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Comment by FPGAhacker | Hacker News Reader

Of course you hear the siren or crazy man or anything, before it passes you if the component of the velocity vector pointing to you is slower than the speed of sound.

But it still takes time for the sound to reach you. And in that time the source has continued to move. So it will be as if you are watching a video but hearing with a tape delay.

If some one was standing 1000 meters away from you, and had a sign that flashed a sequence of numbers, 1,2,3,4,… once per second, and at the same time as the number flashed, they shouted the number loud enough that you could hear it, do you think what you heard and what you saw would be in sync?

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> "Of course you hear the siren or crazy man or anything, before it passes you if the component of the velocity vector pointing to you is slower than the speed of sound."

So, only in aircraft it is different? Magical aircraft physics after all?

> " If some one was standing 1000 meters away from you, and had a sign that flashed a sequence of numbers, 1,2,3,4,… once per second, and at the same time as the number flashed, they shouted the number loud enough that you could hear it, do you think what you heard and what you saw would be in sync?

Of course not.

But to humor you: which is the distinct event in a normally flying aircraft in which you can tie the exact point at which the light and sound signal leave the aircraft towards you so you can use that to calculate the distance? Spoiler: there isn't, you cannot, and that is precisely the point.

There are some examples currently in Ukraine, in which you could use your argument.

Well, in many planes it would be the firing of a cylinder. But you don’t need a distinct event. You look at an instant in time. It’s a fundamental of calculus called an infinitesimal.

Did you read the entire article? I think where you’re getting mixed up is that the article is using some poor assumptions and a broken thought experiment to derive a scheme for calculating or estimating the distance based on the sound/light mismatch. I don’t think anyone is claiming sound and light don’t travel at different speeds but the explanation in the article is pretty misguided.

I may have missed something, but what I saw I thought was accurate.

Is it in dispute that it takes time for the sound to reach you?

Is it in dispute that you can discern the direction from which a sound came?

Is it in dispute that the aircraft has moved during the time it takes for the sound to reach you?

Is in dispute that the sound emitted in the instant of time the aircraft is in position A will not reach you until the aircraft is in position A+k?

Is it in dispute that there are realistic velocity vectors for which the direction of sound from position A is perceivably distinct from the visually observed position A+k?

What if you imagine instead a boat traveling parallel to the shore on which you stand. Has the boat moved perceptibly from position A by the time the wavefront of the wake generated at position a reaches you?

How about this visual simulation of a moving sound source? https://www.youtube.com/watch?v=StXXPkCMREU

Or how about this video https://www.youtube.com/watch?v=6g6uJTsJ9CE

Do you notice the sound waves are not concentric?

Thank you.

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