Knocking on Heaven's Door - Lisa Randall [98]
Early in the previous chapter, I summarized some of the objections that bloggers and skeptics made about the methods physicists used for black hole calculations, including relying on quantum mechanics. Hawking did indeed use quantum mechanics to derive black hole decay. Yet despite Feynman’s statement that “no one understands quantum mechanics,” physicists understand its implications, even if we don’t have a deep philosophical insight into why quantum mechanics is true. We believe quantum mechanics because it explains data and solves problems that are impenetrable with classical physics.
When physicists debate quantum mechanics, they don’t dispute its predictions. Its repeated success has forced generations of astonished students and researchers to accept the theory’s legitimacy. Debates today about quantum mechanics concern its philosophical underpinnings. Is there some other theory with more familiar classical premises that nonetheless predicts the bizarre hypotheses of quantum mechanics? Even if people make progress on such issues, it would make no difference to quantum mechanical predictions. Philosophical advances could affect the conceptual framework we use to describe predictions—but not the predictions themselves.
For the record, I find major advances on this front unlikely. Quantum mechanics is probably a fundamental theory. It is richer than classical mechanics. All classical predictions are a limiting case of quantum mechanics, but not vice versa. So it’s hard to believe that we will ultimately interpret quantum mechanics with classical Newtonian logic. Trying to interpret quantum mechanics in terms of classical underpinnings would be like me trying to write this book in Italian. Anything I can say in Italian I can say in English, but because of my limited Italian vocabulary the reverse is far from true.
Still, with or without agreement on philosophical import, all physicists agree on how to apply quantum mechanics. The wacky naysayers are just that. Quantum mechanical predictions are trustworthy and have been tested many times. Even without them, we still have alternative experimental evidence (in the form of the Earth and Sun and neutron stars and white dwarfs) that the LHC is safe.
LHC alarmists also objected to the purported use of string theory. Indeed, using quantum mechanics was just fine but relying on string theory would not have been. But the conclusions about black holes never needed string theory anyway. People do try to use string theory to understand the interior of black holes—the geometry of the apparent singularity at the center where according to general relativity energy becomes infinitely dense. And people have done string-theory-based calculations of black hole evaporation in nonphysical situations that support Hawking’s result. But the computation of black hole decay relies on quantum mechanics and not on a complete theory of quantum gravity. Even without string theory, Hawking could do his calculations. The very questions some bloggers posed reflected the absence of sufficient scientific understanding to weigh the facts.
A more generous interpretation of this objection is as resistance not to the science itself but to scientists with “faith-based” beliefs in their theories. After all, string theory is beyond the experimentally verifiable regime of energies. Yet many physicists think it’s right and continue to work on it. However, the variety of opinions about string theory—even within the scientific community—nicely illustrates just the opposite point. No one would base any safety assessment on string theory. Some physicists support string theory and some do not. Yet everyone knows it is not yet proven or fully fleshed out. Until everyone agreed on string theory’s validity