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Originally Posted by Sam5
A single crack comes from a short lightening bolt if you are near the bolt. A multiple crack might be heard if there are some tall buildings or cliffs nearby. I've heard the crack sound from about 50-75 yards away, a short bolt hitting a telephone pole. It was a very short sharp loud crack.
Out here were I live in the West now, we have some 60-ft tall cliffs about a half mile away. We can see thunder storm clouds coming toward us. They are usually fairly small, but they are filled with lightening bolts. The further they are away, the more "booms" we hear, and echoes too. The closer the lightening is, and if it comes pretty much straight down from a cloud that is not very high, we here a sharp crack, with maybe some echo from the cliffs.
I haven't seen the movie. Were they trying to say there were regular distant lightening bolts that had no sound? I don't think that's possible.
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Oh, I see what you were saying now. I was talking about the closeness of the soundwaves regarding a bolt close by creating single boom--nothing to do with echoes. Yeah, with mountains around I think it's harder to distinguish between what is the initial boom or rumbling and an echo. Too, forked shape lightning or spider-veined discharges will cause several booms heard at different times depending on how long each bolt is, and all those sound waves bounce around, and then maybe add to that echoing, and you get those long rumbles that seem to go on forever. I've heard successive cracks that sounded like they were on top of me, but I don't think we get much echo effect here or in Florida. Sometimes the bolts occur so continously, I've reflexively ducked in my car. Lightning is fascinating, but a scary thing. especially when stuck in a convertible.
In the movie, the bolt wasn't very distant. It was also not a flash, more of a stream, if I recall. It had to be very hot, and even if the aliens made up their own form of "lightning," they don't get a pass on what it does to the air. It's goofy, but then it's a movie, and you have to suspend your belief for a bunch of other things as well.
