What Happened Before the Big Bang?

It seems like everyone wants to know the answer to this question - not least the cosmologists at Oxford.

I'm an observational cosmologist - part of my research is on making accurate measurements of the recent expansion history of the Universe. All distant galaxies appear to be receding from us: run this movie backwards in your head and you reach a time (before galaxies had formed) when all the matter in the Universe was packed very close together. Press play, and the expansion of the Universe starts, and this is what is meant by "The Big Bang". Many people try and visualise this as an explosion, viewed from the outside - but that's not quite right, as when we ran the film backwards, we were always on the inside of the Universe. The name "Big Bang" doesn't help!

Jocelyn Bell Burnell likes to compare the expansion of the Universe with the unfurling of a leaf from a bud: a whole, small leaf was in the bud to start with, and after it has burst out it then grows - expands - into a bigger version of itself. After the talk when I heard her use this simile, someone in the audience asked her what happened before the Big Bang. Her answer was an interesting one. She said: as far as we can tell, time seemed to start at the Big Bang, so asking that is like asking what's North of the North Pole. We're not used to thinking of time as a dimension, like degrees North, but that's exactly what Einstein's theory of relativity teaches us we have to do. And why shouldn't the Big Bang mark the origin of time, just like the North Pole is the origin of the latitude-longitude coordinate system?

Pedro Ferreira was there at tea-time when I was recounting Jocelyn's answer. He told us what often happens next: someone asks, well what about everything that's above the North Pole? He likes this, because it gives him a good opportunity to talk to them about extra dimensions! It turns out that many people find the concept of time beginning at the Big Bang a bit unsatisfying - and that includes the cosmology theorists themselves. Tim Clifton explained to me a popular theory that allows for all sorts of things happening before the Big Bang: Eternal Inflation.

The idea is that once, the Universe was so hot and dense that tiny random fluctuations could actually have enough energy to power the "inflation," or very rapid expansion, of a small patch of the Universe that would grow to an immense size and contain all the galaxies we currently see - and in fact make up what we call the observable Universe today. Meanwhile, other fluctuations could have caused other patches of the Universe to expand into what other observers over there would then describe as their observable universe. And in this picture, isolated inflating patches like these could have been occasionally blowing up here and there, forever. A multiverse with a history stretching back into the infinite past! Perhaps a more satisying, but also a more dizzying, notion than time starting at a single Big Bang.

So, might there be a multitude of other universes out there in the bubbling froth? During all this tea-time musing, Joe Zuntz echoed the first part of Jocelyn's answer: the data we have at the moment aren't good enough for us to be able to tell. That's why we're still looking.

You can read more about time, and inflation, over at the Cosmic Variance blog: Sean Carroll is particularly interested in the topic.

Image credit: Exploratorium