Yes, I was being imprecise by talking about "lack of interest". It's not only lack of interest per se; there are many reasons why someone might not think deeply about a subject. Lack of mental energy due to daily responsibilities is, I'm sure, quite common -- even for geeks.<p>And it's even more nuanced than that. Someone might be very interested, on an absolute scale, in some subject. But as long as he's even <i>more</i> interested in social reassurance, gossip, networking, status, and so on, he will prefer conversations that revolve around those instead. It's a matter of priority. Yeah, there's a latent physics geek in his brain, but when he asks you about next week's weather, his goal is imprecise small talk, not a discussion of turbulence models.