Tuesday, January 18, 2005

The theory of everything

There seems to be two types of high energy physicists, those that work in string theory and those that deride it. The main criticism of string theory is that it cannot generate predictions that are testable with current or even near future experiments. Thus it is really a field of mathematics or philosophy. However, both sides seem to agree that a search for a fundamental theory resides at extremely high energies.

Those of us working at eV energy scales, have a very different picture. Philip Anderson probably was the first to voice this alternative view in his famous article "More is Different" (Science 177:393-396, 1971). In that article he noted that each energy scale has its own organizing principles and fundamental laws. Hence, chemistry is not just applied physics, biology is not applied chemistry and psychology is not simply applied biology. Each of these disciplines must be studied in their own right.

On this point, I think most high energy physicists just don't get it. I saw a talk many years ago by Erich Vogt, the then director of the Canadian cyclotron TRIUMF, who started his seminar by outlining the 6 steps or so it takes to construct a cow. He started with quarks and built up the complexity step by step until he got to molecules. After that he said you just combine them and make a cow. I thought that perfectly typified the attitude of some particle physicists who feel that anything bigger than an atom is just quantum mechanics and thus it is just a matter of working out the details. Anderson pointed out that knowing the so-called fundamental laws wouldn't tell us how a magnet works. Spontaneous symmetry breaking is more important to magnetism than quantum mechanics or any other underlying theory.

The aura of high energy physics really dimished for me when I learned statistical mechanics and the renormalization group. Here I found that microscopic interactions may not matter at all. When you go to a large enough scale only gross properties like how many dimensions and symmetries determine the properties of a system. As you go to larger and larger scales, the parameters of the system "flow" in parameter space and eventually converge to a fixed point. Thus, it doesn't matter what the initial condition was, just the location of the fixed point. I think a fixed point theorem is as fundamental a law as any other. Perhaps someday, string theorists will find that there isn't a unique theory. A whole family of theories would be consistent with our universe and that would be perfectly fine by me.

5 comments:

steve said...

Carson,

It is certainly true that each length scale may have its own characteristic dynamics, and that knowing the fundamental - oops I mean short distance - description doesn't necessarily let you understand what happens at larger length scales. Certainly many, many systems in nature (ranging from markets to networks to organisms) are fascinating, complex and unique.

Nevertheless, there is something fundamental and basic about the investigations of particle physicists. You mentioned the example of IR fixed points. Well, not all systems flow to such fixed points, nor does all initial data. You might ask *why* a particular system has its particular properties. These *why* questions can only be answered by looking at a more fundamental description. For example, you might want to know why the magnetic moment of a neutron or proton takes a particular value. To the eV physicist it is an input parameter - a God given constant of nature. But in fact its value can be computed from first principles from QCD. So, what appeared to be one of many seemingly arbitrary constants may turn out to be a consequence of some deeper physics. Perhaps all of the dozens of parameters in the Standard Model will someday be predicted by a more fundamental theory (strings?). On a related note, we might want to know why the universe is the way it is: How did galaxies form? Why is there so much more matter than antimatter? Why do the initial conditions of the big bang seem so fine-tuned to produce a large, long-lived universe? Why are there four dimensions and a Lorentzian signature metric? These will only be answered by the old reductionist approach.

I believe that if you continue to ask these "big picture" questions you will eventually be led to the central issues in particle physics. Whether you regard them as more or less interesting than problems in applied physics or biology is a question of taste. (You can tell from my blog that I am interested in a pretty broad range of problems.) However, I predict that if and when we meet an advanced alien civilization they will have considered these big picture questions with the same fascination that we have!

Carson Chow said...

Hi Steve,

I don't feel that your questions are unimportant. However, I don't see them as being more important than other energy scales. Parameters at one level (such as the magnetic moment of a neutron or that of a macroscopic object) can arise from interactions at a smaller level. No disagreement there. Your example of what sets the basin of attraction for fixed points is exactly what I'm getting at. These questions are not confined to given energy scales. I don't have a problem with the old reductionist approach. I use it myself in my research. My point is that questions at other energy scales are not just fascinating, complex and unique but can also be equally fundamental and independent of the short-distance theory: Is life inevitable? What is consciousness? Can societies be stable?

Anonymous said...

Dear Carson,

Interesting posts and conversation. I will follow along, but there is a problem. The black background makes it too difficult for these eyes to read with any facility. Too late to change eyes :) Nice blog in all but color.

Anne

Carson Chow said...

Hi Anne,

Thanks for the tip. I'll change it.

Carson

Anonymous said...

This comment is somewhat tangential to the topic. I was taken with P Anderson's criticism of String Theory in the NYTimes on 1/4/05 (see end of this text). I believe most, if not all, scientists would be supportive of research aimed at a TOE, but the nature of that effort and the coupling to physical observables is a major source of disagreement.

Physics has historically been a competitive interplay between experiment and theory. Each thrust striving to unearth deficiencies and extend beyond the range of the other. This does not appear to be the case with string theory. String theory is worthy of study as a scientific endeavor, but it seems more suited to the field of mathematics. In that domain, the wisdom and magnitude of investment and effort can be evaluated alongside equivalent research topics.

The reality of increasingly limited resources for academic efforts may have already forced this decision. Certainly within government research labs, string theory research is almost non-existent, as these institutions have been required to focus and account for their budget requests by congressional funding sources. Academic institutions have some luxury to invest in blue sky efforts, but even in this realm publishing is no longer a sufficient condition. Capturing funding is becoming a dominant job activity for academics in the natural sciences at research universities. As with most institutions, politics and strong personalities can influence the course of development and it appears that this is at least partially true in string theory. Although I do not know it as a fact, I suspect that string theory research is part of the NSF HEP charter. However, if NSF gets a $100M budget cut, a synchrotron (jointly funded by NIH) will probably be prioritized higher than the NSF-HEP budget. These circumstances will be increasingly likely with the declining resources and massive debt burden that is being generated by the current US political leadership.

I am not a dogmatic believer in the "power of free markets", and it would not be my preference to allow the markets to decide this matter. Instead judicious decisions by leaders would better serve the science community, thus preserving the possibility of continued investment in "blue sky" research.

This would be a great embarkation point to impugn Bush&Co and more generally US investments in science and technology, but that is probably better left for a different blog or blog entry.

-WJEV




NYTimes 1/4/05 (excerpted from "God (or Not), Physics and, of Course, Love: Scientisits Take a Leap")

-Philip W. Anderson
Physicist and Nobel laureate, Princeton

Is string theory a futile exercise as physics, as I believe it to be? It is an interesting mathematical specialty and has produced and will produce mathematics useful in other contexts, but it seems no more vital as mathematics than other areas of very abstract or specialized math, and doesn't on that basis justify the incredible amount of effort expended on it.

My belief is based on the fact that string theory is the first science in hundreds of years to be pursued in pre-Baconian fashion, without any adequate experimental guidance. It proposes that Nature is the way we would like it to be rather than the way we see it to be; and it is improbable that Nature thinks the same way we do.

The sad thing is that, as several young would-be theorists have explained to me, it is so highly developed that it is a full-time job just to keep up with it. That means that other avenues are not being explored by the bright, imaginative young people, and that alternative career paths are blocked.