# 2013-05-08 - Closer To Truth - Which Laws of Nature Are Fundamental [YouTube](https://www.youtube.com/watch?v=2BLo2SdmjLI) Duration: 00:13:28 ## Transcript ### Robert Lawrence Kuhn 00:00:00 - 00:00:24 David, the laws of physics seem incredible in that they are perceptible to us, we can manipulate them, we can use them for predictions. What does that begin to tell us in terms of their fundamental nature and how can we begin to look at the laws of physics and see what the nature of reality is? ### David Deutsch 00:00:24 - 00:03:17 It's certainly the case, and I think this is now uncontroversial, that if the laws of physics were very slightly different in almost any way, there could be no life in the universe, no complex chemistry and no thinking people and therefore no one who knows the laws of nature. So they are somehow almost infinitely special in that they allow themselves to be, as you said, not just known but also used and they were used before humans even existed to create life and then for the human species to evolve. Now that has been for several decades an unsolved problem at the foundations of physics, why that is so, called the fine-tuning problem. It began in a serious way, people began to investigate this in the 1970s, the physicist Brandon Carter who was investigating the evolution of stars found that if the charge on the electron had been only a few percent different, either larger or smaller, then there would be no life in the universe. If the charge was smaller, then there would be no complex chemistry and no opportunity for life to evolve. So the standard take on this is that this is evidence that the laws of physics as we see them are not the only ones that are instantiated in physical reality. It's rather like the argument, you win the lottery and you say why me and it seems very strange that the lottery should have picked out you and the solution to that is you will realize that that's not such a strange thing if you realize that a million people entered the lottery and one of them had to win. Or if you hit a golf ball and it lands on a blade of grass, you say what are the odds that it's on that blade of grass, however many blades of grass are on the field? But the thing that makes the fine tuning problem more mysterious than just any old random number like a lottery or a blade of grass is that the particular blade of grass that it landed on seems to have a purpose, seems to be tuned as they call it for our existence and this seems to violate one of the first things that was realized at the beginning of modern science which is that humans are not especially distinguished by the laws of physics as the center of the universe or as the purpose of the universe or anything like that but that everything about us is explained by laws that don't particularly refer to us. ### Robert Lawrence Kuhn 00:03:17 - 00:03:19 The Copernican principle. ### David Deutsch 00:03:19 - 00:03:21 Yes, yes that's right. ### Robert Lawrence Kuhn 00:03:21 - 00:04:13 So the explanations that have been given are that and they're radically different and these are pretty much the only two explanations is that in one way we have been designed to be special by some creator god that some people would like or some super intelligent species in which we're simulated, some sort of a creative process, maybe not necessarily a traditional god, some sort of creative process. The other extreme are multiple universes in a cosmological sense in which each one of these multiple universes, an infinite number perhaps picks out different laws of physics so that in the process of this randomized approach one or more would give rise to us and we're in that universe so it's the only one we're in so we're asking the question why are we special. One of those two that's what we're given. Do you like either one of those two? ### David Deutsch 00:04:13 - 00:04:36 No, I think both of those are incapable of solving the problem. The first one, the idea that the laws of physics were designed by someone or something simply raises the question that that thing also has to be fine tuned. It also has the very properties that we're wondering about the origin of in ourselves. ### Robert Lawrence Kuhn 00:04:36 - 00:04:37 Kicks the problem up a level. ### David Deutsch 00:04:37 - 00:04:47 Yes without making it any better. Maybe worse. It's okay to kick the problem up a level if you then have an easier problem but if you have the very same problem then that's an infinite regress. ### Robert Lawrence Kuhn 00:04:47 - 00:04:51 Or it might be a harder problem if that's a non-physical thing. ### David Deutsch 00:04:51 - 00:05:53 Could even be a harder problem in which case it's worse than an infinite regress. Now the other idea which is the one that is greatly favored by cosmologists currently, I'm not entirely sure why but it has become the prevailing theory in cosmology is this idea that there's an ensemble, a vast set of different universes. Now the trouble with that as was pointed out by Richard Feynman many decades ago is that if the only explanation why the laws of physics seem to favor us is that if we weren't here we wouldn't be asking, the overwhelming majority of universes in which someone is asking they are only just asking, that is the universe is only just good enough. There are many more universes where for example this room and its contents have just sprung into existence and will disappear immediately afterwards. ### Robert Lawrence Kuhn 00:05:53 - 00:05:54 A fluctuation. ### David Deutsch 00:05:54 - 00:06:43 Of just a fluctuation and this idea that the universe could be just one in an ensemble suffers from the fatal flaw that most such universes that have the property of containing us only just have it and we're about to die because a sphere of heat is coming in at the speed of light and will extinguish us in the next picosecond. So that means that some principle other than just anthropic self-selection has to be responsible for the fine tuning and it can't be design because that just kicks the problem upstairs. ### Robert Lawrence Kuhn 00:06:43 - 00:06:48 It sounds like there's no solution because I don't got one. I'm waiting to see how you can solve this. ### David Deutsch 00:06:48 - 00:07:50 I don't pretend to have a solution but I think I have an argument why there can be a solution apart from those two. If the solution isn't either of those two then the solution is a law of physics. It's a law of physics that applies in our universe or perhaps in our universe and a trillion others but just having as I said just having multiple universes doesn't solve the problem. They would have to be multiple universes that are tuned so that most things in them don't just only just exist. I think the key is that the laws of physics as we currently conceive them are based on atoms and working out everything that happens from a microscopic level but if we admit into fundamental physics laws about emergent properties such as computation one of those may imply that we exist without being anthropocentric. ### Robert Lawrence Kuhn 00:07:50 - 00:08:11 David, as we consider the laws of nature we always try to find those which are the most fundamental and physicists would have us go deeper and deeper in a reductionist sense to try to find those laws. How do you look at even approaching the problem? ### David Deutsch 00:08:11 - 00:08:58 What I take to be a fundamental law is one that is implicated in many other explanations and the most fundamental laws in physics happen to be reductionist laws of quantum theory and the theory of relativity. Although there are non-reductionist laws like the second law of thermodynamics even in physics but there are other laws. The principle of evolution for example which says that adaptive complexity can only arise through variation and selection is a rigid law of nature and yet is intrinsically emergent so that's another law. The laws of epistemology that say that knowledge is acquired by conjecture and criticism that's another rigid law. ### Robert Lawrence Kuhn 00:08:58 - 00:09:16 So now you've given three radically different kinds of laws from fundamental physics to biology of species to approach to knowledge that are all fundamental but are radically different even in their categories. ### David Deutsch 00:09:16 - 00:09:25 Yes, they are all fundamental in that they are needed to explain many things and we can't explain everything in terms of just one of those strands. ### Robert Lawrence Kuhn 00:09:25 - 00:09:32 And therefore to you explanation is an organizing principle that can unite those. ### David Deutsch 00:09:32 - 00:10:27 That's right and one of the things that looking at it this way helps with is that we can see that laws at different levels of emergence actually mesh together into what I call the fabric of reality into a sort of unified world view which we can then extend. One of the things I'm trying to work on now is extending the theory of computation into the theory of not just what can and can't be done with abstract objects but the theory of what can and can't be done with any object which is a way of looking at physics in the manner of the quantum theory of computation and remarkably that connects not only physics and computation but it also has all sorts of philosophical implications such as optimism comes out of that theory. ### Robert Lawrence Kuhn 00:10:27 - 00:10:37 Well we certainly need some optimism but I'm at a loss to see how we can get optimism from where we are so walk me through. What do you call this theory? ### David Deutsch 00:10:37 - 00:11:37 It's called constructor theory. It's the generalization of the theory of computation to the rest of physics and the way it is linked to optimism is very simple. If you imagine the set of all transformations we want to transform the world into a better world let's say. Now some of those transformations are permitted and some are not permitted by the laws of physics so the question is which ones of them can we actually achieve in real life and the answer to that must be according to constructor theory that the ones that we can achieve in real life are precisely the ones that are not forbidden by the laws of physics. So if the laws of physics say we can't travel faster than the speed of light then we never shall but if there isn't a law of physics that says you can't live to be 500 then living to be 500 is a soluble problem it's just a matter of knowing how. ### Robert Lawrence Kuhn 00:11:37 - 00:11:48 So what are the limitations of physical laws that will give us those ultimate constraints because anything within those constraints is ultimately achievable. ### David Deutsch 00:11:48 - 00:12:31 That's right. So the laws of physics are not actually very onerous in regard to achieving what humans want to achieve. Even travelling to another galaxy although you can't do it in the time fortunately the relativity means that your time will slow down if you travel very fast so if you really wanted to travel to another galaxy in your lifetime and you had the right technology you could do so subjectively. So it's not very onerous the things that we are accustomed to calling evils even the ones that are deemed to be inevitable evils like death are actually just a matter of technology to solve. ### Robert Lawrence Kuhn 00:12:31 - 00:12:36 So you look very optimistically in terms of what technology can achieve. ### David Deutsch 00:12:36 - 00:13:10 Yes and this as I said follows from very fundamental considerations within physics. The thing is if there were a thing that we can't achieve no matter what knowledge we bring to bear let's say it was living to 500 or something there's no law of physics suppose that there's no law of physics that we can't but we still couldn't achieve it well then if we can't achieve that no matter what knowledge we bring to bear then there is another law of physics that says that we can't do that and that's a testable law a testable regularity in nature is a law of physics. ### Robert Lawrence Kuhn 00:13:10 - 00:13:17 So as we push forward as we push knowledge forward as you would like to say infinitely forward as we do this. ### David Deutsch 00:13:17 - 00:13:19 Or unlimited yes. ### Robert Lawrence Kuhn 00:13:19 - 00:13:27 As we do this we will either make progress or discover new laws of physics that constrain us one or the other. ### David Deutsch 00:13:27 - 00:13:28 Exactly.