Is there more than one Universe?

Chris Smith put Josip's question to Imperial College's Stuart Higgins...

Stuart - Do you know what Chris, I have to be completely honest here, I had no idea about this question. Even as a physicist, even having a physics degree, I had to go and consult a more specialist physicist - I had to go and find a cosmologist and ask him. So thank you to Dr Roberto Trotta, Imperial College’s theoretical cosmologist So I went and had a very nice coffee with him and he kind of blew my mind.

There are lots of different ideas here but, what I should say is, these are theories, these are ideas and consequences of the mathematics that cosmologists have come up with. Not all cosmologists agree about these. But in the same way that we know about the big bang model and our understanding of the universe, if you start to look at more complicated maths, start to consider what are the consequences of different models that created the universe, then there are some interesting outcomes. It could be, actually, that our universe isn't the only one, that other universes have budded off at a certain time and have very different properties to our own. That they could have different numbers of dimensions, that they could have different constants to the laws of physics where the speed of light is somehow different, or something else entirely.

And on top of that it gets even more complicated when you consider things like the quantum multiverse. One way of interpreting the kind of mysteriousness of quantum mechanics is that when you make a decision, the universe splits out into all the different variants of different ways that decision could have gone. And so you end up with this very complicated system of theories where you have different universes, each of which might have millions of quantum multiverses on top of them, so it’s very complicated.

And the answer is: these are all theories and we can’t yet measure anything to give us an indication of what they are. They’re consequences of maths.

Chris - Michio Kaku came over from New York and gave a talk here in Cambridge about ten years ago to coincide with the release of his book “Parallel Universes.” And he said: well, one of the ideas of the big bang that occurred in our universe, its origin, you can think of it like the big bang is a white hole which occurs at the arsehole of a black hole in another universe. So sort of one universe is spawning other universes out of it’s black holes. Did Roberto Trotta comment on that at all?

Stuart - He didn’t specifically use that language no.

Chris:: Neither did Michio Kaku, but I’m sort of adding colour.

Stuart - Okay, okay. But it’s very interesting and it is one of those things. So I’m experimentalist and I always want to the see the data, I always want to see what the measurements are but, actually, at the same time you need to be able to theorise these things so you know, as experimentalists, what to look for. And maybe, in the future, when our instruments get better as we’re able to detect more exotic things like gravitational waves, we might start to see signatures of what’s beyond our current understanding of the universe.