It is absolutely the butterfly effect. And of course, it immediately provokes the kind of counterfactual question, what would my life have been like if the butterfly hadn't flapped? And of course, it's an impossible question to answer. But I think on the whole... I think the way to approach these questions is not to say, well, what would have happened if the butterfly had flapped the other way, just to say, if you know everything you know today, would you have made a different decision? And I don't think I would. I think given that things that have happened in my life, I'm pretty happy with the way it's been. I would make the same decision again. That's the right. You don't have a... Well, if I

understand your... Because as well as you correctly, you may have that chance again. But in general, you don't have the chance anyway, so you might as well be happy with what you

did. On this epoch of the universe, I will not have that chance again. But as you say, who knows? Yeah.

Well, I think you should not have your bets right now, just to know the fact that you are happy with what you did. And I brought that up, obviously, not completely tongue-in-cheek because there's a lot of... Because understanding how small perturbations can have huge impacts is a key part of chaos, which we'll get to in the book. And so... I do want

to... Can I just make one point, which I do for strongly about if people at a similar stage in their career to me when I was finishing my PhD are listening to your podcast. Yeah. You know, you can change fields after your PhD. You can do years of post-it, you can change your field and indeed, you know, the technical stuff that you bring to a different field, you'll be surprised that it will be useful, even though at first sight you may not think so. And so I am a great believer in kind of promoting these programs which allow people to swap fields. And so, you know, it's just completely wrong that we're kind of siloized by the time we're in our mid-20s. Yeah. When we're... You know, people are now productive. We don't retire till much later than we did 50 years ago. So you know, we shouldn't be completely typecast by our mid-20s. And you know, the more that can happen, the

better. Well, yeah, absolutely. Not... I used to... It rings important for me for two reasons. When I was used to be chairman of the physics department, I was talking to students about why to choose physics, say, instead of engineering or something else. And I'd point out that physicists were doing all these different things because what you learn in physics is basically how to solve problems. Sometimes when you don't know what the problem is. And that skill is portable. But as you... But the more importantly is this notion of lifelong learning. I... Lestrimatically than you, for my entire academic career, I was a professor of astronomy as well as a professor of physics. From every beginning when I... from the time I first got a professorship at Yale and onward, I always had both those appointments. But I actually never took a course in astronomy in my life. And I certainly didn't... And likewise, even though my fields didn't diverge as much as yours, I've often said and it's true that I learned much more physics after I got my PhD than before. And I think that's the important thing for people to realize. It doesn't end there. But you're absolutely right. Too many people are just feel that they don't want to take that step to study something because they're not certain that they want to do it the rest of lives. But you're never committed.

That's right.