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Why the Grass is not Green and the Sky is not Blue and.... tutoring by Dr Cheevers on Skype


Read Peter Cheevers journalism and short stories 

published by Ether Books

Follow me into my garden and I will endeavour to make my point.  It has been raining and the grass looks very green. A literal and reassuring truth.  This is called the correspondence theory of truth. There is a subject ‘grass’ and it has phenomenological (appearance) greenness. In this way of looking at things, we understand that the greenness inheres in the grass.

But is the grass green? For don a scientific hat and things are not quite what not quite what we observe. We don’t need an astronomer to tell us that the sun does not move round the earth but it is the earth that moves around the sun. But what is your mind-set when you watch the sun setting and rising? In my garden the grass looks very green to me. Yet science informs green do not exist in the external world.

For our experience of colour is created by a combination of four factors:

1.      Wave length of reflected light                                                              

2.      Light conditions

3.      And two aspect of our bodies

4.      Simply, our bodies and brains have evolved to ‘create’ colour.

A crucial thing to remember is that light in is not coloured.  Visible light is electromagnetic radiation, like radio waves, vibrating with a certain frequency range. It is only when the electric magnetic radiation impinges on our retinas, and when our colour cones absorb the radiation, producing electrical signals that are appropriately processed by the neural circuitry of our brains. The qualitative experience that this produces is what we call colour. So the opposition between red and green and blue is a fact about our neural circuitry, not about the reflective properties of surfaces.

Colour is not just the internal representation of external reflectance. And it is not a thing of substance out there in the world. Colours as we call them are not out there in the ‘green’ of the grass, or in the ‘red’ of our blood, nor in the ‘blue’ of the sky (if fact the sky is not even an object it has no surface for the colour to be in). The sky is blue because the atmosphere transmits, only a certain range of wavelengths, of incoming light from the sun and of the wavelength it does transmit scatter some more than others.

As mentioned, our bodies and brains have evolved to ‘create’ colour. We have evolved within limitations to have the colour system we have because it has allowed us to function well in the world. Plant life has been important to our evolution and so the ability to place in one category the things that are green has apparent value for survival. . The same goes for blood and the colour red, the sky and the colour blue. We have the colour concepts we have because of the physical limitations constraining evolutionary advantages.

The eye is a famous example of a supposedly irreducibly complex structure, due to its many elaborate and interlocking parts, seemingly all dependent upon one another. It is frequently cited by intelligent design and creationism advocates as an example of irreducible complexity. In an often misquoted  passage from On the Origin of Species, Charles Darwin appears to acknowledge the eye's development as a difficulty for his theory. However, the quote in context shows that Darwin actually had a very good understanding of the evolution of the eye. He notes that "to suppose that the eye ... could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree".

Look first at how we firstly invert the images of what we observe:

This image shows the passage of light from an object - in this case a tree - through the lens at the front of the eye and onto the retina at the back of the eye.  The tree is standing upright and has green foliage.  Red lines show just five of the many points of light that travel to the eye from the tree to project the complete image.  The red line representing a ray of light coming from the top of the tree is shown meeting the lens at its top and then being bent so that it passes through the centre of the eye (which is, in essence, a sphere) so that when it meets the retina it is at the bottom of the received image.  Conversely the light ray shown emanating from the bottom of the tree trunk, meets the lens at the bottom, passes through the same point in the very centre of the spherical eye and appears on the retina at the top of the received image.  Light from the very centre of the tree passes through the middle of the lens and is not bent, so it remains in the centre of the image on the retina.  In this way the image is show to be a perfect replication of the tree, but is actually upside down on the eye’s retina.

Now look at the complexity of the eye

Colour vision and Evolution:

The ability to see colours presents distinct selective advantages for species. Such as being able to recognise predators, food and mates. Indeed it is thought that...

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