Thursday, July 5, 2012

Higgs unmasked

Today was not like any other day. A historic announcement was made at CERN about the discovery of the Higgs boson, or something very much like it. I joined many others at TIFR in a lecture room to watch the live telecast of the proceedings. I won't review the science of this discovery here in any detail, instead I'd like to share some of the thoughts that went through my head as the lectures unfolded and then later on during the day.

The Higgs mechanism was discovered independently by six researchers in 1964 (only one of whom is called Higgs), based on a physical effect studied two years earlier by Anderson. So the fact that Prof. Higgs alone has become a household name is a shade unfair to the others. But then, you can't expect the press to get all breathless about a Brout-Englert-Higgs-Hagen-Guralnik-Kibble boson! And even if there had been a single discoverer, it's hard to imagine what the corresponding particle would have been called if that discoverer went by a name like Venkatachalapathy, or Klapdor-Kleingrothaus (the latter is a genuine German physicist). Let's just agree that it's good to have a short, snappy name if you want things named after you. Though it's less often highlighted, the other part of the term "Higgs boson" comes from the name of Satyendra Nath Bose whose work described the statistical behaviour of a generic class of particles called bosons. Again, I just couldn't help wondering what would have happened had this Bengali gentleman carried the surname Mukhopadhyay, or Raichaudhuri!

But enough of the flippant stuff. As Feynman put it very well, knowing the name of an object only tells us how human beings refer to it, but nothing about the object itself. What is important about the object under discussion today is that it's a key ingredient of a fairly elegant and simple mathematical theory, the Standard Model of particle physics, that accurately describes the behaviour of everything in the universe.

The last sentence is an over-simplification for essentially two reasons. One is that this theory only describes behaviour not involving the gravitational force. But this is fine as long as one stays away from immense gravitational forces such as those involving black holes or the early universe. Completing the theory to describe gravitational forces is the task of string theory, the field in which I work, but we can leave that story for another day. The second reason why it's an over-simplification is easier to appreciate. Knowing in principle the behaviour of every particle that makes up a jug of water, or a monkey, is almost useless to understand the behaviour of the composite object. This is why research in physics goes in two directions: one is to understand the fundamental constituents, the other is to understand how simple constituents are organised into larger objects that freeze at low temperatures, or bite when provoked, or exhibit some other type of complex behaviour.

Both directions are important. But in practice the "fundamental" and "complex" scientists rather tend to despise each other's preference. The "complex" scientist observes that finding and classifying fundamental particles - like the Higgs boson - is never going to answer questions like "when does water freeze?" or "why do materials superconduct?", let alone the trickiest one: "what is life?" Meanwhile the "fundamental" scientist feels that only by studying the most elementary objects can one aim to find elegant, universal and precise laws. Both sides are perfectly correct.

As someone who has tied his career to the "fundamental" or "reductionist" enterprise, I've seen its fortunes fluctuate quite a lot. It's been very popular through certain periods, while during other periods it has provoked irritation or even fury from scientists in the other camp. There are many possible reasons for this. One is the sheer audacity of the enterprise. Do we really think there can be a "theory of everything"? Another is the expense. Why should the nations of the world pool in a few billion Euros to answer esoteric questions about some particular elementary particle? Yet another is the fact that even the questions we raise, never mind the answers, are very hard for a person to understand without considerable prior knowledge of mathematics and quantum physics. And then there is the apparent indifference to social benefit. Will the Higgs boson cure cancer or mitigate climate change? Our community is seen to respond: "we do not care". Finally, there is the even higher level of grandiosity involved in claims like "particles are merely vibrational modes of strings" given that the strings would have a spatial size that is a million billion times smaller than things we know how to measure.

While all the questions raised above have (defensive) answers, sometimes it's best to let these questions just remain as they are and look at the other side of the picture. And I think today even the skeptics have had a close-up view of that other side, and hopefully have been moved by it. For around six decades, a global community of physicists - divided by everything else but united by their belief in the reductionist enterprise - have collaborated to uncover the secrets of nature. Some have done theoretical work, others experimental, yet others work in the middle ground between the two that's called "phenomenology". Over this period most of these people have never met each other, some have failed to even understand or accept each others' work, many have foolishly pitted theory against experiment (as though either one could ever be sufficient) and engaged in numerous other follies. But enough people gave of their best, and their best has proved good enough. The discipline of the scientific method, plus a collective dedication to the goal, washed out the conflicts and amplified the consensus. And today it's turned out that the whole thing holds together beautifully. It needn't have, but it did - and this for me is the best defence of the entire reductionist enterprise. It works.

So an absurd little particle, postulated for an apparently trifling reason, came to occupy centre stage in our quest and then held out for decades - but in the end it was unmasked by the sustained onslaught of a few thousand people (and, it has to be admitted, billions of Euros). The discovery of the Higgs boson might be the most sustained cooperative enterprise in the history of the human race!

And there's another grandiose statement calculated to annoy people...


sacredfig said...

Always a pleasure to read your posts!

So the fact that Prof. Higgs alone has become a household name is a shade unfair to the others.

But the upshot of this is that Stigler's Law of Eponymy continues to hold true :-)

Meanwhile the "fundamental" scientist feels that only by studying the most elementary objects can one aim to find elegant, universal and precise laws. Both sides are perfectly correct.

Doesn't this contradict exactly what you said in the sentence before this. That understanding the behavior of elementary particles hardly tells you anything about the physical behavior of macroscopic bodies, let alone biology. So clearly, to call these laws "universal" is a bit of an exaggeration. They may be universal in the sense that all particles are said to obey these laws, but they are hardly universal if we are to think of their utility in terms of explaining "everything".

As Phil Anderson already told us in 1972, the problem arises because we think the reductionist approach is merely the reverse of the constructionist approach. As he showed with many examples, this is not true. Understanding the laws that govern the "parts" of the "whole" doesn't at all imply that having known those laws we can apply them to predict the behavior of complex assemblies of these "parts". At each level of complexity of matter, entirely new laws are needed.

the best defence of the entire reductionist enterprise. It works.

I haven't resolved this entirely, but sometimes I think this is a circular argument. I mean what is a reductionist approach if it doesn't work? In other words, the reductionist approach is by definition, primed to work no? If not the Higgs mechanism, maybe something else; we'll keep hacking and sawing and chipping till it all falls into place, and then turn around and say, "See, it works! So the reductionist approach is a priori correct". Doesn't seem very convincing to me.

The discovery of the Higgs boson might be the most sustained cooperative enterprise in the history of the human race!

And there's another grandiose statement calculated to annoy people...

Yes, especially those lesser mortals who collaborate on trifling things like the Human Genome Project or the Microbiome Project :-)

Sunil Mukhi said...

@sacredfig: It's not a circular argument. A possible way for the reductionist enterprise to fail would have been for there to be no Higgs boson under 500 GeV, say, and no alternative discovery to explain why the rest of the Standard Model works. The possibilities for hacking and sawing certain things in a given energy range can be very limited.

As for Anderson, what he says may sound nice but that doesn't make it true. The Ising model is a simple model of constituent "spins" or "tiny magnets". It can be solved mathematically and exhibits the complex behaviour of a phase transition (to/from the magnetised phase). Had it remained unsolved one could have argued that phase transitions represent a new level of complexity for which entirely new laws are needed. But in fact they are not needed.

For more complicated situations we don't know how, or whether, the parts can be used to describe the whole. But we can hardly claim to know that they can't be.

sukratu said...

I am not at all a person well versed with particle physics. However, I find it always very surprising when people claim that the standard model 'strangely' works.

There seems to be a good amount of indication as to 'why' we have fermionic and bosonic sectors for example in particle physics. These, if I am not incorrect are deeply linked to Killing vector symmetries of spacetime (as also Lorentzian structure of tangent spaces). Not too recently, people have uncovered how the concept of 'fields' arises along with superselection (Doplicher, Haag and Roberts), again from very general conditions on spacetime regions (or to be a little physically sensible, the observables of these regions) There are issues of particle physics not captured as yet in such attempts but the label of 'reductionism' or mainly the label of 'intellect zapping mystery' ought to
be corrected by experts IMHO by sharing
these profound insights rarely touched
in masters or graduate school courses.

sukratu said...

Sorry for putting out something technical

But I would recommend going through the
introductions of these articles and working a little on the ontology therein. I would take a view that it indicates that we are not really imagining "particles" composed of other "smaller particles" (the reductionism referred to above) but "particles" as one very special way of describing the world wherein further we may not at times allow the idea of particles composing other particles. From such a standpoint, I would advise caution.

Collide two cars hard and you get separate tyres and door handles and so you conclude that a car has those. Collide them harder and you get maybe even rivets and camshafts and so you say they lie deeper into the structure of a car. Collide them really hard and they explode ( like in our old Hindi films) into flames REACTING with air
around giving carbon, charred plastic which composes....!!!? well well well....I am not stretching a point here.... I feel that we underestimate the vacuum state when we collide elementary particles.

Chittaranjan Gauba said...

I was told that while indeed there were six researchers (working in three teams), including Peter Higgs, who in 1964 independently and almost simultaneously postulated the mechanism by which particles gain mass, of the six it was only Dr Higgs who explicitly pointed out that there would therefore be a particle - and even tried to calculate what its properties might be. No wonder, then, that thereafter the particle was referred to by his name rather than that of any of the others. In fact I would think it's fair!

Chittaranjan Gauba said...

I believe it was Paul Dirac who named "bosons" after Satyendra Nath Bose; and knowing of Dirac's very direct, swift, and non-fussy style of functioning am sure he would not have been in the least troubled if Bose had been named Mukhopadya. Dirac would just have called the particles "Mukhons".

Which would have been just fine, unless of course the need arose to name a particle after an eminent professor at TIFR whose name also begins with "Mukh". This researcher's particles would then have be "Sunons".