How much do they compare? Is one much better?
The best one is whichever one of these single-digit-acceptance schools admits you.
Don’t overlook EECS at MIT. Its got all the applied physics people, so optics, solid state devices and semiconductor materials research. MIT offers a very large variety of physics labs, but Harvard has the really top theoretical people, in my opinion. MIT is a bit more applied but then there are particle physicists in both places. MIT let you find a research project for credit or pay, right away, in a physics UROP as early as first semester of freshman year. Harvard may do that as well, I don’t know.
The feel is different between the two schools, with MIT being overwhelmingly more techy, with a very crowded campus. Harvard has a wider variety of interesting students, and the better humanities libraries by far, and maybe a bit more of a BROADER approach to learning, you don’t major at Harvard you concentrate on a subject. MIT now has a full 20% first generation college students, and locks in at 9% international students. I don’t know those numbers for Harvard undergrads.
You can cross register between the two schools with some limits. I know physics people to be enrolled at Harvard with an MIT advisor for grad school too.
MIT also runs the MIT Lincoln Labs which is superb for summer work and UROPS too, out in Lexington, applied work, in optics, communications, and defense, on an air force base out there. Buses back and forth to MIT campus. They hire a lot of PhD physicists at Lincoln, and some undergrads do get out there.
https://www.ll.mit.edu
MIT Harvard Center for Magnetic Resonance is on the MIT campus:
http://web.mit.edu/fbml/mit_harvard_cmr/index.shtml
the MIT Harvard Center for ultra cold atoms is on both campuses
http://www.rle.mit.edu/cua_responsive/
You can walk between MIT’s student center and Harvard Yard in about 30 minutes or take the T.
The two physics departments, MIT and Harvard, do talk a lot at the graduate level. For undergrads, more separate.
At Harvard, it’s 17% first gen and 12% internationals.for the class of 2022
https://features.thecrimson.com/2018/freshman-survey/makeup-narrative/
The first gen number fluctuates slightly from year to year, but the 12% international has been consistent in recent years, although Harvard, unlike MIT, does not say there is a hard cap.
While true, it’s one of those things that sounds great in theory, but is a logistical challenge. The 2 are on different academic calendars, so breaks do not align, as but one example. Additionally, at least in the first couple of years, there will rarely be an example of why an undergraduate physics major, at least in the first couple of years, would need a class offered by the other college.
Either one will be fine. In fact the physics curriculum for a BS is pretty much the same at any university in the US.