Joseph Schwartz & Michael Mcguinness
A quick primer on Einstein’s life and ideas, and what all that Relativity stuff really means.
The book glosses over the environment of Einstein’s formative years, the ideas that influenced him, and finally his ideas, all in a delightful cartoon (which reminded me of _why).
A few key ideas:
The principle of relativity, according to Galileo: All steady motion is relative, and cannot be detected without reference to an outside point.
According to Einstein, no matter how light propagates when you are standing still, it propagates the same way when moving 97. This becomes a big deal in the Theory of Relativity. Second, light always propagates at velocity C, independent of the source it propagated from. So the maximum possible speed of any physical interaction in the world is C, the speed of light.
But if I’m traveling the speed of light, and you are watching me, how do we both see light moving at the same speed? C is always the same, but the length and time traveled by the light looks different depending on the point at which it is observed 107. Speed (of light) = distance divided by time.
So here it starts to get confusing. Just because two things happen simultaneously from one point of view, doesn’t mean they do from another. If in the middle of a train car a device uses two pointed beams of light to open the front and rear doors, inside the car the two doors open simultaneously. But from a point on the hill overlooking the tracks with the car on them, the back door will open first, but only milliseconds before, because the train is moving forward – the back door is moving toward the beam of light headed toward it, and the front door away.
Page 136 the formula is lain out to prove the above idea, and of course, it works. The idea that length and time are relative, but the speed of light constant, can then be applied to the equations of force: F(orce) = m(ass) * a(cceleration), and work: W(ork) = F(orce) * d(istance). Which eventually lead to the equation E(nergy) = m(ass)c(speed of light)^2, which shows that mass is a form of energy.