11 July 2004

Notes on Brian Greene's The Fabric of the Cosmos

Here's the beginning of a collection of quotes I've gathered from Brian Greene's book.

Part I, Reality's Arena

Chapter 1, Roads to Reality

Page 13

It turns out that the known and accepted laws of physics show no such asymmetry: each direction in time, forward and backward, is treated by the laws without distinction. ... Nothing in the equations of fundamental physics shows any sign of treating one direction in time differently from the other, and that is totally at odds with everything we experience.


As we will see, special physical conditions at the universe's inception (a highly ordered environment at or just after the big bang) may have imprinted a direction on time, rather as winding up a clock, twisting its spring into a highly ordered initial state, allows it to tick forward. Thus, in a sense we'll make precise, the breaking--as opposed to the unbreaking--of an egg bears witness to conditions at the birth of the universe some 14 billion years ago.

Chapter 3, Relativity and the Absolute

Page 46

Einstein's theory of special relativity

In a hypothetical scenario, Bart, travelling at slightly-less-than light speed, chases a beam of light. His sister Lisa watches the event.

What does Lisa see? Well, for every hour that passes, Lisa sees the light travel 670 million miles while Bart travels only 500 million miles, so Lisa rightly concludes that the light is speeding away from Bart at 170 million miles per hour. ... But when Bart returns, he doesn't agree at all. Instead, he dejectedly claims that no matter what he did he saw light speed away at 670 million miles per hour, not a bit less.

Page 67

All this led Einstein to conclude that the force one feels from gravity and the force one feels from acceleration are the same. They are equivalent. Einstein called this the principle of equivalence.


With special relativity, Einstein proclaimed that absolute spacetime provides the benchmark, but special relativity does not take account of gravity. Then, through the equivalence principle, Einstein supplied a more robust benchmark that does include the effects of gravity. And this entailed a radical change in perspective. Since gravity and acceleration are equivalent, if you feel gravity's influence, you must be accelerating.

[ posted by sstrader on 11 July 2004 at 3:18:39 PM in Science & Technology ]