I have a very difficult task. I'm a spectroscopist. I have to talk about astronomy without showing you any single image of nebulae or galaxies, etc. because my job is spectroscopy. I never deal with images. But I'll try to convince you that spectroscopy is actually something which can change this world. Spectroscopy can probably answer the question, "Is there anybody out there?" Are we alone? SETI. It's not very fun to do spectroscopy.

One of my colleagues in Bulgaria, Nevena Markova, spent about 20 years studying these profiles. And she published 42 articles just dedicated to the subject. Can you imagine? Day and night, thinking, observing, the same star for 20 years is incredible. But we are crazy. We do these things. (Laughter)

And I'm not that far. I spent about eight months working on these profiles. Because I've noticed a very small symmetry in the profile of one of the planet host stars. And I thought, well maybe there is Lithium-6 in this star, which is an indication that this star has swallowed a planet. Because apparently you can't have this fragile isotope of Lithium-6 in the atmospheres of sun-like stars. But you have it in planets and asteroids. So if you engulf planet or large number of asteroids, you will have this Lithium-6 isotope in the spectrum of the star. So I invested more than eight months just studying the profile of this star.

And actually it's amazing, because I got phone calls from many reporters asking, "Have you actually seen the planet going into a star?" Because they thought that if you are having a telescope, you are an astronomer so what you are doing is actually looking in a telescope. And you might have seen the planet going into a star. And I was saying, "No, excuse me. What I see is this one." (Laughter) It's just incredible. Because nobody understood really. I bet that there were very few people who really understood what I'm talking about. Because this is the indication that the planet went into the star. It's amazing.

The power of spectroscopy was actually realized by Pink Floyd already in 1973. (Laughter) Because they actually said that you can get any color you like in a spectrum. And all you need is time and money to make your spectrograph. This is the number one high resolution, most precise spectrograph on this planet, called HARPS, which is actually used to detect extrasolar planets and sound waves in the atmospheres of stars.

How we get spectra? I'm sure most of you know from school physics that it's basically splitting a white light into colors. And if you have a liquid hot mass, it will produce something which we call a continuous spectrum. A hot gas is producing emission lines only, no continuum. And if you place a cool gas in front of a hot source, you will see certain patterns which we call absorption lines. Which is used actually to identify chemical elements in a cool matter, which is absorbing exactly at those frequencies.

Now, what we can do with the spectra? We can actually study line-of-sight velocities of cosmic objects. And we can also study chemical composition and physical parameters of stars, galaxies, nebulae. A star is the most simple object. In the core, we have thermonuclear reactions going on, creating chemical elements. And we have a cool atmosphere. It's cool for me. Cool in my terms is three or four or five thousand degrees. My colleagues in infra-red astronomy call minus 200 Kelvin is cool for them. But you know, everything is relative. So for me 5,000 degrees is pretty cool. (Laughter)

This is the spectrum of the Sun -- 24,000 spectral lines, and about 15 percent of these lines is not yet identified. It is amazing. So we are in the 21st century, and we still cannot properly understand the spectrum of the sun. Sometimes we have to deal with just one tiny, weak spectral line to measure the composition of that chemical element in the atmosphere. For instance, you see the spectral line of the gold is the only spectral line in the spectrum of the Sun. And we use this weak feature to measure the composition of gold in the atmosphere of the Sun.

And now this is a work in progress. We have been dealing with a similarly very weak feature, which belongs to osmium. It's a heavy element produced in thermonuclear explosions of supernovae. It's the only place where you can produce, actually, osmium. Just comparing the composition of osmium in one of the planet host stars, we want to understand why there is so much of this element. Perhaps we even think that maybe supernova explosions trigger formations of planets and stars. It can be an indication.

The other day, my colleague from Berkeley, Gibor Basri, emailed me a very interesting spectrum, asking me, "Can you have a look at this?" And I couldn't sleep, next two weeks, when I saw the huge amount of oxygen and other elements in the spectrum of the stars. I knew that there is nothing like that observed in the galaxy. It was incredible. The only conclusion we could make from this is clear evidence that there was a supernova explosion in this system, which polluted the atmosphere of this star. And later a black hole was formed in a binary system, which is still there with a mass of about five solar masses. This was considered as first evidence that actually black holes come from supernovae explosions.

My colleagues, comparing composition of chemical elements in different galactic stars, actually discovered alien stars in our galaxy. It's amazing that you can go so far simply studying the chemical composition of stars. They actually said that one of the stars you see in the spectra is an alien. It comes from a different galaxy. There is interaction of galaxies. We know this. And sometimes they just capture stars.

You've heard about solar flares. We were very surprised to discover a super flare, a flare which is thousands of millions of times more powerful than those we see in the Sun. In one of the binary stars in our galaxy called FH Leo, we discovered the super flare. And later we went to study the spectral stars to see is there anything strange with these objects. And we found that everything is normal. These stars are normal like the Sun. Age, everything was normal. So this is a mystery. It's one of the mysteries we still have, super flares. And there are six or seven similar cases reported in the literature.

Now to go ahead with this, we really need to understand chemical evolution of the universe. It's very complicated. I don't really want you to try to understand what is here. (Laughter) But it's to show you how complicated is the whole story of the production of chemical elements. You have two channels -- the massive stars and low-mass stars -- producing and recycling matter and chemical elements in the universe. And doing this for 14 billion years, we end up with this picture, which is a very important graph, showing relative abundances of chemical elements in sun-like stars and in the interstellar medium.

So which means that it's really impossible to find an object where you find about 10 times more sulfur than silicon, five times more calcium than oxygen. It's just impossible. And if you find one, I will say that this is something related to SETI, because naturally you can't do it. Doppler Effect is something very important from fundamental physics. And this is related to the change of the frequency of a moving source. The Doppler Effect is used to discover extrasolar planets.

The precision which we need to discover a Jupiter-like planet around a sun-like star is something like 28.4 meters per second. And we need nine centimeters per second to detect an Earth-like planet. This can be done with the future spectrographs. I, myself, I'm actually involved in the team which is developing a CODEX, high resolution, future generation spectrograph for the 42 meter E-ELT telescope. And this is going to be an instrument to detect Earth-like planets around sun-like stars. It is an amazing tool called astroseismology where we can detect sound waves in the atmospheres of stars.

This is the sound of an Alpha Cen. We can detect sound waves in the atmospheres of sun-like stars. Those waves have frequencies in infrasound domain, the sound actually nobody knows, domain. Coming back to the most important question, "Is there anybody out there?" This is closely related to tectonic and volcanic activity of planets. Connection between life and radioactive nuclei is straightforward. No life without tectonic activity, without volcanic activity. And we know very well that geothermal energy is mostly produced by decay of uranium, thorium, and potassium.

How to measure, if we have planets where the amount of those elements is small, so those planets are tectonically dead, there cannot be life. If there is too much uranium or potassium or thorium, probably, again, there would be no life. Because can you imagine everything boiling? It's too much energy on a planet. Now, we have been measuring abundance of thorium in one of the stars with extrasolar planets. It's exactly the same game. A very tiny feature.

We are actually trying to measure this profile and to detect thorium. It's very tough. It's very tough. And you have to, first you have to convince yourself. Then you have to convince your colleagues. And then you have to convince the whole world that you have actually detected something like this in the atmosphere of an extrasolar planet host star somewhere in 100 parsec away from here. It's really difficult. But if you want to know about a life on extrasolar planets, you have to do this job. Because you have to know how much of radioactive element you have in those systems.

The one way to discover about aliens is to tune your radio telescope and listen to the signals. If you receive something interesting, well that's what SETI does actually, what SETI has been doing for many years. I think the most promising way is to go for biomarkers. You can see the spectrum of the Earth, this Earthshine spectrum, and that is a very clear signal. The slope which is coming, which we call a Red Edge, is a detection of vegetated area. It's amazing that we can detect vegetation from a spectrum. Now imagine doing this test for other planets.

Now very recently, very recently, I'm talking about last six, seven, eight months, water, methane, carbon dioxide have been detected in the spectrum of a planet outside the solar system. It's amazing. So this is the power of spectroscopy. You can actually go and detect and study a chemical composition of planets far, far, far from solar system. We have to detect oxygen or ozone to make sure that we have all necessary conditions to have life.

Cosmic miracles are something which can be related to SETI. Now imagine an object, amazing object, or something which we cannot explain when we just stand up and say, "Look, we give up. Physics doesn't work." So it's something which you can always refer to SETI and say, "Well, somebody must be doing this, somehow."

And with the known physics etc, it's something actually which has been pointed out by Frank Drake, many years ago, and Shklovsky. If you see, in the spectrum of a planet host star, if you see strange chemical elements, it can be a signal from a civilization which is there and they want to signal about it. They want to actually signal their presence through these spectral lines, in the spectrum of a star, in different ways.

There can be different ways doing this. One is, for instance, technetium is a radioactive element with a decay time of 4.2 million years. If you suddenly observe technetium in a sun-like star, you can be sure that somebody has put this element in the atmosphere, because in a natural way it is impossible to do this. Now we are reviewing the spectra of about 300 stars with extrasolar planets. And we are doing this job since 2000 and it's a very heavy project. We have been working very hard. And we have some interesting cases, candidates, so on, things which we can't really explain. And I hope in the near future we can confirm this.

So the main question: "Are we alone?" I think it will not come from UFOs. It will not come from radio signals. I think it will come from a spectrum like this. It is the spectrum of a planet like Earth, showing a presence of nitrogen dioxide, as a clear signal of life, and oxygen and ozone. If, one day, and I think it will be within 15 years from now, or 20 years. If we discover a spectrum like this we can be sure that there is life on that planet. In about five years we will discover planets like Earth, around sun-like stars, the same distance as the Earth from the Sun. It will take about five years. And then we will need another 10, 15 years with space projects to get the spectra of Earth-like planets like the one I showed you. And if we see the nitrogen dioxide and oxygen, I think we have the perfect E.T. Thank you very much. (Applause)