A Ph.D. is a long, in depth research exploration of one topic. By long we’re typically talking about 6 years. By in depth we mean that at the end of the Ph.D. you will be the world expert or close to it in your particular area.
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In contrast, a Ph.D. program typically requires typically less than 10 courses during the entire 6
years (at CMU there are 5 required “core” courses, and 3 required “electives”). The emphasis in the
Ph.D. is not on classes, but rather on research.
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If you choose to be a professor at a research university, your life will consist of the following
tasks: (i) doing research on anything you like, (ii) working with graduate students, (iii) teaching
classes, (iv) applying for grants, (v) flying around to work with other researchers and to give talks
on your research, (vi) doing service for your department and school (like giving this talk). Note that
I say “your life” rather than your job, because for new faculty, your life becomes your job. It’s a
fantastic job/life for me because I love these activities, so I’m happy to work hard at all of them, but
it’s not right for everyone.