Science Photo Library / Alamy Stock Photo
Space is big, wrote Douglas Adams in The Hitchhiker’s Guide to the Galaxy. “Really big. You just won’t believe how vastly hugely mindbogglingly big it is.” Too right: the edge of the observable universe is some 46 billion light years away. Within that volume there are anything between 100 and 200 billion galaxies, each containing hundreds of billions of stars.
If that weren’t mind-blowing enough, according to the big bang theory – our best stab at explaining how it all came to be – everything exploded into being from nowhere, about 13.8 billion years ago. An infinitesimal pinprick of unimaginable heat and density has slowly stretched and cooled into the cosmos we know today.
How can we get our heads around that? For cosmologist Martin Rees of the University of Cambridge there are two strategies: bury yourself in equations, or draw pictures. “I’d put myself in the picture camp,” he says.
He envisages the expanding universe by imagining himself at one node of a three-dimensional lattice stretching as far as the mind’s eye can see, with the nodes linked by rods, all of which are expanding. That way you can visualise the universe moving away from you in all directions – while recognising that you would see the same thing from any other node. “You understand there is no central position,” he says.
There’s also no discernible edge: periods of accelerated expansion during the universe’s earliest instants and in more recent aeons mean that the horizon of the observable universe is by no means the end of all things. Beyond it are galaxies we will never see because the intervening space is expanding too fast, so their light…
