Are There Many Worlds? David Deutsch in conversation with Markus Arndt

so at the end of April this year I was honored to be invited to Wolfson College in Oxford to document a series of informal presentations and conversations concerning the role of probability in physics this so-called unconference was sponsored by the Utopia foundation perhaps the most polarizing issue to emerge over the course of the discussions was the many-worlds interpretation of quantum mechanics which seemed to pitch some of the more practically minded experimental physicists like Marcus aren't from the University of Vienna against those big picture theoretical physicists like David Deutsch from Oxford who were more willing to embrace this grand view of ever branching parallel universes so for the sake of this video I asked Marcus and David if they wouldn't mind hashing out their differences over their lunch break in one of the corridors at Wolfson that began by asking Marcus how he conceived of the tensions here the parameters from that we all try to solve is why is there this unitary evolution of quantum mechanics which seems to explain everything very naturally and all of a sudden during a measurement this this evolution has to be reduced collapsed in the Copenhagen interpretation and that's I think something that David doesn't like he wants to have everything on the same say mathematical formalism but if you follow it through it leads to realities which seem to multiply and then my question to you is what is really the meaning of reality to you because but I experience only my single reality here yes you put it in terms of how do we make sense of the unitary evolution compared with what we see at a measure and so on I would want to start before that I think we want to understand the world we want to understand how the world is and that that is not necessarily what we perceive our perceptions are at the end of a long chain of of physical processes of which themselves we only have scientific knowledge or indirect knowledge so I would start with the question how do we explain quantum phenomena like interference not how do we make sense of quantum theory which gives the right prediction but first before that how do we explain quantum phenomena so there's there's an interference process and we have interference pattern which we can see without any quantum mechanics that the the result of the experiment cannot be explained by the events that we see now this is not very unusual this happens a lot you know in physics and ultimately every observation is made very indirectly so we have to infer things that that are not there although it infers is the wrong word we have to conjecture explanations so that's where I would start but what makes it then certain that there must be a parallel world in that sense of many infinitely many parallel worlds instead of either some hidden variables although of course as an experimentalist I know that some kinds of in variables have certainly no doubt and do we need the notion of reality more than the notion of information is so to say the the many-worlds thing an information world or a reality world and the thing is sense yes so I that's a very interesting point about the relationship of information to reality because many people think that the concept of information is somehow prior to physics that the laws of information like mathematical theorems they they must be so whereas I tend to view that that what information does and what it can do in the world is determined by physics and therefore in regard to physics physics is a theory of the world of the reality of the world not about the information there is this view that quantum mechanics only tells us what we will see and it's silent about everything as everything else is is just mathematical formalism but I think that that's ultimately leads to solipsism and it is no good philosophically but it's even more important maybe for a physicist it's no good for finding out what the next theory will be if you if you just think a theory it's the predictions of experiments then we would never have got from Kepler's theory to Newton's theorem from Newton's theory to Einstein's because they differ from each other in what in in predictive terms is a tiny amount but in explanatory terms it's an enormous amount changes our whole view of the universe but in terms of predictions coming back to the many-worlds and the predictive power of the many worlds I'm sitting here I can only prove my local world even within my local world I seem to experience all these funny quantum superpositions where you would probably say another part of the multiverse is branching into me again or into my world again but but this this process is kind of experimentally at least at the moment there we in difficult to access and the questions do you have a good proposal how to do it yes so I mentioned interference experiments of interference in an interference experiment we don't even with this notion of seeing things by through the explanation we only see that the let's say the photon exists in two instances rather than rather than that the whole world does and when you talk about your experience at the moment as you say we can only probe whether an experimental outcome is caused by a single history or by multiple histories of an atom molecule I mean you in your talks you gave wonderful example very large objects from from an atomic point of view exhibiting interference so existing in more than one instance when we have quantum computers we will be able to have very large very complex entities existing in super positions so in principle I suggested a long ago before this was remotely on the cards experimental II that if we had a quantum computer on which an artificial intelligence program was running as say with human level artificial intelligence then this entity would be able to experience interference in its own consciousness well some people would say that your consciousness would collapse your reality yes so if that happened that would be huge the average interpretation that or as I would say it would refute quantum theory and that that would be a very interesting problem and that's one of the reasons why scaling up both the size and the complexity and the mass of phenomena that I experimentally observed that can only be explained by quantum theory is very important absolutely agree we need to do that and we just need to close the gap between that and the AI because the AI would not be having this conversation the AI would not be able to make the argument that you just made it would have to say I've only got evidence of many worlds on the scale of my mind but not bigger so and I guess that will always be true yeah but there's something in in the formulation of phrasing of our sentences where we're getting also doubtful that it is when I talk about these things about super positions I always make these quote-unquote when I say a particle is at the same time here and there because there are two words that I don't understand whether I don't understand first the word is so reality the second worst I'm really mean and the third one what does space really mean and we don't have any experimental evidence that the particle is at the same time here and there we just have a physical description the quantum mechanical description that the wave function behaves as if and how can we make the step to the mini-boss then I think we have something slightly more than that again you come from the theory from we are but but I think prior to the theory we have the experience that this thing cannot be explained by single trajectories somebody we know we don't have to believe quantum mechanics to see that so we rule out single trajectory explanations and that we have before we have quantum mechanic if we didn't have quantum mechanics it would be a mystery and we would say that it simply is no explanation well hypothetically could this maybe be explained by some very weird folding of space-time of this case so not really making another multiverse or another branch of the multiverse but really a new 3d or 40s space-time or another 11 is space-time could that jump through a shortcut through another higher dimension so to say for on that to the other yes is the answer calling the multiverse many universes is a bit of a misnomer because the whole point of it is interference and many units parallel universes would indicate separate universes and that this or that these universities that our universe splits into two every time a quantum event happens whereas actually it's only that it's only the electron or the proton or something that's flitting now if this can be explained in another way than by quantum theory then another thing we know from just you know without theory with with just elementary reasoning about the experiments is that this other thing has to be immensely complicated it's sort of 2 to the power of the complexity of what we see and again when we have fully fledged quantum computers we will have computations going on whose results can cannot be explained by any history of the computer that has it single-valued so when when that number is greater than a number of atoms in the universe which will easily be obtained as soon as we have quantum computers so yes there could be another explanation in terms of folded universes or other dimensions or what but those things would have to be as complicated as the many universes and as some people were saying at the other Everett conference these things would contain other that they would contain other instances of people or they would that all they would contain things whose shapes were there are other instances of people and so on and other instances of the quantum computer which would be interacting with our instance and so on so it's really a matter of terminology then whether you whether you call that multiverse or parallel universes or a much higher dimensional reality than in classical concept and in your multiverse concept but there again zillions of branches and hypothetically you could also be here and in this other part of a branch of the multiverse it could be the different different place different time different internal state yeah what does that tell us about your identity does that affect anything about how you feel as a human so to say it certainly has to be taken into account but it's logically it's the same issue as at what am I the same person that I was 10 years ago you know that I will be in 10 years time we if we go back to when I was a baby I certainly was not the same person as I am today there is a continuity between me then and me now but that doesn't mean that the same person because a qua person I have changed drastically and said but the relationship between the past and the present is one kind of thing the relationship between the present and future is a different kind of thing the relationship between one branch ever at branch and another is a different kind of thing but in all cases what what makes us say that those things are real is the explanations that we have all here and now although other scientists would say shut up and measure calculate X we just don't talk about things that you cannot see and the men the other part of the the other branches you don't see so why do you Dan not to shut up yes well first of all I think that that that that attitude involves saying that there are certain questions about reality that you're not allowed to ask you're allowed to ask how the experiment was prepared you're allowed to ask what will the results be you're not allowed to ask how were the results brought about by the preparation so that's what's that therefore it's not an explanation in my terms but and that's what shut up that's really another way of of trying to evade the consequences in terms of reality like like my favorite example is of dinosaurs in the past so there are people who say nobody ever saw a dinosaur and nobody ever will and therefore it's just a frivolity to say that they really exist that most we can say fossils behave as though dinosaurs existed but no paleontologist would accept talking that way even though there is no experimental way of disproving that that manner of speaking so and that's because paleontologists are only interested in paleontology because they want to know what really happened not they not you know if they were very interested in fossils there would be geologists

Channel: Joe Boswell

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Length: 14min 26sec (866 seconds)

Published: Tue Jun 19 2018

Reddit Comments

[u/angrymonkey]

Interesting. I don't agree with his belief that an AI built on a quantum computer would directly experience superposition, for the same reason that we don't currently experience superposition ourselves: the various parallel computations (i.e. brain instances) don't interact with each other. The AI would be multiple distinct intelligences, each one enduring a single self-consistent experience.

By symmetry of exchanging the label of "system" and "world" in that scenario, the parallel AI systems would probably each see our environment as a quantum system in superposition.