“On the contrary”, I answered. “It’s because somebody knows something about it that we can’t talk about physics. It’s the thing that nobody knows anything about that we can discuss. We can talk about the weather; we can talk about social problems; we can talk about psychology; we can talk about international finance – gold transfers we can’t talk about because those are understood – so it’s the subject that nobody knows anything that we can talk about!"

I got the above excerpt from Richard Feynman's "Surely You're Joking Mr. Feynman!".

I always thought that in order to open up a conversation, you must have a topic that you know the person that you want to talk to knows and that, of course, you also know. And to have that conversation to last long, that topic should be of interest to him. Now, after I read Feynman's argument, I stopped for sometime and had a deep thought. It never ever occured to me that we can talk about something that nobody doesn't have even the slightest idea about that subject. Yes. Maybe we can start a conversation about it but after a little while, your partner (I mean the person you're talking to...) will eventually get bored. Behold, here comes silence again! So how can you make a conversation on a topic that both of you do not know? That's what I'm going to find out yet. If only Feynman is still alive, I'll ask him myself.