If a tree falls and nobody hears it, does the tree make a noise? Tricky one! Please consider this twist:
A philosopher, strolling alone in a forest, hears a tree plunging noisily earthwards. Startled, he clutches his chest and dies before the falling tree had hit the ground. So...
Question - did the falling tree stop making a noise the instant the unfortunate philosopher snuffed it?
If the falling tree ceased making noise when the the philosopher died, then the energy of the sound waves rippling through the air at the moment of his death would have been nullified.
This causes us a big headache! Energy cannot be created or destroyed. So our thought experiment leads to a paradox, -an indication that our assumptions are wrong. We must conclude that the tree continued to make noise after the philosopher died, even though there were no observers present. And if true for this falling tree, then why not for all falling trees?
Thought Experiment of Death: One day, in the distant(?) future, you, dear reader, will die!
Question - When you die you will stop observing the Universe. When this happens, will all falling trees, all philosophers, everybody and everything - the whole Universe - stop making a noise for ever? Will everything stop existing?
If you were the unfortunate philosopher in the thought experiment above, then the falling tree will not only continue to exist, it will continue to make a noise too. As will the whole Universe. Only you will be silenced...