Rochelle

me, exasperated, mustard on my face, trying to explain adjunctions to a colleague: you see, if someone Forgets their lunch, it can be regarded, naturally, as Free

NEED some pals to do Bourbaki but for physics

in the case of degenerate vacua, which VeV does the path-integral compute?

oh god, what

Yes! But still, I think there are a lot of interesting things that can be said within AQFT. Like in analyzing the entanglement properties of the vacuum state:

www.sciencedirect.com/science/arti...

arxiv.org/abs/quant-ph...

No, I don't think so. I just need help to understand it. On top of the reasons here, there is the problem of infraparticles (that no experimental result can disambiguate between 'electron' and 'electron + 1 billion soft photons') and of confinement (so the quark fields don't occur asymptotically)

n QFT, an interaction changes the vacuum, the excitations, and so the nature/number of all the particles. I only know to probe this situation via an asymptotic free theory. However, composite particles are by definition not free (or, their constituents aren't.)

/done

It seems to me this is a unique problem in QFT. In QM, systems can occupy the very same quantum states before and after your turn on an interaction; their identities and amounts don't change. They remain who they are, but coupled.

Then there's the question of how to treat neutron states. Neutrons certainly exist! But not at infinity. Maybe we can write a new theory, T', in which neutrons are exactly stable, and be sure to apply this T' only on short timescales.

But what is F, especially when the theory has bound states? How to write down the bound states, their raising/lowering operators, in terms of the basic fields? It is strange, if composite particles are made out of their constituents, for these composites to be described with 1-particle states.

I don't know how to write down and recognize composite particles as states in a Hilbert space. The Haag-Ruelle PoV is you have an embedding of a Fock space F into your interacting space, H; you label any state by its eventual stable scattered components. This F should label the S-matrix elements.

Yes, I see now that it will have many different possible spins, etc. I'm not sure why your proton-electron example works better than positronium? Isn't a positron a spin-1/2 particle with the same charge? (I guess they won't annihilate!)

No, no, haha, it just seems that the answer is not very simple

i asked my professor today how QFT handles bound states, and the answer seems to be "very well, thank you"

well, I am exaggerating. there is also survivorship bias. (when i found good explanation, i was no longer confused.)

every time i have ever kicked myself for struggling with something or for being desperately confused, it has turned out that the subject was a wide-open research program or a hostly-contested philosophical debate

why do you suggest that GR is different in this regard? all of them can be read in the spacetime substantivalist stance. in fact, i should think GR is the worst one for this because completely empty spacetime propagates its own DoF!! (i.e has to 'be' something)

explaining to journalists that trans people have a thing called "being alive" which is as important to us as "have opinion in newspaper" is to them

its a great dress

holy shit heyy haha

how was your birthday??

🫡 more napping

Yeah, but I don't think I have symptoms of long covid. I have always been fatigued.

There are a few conversations from last week I am going to circle back to after tomorrow

(I have a deadline to make 😇)

trying to discern the games you're playing, in a normal way

photo elides slides

i keep drawing copies of the 'Stupid Idiot Loser' somehow??

tarot reading with mugs would be..
a challenge, i would think.

it definitely does portend evil, though, when you pick up your mug upside down

im sure your knowledge of calculus is paying dividends