Mise au point sur l'antimatière

Walter Oelert, un physicien du Forschungszentrum de Julich, dirigeait au CERN le groupe qui avait produit, il y a 10 ans de cela, les premiers atomes d'antihydrogène. Dans cet entretien il sépare le réel de l'imaginaire concernant ses recherches, en particulier dans le contexte du succès de librairie de Dan Brown, Anges et Démons.

Dan Brown's novel Angels and Demons has been enormously popular. A secret brotherhood murders a physicist who managed to produce the first antimatter on Earth. You have surely heard about the book?

I have even read it. Indeed the author has me killed at the very beginning.

Correct. You die and the antimatter stolen from CERN is used to blackmail the Vatican. CERN does produce antimatter, and the contact of antimatter with ordinary matter results in annihilation where large quantities of energy appear. Aren't you scared that one day Brown's scenario may become real?

No, since there is no way to produce and store a large quantity of antimatter.

What does "a large quantity" mean? Are we talking about kilograms?

No, not even about nanograms. I am talking about single atoms. We are not able to produce and store amounts of antimatter that would cause damage of any kind, e.g. that could be used as an explosive, as in the book.

You mean we are not able to now - or ever? Is that a problem of technology or perhaps a result of the laws of physics?

Both. Let us start with technological reasons, which are probably less convincing. Even if somebody could produce lots of antimatter, their main headache would be how to store it. First, they must place it in a vacuum - any other "container" would immediately annihilate, that is disappear! So antimatter must be kept in the very middle of a vacuum by a magnetic field. This is possible, we hope to do it at CERN, but for a few or a few tens of atoms only.

The vacuum must be of the best quality. What we call a vacuum in daily life is far from the ideal. An electric light bulb is not empty but contains a very, very diluted gas. In the CERN "antimatter trap" the gas pressure is 10−17 mbar. This means that on average there are a few tens of thousands of atoms per cubic metre. So even here we have annihilation with "stray" atoms. While it is possible to guard a few hundred antimatter atoms, protecting, say, 1 mg of antimatter from annihilation is practically impossible. And every act of annihilation results in the freeing of a certain amount of energy and degrading of the vacuum. This is a chain reaction.

The technical limit is not a real one. What is impossible today may very well be possible tomorrow. Surely we will learn how to get a better and better vacuum?

I agree that technical arguments may not be convincing. However, in one day CERN produces about 1012 antiprotons. Renovations, equipment maintenance and upgrading, holidays and other interruptions limit the antiproton production to about 200 days a year. In 50 years of operation at CERN about 1016 antiprotons would be produced. Even if all of them made anti-atoms, we would arrive at about one millionth of a milligram of antihydrogen - I repeat, in 50 years!

I must add that in the process of antihydrogen production only a tiny percentage of antiprotons make anti-atoms. Once, I calculated that even if all the natural energy resources of our planet - coal, petrol, gas - were used to produce antimatter, it would be enough to drive about 15,000 km by car. This is physics. It does not depend on our technological development.

So we can forget about antimatter as a future energy source?

Of course! Until we find "natural resources" of antimatter (and I would not count on that), the production of antimatter on Earth for energy or, as in the book, for terrorism will never pay off. Much more energy would be used for its production than we could ever get back from annihilation.

Would you agree that more people learned about CERN from Angels and Demons than from reading scientific information? Is CERN correctly described in Brown's book?

This question is a trap so my answer will be diplomatic. In my opinion antimatter, and thus CERN as the only place where we are able to produce it, came into the book by accident. They were just a background. An atomic bomb at the Vatican would have done as well. I do not want to speak on behalf of the author but I have the impression that he wanted to touch on the conflict between science and faith. History shows that sometimes such a conflict has indeed been seen by the church and the scientific community.

And what about CERN? Is CERN really working on a proof that God does not exist - that scientific knowledge is the real god?

A difficult question. For sure there are many people working at CERN who believe in God and their work actually confirms their convictions. There are also those who do not believe in God but believe in science. For them every discovery may be proof that God does not exist, but it is not true that we are working to prove that.

"Soon all gods will be proven to be false idols. Science has now provided answers to almost every question man can ask." This statement is made in the book by Maximilian Kohler, the [fictional] director-general of CERN. Do you agree?

No, I do not agree. I am sure that science does not contradict faith. One person may say that he studies the laws of nature, another one that he wishes to understand how God initiated or created our world. In my opinion it is the same. Both are doing the same even if they believe in different things. The point of view represented by the head of CERN in the book was very popular in the 1950s and 60s. Not for the first time people believed then that science was close to completion; that technology would save the world. It seemed that building a sufficiently large number of nuclear reactors would solve the energy problem on Earth and so all other problems would disappear. However, people have not become happier and the old problems are still here. We continue to be dependent on nature, which dictates the conditions. I believe that despite more and more knowledge, ultimately it is nature that wins.

Production of the first antimatter atom on Earth brought you great recognition…

Antihydrogen production indeed led to extraordinary publicity. That is probably the reason that this work is considered to be one of 16 very important discoveries made at CERN. In my opinion, and from the scientific point of view, producing the first antihydrogen atom does not deserve such honour; the very production of antihydrogen is not a revolution in physics. It did not bring anything new and we do not care about the production itself but about studies of the antihydrogen atom. This is not at all simple. The first atoms produced moved with almost the speed of light. Indeed, one has to be fast to study such an object. Antihydrogen thus has to be cooled down and locked in a bottle; the slower it is, the better we can watch it. So the real goal is not the production of, but studies of, antimatter. I am sure that at some time physicists will manage to measure its gravitational interactions. That would really be something.

Why are antimatter studies so interesting to the public? Usually it is difficult to sell what physicists do in their large laboratories.

This is not completely true. There are at least a few problems that may be sold easily and in an interesting way even when drinking a good wine at a garden party. One example is relativistic physics - everybody is interested in the fact that the faster you move the younger you are. Another subject is astrophysics or the surrounding universe. It is fascinating to many, probably because we can make certain observations ourselves on a cloudless night. Besides, the astrophysical photographs are so impressive they are printed on the front pages of the daily papers. The curvature of time and space is also an extremely interesting problem. The shortest path between two points is not at all a straight line.

And what about antimatter?

When it comes to particle physics, the problem is complicated. People do not know what we really do. Antimatter is an exception, which is surely due to science-fiction films, where antimatter is very often a subject. Serials gather an audience. If every Monday evening we watch the adventures of the same heroes who conquer the universe in space vessels powered by antimatter, then television characters are quickly treated as one's own family. In this way antimatter has become a family member.

Is your interest in antimatter also a result of those films?

No. I must admit that I have not seen many of them. Discussions on antimatter began much earlier than when the first episode of Star Trek was produced. The ancient Greeks had already discussed it - albeit under different names. One can read about it in the writings of Aristotle or Plato - writings that are rather philosophical according to our modern views. But 19th-century physicists also wrote about it, not yet knowing about the existence of its components.

I was always fascinated by the idea of symmetry, especially between the world and the antiworld. Does it exist at all? I think that studies of antimatter are so interesting because even in our everyday life we like asymmetry. Just have a look at an ancient Greek temple or a medieval church. But not only buildings - look at a Persian carpet. Only those that are factory-made display a full symmetry; the really expensive ones are handmade. Most appreciated are the very small breaks in symmetry, the subtle "faults" of the carpet weaver.

It is said that as a young man you considered being an actor. Would you accept the role of Leonard Vetra, the creator of antimatter at CERN, if a film based on Angels and Demons was produced?

Yes, but only on the condition that they do not take my eye or burn "Illuminati" across my chest with a hot iron. I think that from the acting point of view I would manage - after all Vetra is murdered on the first page of the novel. Does he say anything at all?

Oh yes, but only a little. Exactly four sentences.

Then I am sure I would manage.