# What exactly is implied by Einstein's insight in this scene from the NOVA series “$E=mc^2$ Einstein's Big Idea?” [closed]

In the documentary movie "$E=mc^2$ Einstein's Big Idea?", the narrator says "Einstein had a monumental insight", when Einstein and his close friend were looking at the clock towers in the city. Einstein seems to be so excited here and thanks to his friend to go home and work as I guess but I am very curious what is so exciting here but I can't get what exactly is triggered in Einstein's mind here which is implied by the narrator. Einstein says "I've completely solved the problem." What is the implication here? What is its relation to clocks at different distances? Is it possible for you to describe it to a person who is not a physicist but knows basic undergraduate physics?

## closed as not a real question by akhmeteli, Waffle's Crazy Peanut, Emilio Pisanty, Brandon Enright, David Z♦Jun 4 '13 at 18:16

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• Huh, did the narrator say something else too? If not it is very difficult to guess what he alluded at, at least for me. – Dilaton Jun 2 '13 at 21:18
• I wondered the relation of relativity to clocks at different distance. The narration is about this. – petrichor Jun 3 '13 at 1:22

I'd say it's all about time is flexible and not absolute as until then was thought, being the speed of light the one that remains the same. He would see that clock tower every day on his way to the patent office and suddenly realize (maybe as said in the movie) that if he were traveling at near the speed of light, the clock on the tower would slow down or eventually to stop at $c$ speed; meaning that time is relative to ones motion. Conclusion: the faster the travel, the more time slows for the traveler.
• Well, it's always more complicated than that, we just get to see the final picture, it's said he "used to go away for weeks in a state of confusion". At the time it was predicted by electromagnetic theory that measurements at $c$ would show the effects of motion and would not obey the so called principle of relativity. But Einstein was convinced of the principle of relativity and the only way he found to reconcile it (meaning invariance of $c$ assuming the laws of physics are the same in all inertial frames) [continues] – user24999 Jun 3 '13 at 4:25
• with electromagnetism was to introduce many counterintuitive implications as time dilation, contraction, mass-energy equivalence, spacetime and getting rid of the aether. Time dilation does not imply invariance of $c$, it's the other way around. Big steps in science doesn't come from thin air (Lorentz and Poincaré, for instance, had almost developed relativity at the time) but it sure takes a spark, and Einstein got it, maybe indeed provided by the clocktower; I wouldn't say he was just lucky. – user24999 Jun 3 '13 at 4:27