W.D.Clinger
Philosopher
Mathematics itself is not an empirical science.On my end, mathematics and computer science truly are subbranches of science and probably more difficult to achieve than theoretical astrophysics.
Both computer science and astrophysics encompass substantial empirical science. Astrophysics is considerably more empirical than computer science, I'd say, mainly because a large part of what people refer to as computer science has more in common with engineering than science. Indeed, many of those who think of themselves as computer scientists are paid to do work that has more in common with work done by technicians or engineers than with the kinds of work done by empirical or theoretical scientists. Many universities therefore position their department of computer science within a school of engineering rather than a school of science or arts and sciences.
As for difficulty: Advanced mathematics, theoretical computer science, and astrophysics (both theoretical and empirical) are all so difficult that few people understand all three subjects well enough to compare their difficulty.
Indeed, there aren't a whole lot of people who understand even a single one of those subjects well enough to appreciate its difficulty.
Which goes some distance toward explaining why the above opinions are relevant to this thread.