“Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s long way down the road to the chemist’s, but that’s just peanuts to space.”
Douglas Adams – “A Hitchhiker’s Guide to the Galaxy”.
2,000 years ago we thought that the Earth was the centre of everything. Then we came to realise that we were in orbit around the Sun, and started to get a feel for cosmic distances. Then we started to acknowledge that the Sun was just another star, and all the points of light in the night sky are other suns, possibly with their own planetary systems… therefore the universe must be really big. Then we learned that some of the smudges of light we can see in the night sky are really huge conglomerations of stars called galaxies, and that we probably live in such a galaxy, so we started to realise that the universe must be really, really big. Then we developed technologies that would allow us to examine the properties of the external galaxies, and we realised that the universe is not just really, really big, but it’s expanding, and so we postulated that the universe came from a ‘big bang’. Then we even detected the electro-magnetic ‘noise’ from the big bang.
The cosmos is infinitely interesting, but if you can get a feel for the shear staggering numbers involved… the distances, the number of stars, the masses, the relative velocities, you will go a long way towards understanding it.
If you ignore the Magellanic Clouds (which are gravitationally bound to our own galaxy, the Milky Way), our nearest neighbour is the Andromeda Galaxy.
A light year is a measure of large cosmic distances (actually some 5.9 trillion miles), and it turns out our nearest neighbour is some 2.5 million light years away! Given that nearly all stars are contained within galaxies, that’s an awful lot of emptiness.
And here’s an image called the Hubble Ultra-Deep Field (or HUDF). It was someone’s idea to get the Hubble Space Telescope (HST) to look at an otherwise uninteresting part of the sky, and point it there whenever the HST didn’t have pressing commitments elsewhere in the sky.
It’s a composite of some 800 shots taken between 2002 and 2012, and with a total exposure time of 1,200 seconds. It represents a very tiny area of sky (equivalent to a 1mm square held at arm’s length)… but it contains around 10,000 galaxies.
Regarding the size of the actual Universe, we keep revising the figures upwards whenever we get a new scientific revelation, and right now, some scientists estimate that the observable universe contains up to 2 trillion galaxies.
But that’s not the end of it. The observable universe is that part of the universe where light and other electromagnetic radiation has reached us. Current estimates are that it’s 93 billion light years in diameter. The entire universe on the other hand, may be infinite in size, but if finite, is calculated to be at least 250 times larger than the observable universe. Is your head hurting yet?
But these are just numbers… big numbers admittedly, but still numbers. To put it all into a human context, imagine if the Solar System (which is 5.5 billion miles across) was reduced to a disc 100 meters across, the Sun would be sitting in the middle (of course), and would be 1.5 cm in diameter; Jupiter and the gas giants would be around 1 mm, but the Earth would be about the size of this full stop.
So you’d have a black disk 100m across with nothing in it except a small white marble in the middle, 8 or 9 white dots and a bit of dust. Again, that’s a lot of emptiness.
Suppose we reduce the Solar system further, say to the size of a DVD… on this scale, how far do you think our nearest neighbour, the Andromeda Galaxy is from us?
When I ask people, I get answers like “Oh, ermm 100 meters?”, “Five miles?”.
The answer is just under a billion miles, or ten times further than the Sun. That’s what blows my mind.
I also can’t stop the recurring thought… “isn’t the universe a little over-engineered if we’re the only occupants?”
Rod Jones notes and jottings 