Cosmic Certainties

Konstantin Kakaes reviewed "Fashion, Faith and Fantasy in the New Physics of the Universe" in the Wall Street Journal:

Physics has been at an awkward impasse for the past century. Two theories—quantum mechanics and general relativity—are widely believed to be true. Both have been tested to great experimental precision. Both, though counterintuitive to the layperson, are mathematically compelling to experts. But they contradict each other in basic ways—they cannot both be entirely true. In “Fashion, Faith and Fantasy in the New Physics of the Universe,” Roger Penrose, an elder statesman of physics, considers the problem. As intellectually offbeat as he is eminent—he is known for developing ideas for decades, such as his “twistor” model of space-time, regardless of their general acceptance—he ventures here some novel ways in which the two theories might be reconciled.

General relativity, which is at heart a theory of gravity, supposes that time can be precisely defined and measured, even if observers moving at different speeds, or in different gravitational fields, measure it differently. Quantum mechanics not only puts limits on how precisely one can measure time (and other basic things, like location) but also, bafflingly, requires that nature be fundamentally a matter of probabilities rather than certainties.