(This is the first of two postings. The second one will focus in on the universe as perceived from the viewpoint of a photon).
Light, or more accurately, the electromagnetic spectrum) is an essential component of our understanding of the universe around us. Everything we see needs particles (or waves) of light to be bouncing off it and entering our eyes. These photons carry the message of shape, colour, texture, brightness from the object to the retina of our eye. At this point the message from the photons is converted into nerve signals and these are sent to the sight centres of the brain. Here something “magical” happens and the signals are “converted” into an “image” that is presented to consciousness. This process in itself is shrouded in mystery (how does a small, inverted image on the back of the eye create the huge, vibrant, colourful field of vision that we take for granted every moment of our waking life? Indeed who does the “perceiving” of this image …. an image that only occurs on the retina, not in the brain itself?) But this is a mystery that demands another post. For now I just wish to discuss the external nature of light.
So light is the medium of communication by which the external world is presented to “consciousness”. But what exactly is light?
Well for a start, modern science cannot even make up its mind if light is a “wave” or a “particle”. Now this is of profound importance. A wave is a disturbance in some other substance such as a wave in water or a sound wave in air. The wave needs the substance for it to travel along. Without the substance a wave does not exist. For example imagine those giant ocean breakers without the water. Where are they? Imagine music being played in a vacuum. Where is the sound? In both cases without the medium the wave simply does not exist. But a particle is a very different type of “thing”. It is a solid point that has both location and mass. It is a solid bit of something or other. Particles of light, as we have seen, are called photons. However photons are very strange particles in that they have no mass and, as we shall see later, no location either.
But light shows particle-like and wave-like behaviour. Sometimes it acts exactly as one would expect a solid particle to behave …. Photons can be shot at a surface and it will kick out electrons just like the surface was being hit by grains of sand and being sandblasted. Individual photons can be fired through a slit and will appear as points on a screen the other side of the slit, just as particles would such as bullets fired from a gun.
However light also flows. It can flow round an object. When shone through two slits it acts exactly as a wave would be expected to. It develops an “interference pattern”, a classic wave-effect.
But how can light be both a particle and a wave?
But it gets stranger. Experimentation has shown that in order for light to show particle-like behaviour it has to be “observed”. Without an “observer” it behaves as a wave.
To explain this mystery physicists have suggested that an electromagnetic wave (of which light is the visible part) is not a wave as we understand the term. It is not a wave moving through a medium such as water or air but a wave of “probabilities”. In this way an explanation was found as to how light/electromagnetic waves can cross the vastness of space …. known to be a vacuum. This was for a long time a huge problem for scientists who were convinced (from the experimental evidence) that light was a wave. How is it, they asked, that a light wave can leave the sun and arrive at the Earth eight minutes later when between the Earth and the Sun is empty space, a vacuum? They suggested that space was not empty but was full of a mysterious substance known as “luminiferous aether”. It was this that carried the light waves. However in a very famous experiment by Michelson and Morley in 1887 it was shown that aether did not exist. However if light consisted of particles travelling at the speed of light then no aether was needed.
However the experimental evidence that light was, indeed a wave, was overpowering. Something was clearly wrong. The solution was that light is a wave that contains a probability of finding a particle (photon) in one place or another. Before observation the particle is smeared out over space as a “wave function”. In order for this wave function to “collapse” into a particle in a particular location something has to take place ….. and that something is the “act of observation”.
The big issue is what constitutes an “observer”? Can it be a measuring device or does it need to be a conscious observer such as a cat? Or does that observer need to be self-aware, a “reflective self-consciousness”?
Nobody really knows the answer to this question but the implications are incredible; that photons may need a conscious observer to bring them into existence! If this is true then vision works in a very weird way. As a light wave hits the retina it is technically “unobserved” because it is yet to reach consciousness. As such it can only be a wave at this point. However the wave is then converted into a nerve signal that is sent to the visual cortex to be reassembled into an image. But that image does not consist of photons. It is simply a nerve signal. The recreated image is then presented to consciousness and is “perceived” – the act of “observation”. If we accept the “collapse of the wave function” then where (and when) does the collapse from a wave to a particle take place? It cannot be before consciousness “observes” it, because that act of observation is right at the end of the process when the “wave” has changed to a nerve signal and is no longer light in any form, wave or particle. Can it be that the retina “observes” and in doing so collapses the wave function? But can this be an option? I am very aware that the retina is technically part of the brain, not the eye, but is it is not in any way “conscious” and definitely not “self-conscious”.
So we have this brain-generated “image” of the external world that projects itself into and wraps around our field of vision like a super IMAX picture. However this image is not made up of waves or photons, they have been long lost in the process. This view of the world is, at best, a facsimile and, at worst, an illusion. And of course we have an even deeper mystery …. where are the photons in this model?
So have I missed something?