A Short Guide to Cherenhoof Radiation – Particles Moving Faster than Light · 12:15am Mar 2nd, 2014
As featured in Rock Farms and Nuclear Reactors and Rainbooms and Rationality
“So lemme get this straight,” said Rainbow Dash, “I thought the speed of light was some sort of fundamental constant – the ultimate speed limit which nothing can beat – right?”
“That's true in the vacuum of space,” replied Twilight Sparkle, “but when light moves through some transparent material, it slows down. A light ray shining through water, moves about 23% slower as it interacts with the water. And as the different colours move at slightly different speeds, it can split the white light up to make a rainbow of colours, as I explained in The Art of Rainbow Engineering.”
“So in water, it is possible to go faster than light?”
“In principle, yes, although it's only really possible for tiny, high energy particles. Anything bigger would need an enormous amount of energy, and would slow down very quickly in the water.”
“And that's what makes the cool blue light that comes out of Pinkie's nuclear reactor?”
“Exactly. As we saw in Rock Farms and Nuclear Reactors, the radioactive atoms inside the nuclear fuel rods decay, spitting out high energy electrons. They move through the water faster than light, and when they do, they emit light – Cherenkovhoof radiation."
“Like a sonic boom!”
“A bit... Light is a bit different, as it propagates in a different way to sound, you need a charged particle...”
“Yes,” interrupted Pinkie Pie, nodding vigorously, “it's like, exactly like a sonic boom!”
“Cherenhoof radiation is one way to detect high energy particles,” said Twilight. “We use it to study cosmic rays coming from outer space.”
“Yeah, that's how the Super-Kamiokande Observatory in Japan works,” said Pinkie. “It's just one great big underground water tank surrounded by light detectors to see the flash when particles zip through. And then there's the Pierre Auger Observatory in Argentina with 1600 water tanks spread over a vast area of pampas.”
“You don't always need a tank of water,” added Twilight. “In air, light travels at only 99.97% of it's speed in space. So a very high energy electron can exceed this, and when it moves through the atmosphere it will create a tiny flash. If you have a large array of mirrors to focus the light onto a camera, then on a dark night, you can see it.”
“As done by the HESS telescope in Namibia,” said Pinkie.
“So could this explain the sonic rainboom?” ask Rainbow.
“That's a fair hypothesis,” answered Twilight, “but as Scootaloo discovered in Rainbooms and Rationality, there are many reasons why that doesn't work. Not least, the fact that you can't fly anywhere near as fast as the speed of light in air.”
“Shucks,” replied Rainbow. "Where do cosmic rays come from anyway?"
"That's another story."
“By the way Twilight,” said Pinkie. “What have you done with your telescope? We haven't seen you using it for like forever.”
Dost I sense... a story in the works? Will we be able to learn some astrology alongside our new found knowledge of light and nuclear energy? I can't wait!
Good thing Diamond Tiara never heard of Cherenkov Radiation. Otherwise she'd probably insist the whole class be dressed in radiation suits before going out to see the Rainboom.
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This is why I need to be taught!
Mind is blown.
So very hard.
1886772 It shouldn't, the whole thing is built on misrepresentation. For starters, speed of light in a medium is a completely different thing from speed of light c. Photons always move at c, but if they hit something they are absorbed and later re-emitted producing an overall slower speed. Cherenkov radiation happens when an electric charge (on a charged particle) moves through a medium that can be electrically polarized.
And obviously, the speed at which particles bumping into each other cause regions of increased pressure to propagate (speed of sound) has nothing to do with how the propagation of disturbances in the electric and magnetic fields is slowed down by the disturbances being absorbed and re-emited by particles of the medium. So the Rainboom would only be similar to Cherenkov radiation if magic had polarity, air was magically polarizable, and Dash was breaking the speed of magic in the air, not sound.
I can hardly believe it, but I understood this. Thank you so much.
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Glad you liked it. And nice to know people still read these old posts.
3570268 I have read every post you've made since I first read Rock Farms and Nuclear Reactors. I absolutely love complex sciences.