I once told someone that the speed of light cannot be exceeded and the person looked at me with a puzzled look that says, “how can you be so sure?What if we find something that runs faster?” I tried to explain but he wouldn’t listen. 

Nothing can travel faster than the speed of light according to Albert Einstein. In fact, that speed cannot be reached. Why is this so?

Light is a short way of saying electromagnetic waves which consists of Radio waves, Infrared rays, visible light (which is the one we see and allows us to see), ultraviolet, x-rays and gamma rays. They all travel at a speed of 3 x 108 m/s. 

It is ridiculous to think that a human being can travel at that speed. So scientists got to work and they created particle accelerators which propels particles and causes them to run at a high speed before colliding with each other. An example is the Large Hadron Collider (which is the biggest machine in the world) in CERN. It was discovered that the speed at which the particles travel is directly proportional to the energy applied. It means that if you increase the energy applied the particles will travel faster. The particles travelled at a speed very close to the speed of light and this speed gets closer each time the energy increases. But it never reached the speed of light. 

Sooooo close, yet so far away.

This shows that it is quite impossible to reach the speed of light, not to talk of exceeding it. You might read somewhere that the universe expanded (immediately after the big bang) at a rate faster than the speed of light but we should remember that nothing was actually travelling. 

Why?

Albert Einstein was the one who thought us that there need to be the ether through which electromagnetic waves travel. Earlier scientists had believed that light travels in relative to something else just like we can say a train is moving at a speed relative to the Earth. They had believed that light travels through what they called ether. So different observers moving relative to ether will coming toward them at different speeds, but light’s speed relative to the ether would remain fixed. In particular, as the earth was moving through the ether on its orbit round the sun, the speed of light measured in the direction of the earth’s motion through the ether (when we were moving toward the source of the light) should be higher than the speed of light at right angles to that motion (when we are not moving toward the source). In 1887Albert Michelson (who later became the first American to receive the Nobel Prize for physics) and Edward Morley carried out a very careful experiment at the Case School of Applied Science in Cleveland. They compared the speed of light in the direction of the earth’s motion with that at right angles to the earth’s motion. To their great surprise, they found they were exactly the same!

It was Albert Einstein who told us that there need to be ether if we can believe that light travels through “empty space”. 
Einstein further ​told us from his E=mc2 that when an object travels very fast,it would experience an increase in mass. According to E=mc2, a more massive object will require more energy to move it more. So when an object reach the speed of light, its mass becomes infinite, therefore the energy to move it would be infinite. That shows us that nothing can reach the speed of light. 

The reason light travels at this speed is that it has no mass. 

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