Cosmology is amazing. It allows us to dare to imagine a time when the entire observable universe was compressed into a region of space smaller than an atom. Imagine. The Milky Way, home to 400 billion stars, along with billions of other universes, all compressed into a sub-atomic patch. It feels mind-blowing, doesn’t it? Except it isn’t, really. And what this book is going to do is allow you to answer some of the big cosmic questions while lying down in your back garden after having a few drinks. How old is everything? How big is it? Science can tell you. All you have to do is stare into my amazing eyes and let yourself come on a journey.
Before the Big Bang, the universe was relatively cold and empty – a bit like your brain, I’m guessing – and those particles that did exist were moving apart from each other at a staggering rate. Two particles only one centimetre apart would be separated by 10 billion metres only 4 x 10-36 seconds later. It would probably help if you understood just how small a number 4 x 10-36 really is. Just try to think of the smallest thing you can think of and then imagine it much, much smaller. This period before Big Bang is known as the epoch of inflation. Don’t let’s worry about what happened before the epoch of inflation.
So then we’ve got this Big Bang and everything goes crazy and just 13.8 billion years later here we are with quarks, gluons, quasars, nebulae, black holes and me. That’s a bit of a head-fuck, isn’t it? (By the way, cosmologists define a year as the amount of time elapsed between one delusional scientist writing a book trying to make advanced astrophysics comprehensible to people who gave up on physics after GCSE and another trying to do the same thing.)
Let’s start with working out how old things are. For this, we need to do some maths because we can’t sit around and watch while the universe evolves from hot plasma, as we weren’t around then. Unless you’ve been out in our back garden for longer than I thought! That’s a joke, by the way. A bit of humour always helps in popular science. So let’s start with what we do know. I’m 48. I don’t look it, though, do I? And the oldest living tree is 5,066 years old.
Now look at a map of Africa and South America. You can instantly see if you use Google maps on your iPhone that the continents are moving apart at about 2.5cm per year. So that makes the Atlantic ocean about 180 million years old. We can be more precise about dating things using the half-life of radioactive atoms, known as the isochron method. Just think of a piece of rubidium-87 decaying into strontium-87 and the sun making 9.1 x 1037 helium nuclei per second. Bollocks. I can see your eyes glazing over. Do try to keep up. Anyway, to cut a long story short, the universe is about 13.8 billion years old.
Moving on. Let’s weigh the Earth. Suppose you’re a bloke called Mike and you’re looking at the Fairy buoy when you’re on holiday near Porthcawl. You know that the buoy is 4km from the beach so you get out a serviette and calculate the radius of the earth to be 5,000km, give or take 20%. Unfortunately, you’re not Mike, who is a maths professor, so you can’t follow in the footsteps of Copernicus, Kepler and Newton, so the rest of the chapter will mean next to nothing to you. Even my editor stopped reading at this point. Just trust me when I say the mass of the Earth is 5.97 x 1024 kg. If that means anything to you.
Stars are tiny specks of light in the darkness. But how far away are they? Let’s start by using the parallax to measure my own arm length. Anyway, I’ve noticed my finger moves by about 80 so my finger is 3.25tan (40) away. Unfortunately we can’t measure the distance to Neptune by winking, so we will have to work in parsecs, which are a parallax of 1 arcsecond. Which makes Proxima Centauri 3.26 light years away. There are 165 billion galaxies in the observable universe so there’s a lot more measuring for you to do.
Einstein was an amazing man. He understood that general relativity contains a set of equations, which can determine the shape of spacetime if we know the way that matter and energy are spread about. Here they are. Actually, let’s not bother. It’s a waste of your time and ours. Here’s what I suggest. During the least three chapters on gravity, Big Bang and weighing the universe, just look at some of the pictures and illustrations. The soundwaves in primordial plasma are particularly cool. They’re a good way of passing the time and something may seep in.
Lift your eyes from the anthropocentric and the cosmos awaits you in humbling, awe-inspiring glory. Imagine the journey from the first million-million-million-millionth of a second to the present inflation field where we all exist in10 dimensions of string theory. And if you can’t do that, then just think of me. I’m amazing.
Digested read, digested: Worlds apart.