Recently I had to teach a kids Sunday school on Genesis, and thought what a great idea it is to explain how time was created by exploring Theory of Relativity. Every since I was a kid, Theory of relativity was also shroud in mystery and fascinating. I watched a lot of online videos and explanations, but none can be satisfactory. I can't explain to my students what i don't know, so I thought, why not go from the very beginning and see how theory of relativity come to be?
This brought me back to year 1887, Michelson–Morley experiment. The initial goal of the experiment is to prove there are aether by observing inference patterns of a light source that splits into 2, one perpendicular to earth's rotation, and the other in parallel, and supposedly if there aether exists, light should slow down or speed up depend on if it goes against or in parallel to the aether wind. Note here this theory depend on the assumption that aether is stationary or partially dragged by earth (proposed by Augustin-Jean Fresnel in 1818, confirmed by Fizeau experiment in 1851).
The experience failed and that supposedly disapproves the aether, and severely challenged Hendrik Lorentz's theory that aether is at absolute rest. Then Oliver Heaviside derived the initial length compaction (on magnetic field) to be , and Lorentz (also FitzGerald) build on this idea and applied this to molecules. By doing this the idea of local time also appears, , where t is observer at rest in the aether and t' is one that is moving with regard to aether.
, where t is observer at rest in the aether and t' is one that is moving with regard to aether.
With the help of Poincaré, Larmor etc, it eventual became Lorentz transform:
with Lorentz factor
According the Lorentz transform, when object's speed v is much smaller than speed of light c, Lorentz factor is close to 1, and t',x' etc is very close to t', x'. Only at high speeds the difference shows. Also most likely from Lorentz factor, speed of light became the max speed in the universe, because once something reaches speed of light, the Lorentz factor is not calculable. This is also partially because people use light to synchronize clock, due to light is the only know carrier in the universe with the fastest speed.
And Einstein's theory of relativity is build on Lorentz transform, he took out of the need of aether but kept everything else, officially claimed speed of light is constant to all observers out of necessity of Lorentz transform and mathematical derivation only, with out any other proof, and implied that the speed of light is the max speed in the universe, also without proof. The claim is needed to satisfy Lorentz transform only.
From the above points, it seems Einstien's theory of relativity, on top of that Lorentz transform, is conjured based on a branch of assumption derived from Michelson–Morley experiment. The reader might ask, but don't we have evidence shows that clocks on fast moving rockets run slower? There are a much simpler explanations than Theory of Relativity. Atomic clocks work by atoms oscillating, and on accelerating objects, they are not oscillating horizontally, rather moving in a zigzag pattern due to the movement, and thus will be slower.
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