Читать книгу String Theory For Dummies - Andrew Zimmerman Jones - Страница 62

A modern take on the study of string theory turns the tables and asks, what else could be a good theory of quantum gravity? In this approach, physicists don’t try to construct new theories. Instead, they try to list all the properties that any reasonable theory of quantum gravity should have.

For instance, a reasonable quantum gravity should contain the graviton, and it should look like ordinary (classical) gravity when the masses and distances involved have the right size. There are additional requirements that come from quantum physics and are a little more technical. They ensure that the various symmetries of the theory are realized and that all probabilities always add up to 100 percent. (This may sound silly, but it’s one of the most important concepts in quantum theory, called unitarity.)

The hope is that by considering all these constraints, we can pin down what quantum gravity should look like. This approach is sometimes called bootstrapping (as in “pulling yourself up by your own bootstraps”). It’s not clear if the various requirements that physicists have imposed can nail down a single theory of quantum gravity. However, these constraints actually rule out large families of theories, leaving relatively little space beyond string theory.

If this bootstrap approach can be completed, it might eventually show that any reasonable theory of quantum gravity is inevitably string theory. You’ll find more about this approach in Chapter 14, in the section “Bootstrapping Our Way into String Theory”.