Cosmic Rays and Neutralinos

Pliny and Nostradamus went to a lecture on Tuesday evening, on the subject of cosmic rays. They were astonished to see that the lecture theatre was almost full.

There were three empty seats in the third row between two men. Nostradamus took the middle one, and Pliny sat down next to a redfaced man in a sand coloured coat. The man was talking to two of his friends who were sitting in the row behind him. I felt terrible, he was saying, but I feel a lot better now. We picked the wrong two seats, thought Pliny.

The lecture was not too difficult to understand. There were oval maps of the universe on 2 big screens with the hot spots picked out in red, ringed with yellow. In Argentina, at the Pierre Auger Observatory, they observe rare cosmic rays containing ultra high energy particles of 10 million trillion electron volts. These are so rare they only hit the earth at a rate of about one per week per square kilometre. The red hot spots on the cosmic map were where these particles were coming from, somewhere beyond the Milky Way. Pliny wondered if they were dangerous.

Half way through the lecture the red faced man began to cough. I knew it, thought Pliny.

At question time, nobody asked if the ultra high energy particles were dangerous.

Everyone stood up to leave. The man in the sandcoloured jacket was asked by his friends how he liked it. I kept up, he answered jovially. Then he added, Did you know that every second millions of neutralinos are passing through our bodies, and we aren't aware of them? We're all full of holes, he laughed.

I know! thought Pliny.