About dark matter, the largest, broken, astronomical mirror in the world, and the popularization of science: Gazeta.ru spoke with Massimo Capaccioli, honorary professor at the Moscow State University, professor of astronomy in the University of Federico II in Naples, the head of the project to create the VST telescope of the European South observatory (ESO).

-- Could you please tell briefly for our readers what do you think dark matter is?
-- It's a very difficult question because I really don't know the answer. What is dark matter for non-experts? Well it is the major component of the Universe, it is one third of the total mass and energy of the Universe. And it is probably responsible of our existence because, according to the standard cosmology, galaxies form because there are pre-existant blobs of dark matter onto which baryons pour and then coalesce and then create galaxy clusters, galaxies and stars and finally, after stars, planets. And on one of such planets, you and me are currently standing. But this is a theory supported by excellent observations. It is a theory that will be difficult to discard. Yet it is not 100% proven. In science things become exciting when they are not proven yet, but their proof could fix an important part of our understanding. This is true for the Higgs boson, this is true for dark matter, and certainly true for dark energy. We are making all possible efforts to try to demonstrate that dark matter exists, that a need of a dark component is there. Physicists have tried to give us the particle, and when we have the particle we will know for sure that dark matter is there. It is a subject for young people like you to tackle because it represents in this moment, in my opinion, the forefront of astrophysics, the problem which has to be solved. And it will be solved, one way or another.

-- Ok, and what is your opinion about the alternative theories like the Modified Newtonian Dynamics?
-- Well, I write papers on that. It doesn't mean that I believe that they are correct. The problem is that from the point of view of principles, there is no reason why Einstein equations could not be modified. In other words they've been written in the simplest possible form, but this is not the "truth." So, in principle, they could be modified. In practice are they modifiable? The answer is given by experiments. Thus we have to create experiments in order to prove or disprove the equations. So far I have not seen one single experiment, including mine, that completely disproves these alternative theories, but at the same time I have not seen one single experiment which proves them either. We have to continue and investigate.

One thing that I consider important in this business is the fact that sometimes it is considered to be ether illegal or immoral to touch what Einstein did. That's not true. It was not true for thoughts of Newton, it was not true for Aristotle's cosmology, it will never be true for any physical theory as truth in physics does not exist.

In fact every time we were able to do these things we made major a jump in our understanding of the world. So, sooner or later someone will show that there is something to be changed in Eintein's theory. I wonder whether this is the right time, I wonder whether the alternative theories that are running now are the answer to this need. But sooner or latter we will find a disagreement of the theory with nature. For the time being, American say, it is like jumping from pest to cholera. What you gain using alternative theories you loose on the other hand. The number of parameters is more or less the same, it's only the physics which is different, the intrinsic physics. In both cases you explain observational behaviors by one ingredient. In one case it's a material ingredient in other case it's the geometry of the space. We haven't found so far which is which and we have not found a way to establish which is which. That is why it is necessary to continue the work.

-- Could it be that some fraction of dark matter is in the baryonic form (in the form of cold gas or low mass stars)? And how large could be this fraction?
-- This is a question that you should not put to me, but to the people studying primordial nucleosynthesis. I know nothing about baryonic nucleosynthesis so I can't give you a sensible answer. I can just give you the answer which comes from my readings. We can't bypass the limit of baryonic nucleosynthesis. That we have dark baryons is obvious. The Moon is dark. It shines because of the Sun. It is not completely dark of course because it is a warm body. So it radiates something but it's dark enough. Dead stars are dark. Dust can be very dark. It becomes visible because of its darkness against a luminous nebula. Neutrinos: we have done all we could to use neutrinos to solve the problem. But again neutrinos don't work. I think, for what we know now, most of the dark matter must be non-baryonic and weakly interacting, if it exists. If that is the case we have to find the particle. Someone has to find the particle. May be at CERN.

-- As far as I know you have been awarded the title of honorable professor of Moscow State University. Could you please tell what role does Russia play in modern science and in particular in astronomy?
-- Let me first of all say clearly that I am really very honored that my colleagues wanted to push this title for me and that it is one of the most prestigious things that happened in my career. Not only because every time someone tells you that you are good it's nice. But because those who tell you that you're good are also very good. So this title is very important for me. Russia has always been in the forefront of science. Although communication in the past was difficult for obvious political reasons and still there is a barrier of the language even for me. I don't speak Russian. I can't even understand one word. But in modern world this barrier in science has been completely overcome. The contribution of Russians to astrophysics has been and is tremendously important. There are many theoretical effects which bring Russian names. And there are many discoveries which are named after Russian astronomers.

Russia has been the country with the largest telescope in the world. The 6-m telescope was winning over the Palomar telescope. Russia has pioneered space research. And Russia has a long standing tradition of science.

That is why I like to come here. I like to have Russian colleagues coming to my institute. And I like to collaborate with them because it is not only the present competence which matters. When you stay with a Russian scientist, you stay with an intelligent colleague, may be extremely good, may be as normal as more or less the average in the world, but then you have a human being with a deep tradition in the culture of the country, in the culture of the people, which is very important for me. Because there is not only astronomy in my life, not only astrophysics, not only science. There is music, there is literature, there are friends, there is thinking, there is food, there is atmosphere. And all this I find very pleasant for me in your country. So I'm very proud of being honorary professor at the Moscow State University. It is great opportunity for me to continue my relationship with Russian astronomers and not only.

-- How important is for Russia to become a member of European South Observatory (ESO)?
-- Well, can I reverse the question? How important is for ESO that Russia becomes a member of ESO? Both things are important: it is very important for Russia to become a member of ESO and it is very important for ESO that Russia enters ESO. It is a pity that the competence and the manpower that you have can't be used effectively with the new instruments. Imagine what's going to happen if we are able to complete the ELT (the extremely large telescope) 40-m telescope which will provide incredible observations. I want to tell you the following: modern astrophysics is done in such a way that quite often data are collected and immediately put on the web, so that anybody can use them. This will be true also for the VST telescope, which by the way has been built partly in Russia (the mirror was made in Lytkarino). Is true for the Sloan Survey and so no. The fact that the data are available in the web makes the partnership less important in a way because you don't need to be a member of ESO to access the data. But you need to be a member of ESO to rule the policy of ESO, to rule the programming of the observations, to determine which kind of observations and not simply take the observations that are being made out of the web. And to rule the policy of the new instruments. So it is of crucial importance that a country with a tradition, the competence, the knowledge and a power of Russia joins ESO.

I would be absolutely happy if that happens. In a way it's natural, it will happen, I hope. The sooner the better for ESO, Russia and astronomical research.

-- I know that you have managed the realization of VST. Could you please tell briefly about the instrument, about the main goals and the first scientific results made with the instrument?
-- Yes. VST means VLT Survey Telescope. How was it born? When I was director of the astronomical observatory in Naples I received an enormous amount of money. As it happens in the poorest parts of a country, money comes in bursts, with no guarantee of continuity. This is very dangerous because ether you spend this random money, and if you spend then you will not get any more money and you don't know how to continue the enterprise, or you don't spend it. And if you don't spend it they say: "You don't spend it, you don't need". So it was a very difficult situation and I wanted to do something very important for Naples and for science, but at the same time I wanted to create the situation in which I could use the facility without having problems with the supply of money, because I was almost certain that I was not going to get any other money. So I agreed with ESO to build the large survey telescope, a sort of modern Schmidt type telescope which had been my dream for a long time. And the agreement was that this telescope had to be built by us. ESO was going to provide the dome and to run the telescope. And the camera had to be provided by third party. So we signed the agreement. And the first thing I had to do after I had convinced ESO that we are able to build the telescope was to find someone who was providing the right mirror, because the mirror was pretty difficult to be polished. And there were two possibilities ether Germany or France.

And the German firm offered a mirror made by the Russians. It was the period in which Russia was a little bit unstable, as we understood the situation from the West.

So I had to think about it. I said: "Can I do it or not, isn't it too big a risk?" Then, remembering what Russia is, I said: "No. It is not a risk, I want to do it." And I did. The two mirrors of the telescope were made in Lytkarino. They made a fantastic mirror right on time. Everything was perfect. In fact I had to stop them because they wanted to continue polishing and improving more and more the quality. I said: "No, that's ok as it is." Unfortunately when the mirror was shipped to Chile it was destroyed during transfer. It is the largest astronomical mirror ever destroyed in the world!! So we had to remake it; of course insurance paid everything. And I want to tell you something. When I went to Lytkarino to order the second mirror, Russians could have taken me by the throat. Because you want the second mirror, you have to pay more. They made the same offer as before – incredibly honest. And they did again a very good job. A little bit too long, they took four years to redo the mirror. Finally they repolished the new mirror which is now in operation.

This telescope was not born under a good star as we say in Italy. It was unlucky. But we can rule fortune.

Finally when everything was resettled, we shipped the cell of the telescope. The cell is the unit holding a mirror. Since it is an active optics system, the cell is very complicated piece of art, the most expensive and fragile part of the telescope. And when we put the cell on the ship, the ship left to Chile but three days later it stopped because of an average. When after two month it arrived in Chile the cell was completely rusty. So we had to wait the clearance by the insurance, then bring the cell back, redo everything from scratch and send the cell back. This happened two years ago since then the telescope is operating beautifully at the ESO Observatory on the top of Cerro Paranal, in Chile. It is giving absolutely top quality images that you can see in the press releases in ESO website. We have already collected a number of supernovae in the program devoted to supernovae. But the two major programs which will take 70% or so of the total VST time are two ESO key programs – one is aimed at investigating baryonic oscillations and the other to measure the cosmic shear in order to set a limit to the density of matter and energy in the universe. These two projects will last from three to four years; they started a year ago, so it will take a couple of years more to get a first answer from them. For what we can tell from now, the telescope is doing better than it was expected to do. Part of this is due to the quality of the mirror made by the Russians. This is another gift that I had from your country.

-- What do you think about the popularization of science? Is it worth expending time in it?
-- It is absolutely fundamental for two reasons. The first point is that we scientists need financial support. Fundamental science is not supported by firms, it is supported by governments. And a government has to have a reason to support us and this reason must come from tax payers who like what we do. In order to make it we have to tell them what we are doing. And this is the second part. It's easy to tell what we do because astrophysics has images, it is a science that speaks to the heart of people, to the mind of people, to the fantasy of people. It speaks of something which is, for those who like it, close to God or close to creation and so on. It is something that speaks of monstrous things which do not touch us; it is not like cancer. Those who study cancer do a very important job. But I will never go to hear a conference of persons speaking about cancer because I'm scared. On the other hand I will be happy to look at the images or at the movies, or at the things done by astronomers. This is the way to return to people what we are doing.

At the same time in the modern world - I don't know whether this is true in Russia too, but in the so-called Western world it is terribly true - the young people find it hard to find a job.

Finding a job is a major effort by young person. And in order to find a job, from very early years they start thinking what is most convenient for their life. Is it to become a medical doctor, because medical doctors are always finding a job, or a lawyer, or to go into business? Science is more and more neglected. And especially good guys who could become a very good scientists, if they are not seduced by the beauty of science have no good reason to enter science. This is killing the major drive of progress, of increase of our culture, of our understanding, of our freedom, if you want. So it is very important that we transmit real messages, not fake messages. I hate the science popularization made by those tv programs where they use deep and loud voices and give an impression that a scientist is genius and that spectator is an idiot and will never be able to do this fantastic, beautiful and non-understandable things they are speaking of. In fact one should show that scientists are human beings that have the same rights and the same merits, the same defects as a human beings. That they do this as a job, but this job is providing something marvelous - understanding of nature. I devote for instance certain fraction of my time doing popularization of science to thank tax payers and at the same time to try to fish new talents among young people because the river should not dry. And in Western world the river is getting dry because young people are scared to throw the heart behind the obstacle. They think too much to real life to the bread and the salami and not enough to cultivate their intelligence. May be through science divulgation we can do something good.

-- And the last question: do you have your favorite object or class of objects on the sky? And if yes please explain why.
-- Yes, I have. As a scientist I have certainly favorite class of objects which are elliptical galaxies. But this happens to be so by chance. I explain it to you in this way. When I arrived here a week ago and I was took to the apartments that I have in the main building of the University, everything to me looked strange, different. From the smell to the colors, everything was unusual. A week has passed and now I feel perfectly at home. I've been staying with elliptical galaxies for almost 50 years now. So they are very familiar to me; that's why I like them. But what I have to tell you is that if you change subject, at the very beginning the subject will look strange and not as pleasant as the previous one. But if you become familiar with it, you will start liking it very much. That happened to me during my entire life, when I moved from one site to the other site of the garden of elliptical galaxies.

I'm pretty sure that even now if I were able to jump to another subject and stay there for a sufficient number of years I would start loving it and I would say: "This is my favorite subject".

Science is always beautiful, any type of science – theory, observations, experiments, physics, mathematics... In astronomy there is no one class of objects which is better than another. There is no one single problem which is better than the other. When my students come and say: "I would like to have a dissertation assigned but I don't know in which subject", I tell them: "Look, what about this one?" They say: "Well, I'm not sure because I don't know whether I like it or not" I say: "Don't worry, whatever the subject is, you will like it. Eventually you will become fond of it. And it will become difficult for me to convince you to go to another subject, because that has become too nice for you." So I answer elliptical galaxies only because I stayed with them most of my life.