Occasionally, you’ll see people argue that PhD degrees are unnecessary. Sometimes they’re non-scientists who don’t know what they’re talking about, sometimes they’re Freeman Dyson.
With the wide range of arguers comes a wide range of arguments, and I don’t pretend to be able to address them all. But I do think that PhD programs, or something like them, are necessary. Grad school performs a task that almost nothing else can: it turns students into researchers.
The difference between studying a subject and researching it is a bit like the difference between swimming laps in a pool and being a fish. You can get pretty good at swimming, to the point where you can go back and forth with no real danger of screwing up. But a fish lives there.
To do research in a subject, you really have to be able to “live there”. It doesn’t have to be your whole life, or even the most important part of your life. But it has to be somewhere you’re comfortable, where you can immerse yourself and interact with it naturally. You have to have “fluency”, in the same sort of sense you can be fluent in a language. And just as you can learn a language much faster by immersion than by just taking classes, most people find it a lot easier to become a researcher if they’re in an environment built around research.
Does that have to be grad school? Not necessarily. Some people get immersed in real research from an early age (Dyson certainly fell into that category). But even (especially) for a curious person, it’s easy to get immersed in something else instead. As a kid, I would probably happily have become a Dungeons and Dragons researcher if that was a real thing.
Grad school is a choice, to immerse yourself in something specific. You want to become a physicist? You can go somewhere where everyone cares about physics. A mathematician? Same deal. They even pay you, so you don’t need to try to fit research in between a bunch of part-time jobs. They have classes for those who learn better from classes, libraries for those who learn better from books, and for those who learn from conversation you can walk down the hall, knock on a door, and learn something new. You get the opportunity to surround yourself with a topic, to work it into your bones.
And the crazy thing? It really works. You go in with a student’s knowledge of a subject, often decades out of date, and you end up giving talks in front of the world’s experts. In most cases, you end up genuinely shocked by how much you’ve changed, how much you’ve grown. I know I was.
I’m not saying that all aspects of grad school are necessary. The thesis doesn’t make sense in every field, there’s a reason why theoretical physicists usually just staple their papers together and call it a day. Different universities have quite different setups for classes and teaching experience, so it’s unlikely that there’s one true way to arrange those. Even the concept of a single advisor might be more of an administrative convenience than a real necessity. But the core idea, of a place that focuses on the transformation from student to researcher, that pays you and gives you access to what you need…I don’t think that’s something we can do without.