If fundamental physics were making big progress, I'd be all over it - that's what I wanted to do ever since I was a kid. But it's stagnant: the action is elsewhere, like using category theory to design radical new kinds of software. So these days I get some of my physics fix by studying the *history* of physics.
After studying the hell out of particle physics and general relativity, I went back and dug into the history of electromagnetism, which is really just as fascinating. Now I'm going back to medieval physics - because the idea that everyone was an idiot until Galileo is just plain wrong.
"Natural philosophers" in the 1200s and 1300s developed key concepts, utterly necessary for modern physics, but almost invisible now because we're so used to them - except for students, who find physics really hard because we don't bother to CLEARLY EXPLAIN those concepts: we act like children are born knowing them.
I'm talking about concepts like "the speed of an object at a moment of time". What the hell does that even mean? How can you figure out how fast something is going in one instant of time, when doesn't have time to go anywhere?
Well, that was clarified by calculus, and we credit it to Newton and Leibniz. But they had to have the idea already, in order to clarify it! And the idea of "instantaneous velocity" was developed around 1340 by the Oxford Calculators, a school of thinkers like Heytesbury and Swineshead - geniuses we never hear about.
Now I'm going back further. Did you know that back in 420 AD Martianus Capella had a theory where Mercury and Venus revolved around the Sun? And this was known to thinkers in Charlemagne's day... and also Copernicus! Wow!
@johncarlosbaez At least we have observations we can't explain. Back when I studied physics (mid 1990s) we didn't even have that, since people didn't yet believe the observations that now make us talk about "dark matter" and "dark energy". And I hope we'll one day make progress on this!
@bert_hubert - yes, if I were doing observational astrophysics and cosmology I'd be quite happy nowadays! I try to keep up with that work in a general way. But being a more mathematical sort, I'm mainly *frustrated* by the dark matter puzzle. (Dark energy might just a cosmological constant, though observations might eventually rule that out.)
@johncarlosbaez @bert_hubert regarding dark matter: besides mond, I remember hearing of works on an entirely different alternative explanation of its effects, refusing the Newtonian approximation of Einstein equations. Any thoughts on that? From an outsider, this sounds somewhat elegant
@D3Reo - this class of theories is called MOND or Modified Newtonian Dynamics.
The idea sounds elegant until you see how complicated the equations need to be to come close to 1) agreeing with the many confirmed predictions of general relativity while 2) still giving effects that look like dark matter. There have been many attempts to do this; they're all quite complicated, and I don't think any of them captures *all* the complicated things that we see dark matter do. E.g. there are some small galaxies that seem to have no dark matter, which might make sense if dark matter is a kind of stuff, but seems harder to explain if you're just changing the law of gravity: why would *some* galaxies not follow this modified law?
I'm not saying MOND is a dead duck, just that there are many versions of it, and none of them is a silver bullet.
Here's a great pop article by @startswithabang making the case *against* MOND. Then you should read some in favor of it.
@johncarlosbaez @bert_hubert @startswithabang i had in mind something like square-torsion gravity, of which I have far from a good understanding, but which I thought was different from MOND. Is that not the case? My understanding was that mond works after the Newtonian approximation, whereas theories such as square-torsion gravity are "instead of" the approximation, or with a different approximation altogether. But again, I'm out of my depth here, so any clarification is very much appreciated!