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Originally published in “Tuttoscienze” of “La Stampa” on 10 July, 2002

If it is true that everyone has a right of fifteen minutes of fame, it is also true that not everyone elbows their way forward to claim this right to a quarter of an hour. This is the case of the British physicist and astronomer Jocelyn Bell, who, when she was very young, made an important discovery. In order to introduce it briefly, we can say that when a star has exhausted all its nuclear fuel, it tends to collapse inwards, transforming itself into a celestial body which is smaller and much more dense, and which could take the form either of a white dwarf, a neutron star or a black hole. While white dwarves had been observed from the Nineteenth Century, neutron stars remained for a long period a theoretical speculation, until, in 1967, Jocelyn Bell stumbled on the radio signals emitted by pulsars, a kind of rapidly spinning neutron stars. This discovery was rewarded with the Nobel Prize, but the winner was not Jocelyn Bell. Kindly and quiet, Jocelyn Bell did not elbow her way forward to claim what she deserved, and also in this interview, which she granted me in the splendid city of Bath, where today she leads the Faculty of Science, she confirms her enjoyment of sparkling and never polemical conversation.

The discovery of pulsars confirmed the existence of neutron stars. But, apart from that, why was this discovery so important?

Pulsars permitted us to test many important part of Einstein’s Theory of Relativity Theory. Since they are very precise in “keeping time” , that is, keeping their period of rotation constant, they are the most precise “clocks” that, until today, we have. And we have them dotted all around the galaxy. That’s why we have been able to do many Relativity experiments and test many of the Einstein’s ideas about gravitation.

In 1974, this discovery bore fruit in Nobel Prize for Physics for your PhD supervisor. In spite of your role in this discovery, the Swedish Academy did not mention you at all. Do you think this decision was right?

That was thirty years ago. Back then, we had a more hierarchical concept of science: one only boss did the thinking and many junior students executed his ideas. Today, we have a different picture of how science is done. Science is done by a team of people of different ages and every person makes his contribution. However, the way in which many prizes, not only the Nobel Prize, are conceived has remained the same: they still reward the isolated leader.

At that time, Fred Hoyle, the well-known dissident of the Big Bang theory, was publicly against the decision of the Swedish Academy not to award the prize to you. Did you know Hoyle in person?

He lectured us in Cambridge when I was a PhD student there. He has stayed in my mind because of a spectacular mistake. He improvised a calculation on the blackboard that was wrong by a factor of ten to the power of fifty four. How marvelous it was for us students!

Your worked in radioastronomy, infrared astronomy, X-ray and gamma-ray astronomy: you have a broad background. What, in your opinion, are at the moment the “big questions” about universe?

I see two big questions in which some very exciting experiments are in progress: one is dark matter, the other is gravitational waves.And here we have the link with pulsars. In the binary system of pulsars, in fact, it can happen that the two stars move close together and, finally, they merge and they give off a big burst of gravitational waves. And that is one of the most likely sources of gravitational waves that the detectors of projects VIRGO o LIGO, which were targeted to detect these waves, could catch.

Speaking of dark matter, what kind of things can we reasonably dream up about it?

At the moment we can not see it, but we know that it must be there and we know that it is completely different from the matter that surrounds us. It is not made of baryons, neutrons or protons. But what is it? Are there three or four kinds? How much is there? 95%? 97%? Let us say, the 95%, or more, of the matter of the universe is completely unknown. And that means that all the physics which we have studied at the university is only relevant for a few percent, maybe 5%, of the matter of the universe. And if we have a different matter, we probably need a different kind of physics, so there is a lot of physics to understand.

I presume physicists are happy. In spite of the current explosion of life sciences, there is still work for physicists!


Today, white dwarves and neutron stars are a fact: we really know that they exist. For the black holes, where have we got to?

We are at a point that we have decided to agree that a certain number of objects are black holes, because we have failed to prove that they are not.

Oh! It is interesting that you “have decided to agree” that they are black holes!

Yes. It is interesting _ the nature of proof in astronomy. You said: “we really know that white dwarves and neutron stars exist”. Do we? Really? Physics is an experimental science: we can do experiments, change the conditions and then see what happens. Astronomy is an observational science. We can not ask the stars to twinkle brighter because we want to verify our hypotheses. Proof is very difficult. The following thing happens: we observe the behaviour of a star and, if we are able to prove that it is not a neutron star, or a black hole, because it does not do “the right things”, and if we astronomers agree about that, then we say: “OK, it is a probably white dwarf”, because it behaves in a certain way. But that is as close to a proof that we can get, for all I know.

Let’s speak about extraterrestrial life.

Must I prove you that it exist?!

I will settle for your opinion about the SETI Project for the search of extraterrestrial life. It is a project that provokes every kind of reactions: from skepticism to the joke of an American politician, who, asking for the cut of funding to the SETI, claimed that he haven’t any intention of wasting millions of dollars in order to find aliens, because it was sufficient to spend 75 cents to buy a tabloid full of news about them!

The science which is done in the SETI is serious and rigorous. The problem, from the point of view of funding, is the following: is it important to search for aliens? Maybe, it would be my judgement. The interesting thing is that, recently, astronomers have discovered planets orbiting around stars similar to our Sun. This discovery make more likely the existence of extraterrestrial life.

Let’s talk about a problem in which you are active: women in science. In 1991, you became one of two women full professor of physics in Britain, as against 150 male colleagues. As a woman, do not you think that this fact is depressing?

Absolutely depressing, I believe that today there are 10 of us. Since, in Britain, physics is still a male area, its rules are male rules. The moment in which we achieve a “critical mass” of women, this culture will change. The problem is how we can achieve changes without this critical mass and this was the problem throughtout my life. When I was expecting my first child I went to the chair of the Department to inform myself about maternity leave and he told me “Maternity leave? I never heard of it!”. He was right: that university did not have any maternity leave.

Concluding, today the general public is more interested in the technological fall-out of science (tools and technological instruments) than in science itself. Do you not think that the brain and its ability of speculation remains the most powerful tool of investigation of the universe?

Yes, but nonetheless we had to take seriously the public anxiety about technology. Today the public want to know something about the safety of genetically modified food and mobile phone. And scientists say: “Absolutely sure, trust us”. I think that public no longer accept that. And scientists have to learn to change.

The problem is that we do not know anything about “hot topics” like genetics. What can we say to the public?

That’s true, but scientists must not treat the public as stupid. We must help them to understand what science is saying and what science is not saying. To be in charge and to say that something is absolutely sure is a nonsense, and also giving doubts is giving information.