It’s one of the hazards of physics that occasionally we have to attend talks about other people’s sub-fields.

Physics is a pretty heavily specialized field. It’s specialized enough that an otherwise perfectly reasonable talk can be totally incomprehensible to someone just a few sub-fields over.

I went to a talk this week on someone else’s sub-field, and was pleasantly surprised by how much I could follow. I thought I’d say a bit about what made it work.

In my experience, a good talk tells me why I should care, what was done, and what we know now.

Most talks start with a Motivation section, covering the why I should care part. If a talk doesn’t provide any motivation, it’s assuming that everyone finds the point of the research self-evident, and that’s a risky assumption.

Even for talks with a Motivation section, though, there’s a lot of variety. I’ve been to plenty of talks where the motivation presented is very sketchy: “this sort of thing is important in general, so we’re going to calculate one”. While that’s technically a motivation, all it does for an outsider is to tell them which sub-field you’re part of. Ideally, a motivation section does more: for a good talk, the motivation should not only say why you’re doing the work, but what question you’re asking and how your work can answer it.

The bulk of any talk covers what was done, but here there’s also varying quality. Bad talks often make it unclear how much was done by the presenter versus how much was done before. This is important not just to make sure the right people get credit, but because it can be hard to tell how much progress has been made. A good talk makes it clear not only what was done, but why it wasn’t done before. The whole point of a talk is to show off something new, so it should be clear what the new thing is.

If those two parts are done well, it becomes a lot easier to explain what we know now. If you’re clear on what question you were asking and what you did to answer it, then you’ve already framed things in those terms, and the rest is just summarizing. If not, you have to build it up from scratch, ending up with the important information packed in to the last few minutes.

This isn’t everything you need for a good talk, but it’s important, and far too many people neglect it. I’ll be giving a few talks next week, and I plan to keep this structure in mind.