On starry grains
30,000,000 x 50 x 5 = 7.5 billion cubic meters of sand.
A grain of sand is about 0.1 mm across, so there are 10,000 per meter or 10,000 x 10,000 x 10,000 (or 1,000 billion) per cubic meter.
So we are talking (oh so very very roughly) about 7500 billion billion grains of sand along our Australian coastline. Call it 10,000 billion billion grains.
So how long are all the coastlines on Earth? Australia is the smallest of seven continents, so they must be at least 10 times longer when taken alltogether. Let's say a 100 times to keep things moving along. If that's right, then we have about
10,000 billion billion x 100 = 1 million billion billion sand grains.
1024 grains of sand. We might be wrong by quite a few orders of magnitude here, but before getting too deeply involved in arguing about that, let's forget the sand and move on to the stars.
How many stars in the Universe? That one is much easier!
We live in a typical galaxy, the Milky Way, and we can count its stars with relative ease --- it's really just a matter of peering into space and counting--- there are about 100 billion. And the Universe is filled with galaxies; recently, the Hubble Space Telescope spent a week staring at a randomly choosen patch of the sky and took a photo of the brightest galaxies along a path between our own Galaxy and the edge of the visible Universe. From that one photo you'd reckon there are at least 100 billion galaxies in the entire Universe. Putting both numbers together, we'd expect there to be
about ten thousand billion billion stars in the Universe
about a million billion billion sand grains on the beaches of Earth...
Well! There might be more sand grains on Earth's beaches than stars in the Universe. But certainly, it's too close to call! We cannot possible have estimated either figure so well that we could be sure the stars really are more numerous than the sand grains or vice versa... maybe our coastline estiamte was too small, or the beaches too narrow (or not deep enough). And how many galaxies did we miss with the Hubble images; small faint ones are out there too, there are new ones reported every day...
Google currently lists 2,073,418,204 web
pages. Ten years ago there were none. At least we are in no immediate danger
of websites outnumbering the stars!
This essay was inspired by a conversation with Glen Mackie, who has presented his view in the article "To see the Universe in a Grain of Taranaki Sand"