Thomas Ray's Reviews > God's Equation: Einstein, Relativity, and the Expanding Universe

God's equation : Einstein, relativity, and the expanding universe
Amir D. Aczel, 1999
236 pp.
ISBN 1568581378
Library-of-Congress QB981 A35 1999
worldcat: https://www.worldcat.org/title/gods-e...
https://search.library.wisc.edu/catal...

If the universe was much smaller 10 billion years ago, why didn't photons emitted then from quasars reach the edge of the then-much-smaller universe long ago? How did they keep coming all this time, and reach us only now? This book has a partial answer:

We observe light that left its galaxy seven billion years ago. When the light left its source, the galaxy that emitted it was actually about five billion light years from us. When its light arrives here, that same galaxy is at a distance of about twelve billion light years from us. [The distance increased about 7 billion light years in 7 billion years: the distance has been increasing at about the speed of light. How, then, did the light arrive at all? The book doesn't say.] The redshift we see is due to the stretching of space during the 7 billion years the photons were in flight. p. 8.

The most distant object yet seen is a galaxy 13 billion light years away, receding at .956 the speed of light. p. xiii.

Galaxies whose light has travelled 7 billion years to reach us are receding at about .5c (c = speed of light) pp. 5-6. Closer galaxies are receding /faster/. This means the rate of expansion is accelerating. p. 7. But wait. p. xiii says a 13-billion-light-year-distant galaxy recedes at .956c . Moreover, this is the opposite of the Hubble observation that recession speed is proportional to distance: the evidence of an expanding universe. The book doesn't address the disconnect.

The universe has perhaps 20% of the mass density it would need to stop universal expansion. pp. xiii, 11.

The brightest type of supernova brightens for about 18 days, then fades over the following month. p. 6.

Einstein looked for a way to describe gravitation that would:
Make Newton's laws the same under acceleration as in a gravitational field. p. 32.
Redshift light in a gravitational field. p. 32.
Deflect light in a gravitational field. p. 34.

A circle spinning in its plane about its center experiences length-foreshortening of its circumference, by special relativity; its diameter is unchanged. Circumference < pi*diameter. Space is non-Euclidean. p. 59.

Einstein's equation describing gravitational curvature of spacetime: where:
g_mu,nu is Riemann metric tensor: distance in curved space
T is energy-momentum tensor
R is Ricci curved-spacetime tensor
G is Newton's gravitational constant:
R_mu,nu - 1/2 g_mu,nu*R = - 8 pi G T_mu,nu p. 117.

The book is mostly nontechnical biography of Einstein and some of his colleagues. The equations are inadequately explained.

The author had a Ph.D. in statistics. He wasn't a physicist. He claims to understand general relativity, but this book isn't really an attempt to explain it.

Author's wikipedia page: https://en.m.wikipedia.org/wiki/Amir_...

Proof that sqrt(2) is irrational:
If rational, then there are integers a, b, with no common factor, where a^2 = 2*b^2.
If a is odd, a^2 is odd: but 2*b^2 is even. So a can't be odd.
If a is even, then for some c, a = 2*c; 4*c^2 = 2*b^2; b^2 = 2*c^2. So b is even: a and b have the common factor 2. So there are /no/ a, b with no common factor whose ratio is sqrt(2).
Quod erat demonstrandum. p. 49.

Also answers trivial questions like this:
https://www.goodreads.com/trivia/work...

ERRATA
P. 144 gives (Newtonian) element of distance as
ds^2 = dr^2 - r^2 dTheta^2
Surely he means /plus/.

"On a sphere, there are no nonintersecting lines." p. 51. Sure there are: parallels of latitude, for example. Or small circles generally. There are no nonintersecting pairs of great circles.

Hermann Minkowski lived 1864-1909, not 1909-1964 as on p. 18.