Constant Speed of Light
Einstein’s special relativity (SR) was built upon the assumption that speed of light ‘c’ is constant to all observers irrespective of their relative motion.
Despite no logical or experimental basis, Einstein had convinced the scientific crowd that this constancy of speed of light (SOL) is a law of nature and not just his assumption. I will explain later where and how Einstein had gone wrong and arrived at such a weird conclusion and how the mesmerised scientific crowd carried on with the same.
To get a gist of how weird is this assumption of ‘constant SOL’ – let’s take an example of a train moving at 100kmph towards east.
- A stationary observer standing on the platform measures the train’s velocity as 100kmph.
- An observer moving in the same direction as the train (i.e. east) at 50kmph will measure the train’s velocity as only 50kmph with respect to him.
- An observer moving at 50kmph towards west (in the opposite direction) will measure the velocity of train as 150kmph.
- An observer inside the train will measure the train’s velocity as zero i.e. with respect to him, the train is at rest.
This is what common sense tells us- different observers measure different velocities for the same moving body (whether it is a train or a ball) depending upon the state of motion of the observer.
But apparently, that is not the case with light photons. Relativity preaches that light always travels at the same speed ‘c’ irrespective of the state of motion of the observer. Imagine that we throw a beam of light towards the Moon. Imagine that the light beam travels at speed ‘c’ with respect to us standing on the Earth. Apparently the light beam travels at the same speed ‘c’ even with respect to an observer in a spaceship moving towards the Moon at 100,000m/sec. Also the light photons will apparently be seen to be travelling at the same speed ‘c’ by someone travelling at 100,000m/sec in the opposite direction i.e. from the Moon towards the Earth.
But why did Einstein come out with a such weird proposition? What made the scientific minds fall prey to his wild theory? Read the story in brief.
Time dilation/ Space contraction
To support the above ‘weird behavior’ of light, another weird thing was theorized (one had to, obviously!) i.e time dilatation. To keep the speed of light constant, Einstein made the time as relative.
Apparently different observers/clocks measure different times for the same ‘duration’ in the space, depending on their relative motion. Clocks apparently run slower or in other words time dilates as one moves faster, and hence the speed of light remains constant.
Also time apparently runs slower or time dilates near massive objects.
Another absurdity which came out of the general relativity is that there is no such thing as gravitational force or attraction. Heavy objects like stars apparently ‘curve’ or warp the space-time around them and this warping of space-time is responsible for the perceived gravitational effects.
Apparently planets do not go around the sun or the apples do not fall to the ground, instead all these travel in straight lines in the curved space-time. This curved space time gives us the illusion of planets going around the sun and apples falling to the earth.
(I doubt if we ‘really’ go to the office or to the market, it is probably the space-time that is curved around us which gives us the illusion that we move or do anything!)
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