One of the words I dislike most in my field – or more accurately, a common usage thereof – is “fundamental”. This is because it is usually used as a weapon, very often by people in my area of physics (largely concerned with particle physics, high energy physics, origins questions and so forth), to dismiss the work of others as somehow uninteresting or irrelevant. I don’t like this. Never have. Not only is it often allied to a great deal of arrogance and misplaced swagger, it is often just plain short-sighted, since you never know where good ideas and techniques will come from. A glance at the history of physics shows just how much cross-pollination there is between fields in terms of ideas and techniques. You never know for sure where valuable insights into certain kinds of problems may come from.
Fundamental physics is a term I used to hear used a lot to refer to particle physics (also called high energy physics a lot more these days). This was especially true some years back when I was an undergraduate in the UK, and it persisted in graduate school too, and is still in use today, although I think it is declining a bit in favour of less loaded terms. Somehow, a lot of particle physics is regarded as being all about the “what is everything made of at the very smallest scales” sort of question, first discussing atoms, and then atoms being made of electrons surrounding a nucleus, and the nucleus being made of protons and neutrons, and those in turn being made of quarks, and so on, in this was arriving at a list of “fundamental” particles. There’s the parallel discussion about the “fundamental” forces (e.g., electromagnetism and the nuclear forces) being described in terms of exchanges of particles like photons, gluons, and W and Z particles and so forth. There’s no real harm in the use of the term fundamental in this context, but this is about where the word gets elevated beyond its usefulness and starts becoming a hurdle to progress, and then a barrier. Somehow, “fundamental”, meaning “building block” gets turned, oddly, into “most important”. The issue of what the smallest building blocks are gets elevated to the most important quest, when it is in reality only a component of the story. It is rather like saying that the most important things about the Taj Mahal are the beautiful stones, tiles, and other components from which it is constructed.
Perspectives have evolved a bit since my salad days, with the rise of wider recognition of the connection between particle physics, and astrophysics and cosmology. I think that things are (these days) more widely seen to be the more rich interconnected and beautiful landscape of phenomena that they are, but I still find, especially among younger people, the “building block” attitude to be prevalent.
I raise this since sometimes I find that people don’t understand that there are fundamental and vital questions in other areas that connect to so many interesting areas of physics. Examples of those include some of the matters in which I’ve been interested, especially the last decade, in my research. Therefore the issue comes up a lot when friends (and even colleagues in physics) ask what I am up to. This concerns using string theory to model physical phenomena being seen in experiments in condensed matter, nuclear, and atomic physics. (See here, here, and here for some discussion, and peruse the related posts list below. Also see the rather good Science News article by Tom Siegfried that I missed in earlier postings.) It has begun to be called “applied string theory” by some, which is an unfortunate term since it has both positive and negative uses that are more pointed than any neutral use I can see: On the one hand, it weirdly implies that other work in string theory is not “applied”, as though it was not being used to try to solve physics problems for all this time, and on the other hand, the term “applied” is somehow being used to indicate something less than pure and “fundamental” is going on. That it is merely an application, like using quantum physics to make iphones is to be regarded as merely “applied”, like a mere craft rather than an art, dance music rather than high symphonic composition. These are all distinctions that are more than a little forced, definitely unnecessary, and are symptoms that the person trying to make such distinctions is certainly not hearing the rhythm for the drums.
There’s also a disturbing tendency to attempt to distinguish string theory from “the tools of string theory”. This is rather silly. All that we do in physics, whatever area, is just deploy tools. No tools, no physics. There’s nothing else there. In one of our most successful theories of Nature, quantum electrodynamics (QED) we describe photons interacting with electrons using quantum field theory. We don’t say “the tools of quantum field theory” for fear of imparting more reality to the objects in the toolbox than we are comfortable with. The bottom line is that Nature is Nature and photons and electrons are what they are. The tools we describe them with constitute quantum field theory, and we don’t need to declare whether or not the quantum fields and associated baggage (gauge symmetry, etc) are “out there” in Nature in some Platonic sense. Why bother? We are physicists and not philosophers. We need not (should not) confuse our tools with the things we are trying to describe with them. The same goes for string theory. If we find a place where string theory gives the best working description of the phenomena being studied and observed, why not just call it what it is? It is string theory that is being used, not “the tools of string theory”. There is no distinction.
Many of the physics questions of interest are among the most important in Nature from at least a pragmatic perspective. They often concern (in some guises – but see below) situations where there are certainly more than two bodies interacting at once. There might be very many indeed. Then the game changes considerably. Sure, it is important to know that there’s a description of the innards of the nucleus in terms of quarks interacting by exchange of gluons (in this way mediating the strong nuclear force), but to my mind, just as fundamental is the issue of what happens when a huge number of the quarks and gluons are interacting together at high temperatures and/or densities. This is interesting in its own right, but is also of relevance to questions about the early universe, the cores of highly compact stars (such as neutron stars), etc. Genuinely new phases of matter appear in these situations and their properties are worth studying. Just as it is important to understand the difference between water, ice, and steam (and how to move between those phases as the temperature changes) distinctions that are immaterial from the perspective of just one or two molecules. That some of these new phases are experimentally accessible at facilities such as RHIC (the Relativistic Heavy Ion Collider in New York) and soon at detectors such as ALICE at the LHC (Large Hadron Collider at CERN), and that there seems to be string theory descriptions of aspects of these phases is very exciting.
Such contact with experiment is already being downplayed as somehow “less fundamental” than if we were to see sure signs of string theory physics in a particle physics or cosmology context at the LHC, or in data from Planck satellite. I think that this attitude is very mistaken, not the least because it perpetuates this unfortunate arrogant and short-sighted attitude that one field of physics is less important than another, but also because of a stronger point I will make in a short while.
Just as exciting (possibly more, from some perspectives, since these experiments are more of the bench top or table top variety) is the possible usefulness of string theory in understanding a range of phenomena in condensed matter physics and (ultracold) atomic physics. Again, this is the realm of many things interacting together. Phenomena such as superconductivity (in its various forms), the Quantum Hall effect, various quantum phase transitions between certain types of distinct behaviour, certain behaviours of collections of ultracold atoms (e.g. lithium) are a wide range of diverse physical systems that we are learning to find descriptions of using string theory. Some of these alternative descriptions may not yield any new insights, while others might.
To dismiss all the above as “not fundamental” because we already know (whatever that means) the basic building blocks (quarks, or lithium atoms) of the systems, and the kinds of interaction force involved (which of the known fundamental forces is a player) is, to not mince words, foolish. From an immediately practical perspective such an attitude is missing out on some interesting and important physics issues, but from another perspective, that view places the holder in the position of possibly missing the boat entirely.
It is my view that we will learn a lot about many of the key questions we are asking in string theory’s now-traditional pursuit (particle physics, cosmology, etc – the nature of spacetime at the quantum level, the origin of the universe and its contents and why it is the way it is) from this sort of research. This is not just because there may be cute analogies between different phenomena. I think that it is further than that. For whatever reason, Nature recycles good ideas. I mean this. It is true in Biology, and I think it has some truth in Physics too. An example is spontaneous symmetry breaking (SSB). This shows up in the complicated many-body phenomenon involving interactions between lots of electrons and the lattice of the medium in which they are moving to give rise to superconductivity, the spectacular phenomenon of zero resistance in a real material below a certain critical temperature. It also controls the (supposedly more fundamental) phenomenon of the splitting apart of electromagnetism from the weak nuclear force, at the same time communicating a specific pattern of masses to all of the elementary particles, when we study the universe below a certain energy scale. That’s Nature recycling a cool idea in two very different contexts. One is in the messy world of condensed matter physics and the other is in the simpler world of particle physics and unification of forces. The mechanism is controlled in each case by the same very simple effective model in quantum field theory (determined by a few symmetry principles and some robust general conditions). The different contexts manifest themselves as simply a decoration of the details of that same one robust model. In my view, both areas are just as fundamental as each other.
Those aforementioned phenomena we’re seeing in condensed matter, nuclear, and atomic physics, arising from lots of players interacting together (a term that is often used is “emergent phenomena”) may well be governed by mechanisms that will show up in other areas of physics that have little (on the surface) to do with the original context, such as particle physics and cosmology, quantum gravity, etc, just as happened for spontaneous symmetry breaking. This possibility alone is motivation to study them. Furthermore, one of the exciting things we are learning is that the simple effective models (the analogues of the quantum field theory models for SSB) this time can involve string theory in an essential way. This is not just vibrating strings, but the whole kit bag of things that people often think of as weird, or not even physics: extra dimensions of space, open and closed strings, extended objects (“branes”), quantum black holes, and so forth. They come together. What does this fact suggest to me? It suggests that progress using strings in these “applied” areas (and our work continues to see how far this will go) bode well for finding uses for string theory back in those “traditional” contexts of particle physics, cosmology, quantum gravity, astrophysics, etc. This is not guaranteed to be true, but that Nature seems to recycle phenomena and mechanisms in the way I mentioned above seems to strongly suggest this.
We know from the marvellous successes of 20th Century research that Nature likes and admits quantum field theory descriptions of phenomena (often the same basic phenomena) in many diverse areas. It has happened before, so it can happen again. If we find one place where there’s a useful and essentially string theory description, even if it is in a condensed matter or nuclear context, chances are it’ll show up all over the place too. Upon reflection, if this turns out to be true, it would not be too surprising. We know that Nature already has regimes where extended objects play a key role: strings (flux tubes, particularly when magnetic fields are involved from superconductors, the surface of the sun, etc.) membranes (all over biology), etc. It is not that much of a stretch of the imagination that there could be other regimes where those ideas get played out again. Why not in particle physics and cosmology?
This view is why I caution against the practice of trying to categorize various fields’ research endeavours into “fundamental” and “not fundamental”. It is just wrong-headed. In fact, this is also one of the reasons I enjoy working in this field and training students and postdocs in this field. Whatever the answers turn out to be, a well-trained young person in this field gets a very broad education in all sorts of techniques that will prepare them well for wherever the research of the larger community goes, and maybe whatever the next generations of experiments present us with. A good student of this rich area of string theory is part particle physicist, relativist, condensed matter theorist, cosmologist, astrophysicist, atomic theorist, nuclear theorist, and so forth. That is almost certainly time well spent in preparation for whatever is to come.
The most fun part of all of this is that there are almost certainly big surprises to come. This is a revolution quietly in the making. (Remember, you heard it here first.) Right now, we may or may not be on the right track with our string theory endeavours so far in trying to use those methods to understand our universe’s origins, and whatever lies at the next level of understanding of particle physics and cosmological phenomena. We may not even be close! Strings may nonetheless turn out to be a relevant part of the understanding, but in a key way that we are not seeing right now. We might learn that strings fit, but in a very unexpected way. That’s why all this is exciting to me. It is also possible that there is simply no role for strings at all, but continued progress in making contact with Nature in this “applied” string theory context (if it turns out to be fruitful), combined with a little knowledge of the history of the subject, suggests otherwise. We shall see.
Some Related Asymptotia Posts (not exhaustive):
- Uses For Strings?
- Some Articles
- 24 - Physics Edition (Day Two)
- So What Is String Theory, Anyway?
- Weinberg on BCS
- Quantum Black Holes - Why Worry?
- Atoms and Strings in the Laboratory?
- News From The Front, III
- News From The Front, I
- News From The Front, II
- News From The Front
- Beyond Einstein: Fixing Singularities in Spacetime
- Talk Talk
- Whither String Theory? - Too Soon To Tell
- Exploring QCD in Cambridge
- News From The Front, VI: Simultaneity
- News From The Front, V: Microscopic Weekend Diversions
- News From the Front, IV