Yesterday's HORIZON programme: What is Reality? ..

The non amateur stuff. Hawking, black holes, that sort of thing

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Tony Markham
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Post by Tony Markham »

Quasar wrote:Can anyone tell me why, out of all the Photon's fired by an object, your eyes only pick up the ones necessary to define its distance from you?
The Photon field of the sun for example is as wide as the sun from a certain direction yet our eyes ignore masses of Photons and only choose to make use of the ones it needs. Why do you eyes not see the sun as if it were 2 feet from your face?
Unless of course its our brain that is defining the distances and not our eyes!!!!!
The eye processes all of the photons that enter it.

The eye does not define distance, only the direction of an object. Having two eyes, through the effect of parallax (and interpretation by the brain), gives us an indication as to the relative distances to nearby objects. The lack of a detectable parallax for the Sun tells our eyes (and brain) that the Sun must be much further away than 2 feet. Our eyes cannot actually tell whether the Sun or the Moon is the more distant.

Indeed, it was necessary to send Captain Cook halfway around the world in the 18th Century in support of measurements, based on the transit of Venus, to determine the actual distance scale of the solar system.
Deimos
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Post by Deimos »

Tony Markham wrote:
Quasar wrote:Can anyone tell me why, out of all the Photon's fired by an object, your eyes only pick up the ones necessary to define its distance from you?
The Photon field of the sun for example is as wide as the sun from a certain direction yet our eyes ignore masses of Photons and only choose to make use of the ones it needs. Why do you eyes not see the sun as if it were 2 feet from your face?
Unless of course its our brain that is defining the distances and not our eyes!!!!!
The eye processes all of the photons that enter it.

The eye does not define distance, only the direction of an object. Having two eyes, through the effect of parallax (and interpretation by the brain), gives us an indication as to the relative distances to nearby objects. The lack of a detectable parallax for the Sun tells our eyes (and brain) that the Sun must be much further away than 2 feet. Our eyes cannot actually tell whether the Sun or the Moon is the more distant.

Indeed, it was necessary to send Captain Cook halfway around the world in the 18th Century in support of measurements, based on the transit of Venus, to determine the actual distance scale of the solar system.

Also, I thought your eyes use the photons destined for them to determine colour as well.

Ian
David Frydman
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Post by David Frydman »

I am not sure that the eye processes every photon that enters the eye.
I think some are simply missed by the eye/brain.

I am not sure of this, but I think it highly unlikely that every one of the photons entering the eye is processed.

David.
Tony Markham
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Post by Tony Markham »

David Frydman wrote:I am not sure that the eye processes every photon that enters the eye.
I think some are simply missed by the eye/brain.

I am not sure of this, but I think it highly unlikely that every one of the photons entering the eye is processed.

David.
David,

That is certainly true - a few will be missed - such as those landing on the blind spot and those landing on the retina well off-centre where the density of light receptive cells is lower. The key point though is that the eye performs no selection process.

How the brain interprets the "signals" it receives from the eyes is another question - what we actually "see" can be heavily influenced by our expectations and by our previous experience ... but that is a huge topic that goes far beyond the original question in this thread.
David Frydman
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Post by David Frydman »

Tony,
I know, a huge subject.
I think that even some photons that land on receptors may not all be processed, but in a random pattern and statistically will not affect the image.

David
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