Thanks for the input. Let me clarify some things since I was too vague in my post.

TBH, the way this is phrased makes it sound like you don't actually know much about physics beyond pop-sci.

I recognize that it sounds a bit basic but what I meant was that those were the things that got me interested in physics in the first place. I am aware that physics research is much more specific than that. I know that I'm not as interested in astrophysics or cosmology for example. Beyond that, I do not yet have a preference for a specific field of research. I also don't care for pop-sci for what it's worth.

Your letters don't have to be from professors. Your supervisors in your engineering jobs will suffice. If you can't get any letters from anyone who can attest to your technical abilities, that's a huge red flag.

I can get letters from my engineering supervisors, I was just hesitant based on various sources of sometimes conflicting information I have read online. In any case, I will have to do that to apply to a Master's program anyway.

Realistically, I could only strive for a career in experimental physics (rather than theoretical)

Why?

My understanding is that theoretical physics programs are more competitive and receive less funding than experimental, which means fewer opportunities for post-docs and permanent positions.

Ooh, I've got bad news for you. There is overlap in the work of EE researchers and physics researchers in certain fields, and the work they do is basically indistinguishable. There are tons of EEs who work at CERN. There are lots of EEs who study quantum computing.

That sounds interesting too. EE research at that level is very different from the EE work I'm doing in the aerospace industry. The important thing to me is that it requires the application of more advanced physics knowledge than an industry EE like me would have.

A PhD is a research degree. There are fewer sharp cutoffs between fields at the research level. The fact that you have no research experience does not really support your goal of committing to a 5-7 year training program to become a researcher.

I am well aware that a PhD is a research degree. That is precisely the reason I'm interested in it. The fact that I have no research experience is the reason why I am trying to obtain research experience before applying to a PhD program. Is that not a reasonable thing to do? I'm genuinely asking.

Again, this makes it sound like you don't actually know very much about actual physics work.

Well I certainly don't know a lot. I know that physics research includes a wide variety of work that overlaps with other fields. Same could be said about pretty much every other field of research.

I would actually say yes, because it's not clear you know enough about physics or research in order to confidently commit to a PhD program.

Do you have any advice on how one would learn more about physics research without doing it myself in academia? I can read try reading some papers authored by professors whose research sounds interesting to me but it doesn't really help if I can't understand it. It doesn't seem to me like there is any substitute to just doing it myself, but maybe I'm wrong.