Roger Penrose is a mathematical physicist at University of Oxford.
He made fundamental contributions to the study of mathematical general relativity, such as the Penrose-Hawking theorem and the discovery of the twistor space description of spacetime geometry.
Penrose has highlighted the subtle philosophical issue of the
apparent interrelation of mathematics, physics and the mind (Penrose 94, section 8.7, Penrose 05):
Here the composite arrow from mind over logic/mathematics to nature/physics resonates with the absolute idealism of the Science of Logic.
graphics grabbed from Penrose 05, Fig 1.3
graphics grabbed from Hut-Alford-Tegmark 06
Penrose (controversially) argued that quantum gravity effects on decoherence of quantum superposition causes physics to be non-computable and serves to explain aspects of the human mind such as consciousness, by causing wave function collapse in microtubuli inside neurons. This latter aspect he is more recently developing in more concrete detail in quantum biology (see there for more) with Stuart Hameroff.
In Penrose 03, section 10.3 it is pointed out that the Penrose-Hawking theorem immediately implies that in pure Einstein gravity (general relativity) small compact dimensions of spacetime, as assumed in Kaluza-Klein compactification, cannot be stable. From this the author draws the conclusion that moduli stabilization in KK-compactifications in general and in string phenomenology in particular can never work, a claim later repeated in Penrose 16.
However, all claims of moduli stabilization in the literature concern not pure gravity, but gravity coupled to a gauge field (Einstein-Maxwell theory) or higher gauge field (supergravity) with non-trivial field strength on the compact dimensions, whence called flux compactifications. It is the repulsive force of the gauge field in the compact fibers which counteracts the gravitational collapse.
This is not specific to string theory and can be seen in elementary terms (Freund-Rubin 80) and in simple toy examples such as in plain 6-dimensional Einstein-Maxwell theory (Salam et. al., 83).
Roger Penrose, Shadows of the mind, Oxford University Press, New York, 1994 (Wikipedia entry)
Roger Penrose, On the stability of extra space dimensions in Gibbons, Shellard, Rankin (eds.) The Future of Theoretical Physics and Cosmology, Cambridge (2003) (spire)
Roger Penrose, The Road to Reality: A Complete Guide to the Laws of the Universe, Knopf 2005
Roger Penrose, Fashion, Faith, and Fantasy in the New Physics of the Universe, Princeton University Press 2016 (PP:10664)
Last revised on May 16, 2019 at 12:07:03. See the history of this page for a list of all contributions to it.