If you want mind-expandingly interesting theoretical physics, give the Wolfram Physics Project[1] a look. It is a refreshingly different look at fundamental physics, and one that is perhaps more familiar to a computer scientist's perspective than, say, quantum mechanics.
I have done enough mathematics and have spoken to wolfram personally, it's interesting but not connected enough to existing theory despite his personal genius at QCD
[1]: https://www.wolframphysics.org/index.php.en