Cheerful thought for the day

Out there in the Milky Way galaxy there's a lot of stars. Occasionally one goes nova, rarely supernova, as they explode. There is a sphere of very active radiation leaving such stars. If one went off in our vicinity, up to twenty light years away, say, all higher forms on Earth would be sterilised, at least.

More worrying still are gamma-ray bursters. Gamma-rays are very short wavelength electromagnetic radiation, such as x-rays. When astronomers managed to develop instruments that could detect such radiation , and put them in satellites, they discovered that two or three times per day the Earth is illuminated by an intense burst of gamma-rays coming from somewhere out in space.

So far, all the gamma-ray bursters we've seen are a long, long distance away. But one could light up anywhere. If a pair of neutron stars collapsed on to each other within a hundred light years of Earth, life might survive in the deep seas and the deepest rocks, but the rest of our planet would be dead.

And we wouldn't even see it coming.

Asteroids and comets give you a bit of notice. We have the capability, given a year's run-up time, to tackle small Earth-crossing asteroids now. We can see them coming and plot their arrival. But gamma-rays are electromagnetic: they travel at the speed of light. They could be on their way now: we couldn't know. As soon as we did know, we and our technology would be dead.

Terry Pratchett, The Science Of Discworld, p258-9, abridged.

Although the title is "The Science Of Discworld", it's really the science of our world. And it's fascinating. ^_^