Julian Baggini No one who has understood even a fraction of what science has told us about the universe can fail to be in awe of both the cosmos and of science. When physics is compared with the humanities and social sciences, it is easy for the scientists to feel smug and the rest of us to feel somewhat envious. Philosophers in particular can suffer from lab-coat envy. If only our achievements were so clear and indisputable! How wonderful it would be to be free from the duty of constantly justifying the value of your discipline.

However – and I'm sure you could see a "but" coming – I do wonder whether science hasn't suffered from a little mission creep of late. Not content with having achieved so much, some scientists want to take over the domain of other disciplines.

I don't feel proprietorial about the problems of philosophy. History has taught us that many philosophical issues can grow up, leave home and live elsewhere. Science was once natural philosophy and psychology sat alongside metaphysics. But there are some issues of human existence that just aren't scientific. I cannot see how mere facts could ever settle the issue of what is morally right or wrong, for example.

Some of the things you have said and written suggest that you share some of science's imperialist ambitions. So tell me, how far do you think science can and should offer answers to the questions that are still considered the domain of philosophy?

Lawrence Krauss Thanks for the kind words about science and your generous attitude. As for your "but" and your sense of my imperialist ambitions, I don't see it as imperialism at all. It's merely distinguishing between questions that are answerable and those that aren't. To first approximation, all the answerable ones end up moving into the domain of empirical knowledge, aka science.

Getting to your question of morality, for example, science provides the basis for moral decisions, which are sensible only if they are based on reason, which is itself based on empirical evidence. Without some knowledge of the consequences of actions, which must be based on empirical evidence, then I think "reason" alone is impotent. If I don't know what my actions will produce, then I cannot make a sensible decision about whether they are moral or not. Ultimately, I think our understanding of neurobiology and evolutionary biology and psychology will reduce our understanding of morality to some well-defined biological constructs.

The chief philosophical questions that do grow up are those that leave home. This is particularly relevant in physics and cosmology. Vague philosophical debates about cause and effect, and something and nothing, for example – which I have had to deal with since my new book appeared – are very good examples of this. One can debate until one is blue in the face what the meaning of "non-existence" is, but while that may be an interesting philosophical question, it is really quite impotent, I would argue. It doesn't give any insight into how things actually might arise and evolve, which is really what interests me.