We first have to distinguish astrophysics and astronomy in the strict sense from cosmology. Cosmology deals with the universe, trying to understand the universe in its development and in its essence. Astrophysics, which comes from astronomy, attempts to understand what we see in the universe: stars, galaxies, black holes – what lies between the stars. But we cannot manipulate the objects that we are studying. This is a handicap for the path to certainty. If you can manipulate something, if you can interact or see how objects react to influences, you begin to feel that you can develop certainty. In other words, one might understand things better then. We, however, work with models. We model the objects in the universe and for this reason make different kinds of claims than other branches of physics in the sense that we are not so very driven by theory.
However, astrophysics has something like an intuitive certainty, because we can see the things we are studying. This has to do with the historical telescope. Everyone can see the starry sky, and we have the vision that we still see the same night sky as our ancestors had several thousand years ago. And yet our telescopes are just a further development of the very simple telescopes used a few hundred years ago by our ancestors. There is, therefore, this intuitive assumption that what we see also exists – very certainly –, which is again different than in particle physics, where we first need to create the phenomena we study in enormous experiments. These are, first of all, the two sides of certainty that I would see in astrophysics.
The second part, cosmology, which deals with the universe and the evolution of the universe, is a different case, because of course the empirical basis is much more problematic. Cosmology was traditionally a field that was associated with speculation. If you look at the history, Descartes, Newton, Kant – they put a lot of thought into how our universe is composed, how it works, but of course lacked any really solid observational data. That cosmology has become an empirical science in the narrow sense is a development that started only at the beginning of the last century. Since the beginning of the last century, we have been able to gather more empirical data, we have come to the belief that there was a Big Bang. We also have observed the cosmic background radiation, a very, very important part of the empirical basis of modern cosmology. Over the decades, we have come so far that we would think of cosmology as a well-informed empirical science, an empirical branch of science.
But some today believe that we are currently in a kind of cosmological crisis. And indeed it’s a problem, an interesting one, of course, that we have, on the one hand, more empirical data than ever before, and, on the other, a need to introduce new entities to describe what we do not know: dark energy and dark matter, which account for 96% of our universe and yet we have no idea what it could be. It’s a very alarming record for us truly to understand only 4% of the universe still. And here we turn to particle physics for hope – the wish that particle physicists will help astrophysicists and will perhaps discover something that could be dark matter. But the standard model of particle physics contains no candidate for dark matter. There are of course less elegant alternatives, theoretically speaking. They are much more complicated, we still don’t really understand them; but these could perhaps describe our observations better than Einstein’s General Theory of Relativity. Then again, there are also experiments that confirm the theory of relativity with incredible precision. That means we are not certain exactly how to classify it.
We don’t think that dark energy or dark matter will be anything worrisome, we think we’ll get a handle on it somehow. That’s the hope – perhaps, the vision, if you will. From a scientific-theoretical perspective it is symptomatic of times of crisis, when we are confronted with anomalies, with things we don’t understand, to research in new directions: we vary methodologies, we try to think in entirely new ways. This simply isn’t necessary if everything is already working perfectly. If that were the case we would just have our methodological toolbox that would do the trick every time. We would be working only with entities we already understand well.
In my own work, I can say that I’m dealing with a relatively safe topic. I’m interested in how stars are born, how stars die. This is based largely on observation. On the one hand, I use a model that works to transform physics as observed from our Earth into a numerical code and then I calculate what we are seeing in our Milky Way. Concretely, I deal with shockwaves, which is to say, with explosions, and the question of what happens afterwards. My job is to explain observations of star births and star deaths through models. Which is to say that researchers come to me with their data and say: We’ve registered this and that – what does this tell us about the star? Then I try and answer them with the help of a computer programme. This is the one side of my work.
But then I also make my own observations. Concretely, this means that I follow precisely these events of star births, star explosions and supernova explosions with my telescope in the Atacama Desert. In this respect, I’m treading on relatively safe ground. We make very, very many observations and we have very powerful telescopes. No one really expects any revolutions here, I think. And in this respect, I’m in a field that has a high degree of certainty – still, if you wanted to be petty about it, in turn you could say it’s also a bit more boring. For this reason I’m not so worried about my future, because I know that my work has a very secure theoretical foundation. But you never know! That’s the nice thing about science: you can always be surprised.