Thinking Yourself Under the Table

Imagine being flat on your back under a table in a lecture room or office – what do you see?

Maybe a rough wood surface? This is quite interesting as the pattern is like some unique tree fingerprint. You might also ponder on the fact that this amazing building material was made from air and water using sunlight as a power source but that is not it.

The question is; how are you seeing the underside of the table?

Your brain is interpreting electrical messages from your optic nerve which originated in the cone and rod light receptors in your retina. They are stimulated by photons of light passing into the eye. The light which was focused by your lens was reflected from the bottom of the table. This was in turn the reflection of some small part of the ambient light filling the room. Not only that but if you move your head left, right, up or down the grain of the wood is still visible to you. So the table is reflecting light in every direction possible.

Daylight is white and when we see colours we are seeing surfaces which have absorbed other colours. A red door has absorbed green and blue light and reflected red. Roughly two-thirds of the light has been lost in doing this. It is the same under the table with some of the available light being absorbed by the wood.

The ambient light in the room is coming from the large windows and bouncing around to fill every corner. Every colour in the room is bright and clearly visible to us despite the glass having absorbed or reflected some of the photons.

The sky is blue because the water vapour has absorbed some of the red light and it comes from all directions as the remaining light is reflected by the vapour.

Some of the light from the Sun which hits the atmosphere is reflected back which is why the Earth looks so beautiful from space. A lot of the Sun’s light radiates into space in all directions at once so the proportion getting to the Earth is staggeringly small. The photons must also spread out the further they get from the sun.

To make each photon of light requires a nuclear reaction at the atomic scale – fusion. This process converts helium into hydrogen at enormous temperatures and pressures which releases energy as heat and light.

So, to recap, for every one of the 120 million or so light sensors in our retina we need a constant flow of about 14,000 photons per second to see clearly. There are around 7 million colour sensitive cones in amongst these which need more and lots of photons will be lost in the process.

Every tiny bit of the table has to absorb more photons than this in order to radiate its colour in all directions. The light on the table is a tiny part of the ambient light bouncing around the room some of which is being absorbed to show colours.

The ambient light is a minute fraction of the sky light which is a tiny part of what hits the Earth which is a vanishingly small proportion of the Sun’s total output. How many photons does the Sun need to make just so you can see under the table?

It takes the Sun around six hours to deliver enough energy to the Earth’s surface to power humanity for one year. We only have to find ways to convert that light and heat into electricity. What are we waiting for?

And, more to the point just remind me; why are you under the table?

Source by John Magus

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