Math and physics will always be around, for sure, but always in low demand by employers. That's because companies want people who can design, build, and produce things, and math and physical science degrees aren't about that. So....
There are 5 times as many computer science jobs as math.
There are 10 times as many engineering jobs as physics.
There are more Art jobs than math and physics combined.
There are a LOT more jobs for english majors than physical science majors, but english might be the only liberal arts major like that.
Companies want people who can do the math (all of the top jobs involve that) but more than just doing math an physics.
You can't predict the future opportunities, because if you could predict the future, you would invent it now. There are two developments in technology that promise to revolutionize things in ways we can't even predict now: quantum computing and quantum transistors.
Now consider that when I took computer science many years ago, we wrote PASCAL compilers. My programming language class studied FORTRAN, ALGOL 60, PL/I, and LISP (no kidding). I can remember in the 1980's when what we know these days as object oriented computing was being invented and discussed in ACM Proceedings and IEEE Transactions on Programming Languages. None of Java, Unix, Linux, C or the web existed. NOTHING that we have today in modern web development or corporate IT existed back then.
Adapt or Die.
You will not be doing in your 60's what you know at 21. But you gain knowledge and tools that will allow you to adapt your knowledge to changing conditions, and that's what you go to a good university for. But keeping that knowledge up-to-date after you leave the university is up to you, and that depends on whether you will be out of a job in 20-40 years far more than your degree.