Friday, February 4, 2011

A thought on physics

Often, we physicists consider ourselves at the peak of the scientific fields - it's a well-known sentiment:

But I'm beginning to believe the line is too blurred to argue that the distinction still exists where it once did. Bear with me.
About sixty years ago, when nuclear physics was still a burgeoning field of study, Fred Hoyle (not yet Sir Fred Hoyle) did pioneering theoretical work to show that carbon-12, essentially the basis of all life, needed to have a special "trick" of nuclear structure called a resonance in order to exist as copiously as it does throughout the known universe. By looking at the amount of carbon in the universe and accounting for the temperature of typical stars, he worked out that carbon-12 had to have a resonance of a very specific strength and energy - and years later, that exact resonance was found. Hoyle had made (among many other successes) a tremendous and dramatic contribution to the infant field of nuclear astrophysics (and, by proxy, cosmology); the resonance has since been famously known as the "Hoyle state."
Today, research in nuclear astrophysics continues, but we've come to a point of diminishing returns. We know generally what to expect now - surprises like the Hoyle state just don't arise any longer - and our work has boiled down to measuring cross sections to greater and greater precision and accuracy. Since there are no more Hoyle states to anticipate, we instead anticipate having a bit more beam intensity for our experiments or a bit less background noise. We build better detectors and better facilities to measure the reactions to 20%, 10%, 5%... and while this is important, I'm beginning to believe it's simply another form of stamp collecting.
Those same incredible surprises still exist - in the study of string theory (superstring theory) and quantum field theory (while I acknowledge that other fields, such as neurobiology, are also basking in the glow of their recent growth, I'm limiting my argument to fields within physics). These are the topics all of the popular science books cover, these are where the brightest of the bright go to strive for the next great discovery*. The cutting edge of physics lies at the heart of quantum field fluctuations and supersymmetry.
So where does that leave the rest of us who claim to be physicists? Can we really say that what we do, the measuring of a certain reaction to smaller and smaller uncertainty, is so different from an engineer whose job is to test hard drives to withstand greater and greater forces, or a technician who tweaks an MRI machine to get better and better resolution? Have we ceased to really do physics, and are now just glorified bean counters, relegated by virtue of our aging field to the category of "applied science"? Or can we still truly claim to be physicists, even if we no longer work at the bleeding edge of physics? Perhaps in the end it's all just a matter of semantics, and it doesn't really mean anything. But perhaps it does.

*oh boy... don't tell my string theorist friend I said that!



    This seems semi-relevant.

  2. and this 'sermon' is relevant to you and your research.

  3. Anonymous, thanks for the links (I also enjoyed this one, yet another reason I like Neil DeGrasse Tyson). I think he has a valid point as well - our job as scientists should include letting others know why science is so wonderful.

  4. Steven, thanks. Any thoughts from someone outside the field, who could view this from a broader perspective?

  5. Firstly, it depends on what you mean by the "peak" of science. If you mean "the most fundamental," then physics has (and will always have) that claim. If you mean "the field with most potential for new discoveries and growth," I'd argue that the biological fields gained this status some time ago, when they eventually "came of age" as real sciences (with the advent of understanding of evolution, microbiology, molecular biology and genetics).

    As for nuclear astrophysics, it is important to remember its relationship with observational astronomy. With the improvements in observation, both in resolution and sensitivity, and in the range of observables now available with orbital instruments (light from radio frequencies to high energy gammas, charged particles, neutrons, neutrinos etc) we're starting to get a much more detailed picture of the universe and the range and dynamics of celestial bodies, and interpreting this picture sometimes requires a better knowledge of the nuclear physics involved than we have currently. I'd say this is far from stamp collecting - it's helping to illuminate one of the most exciting investigations humanity has undertaken.

  6. Evil Doctor, is that first premise necessarily true? That's part of my quandary. Which part of physics is the most fundamental? Where is the dividing line between, for example, solid state physics and material science? What makes physics physics?

  7. Obviously, subject divisions are entirely artificial, imposed by ourselves in an attempt to catalog the world and our activities into discrete classes. However, if I was to make as broad a generalisation as possible, physics deals with the general, rather than the specific, and is an exercise in understanding, rather than manipulation.

    For example, if as a nuclear physicist one measures a cross section, or the spin-parity associated with a particular nuclear state, one is trying to determine (within the theoretical framework being used) something which is a manifest property of the universe, uniformly true over time and space. We believe the Hoyle state, measured in 12C nuclei on Earth, has precisely the same nature as in 12C nuclei in Betelgeuse, an AGB star, or in a presolar diamond grain drifting in the interstellar medium. We measure it, and generate models, to understand it.

    Engineering is concerned with how the properties of the universe manifest themselves in particular instances, with a focus on manipulating them. So, lets take your example of solid state physics versus materials "science" (which is really engineering). The generation and testing of a model which describes the properties of materials in a solid state (eg band theory, the photoelectric effect, ...) is solid state physics (science). Engineering is the tweaking of materials (making new compounds, doping crystals, etc) to adjust the properties (already described by theories), to our own ends, such as making a silicon which is more radiation hard, or a diode with a band gap tuned to a particular electromagnetic frequency.

    Of course, most fields involve some admixture of the two (either in the subject being studied, or the way it is being studied. Within nuclear physics, you know intuitively the difference: building a new instrument (an array of detectors, a gas-jet target, or whatever) is engineering. Measuring spectroscopic information of a nuclear wave function, so this can be used to refine a model of how nucleons are exchanged between colliding nuclei all over the universe, is most certainly physics.

    As for your question as to which part of physics is the most fundamental, I'm not sure I know precisely what you mean. Fundamental can relate to the use of information, or to the level of reality to which the information pertains. Take nuclear astrophysics again, and imagine modeling a nova. If you're interested in the nucleosynthesis, you care about the reaction rates, which depend on cross sections (nuclear physics), temperature (thermodynamics/statistical mechanics, the gravitational potential in the system, etc) and hydrodynamics (fluid mechanics). All of these fields are "fundamental" to understanding the nucleosynthesis, even though many of them are large-scale generalisations (statistical models) of reality, and are therefore less "fundamental" than the fusion of two nuclei to make a third nucleus.

    On the other hand, taking fundamental to describe level of reality, I could describe the entire star in increasingly "fundamental" levels, (for example) breaking the nuclei in the plasma down into nucleons, and those into quarks and gluons, etc. But since many of those lower degrees of freedom are locked (due to the energy regime) it's a pointless exercise. The physics of a star is, in fact, more insightful by ignoring those more "fundamental" layers of reality, just as a rotational state in a nucleus is more insightfully described as a rotating rigid body than it is described by a complex admixture of single-particle states, modified by residual interactions. As such, I don't think how "fundamental" an area of physics is particularly important, in contrast with how enlightening it is.

  8. I suppose that to a certain extent, for me, "fundamental" is equated with "simple" and "universally applicable." Which is what I envision physics to be. But it's a sliding scale, and sometimes it's difficult to find a good dividing line.

  9. To give a perspective from outside the field, this inquiry struck me as splitting hairs, or belittling something that doesn't deserve it at all. I suppose when you're so immersed in the field day to day, it's easier to get caught up in questions like this. (Similar to what you said to me when you got your PhD - something to the effect of, "It's easy to forget how brilliant you really are as a PhD when your'e surrounded by others equally as brilliant.") I suppose the daily drudgery of repeatedly measuring things in pursuit of increasing accuracy can seem quite dull and far from the "glamour" of exciting discovery, but that makes me think of archaeologists - their daily drudgery is essential to making exciting discoveries.

    I'm not really aware of the bragging or defending that goes on regarding physics as the most pure science. I'm vaguely aware of some similar attitude in mathematics between "pure" mathematics and "applied" mathematics. I prefer applied most of the time because it seems so much more relevant to me. And higher level pure mathematics is so far over my head that it makes it spin. But I love the purity of lower level pure mathematics. I guess what I'm trying to say is I don't really understand your frustration with trying to pinpoint or define physics (or what you do in physics) as "peak" or "fundamental" or "applicable." It's still brilliant. And we still do what we do because we believe that at some level, it matters. I'm trying to remember the name of a recent big proof in mathematics, but I remember reading that the person who accomplished the proof did so only by building on the work of many others, work which at the time seemed to lead to dead ends and not be relevant at all. I also read that some earlier attempts at this proof ended up being completely irrelevant to the proof but opened up new fields of mathematics that are now used in computing and security and encryption.

    And now I wonder if I'm completely missing the point of the original post, because I feel like I'm dancing around the old cliche of 'what you do (or who you are) matters somewhere, to someone' and I don't think that's really what you were getting at. (It's not what I was trying to get at either, but it seems like that's where I ended up.)



    This is a good point... sometimes we do lose sight of the forest for all the trees!

