Basic Ideas

It is a well known fact that no object with mass can exceed the speed of light. An object’s mass tends closer and closer to infinity as its velocity approaches the speed of light. But what if you were told that there is a phenomena known as Cherenkov Radiation that occurs when an object travels faster than light. It’s shocking how that could be possible.

Let’s Move away from light for a second and discuss well known phenomena, the sonic boom. A sonic boom occurs when a physical object breaks the sound barrier which creates thunder-like shock waves. This phenomena is most famously known to occur on fighter jets. In a similar way, when a particle travels faster than light, it literally produces a light boom. This is Cherenkov radiation.

But, how does a particle travel faster than light? They don’t. Then How? We cheat. Instead of speeding a particle faster than light, we slow down light and pass a particle faster than that speed. Light slows down when it passes through a medium. In air, light slows down by a tiny amount, in water, by 25%, in glass, by 33%. In Diamond, light slows down by 60%. Now, consider a particle travelling beside a light beam at 99% the speed of light. When the particle and the light beam enter a medium, the light beam slows down significantly therefore the electron catches up with it.

Cherenkov Radiation

Cherenkov Radiation occurs when an electrically charged particle such as an electron travels faster than light in some medium. this electron produces a “shockwave” of light or a light boom.

An electron produces an electric field. in a medium, this electric field interacts with the other electric fields produced by electrons in the medium. electric fields interact by the exchange of photons. But, in a medium, these photons are slowed down. Therefore, as an electron travels through a medium it continously emits photons at all points, but the particle “gets ahead” of its own electric as its travelling faster. From this, we get a weird glow which tends to the violet or blue side of the spectrum. In the figure above, it can be observed that a cone is formed by drawing a line that connects the particle with the photons emmited at each point. The end or base of these cones are what is observed as cherenkov radiation.

This can be seen in the Japanese Super Kamiokande neutrino observatory. Billions of Netrinos pass though the Earth at all times. but in this detector which is filled with water, neutrinos interact with the medium and produce the cone of light, Cherenkov Radiation.

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