So I just saw the YouTube video someone posted that showed nuclear reactors starting up, and the first thing I noticed was that they all glowed a very bright, pretty blue. I’m probably an idiot, but I was honestly expecting green, because of many years of dramatized depictions in popular media.
These are probably dumb questions, but:
- Why is it blue? As in, what’s actually glowing in there, and why do we see it that way?
and
- Why do all the movies and comic books and video games go with green instead? Where did that come from?
The blue hue is called Cherenkov radiation. It happens when a particle moves through a medium early fast, leading to light being released. It’s like a sonic boom but for light.
As for the green glow, maybe it’s due to uranium glass glowing green unused UV light.
Really fast
Well that’s the understatement of the week 🙂
When a photon (a light particle) enters a medium, it’s speed drops somewhat. Lightspeed-the-universal-constant, however, is unchanged; so at that point it becomes possible for another particle in that medium to go faster than light.
When that happens, you get Cherenkov radiation.
“Really fast” indeed 😁 (i assume you know this, but I found it worthwhile to add a little clarification that it’s not formula-1-really-fast)
Not really “faster than light”, but faster than light in that medium. The phrase “faster than light” normally refers to moving faster than c, which particles with rest mass can’t really do according to our current models.
Which particles can’t really do according to our current models.
Particles without rest mass can only move at c, not faster than c.
(Sorry for the nitpick)
There’s a bit of miscommunication here.
Nothing travels faster than c, or the speed of light within a vacuum.
The speed of light within a medium (like water) is not c. It is less.
When a particle is traveling at c and slams into a medium like water with enough force it will continue traveling faster than light normally would in that medium, and give off that radiation as it does.
But it is not traveling faster than light as you emphasized. It is traveling at nearly c and getting slowed down. It is often referred to a “light based sonic boom” though because that makes sense. But only when you consider the transition from vacuum to a medium or medium to medium.
Protip: anytime someone points out a thing is traveling faster than light they’re wrong because really: nothing does ever. It isn’t physically possible and the smartest minds on the planet have tried to reason how it might be for nearly a century now, with no progress at all. There are workarounds but they don’t involve “travel” in the real sense, more like displacement.
They used to have radioactive decoder rings and other toys that glowed green in the dark. They also used to paint all sorts of things with radioactive paint to glow in the dark like instrument panels.
