iPad Notebook export for Seven Brief Lessons on Physics
Saturday, December 10th, 2016Quotes from the book I particularly liked:
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In his youth Albert Einstein spent a year loafing aimlessly. You don’t get anywhere by not wasting time on something, unfortunately, that the parents of teenagers tend frequently to forget. He was in Pavia.
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The sun bends space around itself, and Earth does not turn around it because of a mysterious force but because it is racing directly in a space that inclines, like a marble that rolls in a funnel. There are no mysterious forces generated at the center of the funnel; it is the curved nature of the walls that causes the marble to roll. Planets circle around the sun, and things fall, because space curves.
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The difference between past and future exists only when there is heat. …
Boltzmann’s idea is subtle and brings into play the idea of
probability. Heat does not move from hot things to cold things due to an absolute law: it does so only with a large degree of probability. The reason for this is that it is statistically more probable that a quickly moving atom of the hot substance collides with a cold one and leaves it a little of its energy, rather than vice versa. Energy is conserved in the collisions but tends to get distributed in more or less equal parts when there are many collisions. In this way the temperature of objects in contact with each other tends to equalize. It is not impossible for a hot body to become hotter through contact with a colder one: it is just extremely improbable.
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