There was a young man who said, “God!
I find it exceedingly odd
That the tree that I see
Should just cease to be
When there’s no-one about in the quad.”
The underlying presumption in the famously quoted “When a tree falls in the forest and there’s no one to hear it, does it make a sound?” is that in the absence of a conscious entity the forest doesn’t actually have any real existence.
It also echoes the views of the Anglo-Irish philosopher Bishop George Berkeley who espoused a theory he called “immaterialism” which argued that physical things do not really exist except as ideas, until they are perceived by the senses of people perceiving those physical things. Hence his well known expression: “to be is to be perceived”. The theory also denies the existence of material substance and, instead, contends that familiar objects like tables and chairs are only ideas in the minds of perceivers, and thus can’t exist without being perceived.
Einstein’s objection to one interpretation of quantum theory came from the same place. He once asked a friend rather facetiously, “Does the moon exist only when I look at it?”. That’s because the interpretation maintains that, at the quantum scale, reality cannot be taken to exist independently of the act of measurement — obviously by an observer. And, therefore, an observer is needed for things to exist.
So a lot of people quote the following limerick in answer to the limerick mentioned above:
“Young man, your astonishment’s odd;
I am always about in the quad.
And that’s why the tree
Will continue to be
As observed by yours faithfully, God.”
(This piece first appeared in The Economic Times)