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 [tex]{\rm H}_2{\rm O}[/tex] 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.
-cvj
(I meant “QCD strong applications” of course.)
“The tools … 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.”
Hope a big prize is soon awarded for the use of string theory’s AdS/CFT to solve problems in condensed matter physics or QCD string interactions! Maybe when it starts getting prizes for applications, it will be seen in context more clearly, and will need less hype for unification and quantum gravity applications in popular media. 🙂
Newton’s G cannot be calculated, the Standard Model arrives massless. Supersymmetry’s partners refuse to appear, protons do not decay, the Higgs mechanism does not reveal its vector boson. Supergravity, lattice and loop quantum gravity, and above all string and M-theory predict nothing.
Physics is fundamentally flawed for observing the vacuum is isotropic to photons and assuming the massed sector in kind. Quantized gravitation theories require supplementing Einstein-Hilbert action with a parity-violating Chern-Simons term. Do left and right shoes vacuum free fall identically? Load an Eötvös balance with chemically and macroscopically identical solid single crystal quartz test masses, enantiomorphic space group P3(1)21 opposed by P3(2)21, right- and left-handed screw axes respectively. Is there a net non-zero signal? There’s your problem.
kim—
I’m not exactly a mathematician, but I’ll give it a go! Keep in mind that I typically look at math from a formalist point of view; a Platonist would probably answer differently than me.
(I apologize profusely for the length of this post—I have to do it now, because you might not make it to the end!)
To me, asking, “What are the fundamental building blocks of mathematics?” is like asking, “What are the fundamental building blocks of art?” People create art using whatever they have lying around—no material or technique is more fundamental than all the others. And people’s idea of what art is is changing constantly. A European Renaissance artist probably wouldn’t see scrap metal, dirt, or cheap consumer goods as building blocks of art, but a modern European artist might feel differently.
You said, “I was thinking it all begins with the notion of a set and that the notion of a function also plays a part.” In case you don’t know, the fact that this idea is so common right now has a lot to do with our historical context. At the beginning of the 20th century, a lot of mathematicians—most famously, Bertrand Russell and Alfred Whitehead—got interested in trying to derive all of mathematics from a few axioms and rules of inference. They eventually decided to use the notion of a set as the seed from which all of mathematics would grow, and the framework they came up with is now known as axiomatic set theory. It’s true that most of modern mathematics can, in principle, be built up from axiomatic set theory, but I wouldn’t say that sets are therefore the fundamental building blocks of math. Trying to build something like the formula for the volume of a sphere out of axiomatic set theory would be like trying to build a sculpture one atom at a time. To me, saying that sets are the fundamental building blocks of math is like saying that atoms are the fundamental building blocks of art. It may be true in some sense, but it totally misses the point!
Moreover, axiomatic set theory is by no means the only possible foundation for mathematics. For example, there’s a brand-new subject, called category theory, that’s becoming more and more important in many areas of math. Recently, people have started talking about the Elementary Theory of the Category of Sets: an effort to build axiomatic set theory out of category theory. At first, this looks like a step down to a deeper level of description; if sets are the atoms of math, maybe categories are the subatomic particles. But here’s the interesting thing: if you take an introductory class on category theory, the teacher will probably start by describing categories in terms of sets! In fact, my gut feeling is that category theory can be built out of axiomatic set theory (because category theory is kind of like abstract algebra, and abstract algebra is a pretty important area of modern math, and most of modern math can be built up from set theory). So here we have two alternative “foundations”… and each foundation seems to be built on top of the other!
To conclude, I’ll give you my answer to a question you didn’t ask. By inquiring about the “building blocks” of mathematics, you seemed to be asking for tangible objects—things like sets and functions, paints and brushes, axioms and rules of inference, scrap metal and welding torches. If you want to get to the heart of mathematics, you should be looking for intangible things: truth and beauty, pattern and asymmetry, imitation and creativity, proof and intuition. It’s things like these that are the seeds from which all of mathematics grows.
Very interesting post, alot to think about. Is it fair to say that historically, tools/ideas from “fundamental” physics (ie particle physics) have often be applied to “non-fundamenal” areas like condensed matter but not the other way around? I see no reason for this to be true, for example SSB could have been invented to explain superconductors and then applied to particle physics later. But at the same time, I can’t come up with a good counter example. So perhaps there are reasons, sociology based or not, why techniques seem to flow one way more than the other?
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Hi,
I don’t have anything more profound (or even mundane) to say beyond my earlier remark. It is not an issue I can say usefully or interestingly anything about at this time.
-cvj
hi,
I was thinking it all begins with the notion of a set and that the notion of a function also plays a part. What do you think?
What’s your own notion of a function?
Hi,
Interesting!
I’m sorry to disappoint, but I don’t even know where to begin to answer this question. Does it begin with geometry? Algebra? Topology? Is it a meaningful question? Don’t know. Ask a mathematician perhaps. I don’t even know if it is easier or harder a question to answer than for physics.
Best,
-cvj
Dear Clifford,
What are the fundamental building blocks of mathematics in your view?
Is this not a more fundamental question than ‘what are the fundamental building blocks of nature?’ given that the tools you use to describe nature are mathematical and you ‘need not confuse the tools with the things we are trying to describe with them.’ as you say above?
Thanks,
Hi,
I don’t think you can have read my post carefully. In several places I stated that there are central principles to be found in both “applied” physics and that which you consider to be the more noble quest of uncovering “reality”. Whatever drives you to whatever physics you choose, focusing on one and ignoring the other can be a major mistake, from the simple pragmatic stance of finding good sources of ideas, techniques, and mechanisms. It is all clearly stated in the post. I don’t think I need to repeat it all. Please have a look.
Best,
-cvj
Ok, I’ll put it differently, when doing research on fundamental building blocks of reality you are asking the questions to which almost everyone wants to know the answer, questions about the nature of reality and our existence.
You may, at least in principle, discover what this place really is, how it came to be and where it is going. Those are one of the most important questions there are. (I am not claiming you can under them completely but every insight counts here)
For example the discovery of spacetime is one of the most profound discoveries of all time, it has changed our understanding of reality forever.
Working on applied physics is a completely different thing, there are some interesting problems but hardly anything as profound.
Very nice essay Clifford, but I have to admit that I find myself more in sympathy with Weinberg; I can’t help feeling that the “reductionist frontier” is a special place. I do agree that the word “fundamental” is no longer usefully descriptive (if it ever was).
Another point is that it’s a good thing that the reductionist frontier attracts only a tiny fraction of scientists to work on it, because the necessary experimental efforts to explore it are impossible without the vast supporting technology that had to be developed, and the rich technology-enabled societies that can afford the resources.
Hi Clifford,
A very nice essay, thanks. I summarized some thoughts on the limits on reductionism here. You might also find this paper interesting. Best,
B.
PMXVI:- I’ll be careful. (Can’t… type… much more… difficult with… one hand (left)… inexplicably in be-sequinned glove…) 😉
-cvj
Zephir, others: no pet homebaked theories of the universe on this thread please. Thanks.
-cvj
“Um, how about “…But the Kid is not my Son…” ”
Careful, you’ll start looking like Diana Ross.
In Aether Wave Theory the most “fundamental” portion of reality isn’t quantum mechanics or relativity perspective, because they’re rather abstract and remote from our everyday intimate view. Instead of this the familiar geometry of most common colliding particle systems is what serves as a cognitive basis of all further logical extrapolations of reality.
Hi,
Interesting thought about the learning curve. I’m not so sure -once the dust settles- that it is any steeper, relatively speaking, than it ever was. I think that once the toolbox is streamlined (as a result of the kind of research going on now) and organized (put the sharp cutting tools all together over there, the blunt breaking tools over there, the measuring tools together over there) and an instruction manual written, it’ll seem no more challenging than learning new things in any new field.
Right now it is daunting because nobody knows all the tricks, what are the red herrings, and so forth.
Best,
-cvj
This is an interesting take on the role of the theorist in the real world. Maybe one thing has changed over the past thirty years or so. The sixties theorists’ tool kit, that could be, and was, applied with so much success, was forged essentially by Schwinger and Feynman, who drew on their WW2 experiences of life at the sharp end (Greens functions? microwave wave guides and antennae; path integrals? The diffusive separation of Uranium isotopes). The learning curve for the applied, or indeed anything other than ‘fundamental’, physicist who wishes to access the new stringy toolkit is dispiritingly steep; the theorist looks set to retain his/her wizard/ shaman status
Hi,
That’s not the issue. To focus on some narrow aspect of one field or another to make one seem more interesting than another is a trivially straightforward game to play and utterly misses the point of what I’m talking about.
Cheers,
-cvj
What would you rather discover: rules governing the very fabric of reality or rules governing efficient doping of a novel semiconductor?
Um, how about “…But the Kid is not my Son…” 🙂
-cvj
Regarding the pronoucements of Weinberg and others like that: you have to understand the context. People like P. Anderson and R. Laughlin have for some time being making very aggressive and rather obnoxious anti-HEP statements, effectively pushing the idea that condensed matter is somehow *real* physics as opposed to arty-farty string theory etc. Probably Weinberg just wanted to rub their noses in it.
I see what you are saying, *but* to be frank I, and many others, are interested in [for example] the RHIC *only* because of the dazzling possibility that what they are doing there has something to do with black holes in five-dimensional asymptotically AdS spacetimes. If there were no such connection then I’m afraid RHIC would be just another tedious gadget to me. So the dreaded physics pecking order is still lurking in the background. But who cares really?
“(Remember, you heard it here first.)”
I will indeed. Non-professional readers should be alerted that Prof Johnson here is actually the True Father of this whole field*. I got a bit of a jolt recently when looking at his book on D-branes — it foretells all this marvellous “applied string theory” story, and it was written ages ago. So our host here has quite a record as a prognosticator in this line……watch this asymptotically AdS space!
* I hereby prognosticate that he will deny this.
(In fact, I completely forgot that I wrote some of the thoughts in that post! I was clearly channeling some of my earlier post in this one…)
-cvj
Thanks,
I wrote about that article here.
Best,
-cvj
Well, that’s one view. Steven Weinberg recently wrote:
“Most of us do elementary-particle physics neither because of the intrinsic interestingness of the phenomena that we study, nor because of the practical importance of what we learn, but because we are pursuing a reductionist vision. All of the properties of ordinary matter are what they are because of the principles of atomic and nuclear physics, which are what they are because of the rules of the Standard Model of elementary particles, which are what they are because…well, we don’t know, this is the reductionist frontier, which we are currently exploring.”
He went on to talk about superconductivity:
“I think that the single most important thing accomplished by the theory of John Bardeen, Leon Cooper, and Robert Schrieffer (BCS) was to show that superconductivity is not part of the reductionist frontier (Bardeen et al. 1957). Before BCS this was not so clear. For instance, in 1933 Walter Meissner raised the question of whether electric currents in superconductors are carried by the known charged particles, electrons and ions. The great thing that Bardeen, Cooper, and Schrieffer showed was that no new particles or forces had to be introduced to understand superconductivity. According to a book on superconductivity that Cooper showed me, many physicists were even disappointed that “superconductivity should, on the atomistic scale, be revealed as nothing more than a footling small interaction between electrons and lattice vibrations”
I would argue that questions about the “reductionist frontier” are different and more fundamental from questions about “footling small interactions” no matter how interesting and surprising the effects and applications might be and no matter how similar the underlying maths may be.
Do you really have no sympathy for this viewpoint?
Hi Elliot,
🙂
I never really understood the whole “theory of everything” schtick. I don’t think it is helpful. But then I blogged about that a while back anyway. Can’t find where, but here is part of a remark I made in another article:
-cvj
I fully agree with your assessment. However I think there is a meme (correctly or incorrectly) associated with string theory that it represents a “theory of everything” which puts it squarely in the “fundamental” category at least in the mind of much of the lay public.
I can only hope people will read your post carefully and realize that there are other ways of viewing string theory apart from it being a candidate for a the theory of everything.
At least that’s what I got out of it.
(see I told you “some people” would read it)
e.