# Double Equivalence

Wow. So I’ve been wondering how far behind I might be in my lectures for the General Relativity class. I seemed to spend a bit more time than I remember teaching a recap of how to think about rotations, using it as an operational and mathematical brace upon which to build my review/revisit of Special Relativity. I was definitely convinced that I was a bit behind after two lectures on introducing how to study a little geometry using intrinsic quantities rather than by reference to embedding it inside another geometry (e.g., learning to think about a two-sphere in its own right instead of as the surface of a ball – this prepares you for thinking about a three-sphere, for which the ball would be hard to visualize, or draw), and so forth. All solidly useful material for the students (in this and so many other physics pursuits to come), so I do not regret spending time on it, but I did wonder about where I was in the journey…

Anyway, I got to the statement of the Equivalence Principle yesterday, the foundation of the whole of General Relativity. I was feeling quite pleased that we’re starting on this now, putting to use all the hard work we’ve been doing conceptually so far… and thought I’d do a quick post here on the blog to celebrate that we’ve got there. I thought I’d entitle the post “Equivalence”.

I started typing and then thought I’d see if I’d written anything about it here before. Well, guess what? I’d written a post entitled “Equivalence“, which starts out:

Well, Tuesday was a big day in class. We reached a landmark – the introduction of one of my very favourite thoughts of the 20th Century: the Equivalence Principle.

The four-year-ago me is almost in exact sync with the current me, almost to the day, and I’ve been teaching on a different schedule and (so far) from different notes … As a creature of habit, I’m not super-surprised, but it is still amusing…. It matches right down to the same urge to write a blog post about it…

So anyway, why don’t I just let you read the post, since I probably said all I wanted to say there anyway.

-cvj

Some Related Asymptotia Posts (not exhaustive):