Bob Maywood: You recently published a paper about what you call the Penrose region of black holes. We probably all saw the movie, but can you explain what a black hole actually is?
Stephen Appleton: Well, it’s just like I said. A black hole is an object so dense it bends spacetime in such an extreme way that light cannot escape it. That doesn’t mean it’s a singularity as it might not actually be infinite, it’s just that we can’t tell experimentally if it’s actually infinitely dense or just that the deformation of spacetime is so extreme we can’t see its limits.
BM: Are you saying it can actually trap light? So what would we find at the centre? Would it be possible to travel there or live there?
SA: That’s not a valid question. As you pass the event horizon, whether it’s a singularity or not, matter gets stretched to a line that approaches infinity in temporal as well as spatial dimensions. So concepts such as travel and life simply don’t have meaning, just as the laws of physics we take for granted start to break down at the quantal level. Ideas like ‘centre’, ‘travel’ or ‘live’ are just not relevant. And like I said, it’s not like we can experimentally get anywhere close. I’m working on a way of being able to get empirical data from further into the spacetime distortion of singularities than we’ve managed before. If my calculations are correct, we might be able to peer behind the curtain, even just a little.
BM: Your current research then is all about trying to find a black hole and study it in more detail. So are you telling me we’ve never actually seen one of these things?
SA: Yes, that’s right. So far it’s only theoretical.
BM: But you can predict where they are?
SA: Yes, that’s what I’ve been saying.
BM: And that means, I guess, you can use one of your telescopes to actually take a closer look, so to speak?
SA: Yes, exactly. Well, not exactly, that’s a gross simplification. That’s more Disney than science. But essentially, yes.
BM: Dr Collins has been critical of this idea in the past. Does that cause you problems as a married couple?
SA: Listen, we’re scientists. We’re grown-up enough to have a healthy debate about our work without it being a problem in our marriage. Kate is a theorist, she works in ideal forms, in maths and then applies it outwards. I’m an empiricist. For me it’s about what you can actually do – get the data and derive the theory from there. Kate calls it hands-dirty science, she thinks what she does is a purer form. But for me, empiricism is practical, it’s about the world we live in, not some idealised form.