't really explain or tell us about the nature of what things are. But I'm definitely in your camp that whether you call it science or not, we should be interested in what stuff actually is. I mean, when I spoke to Sabina Hossenfelder, I was asking her about if I blew a trumpet.

8:59And I discovered that every time I blow this trumpet, red light turns on over there and i thought that's interesting and i figured out that if i if i blow it harder if it's louder the the light is brighter and if it's a different note it's a different color and i worked out exactly what was going on and so i came up with this predictive machine perfectly accurate i can if i if i play this note at this uh volume the light will do this and i got it right every single time and somebody asked me like why does the light turn on i said well because i blew the trumpet it's like but but why does it do that and sabina hossenfelder sort of said to me that's it that's that's enough that's what science does and i'm like how could you how could you not i couldn't sleep at night if that's what science was about you know if all we cared about was i remember someone telling me that um they wore you can wear these copper bands bracelets that seem to have some medical curative power.

9:54And it's the same with a lot of alternative medicines. But it works. We don't care what the mechanism is. The fact that it works is enough. For me, as a physicist, no, I want to understand how and why. If all you care about is applying some mathematical equation, that for me is, I don't know, that's engineering. Yeah, yeah. A physicist wants to understand how. How did the trumpet get to the light? What is the interaction, the force between them that's causing that to happen? But to what degree do you think that science can answer that question fundamentally? Like, what stuff actually is? Because the reason I ask is because, you know, if I were to ask what a table is, you might tell me this table is made out of wood, and if I ask you what wood's made out of, and so on and so forth, we get down to an atom, an atom's made out of an electron.

10:43Well, what's an electron? and at this point a lot of philosophers of science will say that the only answer is something like well an electron is a negatively charged particle well what does that mean oh it means it acts in this way it repels other negatives yes but that's not what it is that's what it does and so at a fundamental level especially in the quantum realm where we're dealing with what are hopefully or if they're not hopefully we'll find at some point atoms in the true sense of being atomic like like fundamental particles and we're asking what those things are not what they do not how they behave or how they relate to each other, what they are.

11:16Do you think that is a question for the physicist? I think it is, and I think they should try. It may be that we're peeling back layers of the onion. And it's also true that there are different scales at which certain explanations are sufficient. I don't need to understand the workings of the standard model of particle physics to work out how a washing machine works. you know at the level of table it's made of wood and wood has this property that may be enough for my explanatory satisfaction of but i can go deeper and i can talk about it being made of of atoms and atoms being made of smaller particles and it may well be that there's more to come but i don't i think had we stopped had physicists said no it's enough to know that a table is made of wood we wouldn't understand then the nature of atoms.

12:12We have tried to go deeper and very often we have arrived at what objective reality is at a deeper scale. That may not be the end point. Of course, there may not be an end point. We may never reach it. We may not be able to. But there is a truth about the true nature of reality. There's another concern that people have about, well, all we are ever doing is perceiving the world and so building models in our heads. That's epistemology rather than ontology. But there is a real world out there. And I think the job of physicists is to get as close as possible to that objective truth. Yeah, I find it interesting.

12:51I've heard such a variety of views, not just on whether it's accessible to science, but what that fundamental stuff might be. You know, I have Brian Greene telling me it might be vibrating strings. I have Philip Goff telling me it might be consciousness itself. I have theists telling me that it's being and that all participates in God. And the one thing that I've realized is that the people who seem least confident in having a view on what the thing is, the ontology, tend to be the scientists I speak to. Either because they think that explanation consists in descriptions and models and mathematical predictions and stuff, like Sabina Hossenfelder did, or because they recognize that it's a question that's very difficult not to be a bit agnostic on.

13:33And it's like the philosophers who sort of have that kind of confidence. but at the very least I agree with you that it should be a project for whoever you are I think I would side more with that latter view that there's a certain built-in agnosticism in the scientific method that we should not be so confident and sure of our explanations because something may come along tomorrow and overturn those views a good scientist is one who's prepared to change their minds. When it becomes an article of faith or belief, if you are so confident that string theory is the correct description of reality, then you're not doing science properly because you need evidence.

14:15Physics is an empirical pursuit. We need data and we need to observe and we need to be prepared to change our minds. So physicists acknowledge that there have been revolutions in science all the time overturning previous ideas. So what is it about quantum mechanics that makes it so subject to different interpretations and difficulty and weirdness? Is that something intrinsic to quantum mechanics or is that just because it's the newest thing that we're interacting with? Or is it actually about quantum mechanics itself? It is. I think we've, you know, after 100 years, and it's not taken us that long, but I mean, very soon we realize that it's something intrinsic to the description of the quantum.

14:56The way the quantum world behaves is very, and it's not just that it's far removed from our own everyday senses and experiences. It really is strange. and it's like the bump under a fitted carpet. You can move that bump around. You can shove it behind the sofa, behind the TV so it doesn't show up. But that bump is somewhere. You can say that bump is many worlds branching out. You can say it's a non-local field a la de Broglie-Bohm mechanics. You can say the quantum wave function spontaneously collapses. There are lots of ways of explaining. But that weirdness is there. It's where you leave it, where you decide the weirdness originates is what we can't agree on.

15:45Yes. And so people will have ideas. There'll be people listening who are super familiar with quantum mechanics and some who think to themselves, OK, I know about quantum mechanics. I've heard of the double split experiment, something about particles and waves at the same time, two places at once, entanglement. But as we've already indicated, some people have misconceptions about what. So can you help us to dispel one or maybe a couple of important misconceptions about why quantum mechanics is weird and then give us an indication of some of the things that actually do make it a bit weird? Well, I mean, very often one of the most often asked questions I get when I give public lectures is quantum mechanics and consciousness.

16:29And this goes back to work of Roger Penrose and Hameroff talking about the nature of consciousness having some quantum origin. And most quantum physicists will say, look, quantum mechanics is mysterious. Consciousness is mysterious. That doesn't mean the two are connected. It may be that they're connected, but we're a long way from being able to see that. And people say, oh, you know, entanglement, quantum entanglement, this weird property that Einstein didn't like, he called it spooky action at a distance. Two separated particles can nevertheless be part of the same quantum state and therefore instantly in connection, communication with each other.

17:10People say, oh, well, that will explain telepathy, or that'll explain why twins somehow can sense, you know, when the other one is something's happened to the other one, they can sense it, because their brains are quantum entangled. The fact is, these strange quantum phenomena and mechanisms are very much confined almost always to that subatomic realm. They are ephemeral, delicate features that disappear very quickly. We now, in modern terms, we say the quantum effects decohere. The quantum weirdness, the being in two places at once business, dissipates like heat dissipating from a hot object when you put it in the freezer very quickly once you scale up.

17:56So when you scale up to our everyday world, the idea that you can invoke quantum mechanics to describe telekinesis or telepathy or the nature of consciousness or alternative medicines, it doesn't fit with the science. Just because quantum mechanics is weird doesn't mean we're allowed to invoke it to explain any other mysteries we don't understand. Some people might say, for example, it's a little bit weird that some birds, for example, seem to be able to measure the magnetic pole of the Earth and use it to navigate. And it's a little bit strange that they seem to have this ability to navigate just based on this magnetism of the Earth that we can't perceive.

18:42And as far as I understand, especially with some of your work in quantum biology, which is really exciting, one great theory for the way that they do that involves, quantum entanglement in the eye right and so people might say okay let's not jump the gun let's not say anything without evidence but doesn't this weirdness at the quantum level at least open the door to the possibility of a lot more weird kind of macro level stuff it does and i think this is where our earlier conversation about wanting to understand how something happens with the ideas that these birds and certain other mammals have this magnetoreception.

19:22First of all, that was discovered back in the 70s before anyone thought about a quantum origin for it. And even then, it was poo-pooed despite the research being published in one of the top journals in science. In fact, the journal called Science. People were arguing, how can, And, you know, the Earth's magnetic field is so weak. It's one thing sticking you in an MRI scanner and mapping the body because those are huge magnetic fields. The Earth's magnetic field is so weak. How could it possibly have any effect on chemistry inside living organisms? And yet they found evidence that these birds really could sense the orientation of the Earth's magnetic field.

20:06Not like a normal compass, but simply how far away from the North or South Pole they were. The lines of field, the iron filings, if you were to scatter around the Earth, assuming the Earth's a big magnet, whether they're parallel with the ground or vertical. Birds could sense that. And no one knew how that could happen. Where was this built-in compass inside these creatures? We know it works, but how? Well, quantum entanglement inside a protein called cryptochrome inside the bird's retina is far-fetched, but it's the only theory that we can actually explain step by step. There's a whole chain of your trumpet to the light.

20:53There's a whole sequence of mechanisms in the real physical world that start off with this strange quantum mechanism entanglement that will explain how these birds get directional information. It may not be true, but here is an example. But you're looking at two electrons spinning in different directions within a molecule inside the retina. That's down at the quantum level. That doesn't mean you can scale up and say, well, quantum entanglement can explain telepathy, for example. It is strange to think that there are these like effects and truths and mechanisms that just disappear as you get bigger.

21:40And the question that raises for me is that, I mean, famously, the big trouble is that we've got this quantum mechanics over here, and we've got our macro classical physics over here, like Einstein's theory of relativity, and they don't want to go together. Maybe we might want to talk about why they don't go together, but most people know that they just don't somehow. And the goal is this theory of everything or something that will at least unify those two explanations yeah is it possible that for some reason that we don't yet understand things do just work differently at the quantum level such that you will never have a quantum theory of gravity or some classical understanding of quantum mechanics because that sounds weird but it also sounds really weird to me to say that there are all of these things like entanglement and tunneling and stuff that if you increase the size enough they they just vanish into into thin air yeah i mean there are two issues one is you know how how do you move smoothly from the quantum world to our everyday classical world and that doesn't require going on to einstein's general relativity it's just simply where's the boundary between what is quantum what is classical and i think we're starting to understand that okay as As you get more and more quantum systems accumulating, then they become more and more entangled and it's more and more difficult to keep hold of the delicate quantum effects.

23:04It gets washed out. You get what's called decoherence. The early pioneers of quantum mechanics, Niels Bohr and Heisenberg, people like that, talked about there being a sort of a cut, some hard boundary between the quantum world and our classical Newtonian world. And they said, you know, how do you get something from the quantum realm, the entanglement, the two places at once business to our sensible results? We never see two people in the same, you know, one person in the same two places. and they called it some irreversible act of amplification which is just vague now we're starting to understand it's to do with increasing entanglement increasing decoherence where the quantum weirdness leaks away and as a physical as a physical mechanism as something we can understand what we don't yet know is how to unify quantum mechanics with the more accurate picture of the large-scale reality, which is Einstein's general theory of relativity, Einstein's theory of gravity.

24:07And there, it doesn't work simply because the mathematics, the theories are very different. They just don't mesh together. It's an interesting point that you mentioned, that maybe they don't, maybe each to their own domain, and we have to live with that. But there are situations where you would want both to explain what's going on. For example, the singularity at the center of a black hole or the big bang or even if you think about it um imagine a single electron in a superposition a quantum superposition or being two places at once essentially you're saying it's not the electron is into is is is is doubled up it's one electron but its quantum state is spread out what electron has mass uh and and we know from general relativity that mass causes space-time to bend.

25:01Ever so slightly for the case of an electron because it's a very tiny mass. Nevertheless, that would mean that space-time is in a superposition of bending in two different places. Now, if we want to talk about space-time, we need general relativity. Curb is your space-time, general relativity. And yet the superposition thing is quantum mechanics. So there's an example, even though it'd be far too tiny to actually check experimentally, nevertheless, theoretically, in principle, you need both theories to explain it that's interesting so you can't just say well we'll never have to worry about general relativity maybe in practice we never will but in principle we should always need yeah some combined theory never considered the effect of the mass of quantum particles i i read it it's not i mean i read it somewhere someone else very clever pointed this out to think about good example i'll use that but then you know some people might say like well there are all kinds of paradoxes of space which seem to indicate that maybe there is just a smallest possible distance and maybe that's somehow related to space-time and that like if you get small enough or if you get to the to the smallest possible distance it's also the smallest possible unit of space-time and therefore it can't be you know bent or shapen in any way because it's as small as it can get very least it's a it's a bloody mystery isn't it i mean it It is.

26:20And we have ideas and people can spend their whole careers pursuing a particular way of explaining things, whether it's something like string theory or what goes on down at this so-called Planck scale. But the deeper you go, the harder it is to test your ideas. And ultimately, as I mentioned before, physics is an empirical science. We need data, observation, experimental evidence to tell us that our theory is on the right tracks. We don't know how to do that when we are probing reality at such a scale you've been doing a lot of work on time recently and when we talk about this one thing that comes to mind for me as someone who's not a scientist and so i don't know if this is relevant at all but part of the problem with like quantum mechanics is for example these uh these entangled particles seeming to be able to communicate instantly across space the interesting thing about relativity for me is that it shows that time is not linear time travels at different rates depending on like mass spending space time but on the quantum level to talk about this weirdness of like instantaneous information travel does that kind of assume that there is a universal present in other words is the problem of time relevant to the inconsistency between relativity and quantum mechanics?

27:40I believe, yes. I think we're struggling to reconcile not just quantum mechanics with general relativity, but also with the other big idea in physics, thermodynamics. And it's strange that each of those three big pillars of physics describes time in a different way. So quantum mechanics, like Newtonian mechanics, in fact, you know, classical mechanics that we learn at school, regards time simply as a label, as a parameter. It's called coordinate time. So it's basically, here's an equation that describes how something changes. I can work out what it states is at a particular moment. Then if I change that T in the equation, T for time, to some other value, I can crank the handle and work out what that system's doing at that later time or at an earlier time.

28:30That's what time is. It's just a parameter that goes into an equation. General relativity says, no, time isn't just a number. Time is a dimension. It's part of the fabric of four-dimensional space-time. It's a real thing. In fact, it's, you know, all times coexist. And the thermodynamics says, no, time isn't a dimension. It's not a number. It's an arrow. It's a direction pointing from past to future in the direction of increasing so-called entropy. So I think until we reconcile these very, very different pictures of physical time, we're not going to be able to reconcile those theories themselves together.

29:06I think time may not be the central thing that needs to be solved to get it, but I think it's part of that question. Until we understand these different ways of describing time, we're not going to come up with a theory of everything. Yeah. I mean, time sort of looms over everything. You can always forget that it's there for some time when you're talking about atoms and how they interact and stuff. And suddenly you realize that all of that is happening and the conversation that we're having is also happening through time. Aristotle famously said that when he's not asked to define it, he knows what time is.

29:40But the moment someone asks him to explain it or define it, he's like, I haven't the foggiest. I think it's quite boring when people bring physicists on podcasts and ask them things like, do aliens exist or like you know why is quantum mechanics so weird and one of the questions that's that's along that line is like what is time man but i think unavoidably and i'm not necessarily asking for for an overview of the philosophy of time but but for you with with the work that you've been doing what what do you think time is how can we start talking about it well i start with you know what um a number of philosophers uh uh do which is to divide it into two categories There's physical time, which is the time that appears in quantum mechanics and relativity and thermodynamics.

30:26It's the objective, the time that's out there that we try to understand. And then there's what we call manifest time, our psychological time. And it's one of those subjects, we're embedded in time. It's so difficult to extract yourself from it and look at it and study it objectively. We can't help but being embedded in time. And it's the manifest time, psychological time, that gives us this notion that time flows. uh that time that there's a now that's real and that the past has gone and the future has yet to exist um and it's i think one of the main problems is how do you reconcile our psychological perception of time this manifest time with with physical time uh physical time says there's no such thing as flow that's just an illusion but then some physicists and philosophers will go even further and say, look, the whole time itself is just an illusion.

31:19Some would even go as far as saying time is just something we invented to order events or to measure intervals between one event and another. I don't agree with that. I think time is real. I think it exists in the same way that space exists, but not in the way that Newton believed, which said that time was absolute. There's some cosmic clock ticking by the seconds, minutes, and years independently of us. certainly within relativity theory which probably is our best theory of time space time is real it's a fabric of of reality uh reconciling that with the idea that the equations of physics are time symmetric and that the time comes in just as a parameter or that time has a direction from past to future that is still a problem in studying the nature of time and it has been since aristotle and before yeah and it's funny because you know you can you can say all of that and and i still feel like i'm left with this question but like but what is it like what what is the thing that we're talking about you know like you say that well there's this idea that we move through time okay well if time is a dimension like space is well i i can kind of feel like i i can move through space i can move through space i can see what that's like i'm moving my hand but I feel like I'm moving through time but if I try to pay attention to what's it what's it like you know what's it like to wave my hand left and right well I can I can feel it I can move it I can what's it like to move through time maybe because we can't turn it off it's it's kind of yeah impossible to know so I'm not sure what like even mental image to have like when I think of space-time for example in the physical sense of like the three dimensions of space and being warped by objects of mass I imagine as I imagine most people do like a bunch of lines running through space like making all these cubes that grow and expand and that's probably not accurate right but it's close enough that i can kind of think about things in that term but when someone says time and you're picturing in your head like moving through time literally like what imagery are you thinking of what what kind of thing are we are we getting at yeah i mean typically in physics we talk about 4d space time or what we do is is throw away one of the dimensions of space so we only have two dimensions of space and one of time so then we have a 3D block, it's called the block universe that allows us then to maybe get a sense of what space time 4D space time means, that's before you even start bending it, warping it due to gravity but in that picture you're right, you know you can look at space and say well I can get from one place to another I can be over here, I can be over there I can get over there, I can go back there again at a different time but you can't visit different times and yet the block universe would say all times coexist just as all points in space coexist so what is it about what we call now that that's the the present moment that seems to us according to manifest time to be drifting along flowing along the time axis yeah that that is all we can do and then even we think about in cosmology we talk about um well the universe entirely is described by general relativity 4d space time so yeah but the universe is expanding well it's space that's expanding not time and the only way to get that picture is you start off with einstein's equations and you you manipulate them to get a new equation uh called the friedman equations which has space stretching over time and that's that's an equation like newton's equations or quantum quantum mechanics their time appears as like a like a coordinate yeah right that shows so we we have to revert to things changing over time in order to get any sense of them what general relativity tells us about time is not something we can visualize other than mathematically and so much about how we understand these things i think it's down to how we visualize it i mean at one point in some way you i think i'm sure it was you who wrote about this i thought it was quite funny where you said well one thing we know about time is that you know time seems to move forward and then you were like or does it because you could say that if you imagine yourself as still and time is like moving past you then time actually moves backwards and so you were sort of moving through it as it goes yeah i thought oh god yeah okay fair enough i like both of those seem like completely equally legitimate ways of thinking about it time moves forward time moves backwards and i began to realize how much of what i understand about time is just based on the image I have.

35:51Yeah, we think about the river of time flowing from the past to the future. But actually it's not. It's flowing from the future to the past. If you're on a boat moving along, drifting along in the river of time, you're looking backwards. You're looking at the past receding away from you into the distance. The future coming at you, you can't see. It's behind your back. And that makes a lot more sense in terms of the fact that we can remember the past, but we can't remember the future, right? It makes more sense to look at it that way. You've talked about this block universe, which you can sort of imagine being God, like zooming out, seeing the universe, including the beginning of time and the end of time, all at once right in front of you.