Читать книгу String Theory For Dummies - Andrew Zimmerman Jones - Страница 43

Einstein’s theory of general relativity, which explains gravity, does an excellent job of explaining the universe on the scale of the cosmos. Quantum physics does an excellent job of explaining the universe on the scale of an atom or smaller. In between those scales, good old-fashioned classical physics usually rules.

Unfortunately, some problems bring general relativity and quantum physics into conflict, resulting in mathematical infinities in the equations. (Infinity is essentially an abstract number that’s larger than any other numbers. Though certain cartoon characters like to go “To infinity and beyond,” scientists don’t like to see infinities come up in mathematical equations.) Infinities arise in quantum physics, but physicists have developed mathematical techniques to tame them in many cases so the results match the experiments. In some cases, however, these techniques don’t apply. Because physicists never observe real infinities in nature, these troublesome problems motivate the search for quantum gravity.

Each of the theories works fine on its own, but when you get into areas where both have something specific to say about the same thing — such as what’s going on at the border of a black hole — things get very complicated. The quantum fluctuations make the distinction between the inside and outside of the black hole kind of fuzzy, and general relativity needs that distinction to work properly. Neither theory by itself can fully explain what’s going on in these specific cases.

This is the heart of why physicists need a theory of quantum gravity. With the current theories, you get situations that don’t look like they make sense. Physicists don’t see infinities, but both relativity and quantum physics indicate that they should exist. Reconciling this bizarre region in the middle, where neither theory can fully describe what’s going on, is the goal of quantum gravity.