As a physicist I would, of course, answer: be a physics Ph.D.!

But that, of course, is nonsense. Mankind has probably acquired on the order of a million times more academic and practical knowledge than a single person can ever hope to absorb.

So not only do you have to make a decision what field you want to get into, you also have to chose a path to use that knowledge.

There is also the little distinction between encyclopedic knowledge and hands-on experience. Encyclopedic knowledge means that you know that something exists and you can probably make thirty seconds (ideally more) of educated smalltalk about that subject before running out of steam. Practical experience means that you can build a bridge (if you are a civil engineer), talk North Korea out of building nuclear weapons (if you are a diplomat) or perform brain surgery on people (if you are a brain surgeon). In the last three cases it matters very little if you also know the titles and locations of all paintings by Monet because you also have an arts major and specialized on Monet’s works. People with hands on knowledge can also teach other people on the subject. People with exclusively encyclopedic knowledge can usually do nothing of practical value even though they might be interesting at a party.

What I am trying to say is that you shouldn’t try to chose a universal subject for sake of a “well rounded education”. You should chose the subject you are MOST excited about, the thing that gets your blood flowing faster, your heart beating harder and your head steaming. You will soon enough find that even your most beloved academic topic will be hard enough to master and take up all your time and it will take all your emotional resources and then some to be successful in your field.

The Ph.D., by the way, will follow automatically if you are excited about academic knowledge. It is a waste of time, money and chances in life, if you aren’t.