decay. Because they don't interact electromagnetically, that is, with light, they literally can't

be seen!

In fact, detecting a neutrino is kind of like trying to catch a bullet with a butterfly

net – a beam of neutrinos will travel through lead for two years before it stops. (in comparison,

radiation from nuclear fallout can be blocked by about ten cm of lead)

So how do you detect a neutrino? One common way is to fill a big tank with water: we know

light slows down through water, and if a neutrino with enough energy happens to knock into an

electron, the electron will zip through the water faster than the light does! When this

happens, the electron gives off a weak glow called Cherenkov Radiation - it's kind of

like a sonic boom for light, and it allows us to detect the neutrino. The biggest neutrino

detector in the world is a balloon over the south pole that actually uses the whole antarctic

ice sheet as its tank of water!

Neutrinos also tell us that the universe is not the same as its mirror image. If you switch

left with right, clockwise with counterclockwise, almost all of physics, like gravity, electromagnetism,

and the strong nuclear force, is unchanged. However, the weird thing about neutrinos is

that in physics terms, they're all left-handed - their mirror image doesn't exist! So neutrinos

are the vampires of physics.