From astrophysicist Ethan Siegel at Forbes,
t’s one of the most brilliant, controversial and unproven ideas in all of physics: string theory. At the heart of string theory is the thread of an idea that’s run through physics for centuries, that at some fundamental level, all the different forces, particles, interactions and manifestations of reality are tied together as part of the same framework. Instead of four independent fundamental forces — strong, electromagnetic, weak and gravitational — there’s one unified theory that encompasses all of them.
Right now, there are only a few sets of dimensions that the string/superstring picture is self-consistent in, and the most promising one doesn’t give us the four-dimensional gravity of Einstein that describes our Universe. Instead, we find a 10-dimensional Brans-Dicke theory of gravity. In order to recover the gravity of our Universe, you must “get rid of” six dimensions and take the Brans-Dicke coupling parameter, ω, to infinity.
If you’ve heard of the term compactification in the context of string theory, that’s the hand-waving word to acknowledge that we must solve these puzzles.
No matter whether you tout string theory’s successes or failure, or how you feel about its lack of verifiable predictions, it will no doubt remain one of the most active areas of theoretical physics research. At its core, string theory stands out as the leading idea of a great many physicists’ dreams of an ultimate theory. More.
That’s so typical. It’s either a theory of everything or a theory of nothing. Such grandeur can easily do with many puzzles and little evidence. It’s not good news for current cosmology that string theory is the leading idea.
See also: Astrophysicist as advice columnist: Question, should I study string theory?
Fixing the unfixable Drake equation (Ethan Siegel)
Largest particle detector draws a blank on dark matter
Post-modern physics: String theory gets over the need for evidence