WHATEVER you do, don’t ask where it happened. “The most common misconception is that the big bang was an explosion in a particular place,” says , a cosmologist at the University at Buffalo in New York. “That’s just completely wrong.”
The best evidence for the big bang is all around us in the cosmic microwave background, the radiation released once the universe had cooled sufficiently for atoms to form, when it was about 380,000 years old. And that is the point: everywhere in today’s universe was where the big bang was. “It’s not something that happened somewhere, but something that happened everywhere, including the space you happen to be occupying now,” says Dan Hooper at Fermilab in Illinois.
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When cosmologists talk about the big bang, they are talking about an extremely dense, hot state that existed around 13.8 billion years ago and which has since expanded and cooled to make the universe we know today. Extremely dense and hot – but not infinitely so.
The idea that the universe was created from an infinitesimal speck, known as the big bang “singularity”, comes from winding the showreel of an expanding, cooling universe backwards and not stopping until we get to a beginning. But, unfortunately, our current theories of physics can’t deal with space and time on such unfathomably small scales. So we can say nothing sensible about the moment when the universe was a single point, if indeed it ever happened. “We may just have to come to terms with that,” says Kinney.
“The big bang didn’t happen somewhere, it happened everywhere”
However it all started, the big bang that followed wasn’t so much an explosion, which implies stuff flying off randomly, but a perfectly uniform expansion – albeit one that seems to have been, in its first throes at least, unimaginably fast. We have suspected this since the 1980s, when we realised that the temperature and density of stuff in the universe – as seen for instance in maps of the cosmic microwave background – are incredibly smooth. We would naively expect quantum fluctuations to have produced regions with differing densities and temperatures in the universe as it spread out. To explain the observations, physicists invented a split-second growth burst called inflation that stretched the universe so fast the kinks were smoothed out.
Standard timelines of the universe’s first instants have inflation coming after the big bang. But for Kinney, it makes more sense to think of inflation coming first, creating the hot, dense soup from which today’s universe, with its atoms and stars and planets, emerged through a slower process of cooling and expansion. “What we think was the beginning of the universe – this hot equilibrium state 13.8 billion years ago – was in fact the end of inflation,” says Kinney. If that jars, then Hooper recommends thinking of inflation’s “big stretch” not as something separate, but as part and parcel of the big bang.
Then again, not everyone buys the inflation story, not least because it isn’t clear what did the inflating. Some cosmologists prefer to think that the universe began with a bounce, when a previous universe contracted to an extremely hot, dense point where it could contract no more. This would not only do away with the singularity, but also answer another inevitable, yet largely inscrutable question about the big bang: what came before it.
Cutting-edge science throws up all sorts of controversial, nebulous and mind-bending concepts. Here’s your guide to how to think about some of the fiddliest of them:
- In the quantum world, uncertainty reigns – or is it all in the mind?
- Think you understand how evolution works? You’re probably wrong
- Why information could be our route to the universe’s deepest secrets
- Who do you think you are? Why your sense of self is an illusion
- Homo sapiens? Genetic insights suggest we may not really be a species
- Firms and governments use the internet to spy on us. Should we care?
- D’oh! Why human beings aren’t as intelligent as we think
- Extinction is a fact of life. Could we stop it – or even reverse it?
- No more goody two shoes: Why true altruism can’t exist
- Alien life could be weirder than our Earthling brains can ever imagine
- Why it’s time to call time on the ‘nature vs nurture’ debate
- Dark energy: Understanding the mystery force that rules the universe
