Brian Greene: The Speculative Sublime

Charles Dodgson warned a child correspondent of the dangers of living in the looking-glass world of mathematicians like himself, the high price of consistently believing “six impossible things before breakfast”: . . . Don’t be in such a hurry to believe next time—I’ll tell you why—If you set to work to believe everything you will tire out the muscles of the mind, and then you’ll be so weak you won’t be able to believe the simplest true things. Only last week a friend of mine set to work to believe Jack-the-giant-killer. He managed to do it, but he was so exhausted by it that when I told him it was raining (which was true) he couldn’t believe it, but rushed out into the street without his umbrella, the consequence of which was his hair got seriously damp, and one curl didn’t recover its right shape for nearly two days. . . . In all his books, Brian Greene is our tour guide on a journey into his particular looking-glass world—string theory, an exercise in the speculative sublime, a sublime only for aficionados, certainly not for you and me. Here is the abstract of an article cited a respectable 201 times: . . . We show that a string-inspired Planck scale modification of general relativity can have observable cosmological effects. Specifically, we present a complete analysis of the inflationary perturbation spectrum produced by a phenomenological Lagrangian that has a standard form on large scales but incorporates a string-inspired short distance cutoff, and find a deviation from the standard result. We use the de Sitter calculation as the basis of a qualitative analysis of other inflationary backgrounds, arguing that in these cases the cutoff could have a more pronounced effect, changing the shape of the spectrum. Moreover, the computational approach developed here can be used to provide unambiguous calculations of the perturbation spectrum in other heuristic models that modify trans-Planckian physics and thereby determine their impact on the inflationary perturbation spectrum. Finally, we argue that this model may provide an exception to constraints, recently proposed by Tanaka and Starobinsky, on the ability of Planck-scale physics to modify the cosmological spectrum. . . .