What led to the conversation?

W: Did you hear the thunder last night?
M: Did I? It was really loud.
W: I didn’ t see any lightning, though. I thought that thunder and lightning always occur at the same time.
M: They do. It’ s no possible to have one without the other since thunder is a direct result of lightning.
W: Really?
M: Yes. Thunder is caused by the rapid expansion and contraction of highly heated air along the path of an electrical discharge.
W: In other words, lightning quickly heats the air and causes thunder. But if the lightning is there, why can’t we see it?
M: Because it sometimes occurs very high in the clouds.
W: I wonder if it’ s possible to see the lightning and not to hear the thunder.
M: Yes. It’ s possible if the lightning flashes far enough away. Sound doesn’ t travel as far as light.