A little tired from the routine of his traditional area of work – particle accelerators –, in 1992, the North American physicist James Watson Cronin, 68 years of age, decided that he would move on to exploring the energy of cosmic rays. However, he also decided that he would bring to his new field of study, without doubt much more speculative, the pragmatic work philosophy of the community of the particle accelerator physicists, which includes in its pillars to always make use of the best up-to-date technology available for research and, if necessary, to develop appropriate instrumentation to the objectives of each project. It was from with these decisions that he began to idealize the project of the Pierre Auger Observatory of Cosmic Rays which, in keeping with his past experience, is considerably innovative in its conceptual technique and uses a series of pieces of equipment specifically designed for the objectives of the detection of high energy particles.
In 1980, Cronin shared with his colleague Val Logsdon Fitch the Physics Nobel Prize for their discovery of the violations of the fundamental principles of asymmetry in the decay of the neutral k mesons. In July he was in São Paulo participating in the ceremony that marked Brazil’s formal support for the Pierre Auger project. It was on that occasion, at the Gleb Wataghin Physics Institute in Unicamp, that he was interviewed by FAPESP’s chief editor, Mariluce Moura, which follows.
Could you please explain for us, if possible in words understood by laymen, what is anti-matter, a fundamental concept in the discovery that won you the Nobel Prize?
Anti-matter? Fine! It’s a fact discovered empirically for all types of matter. Let’s take, for example, a hydrogen atom: it’s a proton with an electron spinning around it. However, we know that there is an anti-proton. It was discovered and physically produced inside an accelerator. The nature of anti-matter is such that when it meets up with matter, they destroy themselves and simply turn into… shall we say, pure energy or unstable particles and end up transforming themselves into what are called photons or “light particles”. However, the important point is that there would be no life, there would be nothing at all if we had an equal mix of matter and anti-matter. It is extremely important that Nature, in some way, had been able to develop in such a manner that matter dominated, in the galaxies with certainty, and probably throughout the Universe. Consequently, every particle is a twin of an anti-particle, the proton is positively charged, and the anti-proton negatively. And when they come together, the structures annul themselves.
You and Dr. Val Fitch received the Nobel Physics Prize in 1980 for the discovery of the violations of the fundamental principles of asymmetry in the decay of neutral k-mesons. What does this have to do with the relation between matter and anti-matter?
I believe that it is not the case of explaining here and now the details of this violation of asymmetry in k-mesons. What’s in fact of interest is that we found a violation in what we had thought to be an asymmetry between matter and anti-matter. We saw that, in fact, in a detailed study of this elementary particle there was a very small difference in the laws of physics, between the universe of matter and the universe of anti-matter. I believe that the importance of the discovery transcends by far the very physics of particles, because it permits us to understand how the Universe began with a hot big bang, or whatever it might have been, where the energy is so huge that there is no way of separating matter from anti-matter. However, with the violation of asymmetry, and some other details, the resultant asymmetry between matter and anti-matter can lead to a small excess of matter. This is the way in which we perceive things now, we are saying that in the big bang there was almost as much anti-matter as matter, but a little less of the former, something let’s say in the region of one part in a billion. Then all of the matter and anti-matter annihilated each other producing photons, this background of microwaves which is there, which we know about and which we can see. What was left over, was us: one part in a billion. This was all that was needed to make the matter of the Universe. If you were to calculate the quantity of matter, or that is to say, the protons and calculate the photons, it is exactly this factor that you would find of one in a billion.
But in the big bang, what exactly impeded matter and anti-matter from completely annihilating each other?
But they did destroy each other! Only that because of asymmetry, a violation of symmetry, a little bit of the excess was produced. We must remember that it was the physicist Andrei Sakarov, in an article published in 1967 in a Russian magazine, who first put forwards the idea of how an asymmetry between matter and anti-matter could have led to a Universe dominated by matter. Therefore, it was he who was the first person who pointed out the cosmological significance of our experiment, which had been carried out three years previously in 1964.
Could you please establish for us a relationship between your discovery and the most recent cosmological speculations?
You must be referring to the most recent measurement, to the “flat universe”, something of that nature. But I believe that the importance of our discovery in what concerns cosmology, is what we have just been discussing, that is, it allows us to understand why we are in a universe dominated by matter. The new discoveries in cosmology are fantastic. We now know, or so it seems, that the Universe is very flat, it doesn’t have a curved geometry of one kind or another. And we have as well these beautiful signs of as very young Universe, only with 4,000 years, when the background of microwaves was originated.
And the closing of the Universe? Will it enter into a collapse or will it continue to expand?
Well, what all of the current data suggests – and they are data and not mere speculations – is that it is neither going to close nor explode, only gradually get larger. There’s no end to it.
What are your expectations as far as the Pierre Auger Observatory is concerned?
My hopes are that we will be able to collect high energy events, lots of them, and that they will demonstrate, by their character, both what they are and where they’ve come from, as well as what type of energy they have. These happenings should give us the types of clues that we need to decide if there is disorder in our young Universe or what processes are happening within it, if there are astrophysics that we don’t know about etc. Who knows, it might give us some clues to things that we simply don’t understand in new physics, things necessary for us to understand our measurements. Our work, therefore, is to carry out the best measurements possible and, at the same time, to exclude whatever pre-judgments about the answers that we’ll be finding.
Do you see your work at the Pierre Auger Observatory as a natural consequence of that research that was awarded the Nobel Prize?
The only thing in common between one moment and the other is our search for large and important phenomenon. It has something to do with cosmology in a certain manner. It had been present when we carried out the original experiment, even when we had been working in a very tight space such as an accelerator. It always shocked me that there we had carried out something so special, so mysterious and with consequences of such extraordinary magnitude.
You were not looking for what you found?
No. This is what we call “Scienticity”, you do something in one direction, and at the end of the day make a discovery that has extraordinary consequences.
Will the work with the Pierre Auger Observatory make you travel to Brazil with some frequency?
My job, besides trying to stay on a par with what the other scientists are doing, is to attempt to guarantee the political and financial support for the project. We have a project director who really worries about all of the details. That is to say, that I can come to Brazil, go to Vietnam, to Argentina, do wherever is necessary. Here I am certain that we have the support of the state of São Paulo as well as of the Federal government. In Argentina we have extraordinary support from the Province of Mendoza, but as yet we have problems with the Federal government.