I am a beginning phD student in theoretical physics trying to understand how the research process works. I have been wondering how top physicists/scientists actually do research. I would like to work on specific problems and original calculations. However, I find that I would also want to understand how other physicists think about problems/ what the core ideas in my field are by trying to read the original papers in the subject. I am struggling with this process. How to find the balance between reading important papers in my field (older papers with a large number of citations), recent papers, and working on my own calculations. How can I find a problem to work on? I wonder if experienced researchers can give advice on this.
This is only a partial answer to your question perhaps, but I’m two years into my PhD and this is a question I’ve asked myself for a long time. I guess part of the answer is to go get to work on specific problems, read what you need to solve those, and over time you’ll get a sense of what is relevant more generally in the context of your PhD. You’ll find that the amount of literature — both published in the past and published every day right now — is astronomical, so one of the caveats will be to really narrow down what you want to read. This is only possible once you really get a sense of what is relevant for your PhD ; over time you’ll realize some "general" stuff (e.g. reading generalist manuals for field X and/or theory A) will be essential to your success — while other "general" stuff still related to your field won’t be. For instance, I’m in astrophysics, and I can’t even imagine how much time reading everything about astrophysics (both published in the past and published right now) would take. You have to focus on your subspecialty, then go broader as you feel the broader stuff is still essential for your research.
Hope that helps a bit!
You will not earn a PhD in sciences for work done in a vacuum. Alternatively said, no one will care about your original calculations unless they contribute to the existing body of knowledge in a way that advances our scientific understanding or solves a problem. Alternatively said, how will you know that your calculations are original unless you know the body of calculations that have already been done and can acceptably demonstrate that you are truly filling the holes that exist in the already-existing calculations?
As paraphrased from somewhere ... "This PhD defense presents much new and interesting work. Unfortunately, what is new is not interesting, and what is interesting is not new".
In summary, directed to your title, you must not only read literature in your chosen field but also comprehend and put its results in fullest context before you can discover something "original" to do, let alone before you should define how to work on that original idea successfully to earn a PhD.
As to your broader question about how the research process "works", I would close with a synopsis paragraph.
The research process to earn a PhD is not linear or amenable to a consistent, directed road map going from point A (stepping in to it) to point B (ending it successfully). If it was as such, anyone might simply propose to buy a recipe book and get a PhD by completing the steps in its pages. The research process to earn a PhD can include starts, stops, dead ends, and breakthroughs. The process can include short or long bursts of studied literature review, construction or formulation of ideas, and experiments or analysis. The process can encompass ideas gleaned both from the most recent publications in the field as well as from those considered classics in the field. The various stages in PhD research (literature review, idea/hypothesis formulation, experiments or analysis, reporting) can be done sequentially, in purposeful isolation, or in parallel depending on the resources available, time commitments possible, or skills/training at hand. The sequence (review, formulate, experiment/analyze, report) and the path (sequential/parallel) can change at any moment in time, again depending on what currently might be limiting progress for the final work that is needed. Finally, the process can be intimately personal and unique. However it must not be done in a vacuum, especially not in one that purposefully excludes mentors, colleagues, and peers.