system
Given the following post, respond as if you're commenting on Reddit:
human
What part of lightning does the thunder come from? Is it the bolt hitting the ground?
gpt
The bolt doesn't "hit" anything in the sense of an object hitting another object. A lightning discharge is formed when the lightning precursor, a so-called "leader", forms a conducting channel between the cloud and the ground (or between two different parts of the cloud in the case of cloud-to-cloud lightning). At that point, a current can flow through this channel, with the channel acting somewhat like an electrical cable between the two endpoints.

Since the current running through the lightning channel is very high, the channel heats up rapidly. And since hot air expands and displaces surrounding cooler air, this rapid heating causes a rapid expansion of the air in the channel. This rapid expansion generates a shockwave which is what we hear as thunder.

While the initial shockwave is a very brief burst, the sound is distorted and reflected by different parts of the atmosphere having different temperature/pressure and by elements of the landscape. Combined with the fact that the shockwave doesn't originate in a single point, but rather along the length of the lightning channel (which can be several kilometers long), this results in what we call thunder: Not an instant and short "bang", but rather a prolonged rumbling.