Falling Trees, Rainbows and a Gift for Theists

In 1710, Bishop George Berkeley pondered a question that was first formulated (in print) in The Chautauquan (a magazine) in 1883:

If a tree were to fall on an island where there were no human beings would there be any sound?

This is not to say that Bishop Berkeley was some sort of time-traveller but merely that, like many of the theologically inclined, he was attempting to answer a question that had not yet been properly posed.  Berkeley wasn’t really trying to answer the question, but rather to put forward an argument for immaterialism (or subjective idealism) which he makes most strongly in his “Master Argument”:

I am content to put the whole upon this issue; if you can but conceive it possible for one extended moveable substance, or in general, for any one idea or any thing like an idea, to exist otherwise than in a mind perceiving it, I shall readily give up the cause…. But say you, surely there is nothing easier than to imagine trees, for instance, in a park, or books existing in a closet, and no body by to perceive them. I answer, you may so, there is no difficulty in it: but what is all this, I beseech you, more than framing in your mind certain ideas which you call books and trees, and at the same time omitting to frame the idea of any one that may perceive them? But do not you your self perceive or think of them all the while? This therefore is nothing to the purpose: it only shows you have the power of imagining or forming ideas in your mind; but it doth not shew that you can conceive it possible, the objects of your thought may exist without the mind: to make out this, it is necessary that you conceive them existing unconceived or unthought of, which is a manifest repugnancy. When we do our utmost to conceive the existence of external bodies, we are all the while only contemplating our own ideas. But the mind taking no notice of itself, is deluded to think it can and doth conceive bodies existing unthought of or without the mind; though at the same time they are apprehended by or exist in it self.

Berkeley summed up his theory with "esse est percipi" ("To be is to be perceived") so his answer to the question as it is generally posed today would apparently be a resounding “no”.

There are others who would agree with a no verdict, given a slight modification (and an update) to the more common question:

If a tree fell in a forest and there was no-one and nothing there to hear, would it make a sound?

Such a formulation allows those who associate sound with the perception of pressure waves to answer with “no” – because someone or something would have to be around to register the pressure waves as sound for there to be a sound.  Physicists might disagree because those pressure waves are sound, by definition.  But here the difference is little more than semantics.  Those arguing that perception is sound are not arguing against the existence of pressure waves after the toppling of a tree in a deserted forest and physicists are not arguing that the presence of sound (as pressure waves) will necessarily bring a perceiver into existence.

There is a related phenomenon with rainbows, specifically in the fact that you and I never see the same rainbow.

The rainbow that we see in the sky isn’t actually there, it only exists in our heads after light has entered our eyes and been assembled by the brain into the colourful arch shape we recognise.  What has happened is that light has been refracted (and polarised) in thousands if not millions of drops of water, being split into the spectrum in the process before making its way to us.  Once the light has passed through the lenses of our eyes (or the lens of a camera when taking a photo of a rainbow) an image consistent with the rainbow is formed and it is this that is sent to the brain.

We can get all semantic about where the image is, either in the eye or in the brain, but the point is that outside of our heads there is nothing that corresponds with the rainbow that we perceive.  (Some might want to make an exception for a rainbow photo, but this is just outsourcing the image generation process – it has been done by a camera instead of our eyes.)

So how is this similar to a tree falling in a forest?  I’m going to make a rash assumption here that you, the reader, have two functioning ears – but I am not going to assume that your aural acuity is the same as mine.  Imagine then that we stand side by side in a forest and see, in the distance, a tree falling.  A short time later we hear the resultant sounds.

Because we are in a forest with plenty of other trees and maybe even bushes along with various topographical features, the sounds that we hear of the tree falling will be a combination of direct sound (since we saw the tree falling, there’s a clear line of sight) and sound reflected off tree trunks, branches, leaves, rocks, water and so on – along with reflections off each other and ourselves.

Slightly different combinations of reflected sound enter each of our ears (that is my two ears and your two ears) and our brains assemble a single soundscape of the tree falling from the range of frequencies that we detect – but those soundscapes (mine and yours) are not the same.

Additionally, our individual soundscapes – as perceived by us – would not have existed had we not been there interacting in the environment and picking up the sound from our ears in precisely the locations that they were in.  This is nothing magical because, conceptually, we could have put a pair of androids in the forest with recording arrangements that exactly matched our aural equipment and bodies that exactly mirrored our impact on the environment – then they would “hear” the sounds that we would have heard, if we had been there.

However, without someone or something to register those particular soundscapes, the soundscapes simply wouldn’t exist – in the same way as a rainbow doesn’t exist unless someone or something is there to focus light onto a receptor.  The pressure waves from the fallen tree will still be there just as the polarised light emerging from rain drops will be there, irrespective of whether there is a witness or not.

How could this been seen as a gift to Christians?

Unlike Islam and Judaism, Christianity involves a story in which a god is incarnated in human form (but only once, unlike Hinduism in which each deity seems to have a number of avatars – a Hindu may need to correct on this).  To be able to experience a rainbow or the soundscape of a tree falling in a forest, a god would have to be incarnated – because each of these phenomena is a consequence of having a single location and limited perception.

It’s relatively simple for someone like me to come up with the falling tree and the rainbow as examples of experiences that cannot be shared with an omnipresent omniscient god and it is quite likely that there are a range of similar phenomena, some of which might have been important or intriguing enough for a god to take on an incarnation in order to experience them.

The exact details, of course, would have to be sorted out by an apologist or theologian.

Thoughts?

(Theists should be wary of non-theists bearing gifts, by the way.  These gifts could easily be bait for a trap.  It is up to the theist to identify just what the nature of trap is.)