I don't want to sound like this, but I suppose it is relevant. Over the past year or so, I have been getting more into concepts like gravity and such with no goal beyond it other than my understanding. There are technically millions shows to watch, my game queue is officially overwhelming to the point where I hid most of it ( and only kept currently installed items ), but I am spending my leisure time on, effectively, thinking.

I am saying this as I am realizing that when I watched $show, I was really looking for a feel of some sort. Those feels no longer drive me ( with exception of some really well told story or something genuinely novel ).

I guess what I am really saying is:

Thinking is already a hobby in US. To be able to spend your time on things that are not easy, pre-packaged goods, is a luxury that is hard to understand to anyone that hasn't tried it. It is like growing your own tomatoes -- you try it and you can tell the difference.

But it is a hobby and an oddly expensive one if you are going for primary sources.

OK, I'll bite. What are these primary sources? I've got hardback of Weinberg's Principals and Applications and of course MTW's Gravitation (a self demonstrating object), but I'd really recommend Caroll's Introduction for the coverage of cosmology.

Get into the notation and tensor formalism of raising and lowering operators, etc. It really helped make some of the results more clear to me, just as <bra/ket> helped with QM.

Or are you doing high end astronomy or building a back yard Wave detector? That would get truly expensive!