Episode Summary
A hundred years after quantum mechanics was invented, physics is still living with its consequences. Since Werner Heisenberg and Erwin Schrödinger, the theory has transformed science and technology, explaining atomic structure and enabling much of the modern world. But its success has never erased a deeper puzzle: how the quantum world relates to the classical one we actually experience.
Quantum theory is notorious for its “weirdness,” which makes sense: Superposition, measurement, and uncertainty are real physical ideas—but they’ve also been repackaged into “quantum woo” that labels superstitions as profound science.
Despite the mystical nonsense though, understanding how classical and quantum systems relate remains the biggest challenge of the physical sciences, but as my guest on today’s episode argues, some of those difficulties are caused by the famous “Copenhagen interpretation” of quantum physics, which can overstate the observer’s role and understate the continuity of quantum dynamics.
In his account, reality is quantum all the way down, and what we call objects are stable processes, not tiny building billiard balls.
Vlatko Vedral is a professor of quantum information science at Oxford University. He’s out now with a book explaining his theories in a more popular format called Portals to a New Reality: Five Pathways to the Future of Physics.
The video of our conversation is available, the transcript is below. Because of its length, some podcast apps and email programs may truncate it. Access the episode page to get the full text. You can subscribe to Theory of Change and other Flux podcasts on Apple Podcasts, Spotify, Amazon Podcasts, YouTube, Patreon, Substack, and elsewhere.
Audio Chapters
00:00 — Introduction
06:42 — An “observer” in quantum mechanics has nothing to do with a person
15:28 — The confusion caused by the ‘Copenhagen’ interpretation of quantum fundamentals
22:47 — Schrödinger’s cat thought experiment was a criticism of quantum duality views
28:08 — Eric Weinstein’s Geometric Unity speculations
35:11 — How to test new quantum theories
44:16 — Information theory and quantum computing
50:43 — Q-numbers, C-numbers, and quantum logic
56:51 — The advantages of a process physics over a thing physics
Audio Transcript
The following is a machine-generated transcript of the audio that has not been proofed. It is provided for convenience purposes only.
MATTHEW SHEFFIELD: So normally we don’t cover physics on the show too much, I would say. But what you’re doing here is really important, I think, in a lot of ways. So essentially, what you’re trying to do is to say that, and we will get into the details more specifically, but just generically, would you say that you’re trying to say that what people conceive of as classical mechanics and quantum mechanics, they’re not in conflict the way that a lot of people often think?
VLATKO VEDRAL: Yes, I think so. I think you hear all sorts of statements. I think it’s a very nice summary of the spirit of most of my writing, that of course, quantum mechanics was, was a big revolution and it surprised many people at that time. But if you look at it in terms of how big a departure this is from classical mechanics, then it’s very similar to the past revolutions that we had.
So certainly you can recover all of the classical ideas in, in a very special limiting case and the two theories. So quantum mechanics in that sense can reproduce the classical world. And if you [00:04:00] see it like that, you see that there is a continuity going through all of these theories as they develop in the history of physics.
SHEFFIELD: Exactly. And we’ll get further into that as we go along here. But so just to do some, a little bit basic table setting here. I think probably the biggest difference from how people conceive of chemistry or classical mechanics is that quantum objects are not like little tiny billiard balls.
VEDRAL: Yes.
SHEFFIELD: They are processes of things that exist in, in a flux, if you will. But can you just kind of explain that a little bit better than I did just there?
VEDRAL: Yes. I think that’s the key feature actually the technical word is the superposition principle, which actually states that any quantum object, any quantum particle, like an electron or an atom, and we’ve tested it with much bigger objects than than that in the last a hundred years, can actually exist in many different states at the same time.
So you, if you’re thinking about an electron. It could exist within an atom closer to the nucleus of the atom and further away from the nucleus simultaneously. And that’s called a quantum superposition. And that’s of course something that doesn’t have any analog in classical mechanics because in classical mechanics, objects have well-defined positions.
They’re localized. They’re either here or there, but not simultaneously in two positions. And the same with all other properties. If they have an energy, they have a well-defined energy, they have a well-defined velocity. Motion is well-defined. Whereas in quantum mechanics, it seems that you have to acknowledge that actually, we need to deal with probabilities at the fundamental level.
so we can never say for sure where particles are. Unless we make [00:06:00] a measurement to confirm where they are. But even then, very quickly after the measurement, the particle will spread across the space and we’ll assume, this state of superposition of being in many different locations at the same time.
And that gives rise to all sorts of other things that I think are out there in the, public domain. Things like entanglement the effect that Schrödinger talked about a lot, how quantum systems jointly can be in a super position in a way that they’re super correlated to one another. So there, there are all sorts of interesting phenomena, but they can all be explained through this property of being in, many states at the same time.
An “observer” in quantum mechanics has nothing to do with a person
SHEFFIELD: Yeah, exactly. And the idea also the superposition state and how it can be perceived in multiple different ways that gives rise, to the idea of the observer. yes, but a lot, of times, when people who are not physicists are thinking about an observer, they think of it as a person. And that’s not what an observer means in quantum mechanics. and I think that, that ambiguity causes a lot of confusion for people.
VEDRAL: I think you’re absolutely right, and I love the fact that you’re, stressing this right at the beginning of the discussion.
because it leads to all sorts of statements that, that really go well beyond physics. And in fact, they have no support in physics at all, statements. like, if you really observe something, you can change your reality. If you focus on something, you can really make it happen and things like that.
Nothing like that exists in quantum mechanics. what does exist is simply, again, going back to Schrödinger, is that when you make an observation and you’re absolutely right to emphasize that, An observer could be any other physical system, and observation doesn’t need to involve human beings at all.[00:08:00]
In fact, it doesn’t have to be a computer at all. It doesn’t have to be as sophisticated as what we would call, a computer. It could be simply an atom being observed by another atom. and so what happens during the observation is that the states of these atoms become entangled, in Schrödinger’s language, which means that for every position of one of these atoms, there is a corresponding position of the other atom.
So they’re somehow locked in this perfect correlation that their positions perfectly mirror one another, and that’s where the measurement stops. As far as the quantum physicist is concerned, you would say, I’ve now demonstrated that one of these atoms has measured another one. Now, of course you can, and ultimately a physicist does get involved, in confirming this, which means that you will now measure one of these atoms.
And what will happen is that you will see only one of these positions manifest itself. and this is the property that I think causes many people to, speculate and to become confused because quantum physics does not tell us, and in fact, it cannot tell us in advance which of these outcomes you will see when you observe a quantum system.
So this is part, this is something that’s called a Heisenberg Uncertainty principle, which means that if you’re in a position in a super position of different locations, but you insist on asking what location is the system at a given time, you will only get randomly one of these possible locations.
and all we can calculate is the probability to obtain that. So that’s what quantum mechanics gives us. So if you repeat the same measurement many, times and you get an expected value. And then that’s the value that quantum mechanics predicts. But [00:10:00] each individual measurement, if you like, is as far as quantum formalism is concerned.
And as far as all the experiments are con concerned, really random, you cannot predict this outcome. And so that’s what’s interesting. And I kind of developed this in my writings. What does this really mean for our reality? What kind of reality is that? and, I think, but that’s the crux of the question.
SHEFFIELD: Yeah. Well, and, it’s also it appears to be random, but whether it actually is, not known at the present moment.
VEDRAL: Absolutely, and that’s another excellent point that in fact when we talk about two atoms it’s not random at all. the state that you get between two atoms when you make it so that through interaction, one of them measures the other atom is a completely deterministic state.
It’s a well-defined state. It’s an entangle state, admittedly, so it doesn’t have any classical counterparts and shorting a cold entanglement, the characteristic trait, it’s really the trait of quantum mechanics that doesn’t exist in, in any Newtonian classical physics. But nevertheless. There is nothing random about that state at all.
The state is deterministic. And so that’s what’s interesting that if you treat everything quantum mechanically at the level, at the highest level, at the level of including everything into your consideration, you do recover determinism. and that’s fascinating that at the highest level it’s, is deterministic, but at the level of these individual interactions and observations, it looks random.
so this is in fact what most of our research is about to confirm this in, in, in more and more complicated scenarios.
SHEFFIELD: Yeah. and, and that non randomness though, but or indeterminacy like that is ultimately in your view, and I if I’m [00:12:00] summarizing it correctly here is you’re saying that you’re rejecting this idea that measurement is creating many realities it is rather a copying of the state to the local classical object, if you will. Yes. That’s from a observational standpoint.
VEDRAL: That’s right. That’s right. And I think the consistent, the only consistent treatment, and you are right. Obviously physics is a very open-ended enterprise, and our story may well change, with the next revolution in physics. And in fact, my, my latest book is talking exactly about that, that I’m trying to anticipate which experiments we should be doing to probe, and go beyond the current, level of description.
But the statement is that if you treat everything quantum mechanically, and this includes, the system you’re observing, the apparatus you’re using, if you like to use. Other computers, humans as observers, all of that is fine, so long as it’s included consistently into this formalism. And if you do that then you will not get any paradoxes in quantum mechanics is a perfectly consistent account, much like classic.
It is different to classical physics, but it’s consistent in the same way the classical physics is consistent. Of course, it may be proven wrong ultimately that it’s not the ultimate description, but that doesn’t mean that, that it’s not useful in its own domain, which is the current domain.
After all, we’ve had a hundred hundred odd, years, 120 years of experimentation and not a single deviation from quantum mechanics. So I think that gives us, a lot of confidence that that it will be certainly true at a certain level of of generality.
SHEFFIELD: Yeah. Well, part the, challenge that quantum mechanics has had in quantum physics, in extrapolating classicality from that is that because these objects are so small and the things that we have to measure them Yes. Are so big in [00:14:00] comparison, it’s, it’s like trying to say, well, I’m going to measure how a tennis ball behaves by smashing a, bowling ball into it.
And that there, there’s fundamental limitations on how you can do that. and so the instrumentality is, really what has been our challenge in terms of extrapolating further from quantum mechanics as
VEDRAL: Yes, extreme. You’re right. And, I think the major stumbling when we dis, when we discuss, for instance, these outstanding questions as I do gravity, you know what happens with gravity?
It’s the only outstanding force that we haven’t managed somehow to quantize, we don’t really understand what it means to quantize gravity. And while many people would say that there are lots of mathematical problems with with these kind of theories, that it leads to all sorts of infinities, nonsensical probabilities, negative probabilities and things like that.
The real big problem here is that we don’t have a single experiment to give us any clues as to what we should be doing in this direction. And it’s precisely because of what you said, this is a very challenging domain and controlling systems in a fully quantum mechanical way to stay in these super positions while making gravity relevant, is a huge challenge.
And we are probably, at least five to 10 years away from being able to probe that. But we are getting closer, which is, exciting to, to a physicist.
The confusion caused by the ‘Copenhagen’ interpretation of quantum fundamentals
SHEFFIELD: Yeah. Well, and then there’s also, as you’re, as you saying in the book that there’s the challenge of, the conceptualization of Yes. How quantum mechanics is the dominant perception.
So, because of the instrumentality cha challenges a lot of the discussion. Perhaps most of it is tending to be philosophical oriented rather than empirical oriented. And then yes, further add upon that is the challenge that the Copenhagen. Interpretation is so dominant. So, but if you can maybe kind of [00:16:00] get, unpeel that a bit for the audience here.
Yes.
VEDRAL: I, think I think I can explain Copen, so That’s right. So Copenhagen interpretation is really due to Niels Bohr, I guess. He, he was from Copenhagen. And, the question, the way that he tried to understand quantum mechanics, and I think this evolved into an interpretation and, some of the early practitioners did subscribe to that.
So people like Heisenberg is often quoted as being a member of and, of Copenhagen School of Thought. But it’s not clear. If you really read Heisenberg, I think you will see many differences with Bohr. So I think it’s probably fair to say no two physicists really agree with each other on any of these aspects.
But, but, this interpretation of quantum mechanics. Emphasis is the notion of complementarity. So it takes this idea from classical mechanics that you either get particles or you have waves. And in classical mechanics, particles and waves were described by two completely different theories.
We had Newton’s theories for particle, and we had Maxwell’s equations for waves, for electromagnetic waves, and for about 50 years or longer, they peacefully coexisted in, in, in this way. but then when with some of the early quantum experiments people realize that sometimes quantum objects can behave like particles.
And they almost fully comply with Newtonian description. And sometimes they behave like waves. And in fact, you can almost use equations that look remarkably like Maxwell’s equations. After all. Schrödinger’s equation is a wave equation as well. They behave like waves, they can interfere. If you have two slits, then these particles can really go through both of these slits at the same time and produce interference fringes like, [00:18:00] like normal waves of light or water or any other waves would do.
And so, Niels Bohr thought that the main message of quantum mechanics, and this is where it becomes. A bit mystical, and I think this is what promoted some of these views that, that, at least as far as I’m concerned, go well beyond anything that quantum mechanics, is really telling us. The mysticism there is simply how does a quantum object know whether it should manifest itself as a particle or a wave?
And then Niels Bohr would say, well, that’s to do with the observer. That’s how the observer comes into the Copenhagen and becomes kind of, central to, to this interpretation. So Niels Bohr would say, if the observer chooses to witness the wave nature of the object, then the object will behave like a wave.
And if the observer chooses to manifest the particle nature to set up the experiment in that way, then the object will manifest itself as a particle. And you’ve got many, many unanswered questions here which people immediately ask themselves. For instance, when you have a double slit experiment, if you close one of the slits, then the particle will only go through the open slate.
It will really behave like a classical particle. But if you open the other slit, then suddenly one particle, each particle at a time. Seems to be able to go through both of these slits at the same time and produces an interference like, like a wave. So then the question automatically arises, how does the particle going through one slit know if the other slit is open or not?
How does the particle know that at that moment it should become a wave? And this sounds extremely mysterious and mystical. It seems as though quantum objects have a superpower that they can know locally. This is [00:20:00] something that Einstein, of course, disliked very much, and he kept complaining that he couldn’t.
No. And even
Schrödinger himself,
VEDRAL: even Schrödinger actually indeed, Schrödinger was very much against this, this picture of reality. So somehow it adds this mystical properties to particles, and at the same time, it suggests that it’s all about observers. If I, as an observer decide. To witness a wavelike property of these particles, then I can set up the experiment in, in, in, the Wavelike way.
And otherwise, if I monitor the particle continuously and I keep asking the particle, where are you now? I will get a sequence of locations, much like a path, like a trajectory in Newtonian mechanics. And so, so to me, this interpretation it, it happens to be the dominant interpretation, simply because it’s very pragmatic and it’s frequently, extremely easy to work with in terms of calculating the outcomes for given experimental setups.
But if you want to understand what’s going on, it seems to me it’s not the right way to go. Actually, Dirac by the way, Dirac had a, had a fantastic statement about it. Along, along very similar lines, he said. He said, Copenhagen interpretation is good if you need to pass the quantum exam, as an undergraduate at Cambridge, but actually if you want to know what’s going on and understand quantum mechanics, it’s certainly not sufficient.
and I think that’s where we are. that’s why the interpretation has become dominant. But it seems to me less and less so with the recent experimental progress, the fact that we can now prepare larger and larger systems in this superposition of many different states at the same time, seems to [00:22:00] actually suggest that all of these extra systems, observers, anything we include into this, should also be treated quantum mechanically.
They should not be treated any differently. To any other physical object. And of course we haven’t really done experiment at that level to, to test this, but it seems to me that the right way to think about it is not to draw an artificial division between the observers and the observed. And in fact, any paradox when you hear people saying quantum mechanics is paradoxical, here is yet another paradoxical and, counterintuitive feature.
All of this, in my view comes from the fact that we are introducing these arbitrary observers that are completely unnecessary into the picture.
Schrödinger’s cat thought experiment was a criticism of quantum duality views
SHEFFIELD: Yeah. Well, and that does go to the Schrödinger famous cat example. Like he, he wasn’t using that as an illustration of the paradoxical, he was using it as to say, this is an absurd belief.
You shouldn’t think this. and it’s like people took the opposite meaning from what he was doing with that.
VEDRAL: Yes, I think so. Yeah. He was advocating and, I think I, I tried to communicate quantum mechanics in that way. That you should really think about every particle as being part of a, of an underlying field, of a wave that corresponds to this particle.
And rather than thinking about these abrupt, sudden quantum jumps where when you observe something, the state changes in a discontinuous fashion, something unexpected happens in all of this, you should simply think of one wave and tling itself to another wave. And the joint state that’s formed is a state that’s perfectly well described by quantum mechanics.
And there shouldn’t be anything paradoxical about it. And I think if you read sharding as, [00:24:00] this is possibly even his last set of lectures, I think maybe a year or two before he died in the early fifties in Dublin. He does actually talk about this as his ultimate kind of realization. and that’s what quantum Mechanics is all about.
And you are right that in it’s, radically different from how we even teach quantum to mechanics. If you pick up a random textbook it will probably follow some version of Copenhagen actually. It will not be talking about it the way Shadier thought about it.
SHEFFIELD: Yeah. It’s a unfortunate irony.
VEDRAL: Very
unfortunate.
SHEFFIELD: Yeah. And so, but still because of the, the, well, frankly, the dominance of Copenhagen, it’s, it has in a lot of ways, in my view, kind of been a it’s almost like a. It’s like a god of the gaps in physics.
VEDRAL: Yes.
SHEFFIELD: That’s almost what it is. and so it, it can explain something, but it doesn’t actually tell you why it exists or how it is.
VEDRAL: Yes.
SHEFFIELD: It just merely says, well, this is how it functions, appears to function to us at this moment, but it doesn’t tell you anything about,
VEDRAL: no, it doesn’t tell you anything
SHEFFIELD: of how these things are. And like, that’s what this book is about really.
VEDRAL: Yeah. That’s what the book is about. What kind of reality we should be talking about.
And what’s interesting, actually, this is another, common misconception is that you eliminate all of these things like non-locality. people talk about entanglement in the way that you measure one of these particles and suddenly a particle that’s very far away. Mysteriously automatically, suddenly faster than the speed of light, if you like, jumps and assumes the same state.
actually that’s not really what, what’s happening. And, we know that nothing in quantum mechanics violates, special relativity. So I think Einstein really didn’t need to worry about this [00:26:00] aspect of quantum mechanics, but it does assume that we should be thinking about quantum mechanics more like Schrödinger did.
think about these underlying quantum numbers pertaining to all of the systems, and then simply think about interactions that entangle, all of these quantum systems with one another. And then everything happens continuously. Everything is smooth, everything is local. Nothing changes at a distance in an abrupt, way.
And again, this reinforces this message that. All of these paradoxes, all of these seeming violation of other areas of physics like relativity simply happen because we are following this coppen hyken story in which these observers have these almost superpowers to change abruptly states of quantum systems.
And of course, this leads us to conclude certain things that, that sound con contradictory, and in fact, they are contradictory. But nothing in our experiments so far has led to any contradictions. So surely that means that, there is a different story. And that’s why I think short was much closer to that.
SHEFFIELD: Yeah. Well, and the way I that I kind of think about it is and maybe this is dead wrong, but that basically, there is an externality that exists. And then, but we can only access it through a perception of it. And so when we, when you interact with a quantum system, you’re not changing the nature of the object.
You are changing your percepted externality. You are creating a new one for yourself. Yes. It is not so, in other words, there’s not many worlds that are being created. It is. You are creating a new perception for yourself. That’s what you created.
VEDRAL: Yes. I think there is only one world is just, exactly what you’re saying is just that.
The only consistent way to understand it at present is really to quantize everything. So there is one quantum, it’s certainly not a classical world. We know that. Yeah. For a fact. and we’ve disproved that, on all of [00:28:00] these occasions, but I think it’s more appropriate to talk about one single quantum universe.
Yes.
Eric Weinstein’s “Geometric Unity”
SHEFFIELD: Yeah. Okay. Great. Well, okay, so, and then, but because of the, the kind of conceptual and instrumental challenges that we’ve seen, quantum mechanics has seen, and a lot of people trying to advance, interpretations and ideas about it. And one of them, who is this guy named Eric Weinstein, who is, I guess a retired mathematician or something.
Now he does, seems to be only a podcaster now. yes. And, but he, he, released a paper a, a few years ago trying to claim that he had re reconciled, what it partic, space time within a. Extra dimensional space. And, but on the other hand, a lot of his equations, he was just like, well, I don’t have ‘em, and I’m sorry.
I but he’s very angry at people like you lako for, according to him, he says, you are suppressing him, you’re censoring his ideas. but that doesn’t seem to be what’s happening here. It’s mostly like, well, you said the dog ate your equations. That’s what it looks like to me.
VEDRAL: Yeah. To, to me too.
I think you’re right. I don’t know Eric Weinstein myself and, he’s not the only person unfortunately to make claims of that kind. not at all. I think physics is a very open ended enterprise. it does happen to, to conventional physicists, of course, that you come up with an idea, you post it on archive and then you get very disappointed that, there is hardly any response.
This happens, it happens to great ideas by the way that there is, 10, 20 year delay before someone actually realizes that there is something interesting there or that an experiment could be done and so on. But on the other hand, there are many dead ends. And I think, as you said, [00:30:00] if you’re a bit more mathematically minded, you will very easily think about all sorts of generalizations that you could go into.
So, for instance, let me give you a very concrete example. Once you realize that quantum mechanics, relies on complex numbers, so the imaginary numbers, the square root of minus one becomes crucial in, in quantum mechanics. You cannot describe these, wavelike behaviors with real numbers only.
SHEFFIELD: Well, it’s because you’re expanding degrees of freedom beyond like the normal tra traditional scaling Exactly right. You are going into that space. But now if you’re a mathematician, and in fact that’s a perfectly legitimate thing to do for a mathematician, but you mustn’t claim that corresponds to reality then that No, it’s just
a formalization.
VEDRAL: Yeah, exactly right. Yes, that’s right. And I think then you may say, well, why not use even more general entities, there are these quaternions why not use something that goes even beyond complex numbers? And of course a physicist would say, well, we haven’t had any need for that. It’s not that, it’s not that we are conspiratorially blocking all of these, beautiful mathematical obstructions.
It’s just that nature is telling us that what we have so far is sufficient. of course, maybe one day these other formalisms. And we can never know whether they will become relevant in the same way that we couldn’t anticipate that their complex numbers would, they were discovered in in in, in, in the 17th century by some Italian mathematician who basically was solving cubic equations.
and he found a, an interesting way of, writing down some of these solutions. No one dreamt at that time, of course that this would really correspond to some elements of reality. The same with general relativity, non liquidity and geometry. All of these ideas ultimately were absorbed into physics.
But I think to become upset that your mathematical generalizations are [00:32:00] not taken seriously is a bit kind of, immature, right? I mean, as a scientist you should really. You should really understand how this works and I think it’s okay to speculate, but certainly you should not force your own ideas on, onto, an experimental science which of course, already contains methodology, how we find out what’s needed, what’s out there or what’s presumably out there, and things like that.
So certainly there is no conspiracy within the scientific enterprise to block these ideas. In fact, we love crazy ideas. We love to hear that some ideas go beyond the current theory because it gives us extra motivation to go in that direction and try to test these ideas. But they have to be well framed.
You really have to make a conjecture. You have to stick your neck out and you have to say concretely. In what situation and what will happen that’s different to what we already know. And that’s extremely challenging. Of course.
SHEFFIELD: Well, and also you have to be able to specify idea experiments or other, formalization that could falsify your hypothesis.
VEDRAL: Absolutely.
SHEFFIELD: It’s not just to say, this is my proof that it’s true. You have to say, well, if how, this is how it could be false, and here’s how you would know.
VEDRAL: Yes, absolutely. That’s crucial. and like I said, we have, for instance, all sorts of collapse theories in quantum mechanics, and I think I, I would probably say that 90% of practitioners do not believe that quantum mechanics will collapse back to classical physics.
But there are some prominent people like, like Roger Penrose for instance, and many others, 10% probably of physicists believe that there could be some, domain
SHEFFIELD: They’re really doing that in black holes. Like that’s their, For instance.
VEDRAL: Exactly. That’s a big question in black holes. So there are many reasonable ideas there where where things [00:34:00] could, go wrong.
And I can tell you that all my experimental colleagues love this kind of speculations even if they disagree with these speculations, they love them because frequently they tell. How concrete to test whether these ideas are true or not. And we’ve rule out, ruled out many of these collapsed theories, but there’s certainly many other ones that are still outstanding.
So they give us extra motivation to continue with difficult experiments.
SHEFFIELD: Yeah, absolutely. and you really do, and it’s, and it’s, I don’t know how it is for you, but you know, it’s fun reading these papers of, well here’s how these quantum interactions within, black hole, of this type.
But it would be different from this other type. like these, this is these are not ideas that are suppressed. People enjoy reading them, don’t
VEDRAL: They enjoy reading them. It’s okay to be speculative. It’s even okay to say, I don’t foresee an experiment even within, next 50 years. That’s fine.
I mean, many ideas of the past are exactly of that kind, that it took a long time for us to get there, to be able to test them. So we are extremely open to that. And as you say, it is part of the fun of being a theoretician.
How to test new quantum theories
SHEFFIELD: Yeah, exactly. Yeah. So, but, and to that point though, on experiments so that is, one of the, I mean, that is the kind of the, narrative sort of through line of your book here is you’re trying to say, okay, well look, we’re in a, in some ways, because of the, our instrumental challenges and, conceptualization problems, here’s a way to kind of reset some of that and try to experiment on how we could perceive if.
Yes. classicality is, fully derivable from quantum interaction.
VEDRAL: Exactly. Right. and that’s by no means clear. Like I said, we tested objects that are very large as far as an atomic physicist is concerned. So you have objects which contain, let’s say billions of atoms, but that’s still nothing compared to even, let’s say, a [00:36:00] single biological cell.
No one has put a biological cell into a superposition of two different locations. And in fact, many people doubt whether we will ever get there simply because all sorts of other effects, noise from the environment and anything else could prevent us from, doing something like this. But that’s exactly the direction we are taking because what you want to do when you have a theory is you want to.
Test it in domains where you think that it might fail, that’s the more, rather than just confirming it in one domain after another and doing kind of incremental stuff where you think that the theory will anyway up, be upheld. We try to really stretch it into exciting domains where there are reasonable arguments, why it might fail there.
And you already mentioned black holes. Anything to do with gravity is certainly in this domain, living systems as well. We haven’t really tested quantum mechanics much there. Even chemistry. Much of chemistry actually.
SHEFFIELD: Yeah. No, it’s true. So, but, so within this idea though, there, there is the.
Term of, the colloquial term, the qua quantum ghost. So what is that? And, talk about how you want to experiment with these things that we
called.
VEDRAL: Yes. that’s a nice, question, and I thought I, really wanted to talk about it because not many people are thinking about it.
It concerns again this very awkward marriage between relativity and quantum mechanics. So we, have what’s called quantum field theory, and it puts together special, not general without gravity. So it’s relativity without gravity, together with quantum mechanics. And actually some people would call this the most successful description of nature so far.
you can call it the standard model. In fact, it really accounts for all the other three forces other than gravity. However, what’s really interesting in this theory. [00:38:00] Is that when you’re talking about even basic electromagnetic interactions, if you have two charges and you want to explain how these two charges repel each other, if there are two electrons, two like charges, how they repel each other, or if they’re oppositely charged, how they attract each other.
The interesting thing is that in relativity, everything every physical entity, every observable, if you like, every legitimate relativistically legitimate entity has to have four components. So it’s a little bit like three components of space, which is what Einstein realized, in his first, paper on, this topic and one component of time. So instead of thinking about space with three components separately from time, Einstein actually showed that you need to really think of them as one space time. And the different observers perceive differently spatial units and temporal units. They only perceive one joints based on in the same way.
That’s what’s absolute, if you like, in the theory of relativity. So what’s interesting for us is that when it comes to the electromagnetic field, we have the four components that we are talking about, but our standard treatment claims that two of these components. Can never be measured. They can never manifest themselves.
In fact, when we do our calculations, we leave these two components out. However, they must be somewhere there to comply with relativity. You cannot completely forget them, which is why, as you mentioned, they’re called ghosts. So they, serve the purpose to make quantum mechanics comply with relativity.
But then the claim is that they can never be directly measured. And this should kind of raise all sorts of alarm bells to, to a scientist because you’re thinking, wait a second, why do you need to postulate this in the first [00:40:00] place? If you really claim ultimately that you can never have any observable consequences?
So something that I thought would be fun is to really try to think of an experiment where you could detect these ghosts. So this is simply two components of the electromagnetic field. And
SHEFFIELD: What are these two components? If you can just kind of say that. Specify.
VEDRAL: Yes. There are four components. Three of them look like spatial properties of the electromagnetic field.
So they’re telling you, they’re telling you something about the strength of the electromagnetic field at different locations in space. And this fourth component, the temporal component, is telling you about how it behaves in time. So it very much mirrors the space time of Einsteins, which was applied to the three components of space and one component of time.
Here we are talking about three spatial components of the electromagnetic field, telling you about the straight strength of the electromagnetic field in the X, Y, and Z directions, if you like, in the three spatial directions. And then there is this fourth one, which is the temporal component, telling you how the electromagnetic field behaves in time and suddenly.
People say only two of these spatial components are relevant. There is another spatial component that’s not directly measurable. And then there is this, temporal component that’s also not directly measurable, and they’re known as ghosts because somehow the formalism needs to have them to comply with relativity.
Otherwise, you would get instantaneous action at the distance. You could do things faster than the speed of light and, no one would want that. Obviously. None of our experiments are telling us that anything like this happens. So they’re necessary for consistency and yet somehow people say you can never detect particles of these extra components.
You can never get a a, detector, which would detect a photon. Coming from [00:42:00] these extra ghost modes. And so I thought, and, this is again being motivated by shorting as thought experiments. it’s very reminiscent what I have in mind of shorting as cat experiment. Where what I’d like to do is take a single electron, a single charge, put it in two different locations.
And, these are experiments that people do routinely. But now if these ghost modes are real, if they’re really out there, if they have these particles, photons that pertain to them, and and if we really, if they’re not just necessary for consistency, but if they’re really out there, then our theory is telling us that they must somehow couple to this electron, they must become entangled.
To the electron through an interaction. And if you create this entangle state, then that’s something that you could certainly experimentally verify. So what I have in mind is really one electron, which is in two places at the same time, it becomes entangle to these ghost modes. And then I bring another electron in a position of different states, couple it to the first electron, and then ask what kind of outcomes I get.
And actually the claim that I made in a, couple of recent papers is that you could in principle detect this. No one has done this experiment, but I think these are exactly the adventurous experiments because they’re challenging, the current best description that we have of reality. And they’re really asking these questions.
Can we go beyond that? And it would be very interesting. I’m, actually betting on the fact that we could see the effects of this entanglement in much the same way that sch shredding. Talked about entanglement in general, but to me, again, given that it would be more surprising not to see the effects if we didn’t see any effects, I think this would raise a serious question [00:44:00] about our understanding of these fundamental interaction.
The question is then what does, what does that really mean? how come that relativity is telling us one thing, whereas quantum mechanics doesn’t seem to require these extra components.
Information theory and quantum computing
SHEFFIELD: Yeah. Well, and to that point, there, there are some theorists who argue that, information is the fundamental nature of reality.
So, but let, so can we talk about that? But first define what information is within this context. ‘cause again, that’s another uncommon usage here, I think.
VEDRAL: Yeah, very uncommon. I think the tricky bit is really the quantum side. So when, it comes to classical information, first I think is the, simpler one.
I think when it comes to information, to define information, we, we follow Shannon in in probably all sciences, not just in physics.
Shannon wrote a couple of groundbreaking papers in the late forties, and he really talk, talked about communication. He was interested in the channel capacity. How much information can we communicate down a certain. A channel and how do we specify this channel? And this was all about quantum information.
So he, about classical information and then I will talk about quantum. So what Shannon needed is, first to be able to encode information, you need at least two distinguishable states of a physical system. So you need states which you can discriminate with certainty. Of course in our computers, for instance, these states would be the electrical circuits, which are either conducting current or not conducting current.
And you can tell zero one, zeros and ones. That’s it. As soon as you have zeros and ones. going back to George Boole of course, and Boolean logic, I think you can encode information and you can talk about information, what you need. The second crucial concept, and you can now already see why I claim that [00:46:00] it’s much more appropriate to talk about quantum information.
The second concept is that of probability. So Shannon said, if you tell me the probability to get a, the zero value of the bit and the one value of the bit, then I can calculate anything else. I can tell you the capacity of your communication in all sorts of scenarios. It’s actually a universal. A way of talking about information.
So you need bits of information. You need to be able to distinguish two states of, each of these bits. And you need to know the probabilities for various strings of bits, zeros, and months. And so basically that’s what that’s what Shannon did and he showed that you can do anything when it comes to computation.
You can compute anything that’s computable. You can reach any capacity that the channel allows with this. Now the tricky bit with quantum mechanics, and I think that’s where the difficulties arise, is that in quantum mechanics you have in, even with a single system, you have infinitely many ways. Of encoding classical information.
So for instance and this now is going to go back to Heisenberg’s uncertainty. For instance, I could take positions of my object and two different positions are the values zero in one. If it’s in one position, that’s the logical zero. If it’s another in another position is the logical one. However, you can also talk about superpositions.
You can say if it’s in one superposition between these two places. That’s logical value zero, if you like. If it’s in another distinguishable superposition, I can call that logical value one. And the tricky bit in quantum mechanics is that if you put these two together then they do not constitute classical information.
This is something that goes beyond classical information. So my colleague David Deutsch would call [00:48:00] this “super information.” So he would say you have one property in which you can encode classical information, position. You have another property, let’s say momentum, speed in which you can encode classical information.
But when you look at them together, because they cannot be simultaneously specified because of Heisenberg’s uncertainty, they somehow transcend this concept of classical information. So actually a single quantum bit can exist in many infecting, infinitely in principle, in infinitely many different states.
Any superposition of the value zero and the value one, with any arbitrary weights between zero and one, you can have 75% zero, 25%, one are allowed in quantum mechanics. And that’s actually what’s behind the strength of quantum communications and ultimately the quantum computers that we are building. Yeah, so it’s in that sense that I talk about information.
SHEFFIELD: Yeah. And, that is the really fascinating and groundbreaking idea of quantum computing because, the problem with digital encoding and Boolean logic. That it cannot, when you look at a biological system, they don’t operate under zero one. Yes. They operate under this probabilistic structure.
VEDRAL: Yes.
SHEFFIELD: Especially with, like, so like my current, philosophical project is deriving, mindedness from cellular collectivity and perception and all of these, so in other words, like they, they have to agree on what, on something’s there, but what that something is, and it’s bareness is not zero one.
No. and so that’s, the beauty of using, of, trying to move com computation to quantum state, is that you can have that kind of fuzzy, almost analogical logic.
VEDRAL: Yes. You’re putting it in a very beautiful way actually, [00:50:00] to the extent that we talked, so far about how quantum mechanics changed.
Newtonian classical laws. But actually another way of putting it is exactly how you are putting it, that it changed the classical Boolean logic. It’s not a binary logic anymore. The fact that you cannot say that something either is or isn’t, but it could be in a super position, in fact, in multitudes of different superpositions forces us and some people believe that’s how we should be thinking, forces us to change the logic actually to, to adapt, to imp, to basically use a different kind of logic to describe this kind of com computation and communication.
Q-numbers, C-numbers, and quantum logic
SHEFFIELD: and that is also, what you are trying to, to why you’re trying to back classicality out of that as well. Yes. because that is the indeterminacy that we see when, from the measurement problem. Yes. And the observer problem is that if you don’t think of classical objects in that, in the way that we have.
Then this, mystery and this indeterminacy, this randomness, it disappears. Like that’s your basic thesis.
VEDRAL: That’s my basic thesis. Yes. And and, you are right. It’s interesting that, yes, it’s all about consistency. If you mix that’s exactly how you’re putting it. If you take a quantum system that are based is physiologic and you couple it to a classical system that’s deterministic and or based bull logic, you’re simply not going to be able to consistently even put them together.
Because the classical system does not speak quantum logic. It simply doesn’t understand how it ought to respond to a quantum system. And again, we are back to Schrödinger, that’s exactly Schrödinger Schrödinger’s, thought experiment, which says, wait a second, what’s going to happen if I couple another system to a quantum system that’s in a super position? Well, it simply has to join that [00:52:00] superposition. And that’s it. That’s your entangled state. And that’s really the only consistent way of talking about
SHEFFIELD: Yeah. And, people are resisting that though, and I guess that’s,
VEDRAL: people are resisting
SHEFFIELD: really what you’re trying to do.
VEDRAL: Yeah, that’s what I’m trying to do. And, people are resisting. Sometimes people even get angry because they, I guess it’s very difficult to, to get rid of the, cop and hugging kind of, prejudice in many ways. And I think, like I said, we’re all taught to think that way. even in high school, the first time you meet quantum mechanics through Bo’s planetary model of the atomic structure and all of these things, all of these ideas creep in.
And then certainly undergraduate physics, we’re all taught that way. Most popular books are written that way, which actually amplifies this kind. Mystical, side of things, and no one, it leads many people to actually conclude that it doesn’t even make any sense. It can’t be like this, it cannot be consistent.
It must fail. It must collapse. But I’m arguing the other way that, that if you really think of it quantum mechanically, through and through none of these paradoxes, remain actually.
SHEFFIELD: Yeah. Well, and, to that, and, the other way that you kind of bring that home is di discussing that there are two types of numbers.
So with the Q numbers and the C numbers. Yes. So talk about that a little bit, if you will, please.
VEDRAL: Yes. I think this was the, this takes us back exactly to Heisenberg’s first paper, 1925. Last year was the, year of quantum, right. Celebrating a hundred years of his first paper. And that paper is taken as, of course there were many papers.
Before that, that they were already very close to, doing to, to doing things this way. but the breakthrough there, the flash of kind of genius that, that he had and it’s really a magical paper to, to read is that he said something quite revolutionary in, and, it’s, again, [00:54:00] it’s not how we teach quantum mechanics.
He said that the problems of classical physics are not at all the dynamical equations. So if you look at Newton’s equation. Force equals masstones acceleration. Or if you look at Maxwell’s classical equations, as far as Heisenberg was concerned, they’re all fine. Dynamics is okay and we don’t need to modify it.
But the revolutionary idea was that the entities that obey these dynamical equations, which we think of normally in classical physics, is ordinary numbers. So you will say, a particle is located five meters away from me, and in three seconds it will be 10 meters away. And then you can write the equation.
And all of these are real numbers that enter these equations. Heisenberg had this idea that they should be upgraded into what ator called quantum numbers. In fact, Heisenberg simply developed in that paper. He didn’t know what they. They ought to be such objects already existed. They’re called matrices, but Heisenberg, he was only 21, 22, I think.
He wasn’t taught matrices at university. Matrices were already 50 years old then. I think they go back to Sylvester and people like Hamilton. Yeah. but they had no, not much use in physics. And I guess physicists were maybe not taught these things. And so he came up with these tables of numbers.
So rather than needing just one real number, you need really lots of arrays and columns of real numbers, much like a, I think, Schrödinger called them catalogs of information, which is a very colorful way of talking about about matri is one and the same thing. And so Heisenberg said, if you now admit that a position is actually one of these Q numbers.
Momentum is one of the Q numbers energy. Any classical property you can think of gets upgraded into a quantum number, a very complex array of numbers. [00:56:00] Then suddenly everything becomes clear. And he could apply that to spectroscopy. He could reproduce the, spectra that were known at that time. And basically people very quickly developed this idea later applied it to a multitude of scenarios and it became quickly clear that this is the way to think about it.
So I find it beautiful because, and it illustrates discontinuity of quantum physics with classical physics. It, it, says you don’t throw away everything from classical physics. Of course, many ideas in quantum, in classic from classical physics survive and they’re still legitimate. Yeah.
However, what you do need to do is upgrade certain concepts and if you have the right idea what it is that you need to upgrade, then suddenly everything falls into place basically.
The advantages of a process physics over a thing physics
SHEFFIELD: Yeah, and the other interesting thing about conceiving of it, of physical object in this processual way is that you eliminate actually all interaction problems because, the, like within just like regular philosophy, there’s this idea that how can things which have persistence and are objects, how can mental causality make them right, affect them and, basically if everything is a process.
Then there is no challenge of interaction because all, everything is a process interacting with the process. And ideas are just simply proce procedural variables inside of mind, which is itself a process which is made of cellular, entities which are in the cells, quantum fields, made of,
VEDRAL: I, I like the picture that I, very much subscribe to that I, don’t like, dualism or any kind of duality, right?
That you make an artificial split between, our mind or consciousness or whatever the brain does and what the rest of the world does. I think it’s much nicer to think that there is a unity to nature, that we don’t really need this artificial division. [00:58:00] And you’re right, this pops up even in quantum mechanics, right?
That people would say, observers behave differently. Living systems obey differently. But I think. It’s closer to, reality to say that everything is the same. And you’re right, that many of these traditional problems disappear once you see it in this coherent fashion. I agree with you.
SHEFFIELD: Yeah,
VEDRAL: Of course, only time will tell. We haven’t done the experiments yet at that level, but yes.
SHEFFIELD: Yeah. But it does offer a consistency that if everything is simply procedural realization, then it, then all the problems disappear. Agree. So many of problems disappear. I agree.
VEDRAL: Yes, I agree with that.
SHEFFIELD: All right. Well, so, besides this book, do you have any, particular papers or people who want to kind of follow the more, formal academic scientific papers that you want to recommend to people?
VEDRAL: I think the best, the best one that talks about quite a lot of these, issues. And it may be.
A relatively friendly one to, to read is, is a recent reviews of modern physics. So this is, a magazine that publishes reviews that usually talk about, a topical field of research maybe that developed over the last five to 10 years.
So I have a very nice review with my colleague Chiara Marletto. It was published last January, so exactly a year ago. And it talks about how methods of quantum information can be applied to test the quantum nature of the gravitational field. So I think this paper is probably if anyone wants to read a bit more. Formal exposition. Plus, I think these reviews contain an extensive literature at the end.
So I think we have over two or 300 references at the end of this review. So if anyone is interested to read this and see what people have been thinking about along these lines, that’s probably the best place to, [01:00:00] to look at.
SHEFFIELD: Okay, awesome. And then, you’ve also got a Substack that people can subscribe to as well if they want to see more?
VEDRAL: Yes. I think my, exactly. I think my website contains, sections with, with different, degrees of formality and difficulty, but I think I try to write my blogs in a very accessible way.
SHEFFIELD: Okay. Awesome. All right. Well, thanks, for joining me today.
VEDRAL: Thanks very much. Great pleasure.
SHEFFIELD: Alright, so that is the program for today. I appreciate you joining us for the conversation, and you can always get more if you go to Theory of Change show where we have the video, audio, and transcript of all the episodes. Of course the links to the different papers and books that we talk about on all of the programs as well.
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