SPEED OF LIGHT - A UNIVERSAL CONSTANT

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Have you ever wondered what is the speed of light ?

Well this one of the most interesting questions in the world of Mathematics and Physics.

The speed of light in vaccum is a fundamental constant. The most interesting fact about this speed is that if an object moves with this speed in one frame, it has the same speed in any other frame.
This the key fact on which the special theory of relativity is based.

The speed of light is defined to be exactly 299,792,458 m/s.

SPEED OF LIGHT - A UNIVERSAL CONSTANT


  • Perhaps the first attempt to measure the speed of light was made by Galileo. Two experimenter A and B, each having a lantern and a shutter, stands on two small hills. 


The shutter can cover or uncover the lantern. Initially, both the lanterns are covered. One of the persons A uncovers his lantern. The second person B uncovers his lantern when he sees the light from the lantern of A. The first person A covers his lantern when he sees the light from the lantern of B. 
SPEED OF LIGHT - A UNIVERSAL CONSTANT
The time elapsed between the uncovering and covering of the first lantern is measured. During this time. the light travels from the first person to the second person and then back. Knowing the distance and time, the speed of light may be calculated.

This method failed because the speed of light is so large that a human being cannot respond with the required accuracy of timing. If the distance between the hills is as large as 15 km, the time taken by light in going back and forth is only one ten thousandth part of a second.

  • The first recorded speed of light in modern era came through the astronomical observations by the Danish astronomer Olaf Roemer in 1676. The value obtained was about 2.1 ✕108 ( smaller than the actual value ).
  • In 1728, English astronomer Bradley measured the speed of light from his observations. The value was close to the correct one.
  • The first measurement from purely terrestrial experiment was reported by the French physicist Fizeau in 1849. The method was improved by another French physicist Foucault. Yet another method was proposed by American physicist Michelson. 
We would describe each of the above methods in some other post very soon.

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