by DANIEL N. ROBINSON
There is a long, winding, and vexing wrangle among philosophers on the nature and validity of our knowledge of the physical world. Take the example of color. A stroll through the garden reveals a busy bee extracting nectar from a yellow rose. I see the yellow rose owing to certain pigments in the cone receptors of my retina. In a normally sighted person, the neurochemistry of vision operates over a range of wavelengths from about 360 to 760 nanometers (nm) — roughly violet to a deep red. What English-speaking percipients describe as “yellow” is in the near vicinity of 580 nm, a little above the eye’s peak sensitivity. For the honey bee, matters are quite different. Its compound eyes are equipped with three types of retinal receptors — one for very short wavelengths (peaking at 344 nm, or ultraviolet), a medium-type (peaking at 436, or blue), and one for long wavelengths (peaking at 544, or green). Though we and the bee may share floral preferences — revealed in the bee’s foraging and in our table settings — the bee’s representation of the external world clearly includes features to which we are blind.
Were all sources of electromagnetic radiation to fall at wavelengths shorter than 340 nm, the affairs of the world would pass us unseen. (And eyes like ours wouldn’t work very well anyway, since excessive exposure to ultraviolent radiation renders the human lens increasingly opaque as a result of cataracts.) Our inability to see (or to endure) much ultraviolet radiation is a heavy price to pay for our eyesight, but it does protect the human retina from destruction by this same radiation. The moral of the tale so far is that creatures are fitted out for the world as given, and modes of adaptation come at a price.
Is this explanation of human perception no more than a poor glimpse into evolutionary forces? Here we face yet another of philosophy’s enduring engagements, to wit: What counts as an explanation, and what standard is to be applied in evaluating competing explanations?
Explaining the World
In 1814, Pierre-Simon Laplace presented his famous “demon,” as it has come to be known. Imagine a superior intelligence who, knowing the precise location and momentum of every atom in the universe, can account for the past and predict the future from the laws of classical mechanics. For this intelligence, Laplace wrote, “nothing would be uncertain and the future, as the past, would be present to its eyes.” To explain the nature of a thing or occurrence, by this way of thinking, would require that we know with certainty the physical processes at the smallest level, because they determine the events at any larger level.
But then, some two centuries after Laplace, comes Werner Heisenberg and quantum mechanics rendering uncertain any attempt to specify a particle’s position and momentum simultaneously. Of course, uncertainty at the quantum level may impose no barrier to determinism at the macro-level, but even this proposition raises questions regarding the nature of explanation and the level at which scientific explanations are of the right sort.
But why assume there is a fixed and right sort of explanation? Sometimes taken to be the “realist” position in the philosophical debate between realists and anti-realists, the idea that there is a right sort of explanation is predicated on a core of metaphysical precepts. Dominant these days among such ideas is physicalism, which takes physical events and objects to be the sole and ultimate furniture of reality. Explaining such events and objects then calls for what is finally a causal account. In principle, all that is really real, even all that we cannot yet observe, is subject to explanations located within a causally closed system — that is, one admitting only of physical causes.
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