(writing continued from yesterday)
What they did and didn't say was interesting as well. They did a good presentation, accessible to non-physics geeks. They explained:
— how and why General Relativity came about (explains how gravity doesn't go faster than light);
— how Quantum Mechanics was able to relate EM and the strong and weak nuclear forces;
— how Einstein looked for and never found a way to relate Gravity to the other three forces;
— how String Theory was able to relate Gravity to the other three forces; and
— why String Theory is in trouble.
Next week, they talk about whether or not String Theory can be saved. Considering that the narrator of the show is one of the proponents of String Theory, I suspect his answer will be yes.
I wonder if there are significant issues with our understanding of gravity. It seems to me that "Dark matter" and "Dark energy" could be the Einsteinian epicycles. The reason that we postulated and look for Dark matter is because it's the only way for gravity to work the way that our observations of the universe show us. I wonder if the reason we need something as baroque as String Theory to relate gravity to the other three forces is because there are serious gaps in our knowledge of gravity.
Something else that I thought of after we left Conni's was that General Relativity was originally postulated so that gravity didn't violate the principle that nothing could go faster than the speed of light. Yet, Quantum Nonlocality has raised this problem again.