The Universe in a
Grain of Sand

10 August 2012

Suppose you picked up a grain of sand and held it at arm’s length. If you held it up in the night sky, it would block a tiny fraction of the visible heavens. Now suppose instead of of a sand grain it were a tiny window, through which you could see even the faintest light. Finally, suppose you were to take your tiny window and point it at the darkest patch of night you could find. What would you see?

Of course we have such a “window,” called the Hubble telescope, and we did just what I’ve described. We aimed it at one of the darkest patches of sky we could find, in the Fornax constellation. After gathering light for a total of about 55 hours, what we got was the image below.

The Hubble Ultra Deep Field. Hubble
The Hubble Ultra Deep Field.

Think on that for a bit. This image is what we got when we pointed the Hubble telescope at what looked like empty space. Instead of empty space, we found about 10,000 galaxies. These are young galaxies, from about 400 to 800 million years after the big bang. Ten thousand galaxies in a patch of sky the size of a grain of sand.

Of course there isn’t anything particularly special about the direction we looked other than the fact that there wasn’t anything in the way. If we looked in any other direction we would see basically the same thing. Imagine the sky covered with grains of sand, and in each sand grain thousands of galaxies.

It’s estimated that there are 100 billion galaxies in the visible universe. That’s more than 10 galaxies for every man, woman and child on Earth. Those galaxies might have an average of about 100 billion stars. Around most of those stars might be tens of planets. Countless cosmic grains of sand.

And on one of those cosmic sand grains are humans, looking out at the night sky and realizing the universe is much bigger than they once imagined.