Since age 6, I’ve been completely decided: I want to go to school for Musical Theatre and then try my luck at Broadway. It’s been a stretch from the start, but I had absolutely no desire to do anything else…until this year. I took my first Physics AP class, and I’ve been in love since day one. I am surprisingly good at physics, something I’d never experienced with another science. My fascination with space and the bizarre mystery of the universe made me wonder if astrophysics is my new path. Musical Theatre is still my passion, but nothing has ever made me question my childhood dream before. Obviously, it is impossible to double major, so I know a decision has to be made. I’m not looking for someone to decide for me, but I need pros and cons. I need to rationally consider this. Thank you.
I think about it this way: Musical Theater is like the NBA - it’s a ‘star profession.’ Many will try, but only a very few people will make it to the top and do very well. The vast majority need to find ways to support themselves between roles and will never earn enough from Musical Theater to make it their sole career. Its not about ‘talent’ - that is the given. It’s also about having the right connections. Meanwhile, you can study physics, which leads to many possible careers all of which will enable you to earn a living - these jobs are not a ‘star professions.’ You don’t need connections to get into the field. And you will be able to stay engaged with musical theater as a hobby for the rest of your life.
If you really can’t live without Musical Theater, then go for it. I know 3 young adults in my neighborhood who are determined to make it in musical theater: one waits tables between gigs, another works as an entertainer on a cruise ship and the third is temping in NYC between roles. They are, to their credit, self-supporting, but, with the exception of the one on the cruise ship, not earning enough from musical theater to sustain themselves. So, if you think you could be happy doing anything, else, then you probably ought to go that route, where the opportunities are more plentiful and the chances of succeeding are higher.
If you love astrophysics just as much as musical theater then you should go for astrophysics. It pays better, and also you can keep going up in your career instead of down which happens in theater. The reason for this is a lot of times main roles for theater are young people. So as you grow older the majority of parts available to you will not be leads. Also astrophysics gives you a chance to make an actual difference in the world.
Reach for the stars 
You could major in science and do community theater as a hobby. I have several friends who have day jobs in fields they enjoy (social work, education, etc.), but who perform regularly in plays and musicals. They get to pursue a career they love and immerse themselves in a hobby that brings them a lot of pleasure too.
There are not a lot of jobs in astrophysics… but physics majors do have the possibility of getting other jobs that look for “smart people who can do math” (e.g. finance, computers), or some engineering-type jobs (that do not require engineering licensing or accreditation).
It is not completely unreasonable to consider the possibility of a double major, or major and minor, or major and electives in the other. These subjects as majors typically require about 35-40% of your undergraduate course work.
“Obviously, it is impossible to double major,” Have you researched that? Why couldn’t you?
The only caveat is that if you don’t like other sciences, chances are you would be forced to take other sciences with an astrophysics major, at least chemistry. The level of math would be quite high as well.
My thoughts on this:
- yes, it is easier to do musical theater as an EC and astrophysics as your major, as opposed to vice versa
- however, if you really want to do well, as in be able to live on your salary from acting/singing, you have to do musical theater as your major and get connections set up as indicated above
- if there is ANY chance that when you graduate with an astrophysics degree after four years, you would regret it, at least try musical theater
Not sure what year you are, but if you still have time, take a summer program in astrophysics or even a shorter program. I’ll assume you’ve already started musical theater and done it quite a bit through your school and local organizations.
There is another thread about celebrities going to Ivies, and they manage. But many do not go to college at 18.
I suggest that you avoid conservatory BFA programs, because they will be too restrictive. Look at liberal arts colleges where you don’t have to declare a major in advance of entering, and where you can dabble beforehand. American University has a good Musical Theater department. Tufts has always been strong in Theater, also. Carnegie Mellon probably has the most prestigious MT department in the country, but it is separate from other programs there, and so you might have trouble transferring between departments at the university.
I guess that is important to note - certain universities let you apply to only one college, and your classes in other colleges are restricted. Others are completely free, and you could even make up your own major between two colleges.
It is worth the research to see which colleges have both programs, then look into which would allow you to try classes in both areas.
I suggest you read the book, Making it on Broadway: Actor’s Tales of Climbing to the Top, published 2004. It contains interviews with many Broadway actors - some well-known, others perhaps not so much - as they answer all kinds of questions about what it means to be a broadway actor in today’s (2004, but still relevant) world - but just as important, what it’s like to try to make a living as an actor. I paraphrase one of the interviewees who said “making it in this career is like hiking uphill during an avalanche. It should be attempted only by those for whom there is NO other path.” If you can’t see yourself doing anything else, then go for it. If you can see yourself as a doctor, lawyer or Indian chief - do that. It would be easier.
I agree with much of what’s already been said above, but many people at Northwestern pursue a double major including the MT Certificate, which can enable you to deeply explore an academic subject while still getting strong theatre performance training. It might be worth investigating.
To the OP…you wrote that it is obvious that you cannot double major in MT and Astrophysics/Physics. This is true at many BFA in MT programs (though there are some where a double major or a major and minor are possible, such as at NYU/Tisch and UMichigan). However, in my opinion, the best route for you is to pursue BA programs. There are colleges where you could double major in MT and Physics or Theater and Physics, because you’d be a BA student and not have the limitations that a BFA program would entail. Thus, you leave your options open to major in either or both and like many your age, there is no need to decide just yet. Explore both in college and see how it goes. I encourage you to investigate the BA programs in MT that are out there where you would have the flexibility to double major or major/minor or change majors once in college, etc. A BFA path is more appropriate to those who feel 100% certain that they want to pursue MT. There is no need, however, to make such a commitment at your age. Thus a BA path would suit you well.
My friends son wrote a symphony his senior year in HS & captained his HS robotics team. He’s a double major in music/composition & engineering at Western Michigan University. It can be done… You just need to be creative. 
The director of my D’s program told kids if you can think of any other profession that you can have passion for other than theater, do that. Just because of how difficult a performing arts career can be. As I told my D when she was auditioning and waiting for acceptances after a couple reejctons: you will do theater your entire life, you just don’t know if you’ll do it for a living or for a hobby.
Go get an astrophysics degree and minor in theater, Work in astrophysics and do community theater and the like.
I sent you a PM because my daughter was an actor who after a year of successes suddenly said she was switching to Astrophysics and is now back in college taking classes.