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The recent experimental result from the European Organisation for Nuclear Research (CERN) has given the notion that the speed of light (c), long considered to be the ultimate speed limit, is vulnerable to maintain its supremacy in cosmic affairs. This shocking result has had researchers baffled and generated immense interest and discussion among the public. It is too early to predict the doomsday scenario for the speed of light as some suggest. Even with all the attention it gets, there still remain a lot of ambiguous thoughts about this well-known constant of nature.

The speed of light is a constant:
In fact, this statement is incomplete. The speed of light is a constant as long as it remains in the same material medium. Whenever the light enters a denser or lighter medium, its speed and wavelength changes while its frequency stays the same. This explains why the speed of light is slow in water compared to air or vacuum. The amount of slowdown depends on the properties of the material medium known as the refractive index.

Nothing can travel faster than light:
This is exactly what makes the latest CERN result a popular headline. However, this statement is not as general as it seems. When one says that no particle can travel faster than the speed of light, what is implied is that a particle with finite rest mass cannot cross the speed of light limit; in other words, it cannot accelerate to a value faster than speed of light starting from a speed less than the speed of light. Because that process involves infinite amount of energy. But particles with no rest mass can travel at the speed of light.

Anything travelling faster than light goes backwards in time:
This is the notorious conclusion that keeps the speed of light always on tenterhooks. The special theory of relativity declares that there is time dilation when an object is in motion. Time must run slowly when an object speeds up and the time must remain frozen at the speed of light. Now, beyond the speed of light, the relativity equation calculates time as imaginary that is open to many different interpretations. It might point to the possibility of going backwards in time but not a definite conclusion. In order to avoid such paradoxes, Einstein suggested the cosmic speed limit must be equal to the speed of light. Remarkably, it’s his own theories that indicate the probable shortcuts that could be used to travel back in space and time though they still remain hypothetical.

Speed of light is really fast:
This is how the ancient Greeks described the nature of light. However, many attempts were made in the past to measure the speed of light. The speed of light is fast but not infinitely fast. The first successful measurement of c was made by the Danish astronomer Olaus Roemer in 1676. Currently, the value of c has been fixed at 299,792.458 km/s. The measurement with atomic clocks and laser interferometers support the precision of this number.

Is the speed of light slowing down?
As perplexing as these mysteries may seem, there is compelling evidences to believe in this speed limit of the universe. Numerous experiments have proved it and all our scientific understanding from atomic physics to astronomy is based on this concept. The speed of light is independent of the motion of the observer and it does not vary with time or space. However, there are many theories out there that question the unique nature of the speed of light. Some scientists even suggest that it is possible that the speed of light has slowed over billions of years or it might travel at a different rate at other parts of the universe.

It is reasonable to think that we may have to abandon the cosmic speed limit of light when strong and remarkable observations become more and more compelling. It may be painful to see the speed of light losing its ultimate speed tag. But that’s how science works, abandoning the old in the light of new observations and embracing the novel ideas that can thrust humanity to further limits unknown to us now.