Heya, I would echo everything @Theworriedbanana said in this thread--very wise words
I study physics myself so I can provide you a little insight into "a day in the life of"--though I'll also
link to an interview of someone who is an academic astrophysics researcher. So to give you a bit of a breakdown in what you answered you like about physics--if by Doctor Who, you mean all the fantastic and exciting ideas like time travel, space-timey nonsense, you're looking at representations of theoretical physics. Now, studying theoretical physics is a lot different than appreciating it from afar--a lot of popular science is theoretical physics because quantum mechanics and special relatively really captures the imagination! However, in reality--if you do a whole degree of it--be prepared to do a LOT. of maths. Difficult maths. I don't say that to deter, but to give you a sense of what it's really like. Regardless of what kind of physics you do, you'll be taking modules of theoretical physics--which will be a lot less intensive than an entire degree's worth. If you do theoretical physics as a straight degree though, be prepared for lots of maths. If you like using mechanics--you might be more interested in applying your knowledge, and so it might be worth going for an engineering or robotics degree, if the robots in Doctor Who really struck your fancy!
Regardless of which physics degree you take (theoretical or not, applied or not), you have a
LOT of pathways open to you because you will be gaining a lot of transferable skills in your degree: coding (this is a must) and the ability to do a lot of higher-level maths will be your two most honed and used skills in your degree. If you choose to be a researcher, you really should dive head-first into academia ASAP, because it's a tough field that isn't for everyone. Do summer placements--especially if you choose a straight theoretical physics degree, because the academic world of theoretical physics is ruthlessly competitive right now (there is more supply than demand). Search out astrophysicists, physicists in general on Twitter to see what they're talking about, the struggles and joys in academia (there's a big community on there and it's an excellent way to network! Just be sure you have a professional profile). You can still study physics and then go into robotics and engineering--I have seen many people do this--however, if you do this taking summer placements is
not optional. There will be too many straight-engineers with specializations already competing for the same places to not do a summer placement.
As for choosing which of those things are right for you--Twitter, like I said, is an excellent resource. Another thing you could do: search for summer placements now, and read the job descriptions--does that sound like something fun that you want to be doing in the summer? As a career? Look up courses
for engineering,
for robotics,
for physics from any University and then check out the module overview--do the modules really excite you?
Law I can't speak as much about--only to say that, as far as I know, there is a lot of memorization, a lot of rhetoric, and an enormous amount of reading involved. But the things you pointed out that you love about law, can also potentially be combined with physics if that's something you want to pursue. You could become a physics teacher (loads of bursary money involved in this), helping out students. You could become a policy maker for space-technology, or a space lawyer (yes, this exists!). The latter two are likely to be super competitive and rare, but are an illustration that you can take your physics degree loads of places--it's just about being imaginative enough to carve out that career on your own intiative, and grabbing enough experience to enable you to do this.
Good luck, apologies for how long this is, and if you have any more questions please let me know!