# Tag Archives: light

## Cherenkov Radiation (or the Photonic Boom)

I’m assuming many of you will know what a sonic boom is, if you travel fast enough through a medium sound waves will compress in front of you and produce a sonic boom. Of course, this only happens if you are traveling at greater than the speed of sound in a given medium. Cherenkov Radiation can be described as the light equivalent of the sonic boom. So here’s (a simplified version of) what happens. Nothing can travel at speeds greater than c, the speed of light in a vacuum, but light in a medium will travel slower than c and in that sense a particle could travel faster than light through that medium, and when a charged particle travels through a medium at a speed greater than light travels through that medium it excites nearby molecules, which in turn emit light. Doing this requires lots of energy, which is why it’s commonly seen in the cooling tanks of nuclear reactors.

Filed under Physics, Science

## Speeding and Blue Shift

Okay, so I’m assuming speeding on roadways is illegal in most countries, and that driving through a red light is also illegal. Okay? Okay. Let’s talk about blue shift. Blue shift is an application of the Doppler effect to light. Basically, if you travel in the direction opposite a wave, the apparent frequency of said wave increases, and the opposite is true if you travel in the same direction as the wave, the apparent frequency decreases. Since blue has a high frequency and red has a low frequency (as far as light goes) light is blue shifted when moving toward the light source. So now that that’s taken care of, how fast would you need to be going to see a red light at an intersecti0n as a green light. Using the speed of light, a frequency for red light (4.4*10^14 Hz), a frequency for green light (6*10^14 Hz), and Wolfram|Alpha, we get a speed of about 3/10 of the speed of light. That’s fast.