If a tree falls in a forest and no one is around to hear it, does it make a sound?

While the origin of the phrase is sometimes mistakenly attributed to George Berkeley, there are no extant writings in which he discussed this question.

[1] The closest are the following two passages from Berkeley's A Treatise Concerning the Principles of Human Knowledge, published in 1710: But, say you, surely there is nothing easier than for me to imagine trees, for instance, in a park, or books existing in a closet, and nobody by to perceive them.

However, his work did deal extensively with the question of whether objects could continue to exist without being perceived.

"[5] The magazine Scientific American corroborated the technical aspect of this question, while leaving out the philosophic side, a year later when they asked the question slightly reworded, "If a tree were to fall on an uninhabited island, would there be any sound?"

"[6] The current phrasing appears to have originated in the 1910 book Physics by Charles Riborg Mann and George Ransom Twiss.

The question "When a tree falls in a lonely forest, and no animal is near by to hear it, does it make a sound?

As Pais indicated, the majority view of the quantum mechanics community then and arguably to this day is that existence in the absence of an observer is at best a conjecture, a conclusion that can neither be proven nor disproven.

The most immediate philosophical topic that the riddle introduces involves the existence of the tree (and the sound it produces) outside of human perception.

This physical phenomenon, which can be measured by instruments other than our ears, exists regardless of human perception (seeing or hearing) of it.

However, most people, as well as scientists, assume that the observer doesn't change whether the tree-fall causes a sound or not, but this is an impossible claim to prove.

However, many scientists would argue that a truly unobserved event is one which realises no effect (imparts no information) on any other (where 'other' might be e.g., human, sound-recorder or rock), it therefore can have no legacy in the present (or ongoing) wider physical universe.

Of course, the fact that the tree is known to have changed state from 'upright' to 'fallen' implies that the event must be observed to ask the question at all – even if only by the supposed deaf onlooker.

The British philosopher of science Roy Bhaskar, credited with developing critical realism has argued, in apparent reference to this riddle, that: If men ceased to exist sound would continue to travel and heavy bodies to fall to the earth in exactly the same way, though ex hypothesi there would be no-one to know it[11] This existence of an unobserved real is integral to Bhaskar's ontology, which contends (in opposition to the various strains of positivism which have dominated both natural and social science in the twentieth century) that 'real structures exist independently of and are often out of phase with the actual patterns of events'.

Also, people may also say, if the tree exists outside of perception (as common sense would dictate), then it will produce sound waves.