Right now we’re sitting in the middle of a storm. Not rain, though. There’s an invisible shower of subatomic particles pouring down on our bodies. Every second, dozens of cosmic rays zip through your body, millions per day. Most come from our sun, in the solar wind, but some were shot out ages ago from distant supernovas, maybe from even beyond our galaxy. Of course these particles are invisible, unless you’ve got one of these. Behold the COSMOTRON 5000!!! Actually this is a cloud chamber, a particle detector that’s going to show us these invisible cosmic rays. A cloud chamber is an amazingly simple particle detector. It’s just a sealed container with an alcohol-soaked cloth on top, a metal plate on the bottom, sitting on top of a tray of dry ice.
That creates a super-saturated alcohol vapor inside, so that any charged particles that come battering through will rip electrons off of that alcohol and clouds will spontaneously form. You’ll see these beautiful streaks wherever that cosmic radiation comes beaming through. Earth’s magnetic field protects us from most of these high energy particles, diverting them toward the poles where they cause auroras as they react with the upper atmosphere. But even with that force field in place, a few of them do make it down to us. A lot of the radiation that we’re detecting is secondary radiation, which happens when solar particles react with molecules high in the atmosphere like BAM and tear away subatomic particles like WOOSH.
And this is where it gets weird. Particles like muons are unstable, and they should only be able to travel down a few hundred meters from the upper atmosphere before decaying and disappearing. Yet here they are, down at the surface of the Earth. How? The answer is relativity. Because muons are traveling more than 98% the speed of light, they experience a phenomenon, predicted by Einstein, called time dilation. Let’s say there’s a kitchen timer strapped to the muon. Because it’s traveling so fast, to us, from our reference point here on Earth, the kitchen timer ticks more slowly. But to the muon time passes normally.
So from our point of view, the muons exist for much longer than they really should. Their lives are extended thanks to special relativity. That is cool. This ionizing radiation might have helped shape life on this planet. If one of those particles knocks an electron loose from an atom in our DNA, it can introduce a mutation. Our cells have evolved to repair that damage, so most of it’s harmless, but on the early Earth, this ionizing radiation may have produced the first mutations that allowed complex life to exist. Maybe at least. I built this cosmic ray detector for about $30. I put some links down in the description in case you’d like to try it yourself, and I hope you do. If you see anything cool, share your results with me. Who woulda thought, all you need to see invisible time traveling subatomic particles from another galaxy is some rubbing alcohol and a fish tank.