NARRATOR: The Hitch-Hiker’s Guide to the Galaxy is a truly remarkable book. The introduction starts like this: ‘Space,’ it says, ‘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 street to the chemist, but that’s just peanuts to space. Listen . . .’ And so on.
. . . After a while the style settles down a bit and it starts telling you things you actually need to know.
Douglas Adams, The Hitchhiker’s Guide to the
Galaxy: the original radio scripts, Pan Books, 2003.
This post was going to be another instalment of my thoughts on science on religion—about the religious implications of living in a rather big universe—but it’s turned into an unashamed attempt at expressing the sheer size of space. The approach used here is the only one so far that’s worked for me; I hope it might work for you too.
By the way it does not involve describing things as “the size of a football field”, “the thickness of a human hair”, “the length of a London bus”, or “the size of a blue whale”. So if your heart was already sinking in anticipation of those, please feel free to cheer up again. It does however involve an orange. I apologise for that.
Everything’s too big
Imagining big things is difficult. Beyond a certain size, the numbers all blur into “too big to imagine”. So the task I’ve set myself is rather ambitious. For example, astronomical distances are measured in light years—the distance a beam of light would travel in a year. Even the distance it travels in a second is uncomfortably big for the imagination: 186,000 miles, 23 times the diameter of the earth, or two thirds of the way to the moon. Alarmingly, a light year is over 30 million times as far as that. Our nearest neighbour star, Alpha Centauri, is about 4 light years away. These distances are not small.
I do know, though, what a mile looks and feels like. It’s a little less than the distance from here to the bank; I walk it in about 16 minutes. And I know that a train journey to London takes around 3 hours. People who fly regularly know how long it takes them to get to their destinations. This gives us some inkling, at least, of the size of the Earth: Its diameter is about the same as 8,000 walks to the bank, or 1½ flights to America.
Another way to get a sense of how big the Earth is is too go to the beach, stand at the water’s edge and look out at the horizon. Assuming you’re about six feet tall, the horizon is about two miles away. It’s effectively a six-foot-high bulge created by the Earth’s curvature. Now try to imagine what’s over the horizon. More sea, curving away downwards. Mentally double the distances: 4 miles, 8 miles, 32 miles. Feel the earth’s gravity holding you on the ground. Try to get a grasp of what an 8,000 mile sphere looks like.
My task is to somehow relate the distances of space to the everyday ones we have a grasp of. My tool is the Ordnance Survey map: the one you might use when out walking in the country, or the equivalent map if you live outside the UK. I’m going to use the old, inch-to-the-mile maps, printed at a scale of 1:63,360 (the number of inches in a mile). If you don’t remember them, well, the current 1:50,000 maps are the same idea, but blown up a little bit.
Make it smaller!
OK, here goes.
Step 1
Scale: 1:126,720,000 (1 inch to 2000 miles)
Shrink the Earth to the size of an orange. (Fruit is traditional and compulsory in these comparisons.) In other words, make a model of the Earth on a scale of 2000 miles to the inch. At this scale:
- the Earth is a squishy ball of not-very-solid rock, 4 inches across.
- alarmingly, the nice solid crust, on which we live, is less than a thousandth of an inch thick.
- The Sun is a very hot ball of fire, ¾ of a mile away and 36 feet across.
- Alpha Centauri is, I’m afraid, still 200,000 miles away: a bit less than the actual distance to the moon.
Well I can imagine an orange and I can imagine a ¾-of-a-mile walk, but if I’m honest, 200,000 miles still doesn’t mean much to me. Time for the OS map . . .
Step 2
Scale: 1:8,028,979,200,000 (1 inch to 126.72 million miles)
Let’s make a map of the scale model, at a scale of an inch to the mile—that is, shrink everything down again. The new situation is:
- the Earth is now about 1/16,000″ across, or 1/600 of a millimetre. You can see what a millimetre looks like by looking at an ordinary ruler or tape measure.
- the Sun is ¾ of an inch away, and 1/150″ across, or 1/6 of a millimetre.
- our friendly neighbourhood star, Alpha Centauri, is now 3.1 miles away—not quite in our neighbourhood, but walkable in under an hour.
- Our galaxy, The Milky Way, is about 70,000 miles across.
That is, an inch-to-the-mile map of an inch-to-2000-miles map of the Galaxy needs a sheet of paper 70,000 miles across, the Sun is just about big enough to be seen with the naked eye, and the Earth can only be seen with a microscope.
Step 3
Scale: 1:508,716,122,112,000,000 (1 inch to 1.36 light years)
Let’s make another map: an inch-to-the-mile map of our inch-to-the-mile map of our inch-to-2000-miles scale model of our bit of the universe. It turns out it still needs a pretty big sheet of paper, but at least it’s not an unimaginably big one. On this new map:
- the Earth is almost exactly 10-9 inches across, or 1/40 of a nanometre; ¼ ångstrøm. In other words, it’s smaller than a hydrogen atom, the smallest atom in nature.
- the Sun is 1/84,000 inches away, and 10-7 inches across.
- Alpha Centauri is just over 3 inches away.
- The Milky Way is just over a mile across. It contains about 1011 stars; you could imagine it as a mile-wide snowstorm, with the stars scattered like snowflakes (but considerably tinier).
- Our neighbour galaxy Andromeda, in the so-called Local Group (ha!), is 26 miles away.
However, we can’t stop there. What really brought home to me the appalling vastness of space was a map of approximately a million galaxies (just the ones brighter than a certain value) in a small section of the sky. It presented a lumpy grey appearance; the grey was simply the visual result of printing a dot for each galaxy. Not only were the Sun and Earth utterly tiny and insignificant among the 1011 stars of our galaxy; the Milky Way itself was insignificant among the many millions of galaxies in the observable universe.
Think what this means. To find the Earth, you first have to find the right galaxy–the correct dot on the lumpy grey map. That’s not exactly easy. Then, having scaled this tiny dot up so that it’s a mile across, you have to find something smaller than a hydrogen atom, too small to see even with an electron microscope. You scale this up to a decent size, and all of humanity is living on a thin layer less than 1/1000 of an inch thick . . .
The size of space is, in itself, still unimaginable; what I’ve done is to shrink some of it to an imaginable size, by what I hope are imaginable steps. If I’ve succeeded, maybe you now at least have a sense of how unimaginable it is.
I said above that this means we’re totally insignificant. Actually, that’s not the only way to see it. I’ll go into that in another post. But it seems clear that we can’t claim to be any more significant than any other populated planet in the unimaginably big universe. Claiming that it’s all centred on us seems so impossibly arrogant that it simply doesn’t make sense.
At this point a lot of people would look at the world’s religions, which make rather a lot of the importance of humanity to God, and say “Well that proves it. Religion is impossible.” What they really mean is that religion which puts human beings, or a particular tradition’s ideas, at the centre of the Universe is impossible. But that is only one kind of religion . . .
More on that in another post.
The Other Blog Without A Name 
Something is terribly wonderful about being insignificant: You realize that each “now” moment of your life is so precious.
This is beautiful! And I must say, it makes me think that we’re pretty darn special as a species if we (or even just some of us) can mentally grasp things so much more massively immense than ourselves!
I am looking forward to the next instalment, because although I am quite firmly anti-religious, I have always been fascinated by any spiritual notions that use science as a basis rather than treating it as a threat.
I came up with this quite a few years ago, when I’d been reading Cosmology by (I think) Contopoulos & Kotsakis and was trying to give myself an idea of the sizes. Unfortunately I’ve now no idea where it is, which is frustrating because I wanted to check the numbers and maybe go up to the next size scale.
I agree it’s pretty amazing that we can comprehend this stuff–it’s also amazing that we, part of the physical universe, can make sense of any of it, really. And given the sizes involved, it suggests to me that the ability to evolve conscious beings able to do it is in some way inherent in the laws of physics. (That’s not a new idea–it’s the conclusion reached by Ian Barbour, a biologist, in The God Experiment. He treats the whole thing, right back to the formation of hadrons then atoms, as a process of evolution.)
When you say anti-religious, do you mean you object to the idea of God, or to religions and their claims?
If you’ve not already seen it, there’s an earlier instalment in my Believing in God and in science post. For me the fundamental difficulty is consciousness: while science studies things objectively (or tries to), all our direct experience is subjective and therefore inaccessible to science. But the subjective experience is just as real (e.g. pain hurts!) . . . Anyway I’d better stop there or I’ll have written my next blog post as a comment!