Your father asked:
If a plane flies faster than the speed of sound, will he be able to overtake his own sound and hear itself?
Of course he can!
He can catch up because he is faster. But that does not fully answer this brilliant question. We want to know what would practically happen:
But what does it sound like?
We want to catch up with our own sound, so it needs to get away from us first. That means we fly slower than sound in the beginning. For example, your father shouts
Can you hear me?
in the direction of travel.
Now, we accelerate our aircraft to be faster than sound. With that, we create a shockwave in front of the plane, which can be heard as the sonic boom. Practically, the whole situation is really loud
We hear no difference.
It does get louder, but not noticeable.
But in theory, we can think about what we would hear when it would be quiet, and we could use the air molecules in front of our shockwave as a microphone.
But if we could hear it anyway?
Then, we would actually hear "Can you hear me?", but in very deep voice, so deep that it is to deep to be heard by a human. The words were spoken in some seconds, but we reach the sound waves only slowly over some minutes.
We would hear a very deep voice...
And as we creep up to our sentence from behind, we catch the last syllable first, because that is what we said at the latest time, so it had less time to go away. The direction of the time in the sound is flipped.
Speaking the words backwards!
It's a very deep
¿em raeh uoy naC