2021-08-13 ToKCast David Deutsch answers a question about the nature of the laws of physics. A question for David 7
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Duration: 00:11:34
Transcript
Brett Hall
Welcome to ToKCast and episode seven, or question seven of my series of questions with David Deutsch. This is a question that actually follows directly on from episode one, or the first question that I gave to David Deutsch about the reality of abstractions. One particular special kind of abstraction is the laws of physics. The laws of physics are a kind of abstraction. After all, they’re not made out of physical stuff. So whether or not they’re just in the class of abstractions themselves, or they’re something different entirely, we don’t really know. We don’t really know what the nature of the laws of physics are. This has led, among other things, to some people, philosophers, to deny the actual existence of laws of physics. They say things like, well, there are just conjunctions of events, aren’t there? You know, this thing happens and that thing happens. But to infer, to take the extra step, to say there’s some sort of law of physics governing, prescribing, describing something like that, supervening on top of all of the material stuff in the universe, that’s a step too far. What you’re doing there is you’re just using your imagination to think into existence, something that doesn’t have a real independent existence all on its own. All there are are the events, the events that you can see and hear and feel and touch, the things that you can observe. And as you will hear David say here, the crucial part about that kind of argument is that it always presumes that the one thing that does exist are either the observations, which you have direct access to, or the things in themselves that you’re actually observing with your senses. So there’s always some sort of spurious, empiricist type assumption sneaking in to these arguments that deny the existence of things like the laws of physics. And using that kind of argument, you deny the existence of anything as people do. People go the whole hog and just deny the reality of abstractions. They just say that the fundamental particles exist. Again, that presumes that what they’ve got access to, their observations are somehow not able to be mistaken. And yet we know that of course we make mistakes all the time, errors creep into our observations. Observations are theory laden. What we have access to are ideas. Ideas come first, theories come first. And then using those theories, we are then able to figure out what the observations mean. So why do we say the laws of physics exist? Because they’re part of the explanation. They’re part of an explanation that we are forced to accept if we want to try and understand the world. They’re our best attempt to understand what’s going on in the world. There are things about whose existence there’s rarely any debate. Released almost simultaneously with this is the conversation that I had some months back with Christopher, part two of my conversation with Christopher of the Do Explain podcast. And in that podcast, we do discuss the nature of existence. And I bring up at one point, I think the example of cats, carrots and cars, just to name three things about which there’s rarely any debate that these things exist.
Brett Hall
Unless of course you go along to an undergraduate philosophy class and then people start complaining about whether or not tables exist, for example. And they start banging the table to say, does it really exist or just do the atoms exist? Some people do deny not only the reality of abstractions, but they also deny the reality of anything that’s emergent and say, well, it’s just fundamental particles. This seems to deny the emergent simplicity of things. A cat is not just the random motion of atoms or particles in the void. It’s an organized structure, obeying laws, emergent laws, like laws of evolution by natural selection, for example, that are not easily accounted for by a simple description or explanation of the predictive laws of physics. So we say these things exist. Things exist in so far as they appear in our deepest explanations of reality. And there are lots of different levels of explanations of reality. There’s the emergent kind, there’s the fundamental foundational kind out of which the particles consist. There’s the explanations of abstractions. There’s also some problematic things as well. So for example, we say that consciousness exists. We say that free will exists because both of these things appear in imperfect, granted imperfect explanations of the world, but to do away with them would be to do away even with the best explanation that we have with so many open questions of those particular things. Now, some people might say, well, if you’re invoking something like consciousness, why not invoke something like a ghost? Why not just start believing in ghosts? We can’t observe consciousness, can we? In the same way we can’t observe ghosts. No, they’re not symmetrical. A ghost is never required to explain any phenomena out there. Anytime you hear a strange noise at night when you’re staying in an old house, the better explanation is that the wood paneling is settling as the air becomes colder at night. It is not that a spirit from the netherworld is visiting you in your room just as you’re falling asleep. Nor is that smudge on the photograph evidence of a phantom from another dimension. That is just a silver emulsion on old film. There are always better explanations for these things. But when it comes to consciousness and when it comes to free will, we require those things in order to explain stuff, even if we don’t have a complete explanation yet. They’re part of trying to frame the question, I would say, to actually formulate what the problem is. Whatever the case. Today, I’m just talking to David briefly about the existence of the laws of physics and what the nature of that existence happens to be. So enjoy this question.
David Deutsch
Another thing which I think is still slightly mysterious is what kind of an abstraction the laws of physics are. Some people think precisely by arguments such as you’ve mentioned, there really are no laws of physics. All there are are physical events and physical processes. And laws are just a kind of way of summarizing physical events and processes. They just are. So because I see that looking out of the window, I can see that the sky is cloudless at the moment. That is some kind of emergent consequence of the laws of physics. But if it’s true, then people who deny that there are laws of physics will say, well, that’s just a fact about the universe. And you could summarize it and say that on three of the four days of this week, the sky was clear. And that’s not a law of nature. So why should there be anything special about the statement that nothing can exceed the speed of light? Well, it’s because the statement that nothing exceeds the speed of light is not just a prediction. It is an explanation. It’s an explanation of how the universe is. That the universe is a four dimensional pseudo-Riemannian manifold with a metric and so on and so on. And the fact that the speed of light is finite emerges from that explanation. And you could write down all the predictions that follow from that in a sort of infinitely long list of things like this dog can’t run faster than light and this car can’t travel faster than light. And once you’ve made that infinitely long list or maybe just very long, very, very long list, you would have written down everything that can be deduced about what happens in nature, but you wouldn’t have ever listed that law. And you wouldn’t have ever mentioned manifolds and four dimensional or anything like that.
Brett Hall
Well, you’d have some significant explaining to do, …
David Deutsch
Wouldn’t you? Well, if you wanted explanations, you’d have a lot of explaining to do. You would in fact have all the explaining to do at the end of that huge process that you had at the beginning. You wouldn’t have explained anything.
Brett Hall
We were just talking about the nature of physical laws and whether or not, and to what extent they might be pure abstractions or a kind of abstraction of some kind. And I was just thinking out loud to myself that for anyone who denies the existence of physical laws in their own right, laws of physics, and to just say, well, there are just facts of the matter about the universe. For example, the orbits of planets going around stars are approximately circular or elliptical, then those facts of the matter, those regularities in nature seem to be crying out for an explanation. So to deny that there would be really existing physical laws behind those regularities in nature seems to me to be going to a lot of work to avoid what might otherwise be called Occam’s razor. Well, isn’t the simple explanation, there are physical laws out there governing these things.
David Deutsch
Yes, of course, if somebody insists on the non-existence of explanations, exactly like insistence on the non-existence of anything, you can’t be proved wrong. But I think the motivation for denying the existence of laws is the old mistake of empiricism. It is the assumption that raw facts or raw sensory impressions have a privileged status in that we can access them directly. And people contrast this with things like laws and explanations in general, which they say we can’t access directly. So they have some kind of a lesser reality and we can in principle not insist on their being real. One can insist on their not being real and it doesn’t make any difference. The trouble with that is that exactly the same is true of sense impressions as well. And so this argument that abstractions don’t really exist or that laws don’t really exist and so on, hidden in there is the assumption that sense impressions or that kind of thing do really exist in some sense of really, which is itself a mistake. That all knowledge is conjectural, all observations are theory-laden. There is nothing that is an authoritative source of knowledge, everything is conjecture. And so once you’ve realized that everything is conjecture, but that knowledge can still exist, then the reason for making a distinction between different kinds of existence. Well, no, there is a distinction between different kinds of existence, but the justification, the motivation for denying that certain things exist, even if we need them in our explanations, goes away.
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