July 07, 2004
Thinking About Physics (Part 1)
Ed's recent link to this Slate article about Brian Greene, together with this post by Sean Carroll (and particularly the accompanying comments) have finally given me sufficient motivation to write down (at least in preliminary form) some things I've been wanting to say about physics for some time now.
The resident head of the dorm I lived in during the past two years was a philosophy graduate student with an interest in philosophy of science, and we have had several interesting discussions about the philosophy of physics. As a graduation gift he gave me a copy of Roger G. Newton's Thinking About Physics, a book by a mathematical physicist addressing certain issues in the philosophy of physics. I mention it here because Newton explains some things with more clarity and depth than I could hope to in a blog entry. I don't entirely agree with him on everything, but mostly I think his ideas are very reasonable.
Without getting ourselves into metaphysics, I think that (almost by definition) a scientist must believe certain things about the world. Namely, an external, real world exists, and it is possible to learn about it through our senses. Based on the sense-data we collect, we attempt to understand how the world works. From here, I think it's unreasonable to assume that it is possible to obtain definite information about the world in itself. We can formulate theories about the world, and test them, but in any case we only know that a theory is valid in those regimes of energy, distance, or other settings in which we have tested it. With this is in mind, it's impressive that we have a theory -- the Standard Model -- that, to the limit of our ability to test it, appears to describe all phenomena below a certain (large) energy scale. We also have a theory -- general relativity -- that, to the limit of our ability to test it, describes the way that gravity works.
From here we hope to form a coherent theory, including as limits the very well-tested theories that we already have, but also describing a wider range of phenomena. This is the goal of string theory, and it is a goal to which I have no objection. On the other hand, the Slate article presents Greene's view as teleological: that is, we are moving toward an ultimate theory of the universe. I find this viewpoint hard to accept. There is, of course, the simple objection that even if we find "the fundamental theory" (whatever that might mean), moving from that to an understanding of chemistry or biology or human behavior is nontrivial (or even impossible). But even beyond this, I find it questionable that a "fundamental theory" even exists. The universe certainly exhibits regularities that we can elucidate and try to understand, but I am skeptical of any claim that at its core the universe is mathematics. I find it much more likely that mathematics is entirely a human construction that happens to be very good at describing the world around us. Our mathematical theories give us increasingly powerful ways of understanding the world, covering an increasingly wide range of phenomena, but to expect that one day a single mathematical theory will encompass all of reality seems to me terribly arrogant.
None of this, I should add, addresses the issue the Slate article set out to answer, namely, where does Brian Greene stand as a physicist? As I am not a string theorist, and my knowledge of algebraic geometry is still too weak to understand many of Greene's papers, I'm not so well-equipped to answer that question. My impression is that Greene is a good physicist, who made important contributions to understanding topology change in string theory. Perhaps more importantly from the standpoint of the article, his recent work has been focused on string cosmology. While still a long shot, there is some hope that understanding the implications of string theory for inflation will give testable predictions for experiments in the next decade or two. Sheldon Glashow might scoff, but I think it's unwise to discount this possibility at this point.
So, I suppose the upshot of this is that one can do good physics even while having the (to my mind) unsupportable opinion that one is approaching a "final" theory. This post has grown long enough, but I would also like to say some things about the issue of "wave function collapse" in quantum mechanics, which came up in Sean Carroll's comments. This I will do in another entry soon.Posted by Matt at July 7, 2004 11:08 AM
This post is so pointless (please don't view this comment as a personal attack, however). All the points that you are making are seriously cliche. All the physics and math you are learning now are pretty much useless and have zero value to humanity besides the self-righteous "life of the mind" value of knowledge for its own sakes.
I would be more interested in you explaining why you are interested in what you are doing, seeing that high energy physics has, practically speaking, essentially zero future, regardless of how current theories are correct or not. The more important question in physics now is in application of theories in cosmology, or, maybe soft/hard condensed matter. And it's philosophically pointless too. So you can construct the entire universe via the new and improved string theoretic Standard Model. So WHAT? What's the point? You can't *predict* anything beyond quarks. Anything that have no predictive value isn't really science. To any other scientist who does anything that is not HEP, Standard Model is basically the same as Creationist Theory. You can't even predict the dynamics of a proton from its composite quarks from QCD. What the hell is the point?? The answer: there is no point. It's intellectual masturbation. In fact, the entire field of HEP is a large collective mass of self-indulgence.
Please, justify to me why you would want to do physics? Please...
As far as the "point" of this post goes: I'm not claiming to have expressed any profound original insight. However, it's certainly true that there are those who have a teleological conception of science, and that one can think they are wrong while still thinking that they do good science. I think that to a certain extent the Slate article conflated one's conception of science with one's scientific merit, and it's worth emphasizing the distinction.
Now, you use the phrase "zero value to humanity besides the self-righteous 'life of the mind' value of knowledge for its own sakes." Here I'll largely agree with you: the best reason for doing mathematics, or physics, or any of a number of other academic disciplines, is for knowledge. I disagree, however, that this is "self-righteous," and I think that it does have value to humanity.
You may have heard the story of how Bob Wilson was once asked in front of a Senate committee to explain how Fermilab contributes to national defense. "It has nothing to do directly with defending our country," Wilson said, "except to make it worth defending."
While I'm aware that the average person is not particularly concerned with high-energy physics, I'm optimistic enough to think that most people, at least in certain phases of their life, are curious about the way the world works. High-energy physics is answering basic questions. We are driven by our intellectual curiosity. Call it self-indulgent if you like, but I like to think that this curiosity is present in everyone, to greater or lesser extent.
(Returning to the original subject of the Slate article, Brian Greene has done a very good thing in making things that we know about our world accessible to the public, helping to bridge the gap between indulging the curiosity of physicists and indulging the curiosity of the public at large.)
It is simply not true that high-energy physics has no future, and it is puzzling that you mention cosmology, since that is one of the major arenas of experimental interest that will guide the future of high-energy physics. There will be experimental results from outside cosmology as well, though. In the next decade the Large Hadron Collider will turn on and will give us great insight into the origin of mass. You may think that this is not worthwhile, but I and many others would disagree with you. Given the opportunity to come closer to understanding the origin of something as fundamental as mass, don't you think we should pursue it?
As for understanding protons in terms of QCD, this is highly nontrivial, but lattice QCD has improved dramatically in recent years. Field/string dualities might also give us a better understanding of how to do the difficult calculations that arise in QCD. Lots of approaches to understanding QCD are under active investigation now. But there is much we already understand. Is there no satisfaction in knowing the underlying behavior that holds together an atomic nucleus? Perhaps not for you. Perhaps not for many others. Still, a large number of people, including many who are not physicists, have a deep curiosity about the nature of the world around us, and high-energy physics is uncovering answers to their questions and will continue to do so for quite some time.
This is not to demean other fields of science, practical or not. All sorts of science are similarly providing answers (and new questions) in much the same way. Even in the more practical fields, I think that many scientists would acknowledge intellectual curiosity as a strong motivation for their work.
Are you suggesting, Matt, that there is no "fundamental theory" meaning there is no fundamental reality? Are you saying, as Dyson did in the New York Review of Books, that there is a fundamental theory for big things and one for small things, but they work independantly? Or are you saying that there is a fundamental reality that is undiscoverable by man and undiscribable by mathematics?
I'm not suggesting there is no fundamental reality, or that there are independent theories for different parts of nature. I think there is a fundamental reality. I also think that particle physics and gravity must be unified; studying the early universe, for instance, would require both. I would more or less agree with your last statement: we apprehend reality only indirectly. It is certainly describable by mathematics, and I doubt we will ever find something "better" than mathematics for describing it, but I have my doubts about saying that reality fundamentally is mathematical. At this point I'm getting uncomfortable with how metaphysical this is getting, though. I just have a feeling that the universe is surely interesting enough that we won't have a "final" description of it within a few hundred years of systematically beginning to do science.
Just to play a little more devil's advocate here... You still didn't answer my question, what is your justification for pursuing physics. It seems to me that everybody has intellectual curiosity. You are obviously interested in other branches of science, I assume. Or philosophy, or literature, or anything else we can come up with. To me at least, I don't think HEP is really the most intellectually satisfying subject that people can pursue at this point, simply because there is nothing left to do that would provide any more insights into ANYTHING ELSE.
How can you justify yourself of your existence based on pure intellectual curiosity? What about all the people out there who can barely make a living? I'm assuming you don't give a damn about squandering your extremely intelligent mind on something as trivial as physics when you could make so many people's lives much more than they are if you work on social policy, for instance.
Matt gave a pretty enthusiatic response to your rather aggressively asked question, Sean. Though he didn't attempt a direct response (how could he without invoking the cliches you detest?) to why he does physics his apparent devotion to it seems to answer your qestion quite well.
What about all those people out there who can barely make a living ? Why should Matt (or anyone else of ability) be held back by those who fail to provide for themselves ?