AT THE SPEED OF LIGHT

Light takes 3+ seconds to travel from the moon. It takes 8 minutes and 17 seconds to travel from the sun. The nearest star alpha centauri is 4.37 light years away. So light propagation is not instantaneous as we experience every day. It has finite speed 300000000 met/sec in vacuum.

When light travels in denser medium like water or glass, it slows down. In glass, it travels at 2*10 ^8 met/sec speed. The ratio of speed in vacuum to the speed in glass is 1.5 and it is the refractive index of the glass.

Discovery of speed: Ole roamer observed Jupiter through telescope. He was able to see the shadow of its moon 'Io" on the face of Jupiter as a blackspot. When the Jupiter was close to earth, the spot appeared at one place; when the Jupiter was far away from the earth, the shadow appeared at another place. From these observations, he was able to calculate the speed of light.

Einstein said: "The velocity of the light is independent of light source speed and observer's speed". A car speed is relative to the earth surface or another car speed. But the light speed is absolute, not relative and a constant. This principle is the 'corner stone' of theory of relativity.

Einstein also said: "The light speed is maximum attainable speed in nature". That is, nothing can travel faster than light. Some scientists say this barrier will be broken in future and we will be able to travel faster than light in space.

Light speed plays an important role in Einstein's topmost formula E= mc^2.

So what is speedier than speed of light? One can answer philosophically, it is the speed of thought.

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