Particles that Travel Faster than the Speed of Light
Once described as the fundamental universal speed limit, some particles in special scenarios can exceed the speed of c, resulting in rather peculiar phenomena.
Preceding the 1900's, time, space, mass, and energy were thought of as separate entities. While seemingly unrelated elements, it was the world's most famous scientist that fundamentally changed the way physics were thought of to this day. Einsteins last of his four famous papers submitted on September 27th, 1905 concluded that m = E/c2 which was then rearranged into the more iconic form of E = mc2. The famous equation is the fundamental driving force which led to many great revolutions in particle physics. Perhaps the most interesting of which today are the world-renowned particle accelerators.
The most famous of which is perhaps the Cern Large Hadron Collider (LHC) located in Geneva, Switzerland. The accelerator is a prime example of demonstrating the links between mass, energy, and the universe as we know it. The LHC is capable of accelerating particles upwards of 99.999999% the speed of light, or 299,792,455 m/s. The LHC accelerates particles to a velocity just 0.000199% faster than the next fastest accelerator, only accumulating just 600 m/s more. The LHC also requires nearly 16 times more energy to acquire merely a fraction of a greater speed. The accelerators are excellent demonstrators as to the exponential growth required to make particles go faster. To reach the speed of light, an infinite amount of energy must be deposited which is quite evidently impossible if an object has a quantifiable mass.
Bending the Rules
Since first described as the universal limit, physicists have since discovered special entities that can reach superluminal (faster than light) speeds which still abide by the universal rules set by special relativity.
While the speed of light cannot be exceeded from within a perfect vacuum, it is true that the speed of light is not the same from within other mediums. In water, the speed of light is 25% slower, giving a window of opportunity under special circumstances for some particles to exceed the limit.
The speed of light is reminiscent of the speed of sound in a multitude of ways. As the speed of sound is exceeded, an audible sonic boom can be quite easily heard. In much the same way, particles that exceed the speed of light produce a sort of "luminal boom" which can be directly observed with human eyes. The effect is called Cherenkov radiation and is evident as a blue glow within nuclear reactors, such as the image below.
Cherenkov Radiation within a nuclear reactor core [Image Source: Wikipedia]
Since light is slowed by 25%, in fission reactors the atomic explosion propel high-energy particles over the speed of light in water. Similar to a shock-wave, as the electrons within the reactor exceed the speed of light photons begin to accumulate behind in bunches, resulting in the emission of a luminescent boom generally as blue light, however it can also become ultraviolet.
Similarly, the Sudbury Neutrino Observatory located in Ontario, Canada, observes Cherenkov Radiation by recording the "luminal boom" released when Neutrinos (changeless particles with a minuscule mass) undergo reactions. As the Neutrinos pass through the heavy water chamber, they undergo reactions which expel electrons at speeds greater than the speed of light, thereby emitting Cherenkov Radiation that is then detected, confirming the presence of Neutrino.
[Image Source: Berkley Lab]
Cherenkov Radiation does not disprove the current understanding of particle physics and the theory of relativity. Rather, it opens the doors to the peculiar behavior of particles in the quantum realm, gradually unlocking the secrets of the universe.