2012-10-22 Edge Constructor Theory and the Real Reality
Duration: 00:46:49
Transcript
David Deutsch
… some considerable time ago we were discussing my idea new at the time for constructor theory, which was and is an idea I had for generalizing the quantum theory of computation to cover not just computation but all physical processes. And I guessed and still guess that this is going to be, this is going to provide a new mode of description of physical systems and laws of physics and also new laws of its own which will be deeper than the deepest existing theories of which the deepest are quantum theory and relativity. And at the time I was all enthusiastic about this and what intervened between then and now is that writing a book took much longer than I expected. But now I’m back to it and we’re working on constructor theory and if anything I would say it’s fulfilling its promise more than I expected and sooner than I expected given how we’re working on it. One of the first rather unexpected yields of this theory has been a new foundation for information theory. There’s a notorious problem with defining information within physics, namely that on the one hand information is purely abstract and the original theory of computation as developed by Alan Turing and others regarded computers and the information they manipulate purely abstractly as mathematical objects. Many mathematicians to this day don’t realize that information is physical and that computers there is no such thing as an abstract computer only a physical object can compute things. And on the other hand physicists have always known that in order to do the work that the theory of information does within physics such as informing the theory of statistical mechanics and thereby thermodynamics, the second law of thermodynamics, information has to be a physical quantity and yet information is independent of the physical object that it resides in. So I’m speaking to you now information starts as some kind of electrochemical signals in my brain and then it gets converted into other signals in my nerves and then into sound waves and then into the vibrations of a microphone, mechanical vibrations, then into electricity and so on and presumably will eventually go on the internet and so this something has been instantiated in radically different physical objects which obey different laws of physics and so on and yet in order to describe this process to say what has happened during this process you have to refer to the thing that has remained constant throughout the process which is only the information rather than any physical thing like energy momentum and so on. The way to get this substrate independence of information is to refer it to a level of physics that is below and more fundamental than things like laws of motion that we have been used to in the past thinking of as near the lowest most fundamental level of physics and that’s what constructor theory is.
David Deutsch
It’s a level of description of physics, physical laws and physical systems that is more fundamental than the existing prevailing conception of what physics is namely particles and waves and space and time and an initial state and laws of motion that describe the evolution of that initial state. What led to this hope or this kind of way of hoping that there will be this new kind of foundation for the laws of physics was really the quantum theory of computation which at the time I had thought for a while that the quantum theory of computation is the whole of physics and the reason why it seemed reasonable for a while to think that was that a universal quantum computer can simulate any other finite physical object with arbitrary accuracy and that means that the set of all possible motions which is computations of a universal computer corresponds to the set of all possible motions of anything so there is a certain sense in which studying the universal quantum computer is the same thing as studying every other physical object. It contains all possible motions of all possible physical objects within its own possible diversity and so I used to say that the quantum theory of computation is the whole of physics because of this property but then I realized that that isn’t quite true and there’s an important gap in that connection namely although the quantum computer can simulate any other object and can sort of represent or be any other object so that you can study any object via its characteristic programs what the quantum theory of computation can’t tell you is which program corresponds to which physical object or which physical system. Now this might sound like an inessential technicality but it’s actually of fundamental importance because not knowing which abstraction in the computer corresponds to which object is a little bit like having a bank account and them telling you oh your balance is some number unless you know what number it is you haven’t really expressed the whole of physics the whole of the physical situation of you and your bank account and similarly if you’re only told that your physical system corresponds to some program of the quantum computer then you haven’t said which then you haven’t specified the whole of physics so then I thought well what we need is a generalization of the quantum theory of computation that does say that, that assigns to each program the corresponding real object. Now that was that was an early conception of constructor theory um making it directly a generalization of the theory of computation but then I realized and I had already realized this at the time um that um that’s not the way to go because that still tries to cast constructor theory within the same mold as all existing theories and therefore it wouldn’t solve this problem of providing an underlying framework it still would mean that just as a program has an initial state and then laws of motion that is the laws of the operation of the computer and then a final state which is the output of the computer so uh that way of looking at constructor theory would have made um would have simply been a translation of existing physics it wouldn’t have provided anything new the new thing which I think is the key to uh the fact that constructor theory uh delivers new content um was that the laws of constructor theory are not about an initial state laws of motion final state or anything like that they are um they are just about which such transformations are possible and which are impossible and the laws of motion and that kind of thing are sort of indirect remote consequences in some cases of just saying what’s possible and what’s impossible and also that the laws of constructor theory are not about the constructor they’re not about how you do it only whether you can do it and this is by the way this is analogous to the theory of computation this theory of computation isn’t about transistors and uh wires and input output devices and so on it’s about which transformations of information are possible and which aren’t possible and because we have the universal computer we know that the possible ones correspond to a program for a universal computer but the universal computer you can make in lots of different ways that’s inessential to the deep laws of computation similarly in the case of constructor theory what’s important is which transformations of physical objects are possible and which are impossible when they’re possible you’ll be able to do them in lots of different ways usually you’ll be able to achieve them in lots of different ways when they’re impossible that will always be because some law of physics forbids them and that is why as Karl Popper said the content of physical theories of any scientific theory is in what it forbids and also in how it explains what it forbids and similarly if you have this theory of what is possible and what is impossible it implicitly tells you what all the laws of physics are and that um basis very simple basis um is proving very fruitful already um and I have great hopes that that various niggling problems and notorious difficulties in existing existing formulations of physics will be solved by this single idea may well take a lot of work to see how but uh that that’s what I expect and I think that’s what we’re beginning to see in some ways it’s uh this theory just like quantum theory and relativity and anything that’s fundamental in physics overlaps with philosophy and uh having the right philosophy which is the philosophy of Karl Popper basically is although not essential it is extremely helpful to avoid going down blind alleys so um the Popper I suppose is is most famous for his uh criterion of demarcation between science and metaphysics uh which uh which is that scientific theories are those that are in principle testable by experiment and what he called metaphysical theories I think would be better called philosophical theories are the ones that can’t and this is often misunderstood um as claiming that only the scientific theories are worth having now that as Popper once remarked to John Haugeland is is a silly interpretation for example Popper’s own theory is a philosophical theory and he certainly wasn’t saying that that was an illegitimate theory so uh Popper actually investigated in great detail what being tested being testable is not as simple a concept as it sounds and he investigated in great detail and laid down principles um which leads me to the question so in what sense is uh is constructor theory testable because um uh if it’s just uh constructor theory consists of a language in which to express other scientific theories well that can’t be true or false it can only be convenient or inconvenient but also laws but these laws are not about physical objects they’re laws about other laws they say they say that other laws have to obey constructor theoretic principles um now um that um raises the issue of how you can test a law about laws because you know you if it says that laws have to have such and such a property you can’t actually go around and find a law that doesn’t have that property um because experiment could never tell you that that law was true well this fortunately this problem has been solved by Popper and you have to go indirectly in the case of these laws about laws which I want to introduce the standard terminology that laws about laws should be called principles, and a lot of people already use that kind of terminology but I’d rather make it standardized that you talk about for example the principle of the conservation of energy um which is a statement that all laws have to respect the conservation of energy perhaps it’s not obvious to you but there is no experiment that would that would show a violation of the conservation of energy because if you did if somebody presented you with an object that produced more energy than it took in you could always say ah well that’s due to an invisible thing or a law of motion that’s different from what we think or maybe the formula for energy is different for this object from what we thought so there’s no experiment that could ever that could ever refute it and in fact in the history of physics the discovery of the neutrino was made by exactly that method that it appeared that the law of conservation of energy was not um being obeyed in beta decay and then uh the Pauli suggested that maybe the energy was being carried off by an invisible particle that you couldn’t detect um well it turned out that he was right but the way you have to test that is not by doing an experiment on beta decay it’s by seeing whether the theory the law that says that the neutrino exists is successful and independently testable so it’s the testability of the law that the principle tells you about that in effect provides the testability of the principle um one thing I think it’s important to stress about constructor theory is when I say we want to reformulate physics in terms of what can and can’t be done that sounds like a retreat into operationalism or a retreat into positivism or something you know that we shouldn’t worry about the constructor that is the thing that does the transformation but only in the input and output and whether they are compatible but actually that is not how it works in constructor theory constructor theory is all about how it comes about it just expresses this in a different language and I’m not I’m not that familiar with um the um very popular idea of cybernetics that came about a few decades ago but I wouldn’t be surprised if um those ideas which proved at the time not to lead anywhere were actually an early avatar of constructor theory and but if I’m right we’ll only be able to see that with hindsight because um some of the ideas of constructor theory are really um impossible to have uh until you have the conceptual framework that is post quantum theory of computation where i.e., after the um theory of computation has been explicitly incorporated into physics not just philosophically and that that’s what the quantum theory of computation did I’m not sure whether von Neumann used the phrase constructor theory, or whether he just called it the universal constructor. von Neumann’s work in the 1940s um is another place where constructor theory could be thought to have its antecedents von Neumann was interested in different issues he was interested in how living things can possibly exist given what the laws of physics are this was before DNA and before the DNA mechanism was discovered he was interested in issues of principle how uh the existence of a self-replicating object was even consistent with the laws of physics as we know them um and so he realized that there was a uh an underlying um logic an underlying algebra something like that in which one could express this and show what was needed and he actually solved the problem of uh of how a living thing could possibly exist basically by showing that it couldn’t possibly work by literally copying itself it had to have within it a code a recipe a specification or computer program as we would say today uh specifying how to build it and therefore the self-replication process had to take place in two stages and he did this all before the DNA system was known but he never got anywhere because well from my from my perspective he never got anywhere with constructor theory or with realizing that this was all at the foundations of physics rather than just the foundations of biology because he was stuck in this prevailing conception of physics as being about initial conditions laws of motion and final state where among other things you have to include the constructor in your description of a system which means that you don’t see the laws about the transformation for what they are so when he found that he couldn’t make a mathematical model of a living object by writing down its equations on a piece of paper he resorted to simplifying the laws of physics and then simplifying them again and again and eventually invented the whole field that we now call um cellular automata but which is a very interesting field but it takes us away from real physics because he abstracted away the laws of physics what I want to do is to go in the other direction to integrate it with laws of physics but not with laws of physics as they are now but with the laws of physics that have an underlying algebra that resembles or is a generalization of the theory of computation several strands led towards this and um I was sort of um lucky enough to be placed in more than one of them um I guess the main thing was that starting with Turing and then Rolf Landauer who was a lone voice in the 1960s saying that computation is physics that because the theory of computation to this day is regarded by mathematicians as being about abstractions rather than as being about physics Landauer realized that the concept of a purely abstract computer doesn’t make sense and the theory of computation has to be a theory of what physical objects can do to information Landauer focused on what restrictions the laws of physics impose on what kinds of computation can be done and unfortunately that was the wrong way around because as we later discovered the most important thing about the relationship of physics with computation or the most striking thing if not the most important is that quantum theory, i.e., the deepest laws of physics that we know permit new modes of computation that wouldn’t be possible in classical physics so once you have established the quantum theory of computation you then have you’ve got a theory of computation that is wholly within physics and it’s then natural to try to generalize that which is what I wanted to do so that’s one of the directions von Neumann um was motivated really by theoretical biology rather than theoretical physics but another thing that I think inhibited von Neumann from realizing that his theory was fundamental physics was that he had the wrong idea about quantum theory he had settled for and was one of the pioneers of building a sort of cop-out version of quantum theory that made it into just an operational theory where you would use quantum theory just to work out and predict the outcomes of experiments rather than express the laws of how the outcomes come about and I think that was one of the reasons why von Neumann never thought of his own theory as being a generalization of quantum theory because he didn’t really take quantum theory seriously his contribution to quantum theory was to provide this set of von Neumann rules that allows you to use the theory in practice without ever wondering what it means I came from a slightly different tradition via Hugh Everett and Karl Popper. In their different ways both of them insisted that scientific theories are about what is really there and why observations come about not just predicting what the observations are and therefore I couldn’t be satisfied with just an operational version of quantum mechanics therefore I had to embrace the Everett or many universes interpretation of quantum mechanics from the present point of view the key thing about that is that it is a realistic theory as the philosophers say that is it’s a theory that purports to describe what really happens rather than just our experiences of what happens once you think of quantum theory that way it’s only a very small step to realizing that the quantum theory of computation, which was my earlier work, is not sufficient to provide the foundation for the whole of physics so what’s the rest well the rest is constructor theory what’s needed in constructor theory is to express it in terms that can be integrated with the rest of physics formulae, equations and so on because only then can it make contact with other scientific theories and the principles of constructor theory then constrain the laws of other theories which I call subsidiary theories now the constructor theory is sort of the deepest theory and everything else is subsidiary to it constrains them and that then leads to contact with experiment so the key thing to do uh apart from um guessing what the actual laws are is to find a way of expressing them and so the first item on the agenda really is to set up a constructor theoretic algebra that’s that’s an algebra in which you can do two things one is to express any other scientific theory in those terms uh it’s the analog in the prevailing formulation of physics would be something like differential equations but in constructor theory it will be an algebra um and then to use that algebra also to express the laws of constructor theory which won’t be expressed in terms of subsidiary theories they will just make assertions about subsidiary theories so we’re working on that that algebra and um it’s a conceptual jolt to think in terms of it rather than in the in the terms that have been traditional in physics for the last few decades so we try and think what it means find contradictions between different strands of thought about what it means realize that the algebra and the expressions that we write in the algebra doesn’t quite make sense change the algebra see what that means and so on so it’s a it’s a process of sort of doing maths doing algebra by working out things interleaved with trying to understand what those things mean and this is this is really um very much mirrors how the pioneers of quantum theory developed their theory it was the same thing and in fact one of the formulations of quantum of quantum theory namely matrix mechanics as invented by Heisenberg and others isn’t based on the differential equation kind of paradigm but is is more algebraic and it in fact can be seen as a precursor of constructor theory um uh the um the algebra is um well we haven’t yet succeeded in making a viable algebra but even with the um rudimentary form of it that we have now we have got some remarkable results um and this was mainly done by Chiara Marletto, the student that I’m working with um which um uh have almost magically provided a deeper foundation for information theory than was possible within physics before like all fundamental theories um it’s difficult to um predict what effect they will have precisely because they are going to change things at a fundamental level but there is one big thing that I’m pretty sure the constructor theoretic way of looking at physics has to offer our world view in terms of everyday life and our lives and that is in terms of optimism um optimism in my uh terminology doesn’t mean expecting that things will turn out well all the time it’s a very specific thing and which I think captures the historical sort of philosophic philosophical uh trend of what optimism has meant if you remove the nonsense and that is the optimistic view is that is not that problems will not occur but that all problems and all evils are caused by lack of knowledge and the converse of that is that all evils are soluble given the right knowledge and knowledge can be found by the methods of conjecture criticism and so on that we know uh is the way of creating knowledge and although this sounds very this sounds like a statement at a very human level because it’s about knowledge and evils and being able to do things and so on it is directly linked with constructor theory at the most fundamental level because the fundamental dichotomy in constructor theory in terms of which it claims the whole of science is to be formulated is the difference between transformations that are possible and those that are impossible and there isn’t a third possibility that’s the thing the whole thing doesn’t work if there’s a third possibility so if a task a transformation is impossible then constructor theory says it must be because there’s some law of physics that makes it impossible and conversely if there isn’t a law of physics that makes it impossible then it’s possible there is no third possibility so what does possible mean in the overwhelming majority of cases well some things are possible because they happen spontaneously but the overwhelming majority of cases of things that are possible are possible because the right knowledge embodied in the right physical object would make that happen so the dichotomy is since the dichotomy is between forbidden by the laws of physics and possible with the right knowledge and there isn’t any other possibility this tells us that all evils are due to lack of knowledge now I think this is counterintuitive it’s contrary to conventional wisdom and it’s contrary to our intuitive or at least culturally intuitive way of looking at the world I myself find myself grasping for a third possibility you know isn’t there something which we can’t do even though there’s no actual law of physics that says we won’t be able to do it well no there can’t be uh this is uh built into constructor theory there’s no way of getting around it and I think once you’ve seen that it’s at the foundations of physics it becomes more and more natural it becomes more and more sort of um obvious in the sense of uh well it’s weird but what else could it be I mean it’s rather like it’s rather like the intuitive shift that comes from realizing that people in Australia really are upside down compared with us and they really are down there through the earth you know one can know this intellectually but to actually think in those terms takes an effort it’s something that we all learn at some point and accept intellectually at some point if we’re rational but then to incorporate that into our world view changes us it changes us because whole swathes of supernatural thinking are made impossible by truly realizing that the people in Australia are upside down and similarly whole swathes of irrational thinking are made impossible by realizing that in the sense I’ve just described there is no third possibility between being able to do it if we have the right knowledge and being forbidden by the laws of physics the um stereotype of how new ideas get into fundamental science is that somebody has the idea everyone thinks they’re crazy and eventually they’re vindicated I don’t think it happens like that very often I mean there are cases where it has happened like that but I think that much more often and this is my own experience when I’ve had new ideas is that it’s not that people say you’re crazy that can’t be true they say yeah that’s nice well done and then they go off and ignore it um and then eventually people say oh well maybe it leads to this and maybe it leads to that and maybe it’s worth working on maybe it’s fruitful and then eventually they work more on it this has happened to several of the things that I’ve done and this is what I would expect to happen with constructor theory I haven’t had anyone tell me that this is crazy and it can’t be right um but I’m certainly in the stage of most people or most physicists saying well that’s that’s nice that’s interesting well done and then they go away and ignore it no one else is actually working on it at the moment several of our colleagues have expressed uh something between curiosity and substantial interest which may well go up as soon as we have results at the moment there’s no publication I’ve submitted a philosophical paper which hasn’t even been published yet when that comes out uh there it’ll get a wider readership people will understand what it’s about but physicists want results in philosophy you can write a paper that just has hopes in it or interpretations of things but in physics you need results when we have our first few papers that have results I think that an exponential process of people working on it will begin if it’s true of course it might be that some of these results are of the form it can’t be true in which case it will end up as an interesting footnote to the history of physics so I had to write the philosophical paper first uh because uh there’s quite a lot of philosophical foundation to constructor theory and to put that into a physics paper would have simply made it too long and to physicists too boring so I have to write a thing that I can refer to so the philosophical paper first and then the next thing will be well the next thing was going to be constructor theory algebra which is the language and showing how the language and formalism and showing how both old laws and new constructor theoretic laws can be expressed but now it’s likely that the first paper on constructor theory will be constructor theoretic information theory because it’s yielded unexpectedly good results we’re talking about the foundations of physics here so the question is whether the theory is consistent whether it’s fruitful whether it leads to new discoveries these foundational theories are of interest to people who like foundational theories but their usefulness comes in their fruitfulness later so quantum theory is again a very good example almost nobody is actually interested in quantum theory except a few people who work on the foundations of quantum theory but everybody now several decades after its discovery everybody who works on microchips or everyone who works on information or cryptography and so on has to use quantum mechanics and everybody who wants to understand their position in the universe you know what we are has to take a view about what quantum theory tells us about what we are for example you have to take a view about whether it’s really true that we exist in vast numbers of parallel copies some of them slightly different some of them are the same as I think quantum mechanics inevitably leads to or not but there’s no rational way of not taking a position on that issue well although apart from the issue of optimism which is an unexpectedly direct connection to the everyday level we can’t tell at the moment what constructor theory will tell us about ourselves and our position in the universe and what every reasonable person should know until we work out what the theory says which we can’t do until we work it out properly within the context of theoretical physics I’m interested in basically anything that’s fundamental so it’s not confined to fundamental physics but for me that’s what it all revolves around in the case of constructor theory how this is going to develop totally depends on what the theory turns out to say and even more fundamentally whether it turns out to be true if it turns out to be false that that is that one cannot build a foundation to physics in the constructor theoretic way that will be extremely interesting because that will mean that whole lines of argument that seem to make it inevitable that we need a constructor theory are actually wrong and whole lines of unification that seem to connect different fields don’t connect them and yet therefore they must be connected in some other way because the truth of the world has to be connected if it turns out to be wrong the chances are it will be found to be wrong long before it’s falsified this again is the typical way in scientific theories what gets the headlines is if you do an experiment and you predict a certain particle and it doesn’t appear and then you’re proved wrong but actually the overwhelming majority of scientific theories are proved wrong long before they ever get tested they’re proved wrong by being internally inconsistent or being inconsistent with other theories that we believe to be true or most often they’re proved wrong by not doing the job of explanation that they were designed to do so if you if you have a theory that is supposed to for example explain the second law of thermodynamics and you know why there is irreversibility when the fundamental laws of physics are reversible and then you find by analyzing this theory that it doesn’t actually do that then you don’t have to bother to test it because it doesn’t address the problem that it was designed to address if constructor theory turns out to be false it’s I think it’s overwhelmingly likely that it’ll be by that method that it just doesn’t do this unification job or foundational job that it was designed to do um turning out to be wrong is not a disgrace you know it’s not like in politics where if you lose the election then you’ve lost in science if your idea that looked right turns out to be wrong you’ve learned something
Edge interviewer
Something I want to just ask you about this whole uh your shtick about explanation yes it seems counter to what the poets would tell you uh oh I’m not so sure it’s all the Stevens the blah I don’t know about that the thh yes the most important word is the next word the to be said he said theory of description matters most and Pound said that there is description and there’s the village explainers you know so it’s I’m just interested in …
David Deutsch
Well I’m not aware of all that little subculture you’ve described
Edge interviewer
But you haven’t read by the way chan brock
David Deutsch
Afraid not
Edge interviewer
That definitely should be as popular as your theory. Okay, but tell me about it. This is obviously what you’ve been thinking about for years. Talk about it in that context without saying in my book. Yeah, yeah.
David Deutsch
So one of the central uh philosophical motivations for why I do fundamental physics is that I am interested in what the world is like that is uh not just the world of our observations what we see but the invisible world the invisible processes and objects that bring about the visible because the visible is only the tiny superficial and parochial sheen on top of the real reality and the amazing thing about the world and our place in it is that we can discover the real reality we can discover what is at the center of stars even though we’ve never been there we can find out that those cold tiny objects in the sky that we call stars are actually million kilometer white hot gaseous spheres now they don’t look like that they look like cold dots but we know different we know that the invisible reality is there giving rise to our visible perceptions now that science has to be about that has been for many decades a minority and unpopular view among philosophers and to a great extent regrettably even among scientists they have taken the view that science just because it is characterized by experimental tests has to be only about experimental tests but that’s a trap that means if that was so it would mean that science is only about humans and not even about humans but about human experience only it’s solipsism it’s purporting to have a rigorous objective world view that only observations count but it ends up by its own inexorable logic as saying that only human experience is real which is solipsism so I think it’s important to regard science not as an enterprise for the purpose of making predictions but as an enterprise for the purpose of discovering what the world is really like what is really there how it behaves and why which is tested by observation but it is absolutely amazing that the tiny little parochial and weak and error-prone access that we have to observations is capable of testing theories and knowledge of the whole of reality that has tremendous reach far beyond our experience and yet we know about it that’s the amazing thing about science that’s the aspect of science that I want to pursue
Markdown