It’s common and remarkable. Why?
I’m talking about an old friend. Someone you haven’t seen in years: two, three, five years. You meet and it’s just like old times. You’re right back where you were the last time you’d been together. As though no time had passed.
What’s that say about friendship, but also about minds, brains, and time?
If we didn’t have a calendar to measure the time between, would the easy familiarity seem less remarkable? But still, we do measure time by daily sun-cycles, monthly moon cycles, and yearly sun-cycles.
If a friendship is a succession of brain states – one in each party to the friendship – then the meeting is simply one more in the succession. It joins the last state in the succession and so the friendship continues on.