When I was 10 I wanted to be a theoretical physicist. At age 18 I went to Warwick University to study theoretical physics but was repelled by course content which seemed to replicate the worst of A-level experimental physics and I was then waylaid into the worlds of politics, philosophy and then maths, computer science, psychology and artificial intelligence.
Over the years I read the popularisations of quantum mechanics, relativity and cosmology, and even skimmed the textbooks. But particularly in theoretical physics, there is no substitute for actually studying the material and getting into the calculational details with colleagues.
I am therefore seriously considering signing up for most of the Open University’s third level physics courses. In 2008 this would mean doing Electromagnetism (SMT359) and Waves, Diffusion and Variational Principles (MS324). In 2009 I would do The Quantum World (SM358) and Space, Time and Cosmology (S357).
These constitute four out of the five third level physics courses, (counting MS324 as physics really). The remaining course is about stars and galaxies: interesting, but maybe for later.
Do I know this stuff already? Yes, at some conceptual level, like anyone who is educated in one area and who takes an informed interest in another. But at the level of being a practitioner, no.
Since physics, like maths, is highly incremental, thinking about the more advanced formulations of quantum mechanics and general relativity depend upon a substantial internalisation of mathematical tools, concepts and techniques at an advanced undergraduate level. So yes, this would be a lot of work, but precisely because of that, it would be worth it.