Tuesday, January 6

How big IS the universe, anyway?

As a kid I was always fascinated by the question of whether there were other sentient beings in the universe.  On the one hand, at the time astronomers thought that planets were incredibly rare, so that suggested we didn't have any company.  But on the other hand, the universe is a really big place, which suggested the opposite conclusion.

All I want to do right now is give you just the glimmer of an idea of how big the universe is.  So let's start with just our galaxy--the Milky Way--which is just one of many in the universe.

A galaxy is a huge collection of stars.  Huge.  Ours has somewhere around two hundred Billion stars.  Light--the fastest thing we know of--takes just over 100,000 years to go from one edge to the other.

To get an idea of how big this is, if our galaxy spanned a football field, our Solar System would be about the size of a grain of sand.

And as noted above, our galaxy is just one of many--and it isn't particularly large as galaxies go:  The neighboring Andromeda galaxy is estimated to have a trillion stars--five times more stars than our Milky Way.

When humans realized that the fuzzy smudges they could see were actually galaxies much like our own but incredibly farther away than the stars in our own galaxy, it seems to have been a sobering perspective.  Back in the day astronomers could see a almost a hundred of these other galaxies.

But as technology improved--especially after we got good enough to launch big telescopes into space, so they wouldn't have to look through the distorting atmosphere--that estimate turned out to be low.  In fact, quite a bit low. 

It's now estimated that there are 170 Billion galaxies.

So next time you run into someone who thinks the universe revolves around them... Nah, it won't do any good to tell 'em any of this.  They wouldn't get it.  In fact, literally could not.  Cuz what matters to these people is what they feel about things, facts be damned.

Hopefully you won't meet very many people like that in your lifetime.  But if you should run into one, I hope you'll remember this little article.

Next time I'll explain a thing called the Fermi paradox:  If there are (as seems likely) tens of billions of habitable planets in our own galaxy, and if life developed on just one out of every hundred-million or so, why don't we see any evidence of those beings?


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