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COSMOLOGY/ The Nobel laureate Mather: many questions are posed by the universe

The cosmologist John Mather spoke yesterday at the Rimini Meeting. In this interview, he talks about the CMB measurement performed with the COBE experiment and about his next project, the James Webb Space Telescope.  

big-bangR375_31lug09.jpg (Foto)

The cosmologist John Mather was awarded the Nobel Prize in Physics in 2006 for his work on the COBE observatory with George Smoot. COBE was the first experiment to measure the blackbody spectrum of the Cosmic Microwave Background radiation. He spoke yesterday at the Meeting of Rimini on the topic “The human experience of discovery”, alongside the paleoanthropologist Yves Coppens, Professor Emeritus at Collège de France, the physicist Charles Townes (Nobel Prize in Physics in 1964), introducing Marco Bersanelli, professor at the University of Milan.

Your most famous discovery is obviously the measurement of the spectrum of the Cosmic Microwave Background with the COBE satellite. Were you always a cosmologist? What made you interested in cosmology?

No, I wasn’t always a cosmologist. In graduate school I wanted to be a particle physicist. That seemed very exciting: it was the current great challenge of the intellect, for science to understand how particles worked together. And the understanding of the fundamental forces of nature was going to be achieved that way. However, when I went to look for a thesis project, I interviewed various professors to see what was exciting: there was a possibility to measure the Cosmic Background Radiation, which had just been discovered a few years before. That seemed like a good idea for a graduate student project and I started working on it. I did a thesis project on this background radiation, which required the use of an instrument hanging on a high altitude research balloon. The instrument flew, but there were at least three different reasons why it did not work: I had to write a thesis about a project that did not quite work. So I thought that at the end of that project, I would do something else: I would become a radio astronomer. I tried to do that and found a position in that field: however, six months after the position started, NASA requested proposals for new satellites, to do scientific research. This was just five years after the Apollo Moon landing and NASA was looking for new science. And so I told my advisor: “well, my thesis project didn’t really work out that well, but it would have been a lot better if we could do it in outer space, because the atmosphere of the Earth prevented precise measurements”. We called up our friends and wrote a proposal to build a small satellite to measure the Big Bang radiation and to look for the light from the first galaxies. We wrote the proposal and eventually NASA accepted it. This is how I became a cosmologist.

This morning you spoke about the results of the CBR spectrum in a way that made us think of the title of this meeting, which reads “Knowledge is always an event”: you told the story of your discovery as something that happened. Can you tell us the story again? Do you think that you agree with our title?

That knowledge is always an event is certainly true. And it’s very different for each person that is participating in this knowledge. When we launched the Cosmic Background Explorer satellite (COBE), I thought I knew what we would find. I thought that it would have been very surprising if the universe had done anything besides the hot Big Bang, with a perfect blackbody spectrum for the Cosmic Background Radiation. We designed an apparatus that would be capable of making an extremely precise test, to see if this was true. I thought that we had to make a very brilliant experiment, or else it would not actually tell us anything. We promised a sensitivity that would find small deviations of only one part in one thousand from perfection: eventually it turned out that the instrument was capable of measuring only one part in twenty thousand, fifty parts per million deviations from perfection. And that was the final answer that we obtained: the hot Big Bang explains the measurement within an accuracy of fifty parts per million. When we showed the first version of this chart to the astronomical society, we received a standing ovation, which completely amazed me. I thought: “everybody knows that this is the right answer”, but the general population of astronomers did not know. They had seen many bad measurements and many strange theories to explain these bad measurements and it really was in doubt that the hot Big Bang was the correct story. We went from measurements that were just terrible to measurements that were very good, all in an instant and this was a tremendous experience for people. I remembered thinking “why are they so excited”? I knew this was the right answer, but I was the only one that did. Of course it took many years of preparation to achieve this: it was fifteen years from the proposal to the launch, but then we got this first scientific result within weeks.

In 2007 you gave a talk at the Goddard Institute for Space Studies in New York City. You were discussing the fact that we are now transitioning from a matter-dominated universe to a dark energy-dominated one, and at some point you said something very striking: “This is one of the multiple aspects in which we can see just how lucky we are to be here”. Can you elaborate on this point?

I guess that everything specific that happens, including the details of how we have two recorders sitting on the table and how we are having this particular conversation, reflects a complete complexity, in the way the laws of nature have worked out. Nature likes to produce complex things, which is a wonderful fact. It’s not something that scientists could have guessed, without knowing that this was the right answer. If we go back a little bit into the cosmology, we could imagine how the Universe would be like if any of the constants of nature was just slightly different: we wouldn’t have chemical elements in the right abundances, the Earth wouldn’t have the right temperature, there wouldn’t be water in the right amount. Maybe there would be another place somewhere else in the universe where life could exist, but maybe not. This is one of those things where you can’t actually do statistics: there is only one universe that we can measure, so we don’t have any way of calculating probability. But I still feel completely amazed at all of the features that we discover in the universe.

This brings another question, the question about the object of science. Do you think that science should try to address the “big” questions (are we alone in the universe? what are doing here, etc.)? Or stay at a “safe” distance from them?

I think that people want us to pursue these questions as far as we can. People are a little bit afraid of the answer, sometimes, but other people say: “well, of course we have to do this”. And so, for instance, if you ask why would the public support NASA, I think one of the great excitements for the public is the question of life elsewhere in the universe. It would change our understanding of ourselves, if we knew that the universe is alive elsewhere, even if we can never communicate with beings on another planet, because it’s too far away or we don’t know how to do it: just the very idea that we are not the only place in the universe with life would be extremely exciting for philosophy and for our understanding of nature. And of course theologians would have to think about that too, and they have, of course. The Vatican as you know has had an observatory for well over a century with big telescopes, and has had conferences on cosmology. Georges Lemaître, the mathematician who predicted the Big Bang, actually was a Jesuit Father as well, and he got to visit the Pope: the Pope wanted to know whether the Big Bang theory supports the biblical story, and Georges Lemaître, the Jesuit Father, said: “no, we are talking only about science, today”. That was very interesting: the question of science connecting to religion has been going on for a very long time and Galileo was not the first or the last.

Your next project is going to be the James Webb Space Telescope: can you tell us about it?

I’m now the chief scientist for the James Webb Space Telescope, which hopefully is going to be launched in 2014, 5 years from now, to be the even bigger and more powerful telescope that follows after the Hubble Space Telescope. It’s a joint project between NASA and the European and Canadian Space Agencies and will carry infrared instruments, which will extend the discoveries of the Hubble Space Telescope into places where Hubble cannot see. Although is wonderfully powerful, Hubble cannot see far enough away, to get close enough to the Big Bang, to answer the questions that the astronomers have today. The expansion of the universe stretches out the light from the distant galaxies into infrared wavelengths, but the Hubble does not detect those wavelengths, therefore we need an infrared telescope. And that means that the telescope has to be cold, much colder than room temperature, otherwise the telescope itself will glow in infrared radiation. So the telescope will be cold and will be far away from the Earth, 1.5 million kilometers away, around what’s called the Sun-Earth Lagrange point L2, the same place where they put the Planck and Herschel observatories quite recently. Finally, another challenge about the telescope is that it is much larger than the rocket, so it will be unfolded and adjusted into the correct shape after launch. It is the first time that we’ve tried to do this, as far as I know, with a large telescope in space (the telescope’s aperture is 6.5 meters, while the rocket’s inside diameter is about 4.5 meters): it will unfold like a butterfly, coming out from the rocket.

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