abc.net.au By Dr Natasha Hurley-Walker 8/12/2018
"Space is big. Really big. You just won't believe how vastly, hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space."
Douglas Adams was right. And not only is space big, we don't know what it's made of.
Astronomers have worked out that only about 5 per cent of our universe consists of baryons — the particles which make up atoms, which in turn make up molecules, which in turn make up everything we see, touch, smell, and taste.
About 20 per cent is dark matter — a mysterious substance that interacts with our universe only through its gravitational pull — and the rest, a whopping 75 per cent, is dark energy, a cosmic field that permeates everything.
It might sound the stuff of science fiction, but it is the best explanation of the large-scale features of our universe.
Dark energies
Baryons and dark matter tend to clump together due to their gravitational pull, while dark energy pushes everything further apart. And that's causing our universe not only to expand, but to accelerate in that expansion.
We've estimated the rate of acceleration by using the Planck telescope to map the cosmic background radiation left over by the Big Bang. Final data, released by the Planck mission last month, reaffirm that dark matter and dark energy must exist, even if we don't know what they are.
In a few hundreds of billions of years, everything but our nearest neighbouring galaxies will have moved out of reach: no matter how fast future humans might travel, we'll never be able to reach anything else.
A recent study speculated that if an alien civilisation grew to the point where it needed whole galaxies as energy sources, it might have to leave its own galaxy and "mine" other galaxies for stars, reconfiguring the cosmos itself, before it all expands out of reach.
Farfetched? If you're advanced enough to worry about the stars going out, perhaps it's just contingency planning at its finest.
Aliens and dark energy aside, there sure is a lot of space — we know the universe is at least 30 billion light years across, and might even be infinite.
What is in this space?
Mostly, nothing.
But almost everything that is out there, is hydrogen.
Hydrogen: mostly hot air?
Hydrogen is the lightest element — it is simply a single electron and a single proton, orbiting each other.
Hydrogen can be found everywhere, from hot, dense stellar nurseries where new stars form, to the cold and tenuous voids between galaxies.
It's the most abundant element in the universe, making up 75 per cent of all its atoms.
"The two most common things in the universe are hydrogen and stupidity," said American writer Harlan Ellison.
More:
http://www.abc.net.au/news/science/2018-08-12/what-is-space-made-of-its-complicated/10078824
