原创 Thought-provoking trivia: Island universes

I was reading this month's issue of Discover magazine a few nights ago. At the back they had a piece titled "20 Things You Didn’t Know About Galaxies." The first point was that one of the first people to speculate that the Milky Way was not the only galaxy in the universe was the 18th century philosopher Immanuel Kant, who coined the term "Island Universe" to describe a galaxy.

Well, I for one thought that was pretty interesting. Previously, I'd thought no one had even considered the idea of galaxies until the 1920s when Edwin Hubble provided convincing evidence that the cloudy patches called nebulae in the night sky were located well beyond the Milky Way.

But that wasn't what grabbed my imagination. We've all heard size comparisons about different things, like "If protons and neutrons were the size of apples, then an electron would be the size of a..." Well, the author of the Discover article, Katherine Kornei, had something similar to this, but it was one I'd never heard before. This nugget of knowledge was as follows:

If the stars within galaxies were shrunk to the size of oranges, they would be separated by 4,800 kilometers (3,000 miles). If galaxies were shrunk to the size of apples, neighboring galaxies would only be a few meters apart.

I don’t know why, but this really made me think. I can't say exactly what it made me think, just that this little tidbit of trivia has lodged itself firmly in my noggin. How about you? Do you find this particular factoid to be of interest, or are you thinking "Everyone knows that" whilst trying to suppress a yawn?