Disclaimer
This is an article where I discuss the pros and cons — as I see them — of getting a PhD in a technical, abstract field like pure math or theoretical physics. I did such a thing myself (a while ago, but not so long ago that these thoughts are completely irrelevant) and my general outlook on such a thing is positive. However, please do not make such a big decision purely on what you read here. Such a decision should be taken very seriously, and you should consult with many independent sources on whether or not such a thing is right for you.
With that disclaimer out of the way, let me dive in to some of the pros and cons of PhDs (at least from my perspective).
A story from my undergrad
I distinctly remember being an undergrad (math and physics major) sitting in the office of one of my favorite professors (a biophysics professor) and talking to him about whether or not I should go on to the PhD. After not making any progress for a while, I simply asked him: "Are you happy you got a PhD?"
Keep in mind that this was a dude who had a tenured professorship at a top university — the top of the mountain by academic standards. I thought for sure that his answer would be an immediate and confident "yes". It wasn't.
After a long pause and a look of bewilderment, he simply said "Well, it's a weird way to spend your 20s." And that, my friends, is true. This brings me to my first Con.
Con #1: Weird way to spend your 20s
Unless you're a child prodigy, you're probably going to be starting your PhD around the ages of 21, 22, or 23. (If you're much older than that and considering a PhD, then first of all good on you, and secondly a lot of this article won't apply to you – my apologies.)
This means that you'll probably be working on your PhD for the meat of your 20s. With luck, you'll be done at 27, and without luck you'll be done at 29, maybe even 30 depending on your chosen field.
When you're 21 it's hard to imagine how you'll think when you're 30% older than you are. Plus, when you're an undergrad asking about doing a PhD, you're in an environment where all or most of your friends are also undergrads, and it's therefore hard to imagine you and your friends' lives diverging too much.
I therefore want to paint a clear picture of what your 20s will look like while doing a PhD. This will sound very negative, but I don't mean it to be that way. I just want the picture to be clear. Plus, I'll get to some Pros later.
Suppose you start a PhD while some significant fraction of your friends do not. You will work a lot, and the Monday through Friday schedule that the rest of society adheres to will mean very little to you. Your friends will work significantly less and have their weekends (largely) to themselves.
You will be broke. Really broke. Your friends will probably not be. Your friends don't need to become titans of Wall Street for this statement to be true. You'd be surprised how little money you need to "not be broke" when you're a 23 year old. Your friends will make more than that number (probably), and you will make less than that (definitely).
These are, in my opinion, the two biggest causes for the aforementioned "weirdness" — lack of time, lack of money. And don't get me wrong, I was (and still am) about as idealistic as they come — but you can't eat mathematical beauty or pay rent with the papers you read.
This set of circumstances is not that "weird" or brutal in your first year, maybe even two, after undergrad. This is because you're already used to having very little time and even less money. But when you're 27, still have 2 years left, and have a net worth of 0, and looking at some of your friends who have spent the last 5 years working way less hard and who own assets (hopefully not just crypto), you might feel...weird.
Again, I was personally very comfortable living in this state of affairs, but it's vitally important that you internalize what this might look like for you and your circumstances. With this Con out of the way, let's move on to a Pro.
Pro #1: Research Bliss
PhD life is research bliss. I would argue that these 5-7 years of academia are the "best" years in terms of actually being able to learn a ton and just do research. It's the only 5-7 years where you don't really need to worry about where your (little) money will come from. You might have to do some teaching but you (almost certainly) won't be worrying about whether or not you can keep doing your research for the next year or two. That comes from the grant(s) that your supervisor needs to worry about, and you get to spend your time working (which is great).
So, if you really love your subject and you want to become a world expert in some part of it, a PhD is a great thing to do. How academia treats you after the PhD is a different story — then you might have to spend a good fraction of your time applying to grants and serving on committees, i.e., not doing research — but during your PhD that is not your problem.
That said, thinking about what will come after your PhD is hugely important, which brings me to the next Con.
Con #2: More School Isn't Always Better
Up until about the end of undergrad (and even this, now, is reasonably up for debate), we are taught that "more school = better." Here, it is implied that "better" means better job opportunities — more financial success. Therefore many people make the often "wrong" assumption that "more school" — i.e., getting a PhD — is better for economic success.
This is very often not true, for a couple reasons. First, getting a PhD is not "school" the way you often think about it. Most of the value, for better or worse, in "school" as we typically think about it (i.e., up through undergrad) is in providing a way for you to stand out relative to your peers. That sounds harsh, because it is. GPAs are only meaningful because we know, roughly, how to compare them. PhDs are not like that. (No one has ever looked at my grades from the few courses I took as a PhD student, and most of those courses had zero or optional homework and no exams.)
So, if you're thinking of doing a PhD and not certain that you want to stay in academia forever by pursuing a tenured position, please think carefully about what your exit strategy might look like and whether or not you're learning the necessary skills during your PhD to get a reasonable job after your PhD.
Pro #3: Massive Confidence
The single most valuable thing I obtained from my PhD is not a deep understanding of the geometry of scattering amplitudes in highly supersymmetric quantum field theories — but rather the massive confidence that completing the degree gave me. To be clear, it's not the degree itself — I never refer to myself as "doctor" and I hope no one ever does. It's the feeling of having taken stuff that was once really intimidating and scary, and mastering it.
In particular, I now genuinely feel like there is nothing that a human can learn, that I cannot. This is not to say that I know everything, or that I ever will. It is to say that if something can be learned, I can learn it. That's an awesome feeling, one that has helped me tremendously in my career (outside of academia) ever since. It is a feeling that is earned after spending years doing hard s**t. There are plenty of ways to spend years doing hard s**t, but a PhD in a field you love is a particularly good way of doing so, in my opinion.
Pro #4: Awesome People
There are buttheads in every field, in every industry, and at more or less every age. That said, people who decide to pursue PhDs are people who are happy to turn their backs on riches and pursue knowledge. They tend to be curious and humble people. In academia, you encounter some of the smartest friggin' people in the world. People so smart that they make the people who you think are the smartest — your supervisor(s), postdocs in your group, etc. — tremble in their boots. Encountering people like this makes you humble in a way that few other things can, and so as a PhD student you get to hang out with other smart-but-humble people, which is awesome.
There are of course butthead PhD students, but the butthead ratio is pretty low. Many of my best friends today are people I met during my PhD years, and there's no amount of 401k that I'd rather have in return for those relationships.
To Be Continued...
We get asked about PhD and grad-school things a lot, so it'll be something we probably write about a lot more. For now, we'd love to hear your thoughts on what we've talked about so far. If you're someone who's considering making the many-years-long commitment to a PhD and want to bounce ideas around, feel free to reach out!