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NOTES
Page 291: "Do the laws of physics permit highly advanced civilizations ..." Barrow, Impossibility, p. 143.
Page 294: "In 2056, I think you'll be able to buy a T-shirt..." Max
Tegmark, New Scientist Magazine, November 18, 2006, p. 37.
Page 296: Today the leading (and only) candidate for a theory... The
reason for this is that when we take Einstein's theory of gravity and add
quantum corrections, these corrections instead of being small are infinite.
Over the years physicists have devised a number of tricks to eliminate these
infinite terms, but they all fail for a quantum theory of gravity. But in string
theory these corrections vanish exactly for several reasons. First, string theory has a symmetry, called supersymmetry, which cancels many of these divergent terms. Also string theory has a cutoff, the length of string, which
helps to control these infinities.
The origin of these infinities actually goes back to classical theory. Newton's inverse-square law says that the force between two particles is infinite
if the distance of separation goes to zero. This infinity, which is apparent
even in Newton's theory, carries over to the quantum theory. But string theory has a cutoff, the length of the string, or the Planck length, which allows
us to control these divergences.
Page 299: "We would then be able to observe them in the sky.. ."Alexander Vilenkin, New Scientist Magazine, November 18, 2006, p. 51.
Page 300: Astrophysicist John Barrow summarizes this logic this way...
Barrow, Impossibility, p. 219.