This year's Lindau meeting coincided with the biggest particle-physics discovery in a generation. Theoretical particle physicist Martinus Veltman, emeritus professor at the University of Michigan in Ann Arbor, shared the 1999 Nobel Prize in Physics for his work on the 'standard model' of particle physics — the theory that predicted the Higgs boson. Yet he has spent the past 30 years doubting whether the Higgs exists.
What, basically, is the Higgs boson?
There is really no classical picture. The quantum field theory of weak interactions (which is comparable to, say, electromagnetic interactions) shows mathematical difficulties that can be traced to the non-zero mass of the intermediate particles, the W and Z bosons. A solution to this problem was to suppose the existence of a field extending through the Universe. Then the intermediate particles could interact with this 'Higgs field' and acquire energy, that is, mass. In quantum field theory, whenever there is a field there is an associated particle, for example the electromagnetic field has the photon. While the photon is massless and has spin 1, the Higgs boson is massive and has no spin.
What does the discovery of the new particle mean to you?
I reacted rather coolly at first, but now that I've had some time to reflect I've found myself getting wrapped up in what it means. The prediction of this particle was made 50 years ago, and now we have found it. It's really a very amazing consequence of the theory. The Higgs is a particle that should be there for rather abstract theoretical reasons; through the years I have investigated the consequences of it not being there. The discovery means I will abandon this effort, at least for a while.
Why did you ever doubt its existence?
First, this animal was supposed to be everywhere, giving mass to the other particles, yet it had escaped detection for 30 or 40 years. Second, since the energy of the Higgs is distributed all over the Universe, it should contribute to the curvature of space; if you do the calculation, the Universe would have to curve to the size of a football. That's one of the biggest problems in particle physics.
Are you now a convert?
It is not a matter of belief and emotion. I just look at a situation and I wonder: what is the evidence? The hunt for the Higgs started in the early 1970s, and every year there would be another joker predicting that it is just around the corner. I concluded that the chances of it not being there were higher.
Fortunately I got a call before the CERN announcement to tell me the result, just to prevent me saying something stupid at Lindau like “the Higgs doesn't exist”!
What role did your work play in predicting the Higgs boson?
My research concerned the mathematical formalism that you need to understand the 'renormalizability' of a certain class of quantum field theories including the electroweak standard model. Before that, you couldn't make a single prediction because you didn't know how to calculate things. It's similar to what Richard Feynman and others who got the Nobel prize did with quantum electrodynamics in 1948.
Did you ever work with Feynman?
We never published together, but once in 1983 we went for a hamburger and shared our dislike of supersymmetry.
Won't supersymmetry explain dark matter?
Of course it won't. People have been looking for this stuff since the 1980s and are just talking ballyhoo. Isn't it more likely that we don't understand gravity all that well? Astrophysicists believe in Einstein's theory of gravity with a fervour that is unbelievable. Do you know how much of Einstein's theory has been tested at the distances of galaxies where we 'see' dark matter? None of it!
boxed-text Feynman said that if you couldn't explain something to a first-year under graduate, then you didn't really understand it. Can everything in physics today be explained in such a simple manner?
Since relativity and quantum mechanics came along you can kiss your imagination and intuition goodbye. The Higgs field is an example of something that you have a hard time explaining to anybody, and so is the fact that nothing can go faster than light. You need mathematics to cope.
What do you make of the huge public interest in the Higgs story?
Well, that's certainly none of my doing. As you saw with the faster-than-light-neutrino story, you begin in the centre of attention and enjoy it, then a little while later the thing goes down the drain and you've got egg on your face. That's the risk you run and it's the same with the Higgs. Although it's very unlikely that CERN is wrong, can you imagine the damage that would be done if they were?
So you're not a fan of CERN's Large Hadron Collider (LHC) collisions being likened to the Big Bang?
There will be nothing that comes out of the LHC that even vaguely helps us understand the Big Bang any better. It's outrageous baloney coming from cosmologists and astrophysicists who want to share some of the success of particle physicists. The Big Bang had an incredible amount of energy — a whole Universe-worth — whereas the amount of energy in the LHC collisions is nothing by comparison.
Do you ever discuss particle physics with your wife?
No. That's the loneliness of the theoretical physicist. I never was really capable of discussing physics with my family, with the exception of my daughter, who was also a particle theorist before moving into the banking world.
Who should get the Nobel prize for the Higgs?
There is only one guy who predicted that there should be a particle with non-zero mass: Peter Higgs. Robert Brout and François Englert discussed the same mechanism two months earlier, but they never got around to predicting this scalar particle. So Higgs should get the main credit, then Englert in second place. Brout is dead, so that leaves Tom Kibble, who I would say was working more on reality than Higgs was. Kibble is the most modest man on Earth and he deserves a lot more credit than he gets.
What keeps you awake at night?
There are still lots of problems that the Higgs doesn't solve. Why are the elementary particles arranged in three different families that are the same in all but their mass (for example, the electron, muon and tau)? You cannot build a machine to answer that type of question. But that is also the sad thing about the Higgs, which is why I wanted there to be no Higgs boson: it closes the last door on the standard model.
Will this end our subatomic exploration?
Oh no, this will never happen. Exploration is part of human activity. Suppose that we decided not to build any more particle colliders, and 50 years from now we're sitting there in a room staring at each other. Don't you think that at a certain point someone will say: shouldn't we at least have a look?
Interview by Matthew Chalmers, a freelance science writer based in Bristol, UK.