We understand the universe pretty well back to very early times, but at some stage our currently applicable theories – QM and GR – cease to be applicable because the extremely early universe is both very small and very dense. This means we need both QM and GR to work there and, as I mentioned earlier, they don’t play well together. We therefore require a quantum theory of gravity. We have very few ideas about how to make a successful one of these, for example string theory, and none of them have yet been able to tell us anything we can be confident about regarding the early universe. So my answer to the question is that we don’t even know whether it makes sense as a question yet, much work remains to be done and people are trying hard to push our understanding back to earlier and earlier times in the universe. “We don’t know.”

As for changing gravity. I told them we can change gravity, but that how we do it is highly constrained. I mentioned recent attempts in which I (and Sean) have been involved, what others are doing, and said it’s an area of active, but as yet speculative, research. Again, the main message is that this is a frontier topic, so like any good scientist all I can do is provide a feel for the research directions, be clear about what are tested results and what are speculations, and say “We don’t know yet”.

“Strings?” was the very first question and was asked by a nice smart man who was fascinated by the whole subject and who stayed around to ask a lot of good questions at the end. He really meant “I’ve heard of these things called strings, and heard that they might help solve some of the issues you mentioned. Can you tell us something about them?” I did my best, explained the broad stringy picture, why it was exciting, why it wasn’t part of our view of the real world yet, and gave some examples of how people were using string theory to try to address some cosmological questions.

That “Strings?” question sounds funny because I can hear someone saying it in a sort of “Really?” sort of way.