we Know that nothing can travel Faster Than light in vacuum
In medium like Water light travel a Little Bit Slower Because
Light  interacts With Medium particle that decrease its speed. In medium another
Potential particle Like Electron Can Travel more Faster Than light
When Electron travel Faster Than Light Exhibits Cool blue Glow in Water.
This phenomenon is Known as Cherenkov  Radiation in the honour of Russian physicist Pavel Cherenkov. What is the reason of blue Glow?
to explain Let's do an Experiment if we Drop a pebble in Water
Circular Ripple Will Spread From The Entry point. If we Drop pebbles
Continuously At a Regular Time
Interval a Series of Concentric rings all
Moving Out with the same Speed Will be Formed but What happens if we Move our hand Along As we Drop a pebble.
We might Get Then a Series of rings That are no longer concentric but rather Crowded together in the direction of Our hand is moving.
The Amount of Crowding Depends on how fast our hand moves relative to how fast ripples move.
If we move our hand at The same Speed in the rings moves then All the rings Will touch in the point.
What happens if we Move source of ripples Faster Than ripples can spread?
 Watch This Bird
See the V-Shape wave spreading from the bird
It is swimming Faster Than The Speed of ripples It creates so
Individual Wave can Never Spread in front of It Instead This V-Shape Wave is formed.
Angle of V depends upon Bird's Speed.
This is an Example of shock wave and 2d. Now Let's consider a Three dimension case a
Rifle bullet or an aircraft travels not on a surface But Through a medium, the atmosphere.
Pressure waves That travel in three dimension through a medium are called Sound wave and Speed Which They travel is speed of Sound.
Now Just as with our swimming Bird if The Aircraft is traveling Faster Than The Speed of sound then the Wave cannot propagate
Ahead of object and Wave spreading in three dimension attaching with The aircraft create a cone.
This is called Sonic boom associated With Aircraft. Now Just as Aircraft
If an Electron travels
faster Than light There Will be a wave cone after that but Now this time This is a cone of Photon Because
Electron Traveling Faster than light Wave and our Eyes Will recognize these Photon As blue color light.
This blue Light also Known as Cherenkov light we Can see cherenkov light in  Nuclear Reactor Because of Nuclear Fission
in which electrons flung Out in a Very high speed Because of another particles fission.
