Thursday, September 02, 2010

What Rainbows Cannot Be

Rainbows are clearly not ordinary objects, being more like mirages than oases. But they are just as clearly not fictional objects. One’s conception of a rainbow may well contain false presuppositions, but in that way rainbows do resemble ordinary objects. Consider a red apple. Perhaps what is really there is a 10-dimensional collection of particle-strings within a 4-dimensional block universe, with the red and the spheroid existing only in the minds of certain kinds of potential perceivers of that collection. (That modern scientific hypothesis is not a million miles away from theistic idealism, of course.) Anyway, suppose some fictional meteorologists defined ‘rainbow’ to be a specific sort of event. They might do so because such a technical convention suited their scientific needs better than the rather vague ordinary meaning. And of course, an event is a kind of object (especially in a 4-Dimensionalist world). Now, some relatively arbitrary choices may well have been made as they specified their referent of ‘rainbow’. But that does not mean that rainbows cannot be objects. They are, after all, intentional objects, over which we might quantify. And of course, our intuitions that rainbows are not objects all derive from the fact that they are not ordinary objects. I mention this because it strikes me as similar to Benacerraf’s famous argument about what numbers cannot be.


Sylvia said...

From the viewpoint of a physicist a rainbow is not an object - not even a non-ordinary one. A rainbow is not an event either.

The appearence of a rainbow not only requires sunlight and fine particles of water, but also an observer at the right position.

Therefore, I would call 'seeing a rainbow' an event; the rainbow is the optical illusion of an object triggered in the observer by the external state of affairs (plus the background knowledge of the observer, such as the past observation of bridges and coloured objects).

Thus, the illusion can be explained and happens for real. It is not a fiction that you 'see a rainbow', but although this sentence has the same form as 'see an apple', it is not entirely the same type of event. (Just like seeing a ghost falls into another category.)

Someone may have reasons to start calling apples, rainbows and ghosts 'objects', but then the word 'object' has a different meaning than when it can only be used to refer to apple-like things.

Although you can see representations of numbers (in words, digits, ...), you can not even have the illusion of seeing a number. I guess this means that numbers fall in a different category than apples, rainbows or ghosts, but I do think the analogy between rainbows and numbers is of some use:
- both phenomena are related to the interplay of the external world and an observer,
- the fact that they are illusion-like does not deny the fact that they have consistent and predictable properties.

This is just my way long of saying: thank you for your post. It made me think. :)

Sylvia said...

When I first read your post I did not get the analogy between rainbows and numbers, for the simple reason that we can see the former but not the latter.
Then I started thinking about the difference between seeing an apple and seeing a rainbow.
And in the end I came to the conclusion that numbers may be somewhat like an invisible rainbow. :-)

This was my line of thoughts. Despite the similar wording, 1) 'seeing an apple', 2) 'seeing a rainbow' and 3) 'seeing a ghost' point to three different types of phenomena.

1) The apple. Apart from perceiving it, we can interact with an apple in various predictable ways: e.g. touch it, throw it, or eat it.

2) With a rainbow, none of the above interactions are possible: we can see it or photograph it, that is about it.
Whereas an apple is a physical object, a rainbow is not.
The rainbow is not really 'out there', but rather an optical illusion that occurs when sunlight, droplets of water and an observer (possibly just a camera) are positioned in a particular way.
Despite the illusion-like nature of a rainbow, its occurence is just as predictable as the horizontal acceleration of an apple when thrown in the air.

This distinghuishes it from yet another phenomenon, that of delusions, hallucinations:

3) Ghost-'appearances' may follow some rules too (such as the increased likelihood of having hallucinations after taking LSD), but they are far more complex than in the rainbow-case (under equal external conditions such as lighting, very specific details of the psychological condition of the observer may lead to the hallucination or not).

Numbers are yet another phenomenon: we can see numerals, but we cannot see numbers. (I would not even know how you could have the illusion of seeing a number.)
They don't seem to be out there in the world, but wathever they are, they do seem to follow relatively simple rules, indifferent of fysiological and psychological state of the person thinkin about them.
In that respect, numbers do resemble an invisble rainbow.

This is just my way of saying: thank you for this post - it made me think! :-)