Friday Science: Does time have an arrow?

It's time for another chapter in Brian Greene's, The Fabric of the Cosmos.

My first five summaries were:

a. Overview
b. Spinning Space Buckets
c. Relativity and the Absolute
d. Particles Separated at Birth
e. Does time flow?

1. My apologies to Dr. Greene, but I found this chapter very annoying. The basic flow of the chapter is clear enough: 1) All the king's horses and all the king's men can't put Humpty Dumpty together again because of entropy, 2) The math however would suggest that it is just as likely that Humpty Dumpty was splattered thirty minutes ago and did get back together again, 3) But, no, the universe doesn't work this way when you consider that the overall entropy of the universe has steadily decreased since the Big Bang.

It was somewhere in #2 that I stalled. I couldn't figure out where he was headed with it. I stopped reading for about a week. :-) My apologies.

2. "Entropy is a measure of the amount of disorder in a physical system" (154). It is the tendency of events toward a multiplicity of possible variations rather than toward a smaller number of variations. There are lots of possible combinations of splattered egg. There are not as many ways for an intact egg to hold together. Many possible variations is called high entropy. A lower number of variations is low entropy. "Physical systems tend to evolve toward states of higher entropy" (155).

3. He spends several pages in the middle of the chapter arguing that it is theoretically just as likely that a glass with ice in it was a glass with dissolved water in it thirty minutes ago. There are some graphs and I believe him. But we readers probably don't know enough to understand why, so the fact that he eventually comes back to reaffirm what we all believe--ice cubes don't form out of standing drinks on their own accord--was annoying to me.

4. In the end, he suggests that the factor of gravity in the early universe somehow implies that the crunched universe of the Big Bang was in a lower state of entropy than today. He argues that, in fact, the entropy of the universe has been steadily and continuously increasing since the very beginning, even if evolution and all sorts of other incidences of order have taken place.

So he's going to suggest why in future chapters. It's like a teaser. :-)