I have a interdisciplinary PhD (media arts and technology). Personally, I think any PhD could pull from multiple disciplines and, really, most dissertations must to some extent. If you are doing something new in your field, you need to at least check what is relevant in other fields.

It’s good to know interdisciplinary programs are an option, and I wish I knew sooner, but I’d recommend joining one only if there’s a good reason. In other words, I’d suggest looking into a more typical program by default. The reason is that you will have to work with established disciplines at some point. For teaching positions, you will probably need to demonstrate both that you can do innovative research (thus the requirement of a dissertation) and that you can teach more broadly. And just generally, academics are actually pretty conservative as a whole, so you’ll have to fit your research into their view. Having a PhD in an established discipline just makes it easier to do that.

But the programs are still useful. For me, it would have been pretty difficult to get into a music or art program based on my past studies and work. I wouldn’t necessarily plan on doing that from the start though, because I could have studied music and engineering (for example) from my undergraduate degree onward.

Getting a PhD is not really about learning a lot in a particular field—it’s about contributing or demonstrating the ability to contribute to the research of that field. The process of getting a PhD involves or requires a lot of knowledge in some academic discipline, so it’s great if you are interested in learning about that area, but what you’ve researched—your dissertation (or equivalent)—is really what your PhD is.

As a PhD, I personally wouldn’t necessarily look down on someone with multiple PhDs, but I’d wonder why they chose to do that. Wanting knowledge from multiple areas is not a good reason because (1) you can learn things without getting a degree, (2) you could use multiple areas of knowledge to get a single PhD, and (3) you could do further research in an academic position, like postdoc or professor. Sadly, the third reason is easier said than done, but is not any easier with multiple PhDs—actually much harder—so why bother?

In my opinion, wanting to know about multiple fields is neither a bad thing nor particularly special. The trick is to have a life where you have the opportunities to do the research you want. What you get a PhD in should ideally be whatever helps you get on that path.

From what little I know from this thread, it sounds like you should be someone considering getting a PhD. My suggestion is to start looking at what graduate students and professors are working on. Try to start being a part of the academic world as soon as possible, which means independent research but also taking advantage of the academic community at your university.

As for what field you should study considering future technology and society, my opinion is to forget about all that. Definitely think about what you should avoid studying based on what the future holds (although I think those concerns are exaggerated), but don’t study something because it may be the next big thing. Study what you’re interested in and what can help you get the type of job and have the type of life you want.