Cherenkov Radiation: What If Something Travels Faster Than The Speed Of Light?

Have you ever noticed that when a supersonic military aircraft passes overhead
at a very high speed, it leaves a thunderous boom in its wake? That tremendous cracking sound actually has
a formal name – a SONIC BOOM. This intense phenomenon occurs when
an object – in this case, an aircraft – travels faster than the speed of sound in air. This might naturally lead to the question
does light also have a sonic boom equivalent? Does anything unusual happen when something
travels faster than light? In 1934, a Soviet physicist named Pavel Cherenkov
observed that a water bottle emitted blue light when bombarded with radiation. This blue-colored light was also emitted from
a number of transparent objects in the proximity of a radioactive source. This intrigued Cherenkov, and he conducted
a set of experiments to understand the origin of this strange phenomenon. Cherenkov irradiated various liquids with
gamma rays from a 104 mg radium source. His initial objective was to study fluorescence
emission induced in uranyl salts. In his early experiments, Cherenkov made naked-eye
observations, which was very difficult and required high levels of patience and experimental
skill. Through his experiments, Cherenkov noted that
light was emitted even when a vessel contained only sulfuric acid – the solvent for the uranyl
salt. He also demonstrated that such a light was
observed even when different solvents were used This led him to conclude that irrespective
of the solvent used. if a particle travelled faster than light
in a given solvent, light was emitted. This light came to be known as CHERENKOV RADIATION. The next logical question is, where does Cherenkov
radiation come from? You have likely heard that nothing can travel
faster than light. And that is entirely correct, but only when
the medium in question is a vacuum. So, while it’s true that nothing can travel
faster than light IN A VACUUM , in certain other mediums, such as water, a particle’s
velocity can be greater than the speed of light because light slows down significantly
when it travels through water. Therefore, when a particle – like a fast-moving
electron – travels at a speed higher than the speed of light, the Cherenkov effect occurs. As a result of this effect, Cherenkov radiation
is produced. Cherenkov radiation is analogous with the…. well known sonic boom effect we discussed
earlier. The former occurs in the case of light, while
the latter…. is observed when sound waves are involved. With that in mind, let’s take a quick look
at how and why a sonic boom occurs. If you were to visualize sound waves, they
would look like rings originating from a sound source, growing in size as they move away
from it. These rings actually represent the crest of
sound waves. When the source is stationary, the crests
emanate and grow bigger in a symmetrical pattern. However, when the sound source starts to move,
the crests that travel in the same direction as the sound source get squashed together,
causing each wave to reach the observer swifter than its predecessor. As a result, there is an increase in the frequency
of the sound. That’s why an ambulance or police siren sounds
different when it approaches you, as opposed to when it moves away from you. This change in the frequency of a moving wave
in relation to an observer is called the DOPPLER EFFECT. The sonic boom caused by supersonic aircraft
is actually a special case of the Doppler Effect As the aircraft breaks the sound barrier,
that is, exceeds the speed of sound in air, a sudden pressure change occurs, which causes
shock waves to travel away from the aircraft in a cone at the speed of sound. This rapid change in pressure waves sounds
like a thunderous crash – the “boom” that you hear when a supersonic jet passes overhead. It’s pretty similar in the case of light. Remember that light travels at different speeds in different mediums, depending on how photons interact with the atoms and molecules of the medium in question. For instance, light travels fastest through a vacuum like space, but when it travels through water, it moves at only 75% of its speed in a vacuum. In glass, light travels even slower, and while traveling through diamond, light travels the slowest among all these mediums. Therefore, in any of the mediums where light
travels slower than its speed in a vacuum, it’s possible for some faster-moving particles to move faster than light in that particular medium. This is exactly what happens in nuclear reactors. During nuclear fission, the nucleus of an
atom breaks open and releases charged particles – like fast-moving electrons – at extremely
high speeds. When these electrons pass through the water
surrounding the nuclear reactor, they interact with various water molecules along their path. This causes them to release a bunch of photons. Thus, when a ton of fast-moving electrons
interact with water molecules, they release a cascade of light, which collectively take
the form of a bluish glow called the Cherenkov radiation. Just as an object moving faster through the
air than the speed of sound produces a sonic boom Cherenkov radiation is produced when a particle moves faster than the speed of light IN THAT particular medium. So, the next time anyone claims that nothing
can travel faster than light, consider reminding them that’s only true when light travels through a vacuum. In other mediums, particles do exist that can travel faster than light

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