## Friday, December 09, 2005 ... //

### Lenny's book is out

Amazon.com will start to sell Lenny Susskind's book on Monday but you may be able to find it in your favorite bookstore right now. I've seen the first chapter and it is very poetic, slightly more mysterious than expected, but otherwise matching expectations. Peter Woit is looking at his book from his own, characteristically destructive viewpoint. We have discussed the review at TechCentralStation and George Ellis has another one in Nature.

#### snail feedback (1) :

Dear Lubos,

Susskind writes there: "It's Einstein's theory of gravity-the General Theory of Relativity- that explains how the universe expanded from the initial hot Big Bang to its present large size. The properties of gravity, especially its strength, could easily have been different. In fact it is an unexplained miracle that gravity is as weak as it is."

This is not good for reasons which are clear on my blog and webpage about the big bang. GR as used for cosmology assumes implicitely that gravity is not a pushing effect due to the reaction to surrounding expansion. If this is not assumed, you find that the expansion is not slowed down by gravity, without having to invent dark energy. Also, with the mechanism for gravity, you find that (for the same reason) the critical density calculated by GR is wrong by the factor of 0.5e^3. Also, the strength of gravity is no miracle but provable from the measured big bang characteristics.

Susskind is good where he writes: "The gravitational force between electrons and the atomic nucleus is ten thousand billion billion billion billion times weaker than the electrical attraction. Were the gravitational forces even a little stronger, the universe would have evolved so quickly that there would have been no time for intelligent life to arise. But gravity plays a very dramatic role in the unfolding of the universe. Its pull causes the material in the universe-hydrogen, helium, and the so-called dark matter-to clump, into galaxies, stars, and finally planets. However, for this to happen, the very early universe must have been a bit lumpy. If the original material of the universe had been smoothly distributed, it would have stayed that way for all time. In fact, fourteen billion years ago, the universe was just lumpy enough-a bit lumpier or a bit less lumpy, and there would have been no galaxies, stars, or planets for life to evolve on."

That is nicely written!

Best wishes,
Nigel