Science|Can You Make a Snowball of Neutrinos?
“Exactly how many neutrinos would you have to make a snowball? Can it feel cold and squishy in case you were struck in the face, or would it only pass ?”
— Hugo S., Montpellier, France
You’re getting hit in the face by neutrinos right now. Trillions of all neutrinos, the majority of them emitted by the sun, are streaming through your head as you read this. Every second, 100 billion neutrinos pass through each of your eyeballs.
You do not observe this constant bombardment since neutrinos barely interact with ordinary matter. Not only do they pass through your face they generally pass through Earth. In fact, if you’re an astronomer who would like to discover neutrinos, you put your sensors deep underground. Dirt and the rock block out other sources and cosmic rays of noise, allowing neutrino detectors to pick up ghostly neutrinos’ faint signs .
Neutrinos are extremely light, so you would require lots of these to make a snowball. For a long time, researchers thought that neutrinos, for example photons, didn’t weigh anything at all, but it turned out they’ve a mass. It’s still not clear how much (or little) that is, just, but it might take about 300,000,000,000,000,000,000,000,000,000,000,000 neutrinos to weigh up to a snowball. You may also write that in scientific notation as 3×10³⁵, but occasionally it is nice to write out all the digits as a reminder of just how mind-bogglingly big these numbers are.
If you attempted to pick up a snowball made from 300 decillion neutrinos (I had to look up the word for that number) it’d fall right through your hand. Slow-moving neutrinos pass through thing more easily than fast-moving ones, so just a few, if any, of these 300 decillion neutrinos would interact with your hand at all. They disappear in the ground and would drop right through your hands.
Because neutrinos so rarely interact with matter, all the ones that scientists have discovered have been high heeled specimens moving at almost the speed of light. But the universe is probably filled with ones , also. The Big Bang made plenty of neutrinos, and many should be drifting us around. Because these”relic neutrinos” are moving much slower than the speed of light, astronomers occasionally refer to them as”stationary,” even though they’re still traveling at a few million miles per hour.
In the event the snowball were coming in you as fast as the solar neutrinos inside had been moving, a lot of them would socialize with your entire body, most likely by bouncing off an electron at one of your atoms. You probably still would not feel the impact, but it would likely deliver enough energy to supply you with a dose of radiation.
Perhaps it’s for the best that there’s no easy method to produce a snowball made of neutrinos. You will have to stick to snow unless you’ve got a particle accelerator lying around your yard.