Back    All discussions

Light: The First Frontier
[See also:
Upside down, round and round
Through the Looking Glass: Is the distinction between "real" and "virtual" image real?

Where should this thread be placed? Cognitive Sciences, along with my other threads about vision and other brain processes? Or by Physical Sciences, along with the countless myths on which contemporary science is built?

Light is a subjective phenomenon, only known to living creatures as far as we can tell. But it is also a physical phenomenon that stands at the basis of modern science. The way physicists understand light is since du Broglie (1925) the way they understand matter. From gravitational waves to an expanding universe, all depends on how we interpret light phenomena. To change the perception of light in science is to change science itself.
However tempting that maybe, my objectives are much less ambitious.

Allow me to start with a simple mirror and invite you to step inside with me. Who knows? Maybe we will encounter Alice in our journey. Just as long as we make sure to avoid the evil queen. No need to loose our heads on this. [ There has been enough of this already.]

A simple mirror
Mirror images, just like real objects, must appear upside down on our retina, otherwise we would not see them straight up. Likewise, real objects appear upside down on the wall as projections in a camera obscura. The fact that we see them also upside down may wrongly suggests that both processes, projections on a mirror or on a wall, are inverse of each other, while they are, probably, exactly the same.
Let us now assume that we somehow, miraculously, were able to draw the mirror image on the mirror, not the way it appears to us (straight up), but the way it "really" is. Upside down, just like a projection on the wall.
What can make such an upside down image look straight up?

Here is how the situation could look like when drawn with a simple application like Paint:
ObjectMirror/Wall/Retina Perception

Here is now the difficulty. If we say that the mirror image is the same as the real image, we have to explain how light can in one case be reflected upside down on a wall, and in the other case, straight up on the mirror. How would light know whether it is going to meet a wall through a pinhole, or a mirror? Sounds familiar? It could be drawn right out of a quantum hat!

Okay, let us then assume that there is no difference between a mirror and a plain wall, and say that the image of the upward arrow as a real object will itself be downward on the mirror. This downward arrow will create the image of an upward arrow on our retina, which would make us see it as a downward arrow. And that is not good either!

There is obviously a difference between a wall and a mirror, the question is, what is this difference if it is not the way light is projected on each of them? Maybe it is the way it continues its travel after it has reached the mirror or the wall. Let us see how far we can get.
An obvious solution would be that the light reflected by a mirror follows another path than the light reflected by a wall. A mirror would then simply reflect the light back, wherever it comes from. That would mean that the (invisible) image of a downward arrow on the mirror would be duplicated on the retina, and that would make us see correctly an upward arrow.

This analysis, if it is correct, would disprove the classical view of real and virtual images which somehow ignores the way light has to be reflected on our retina for us to get a "normal" image. Our retinal image is exactly the same as the mirror image, except for the change of perspective. What is up in reality appears up, and down appears down.

What about the rule of equality between the angle of incidence and the angle of reflection? The rule is certainly valid, as long as we do not confuse it with how our perception works. We can see a ray of light bouncing off a surface at exactly the same angle as it hits that surface. The angle at which we see this ray has nothing to do with its angles of incidence and reflection. They are two different physical/optical processes. We need a new Theory of Vision.

The Myth of Refraction
Draw a straight line on a piece of paper, and now put a prism or a glass slab over it. You will see, after some shifting and rotating, the line itself being shifted and rotated. You know that the line you have drawn on paper has not moved, and to make sure that this not the case, you draw a long line that spills over to both sides of the prism. Still, the part under glass changes direction with the orientation of the prism.
An obvious mistake in comparing the line drawn on paper, with one ray of light, is to point at the obvious difference. While the line remains unchanged outside of the prism, the ray of light exiting the prism has definitely been shifted relative to its incident angle. A static line behaves differently than a dynamic ray of light. Or so it seems.
But then, what would happen if the shifted or rotated reflection itself became a source of light? Imagine the incoming ray of light being reflected on one of the inner surfaces of the prism, maybe more than one time, and from there to the outside? The exit angle would certainly be different from the incident angle. Also, just like convex and concave mirrors create different images, different substances, like oil or diamond, will also create different reflections. The regularities of Snell's Law would still be valid, and the concept of refracting index would keep its meaning. Only the context and interpretation would differ. We would not need light to behave differently in different media. We do not consider the changing of direction caused by a mirror as an exception to the rule that light is propagated in straight lines, and so maybe be we should not consider the passage of light from one medium to another to be any different.

In other words, the idea that different parts of a light wave enter a prism, or any other medium, at different speeds is completely superfluous. What we need to understand is how light is reflected in and out of the medium.
I am sure an appropriate computer program would be able to calculate all the possible angles.

Light: The First Frontier
For a New Theory of Vision: Some preliminary Remarks
How come we see a ray of light that is not directed at our eyes, say a horizontal ray crossing the space in front of us?
We have to distinguish the particles, whatever they are, and however they are moving (or not), which make up the ray and form a horizontal bright track in the darkness, and the particles, or whatever they are, that impinge on our retina and make us see the ray.
Maybe, unsurprisingly, we do not need light to see light. A candle or an oil lamp by a window guide us through the dark paths in the forest as surely as if these paths themselves were brightly lit. That of course does not prevent us from stumbling on stones, holes and fallen branches.
We do not see what is right in front of us, even though we see the dark line that links us to the light as if it were an invisible rope. We are able to follow the dark to the light, but we express that by saying that we follow the light itself. No matter, one expression is as legitimate as the other.
There is therefore no difference in finding my way to the light in complete darkness, and purposefully walking in the light towards an object that has attracted my attention, except for practical conveniences.
Physicists speak of invisible light when they refer to infra-red or ultra-violet rays, maybe it is time to add darkness to this list, but rather than consider it as a form of invisible light, darkness should be known as the other form of visible light.
Can that help us understand what happens when we are looking at, say, a spotlight sweeping an area of space, while we are hiding in the dark as a prisoner attempting to escape his prison?
Doe this spotlight send at the same time particles in our direction that make us see it?
What else could it be? Unless we want to introduce a novel version of action at a distance?
This is at the same time where my role as a philosopher ends. The nature of these particles, waves, or whatever scientists will want to call them, is something that cannot be determined by thought alone. It is an empirical issue par excellence and should be therefore left to physicists.

Light: The First Frontier
Ether and Dark Matter
The concept of the ether created unsolvable problems because of contradictory exigencies. As Huygens' Light Theory: A Text Analysis shows, it was often understood just like normal matter was, made of hard particles that made the propagation of light possible, and that permeated every interstice of free space. At the same time, objects were supposed to move freely in it without impedance. A sheer impossibility.
The concept of Dark Matter could be understood as the last form the concept of the ether has taken. Just as the latter, it is supposed to be omnipresent and at the same time allowing free movement of matter.
Interestingly enough, there always has been a physical phenomenon that united both contradictory properties without any difficulty: light.
Objects can move through bright space without interrupting permanently its passage unless they remain stationary. And even then, light very often finds a way of going around obstacles.
When we consider the fact that where there is no light, there is darkness, and we dare consider both as the opposite faces of the same coin, then we can truly say that light permeates every free inch of space and every interstice in any object.
So, instead of looking for an elusive dark matter, we should perhaps acknowledge what has always been right in front our eyes: light, in both its bright and its dark form.
Maybe there is no vacuum after all.

Light: The First Frontier
Can Particles Interfere?
Why not? What would otherwise be the sense of spending billions of euros or dollars on giant accelerators? Isn't that what interference in fact is, collision of two elements, or waves, and the creation of a new one, or the annihilation of both? How come scientists forget that according to their own beliefs matter, just like light, is both a wave and a particle? When you build a particle accelerator, aren't you at the same time building a wave accelerator?
Let us, once again, go back to sound and hearing and ask ourselves how a sound could be canceled out by its own anti-sound. I will assume it is possible and that explanations given are correct. How would that work for our hearing, how could a sound we hear suddenly vanish because of another sound?
Well, it very simple really, at least in theory. The specific (group of) neurons that were previously activated will have to cease being activated without other neurons taking their place. Piece of cake.
Just make sure that the new sound counters the movements of the membrane in such a manner that it stops having any contact with the neurons.
Very complicated indeed, and I would have no idea how to do that, but I can imagine the way a mathematician would approach the problem.
We have a surface that can move up and down in a "wavy form", which means that it can take different shapes, and that by each of its shapes, different points of its surface come in contact with a surface close and parallel to it. Each point of contact represents a neuron. The mathematician now has to find the equation that would reduce the number of contact points of each shape (close) to zero.
It is therefore theoretically possible to create anti-sound, and that by discrete values of variables. We have our interference of particles.

How about light? Scientists are all convinced that we can create darkness by adding light to light. I agree with them, just not on how to interpret this darkness. But how would it work for our perception?
It would seem that, unlike sound, where we can cancel the movements of a membrane directly, instead of simply creating anti-waves in the air itself, we would have to destroy the light before it reaches our eyes.
But, is that possible? We have already seen that when light waves allegedly interfere with each other we always see the color of the background as it is, whether it is white or black. We would almost get the impression that interference is just another word for transparency. But then light is also transparent in a prism or in clear water, and it reappears again when it hits other objects.
Also, remember that we can get dark colors by adding pigments, therefore particles, together. Of course, these pigments have to reflect, or absorb light... waves.
But what does it mean that an object absorbs all light? Black objects, even black holes, if they exist, cannot be invisible. Remember, we do not need light to see light, therefore even if a black object absorbs all light, it will still be visible as a black object. In fact, the blacker it is, the more contrast it will form with its environment, the more visible it will become. The idea that we could not see black holes sounds simply wrong to my ears. Of course, if such a black hole is simply as dark as empty space, we will not see it.
Interference is not an all or nothing process. The degree to which light waves allegedly interfere with each other determines the level of "darkness" involved. We can always say that a color looks darker because of the number of dark individual spots in its surface. We are seeing only the colored spots, and because they are less densely distributed, they appear darker to our eyes.
That reminds me of the blind spot, and the illusion of the fill-in processes attributed to the brain. If the brain were capable of such a feat, why does it not fill in all those dark spots created by interference, and show us only brightly lit surfaces?
If it does not, what does our retina look like when we are looking at interference patterns? Would we distinguish bright spots, activated cells, interspersed with dark ones, where no light has fallen?
Imagine then that we are, once again, standing in the dark, and looking at those interference patterns on a screen far away from us, maybe even using opera glasses. What would our retina look like then? And how would our brain distinguish between the dark spots that are the result of interference with the surrounding dark? Would it need to?
Can't all these dark spots be considered the same as the blind spot? If so, shouldn't they also be "filled-in"?
Also, since no light is falling in our retina, how could we distinguish activated cells from non-activated cells?
Physiologists have long found out that retinal cells are always active. They call that a threshold, and assume that it is something like a default setting without any meaning. What if instead this threshold only reflected the fact that there is always something to see, even if it is complete darkness? By the way, remember the scene in the Matrix, right after Neo has chosen the red pill? He was in a completely white environment. Imagine such a monochromatic space with no shadows at all to distinguish one object from another, and you will understand that we are blind anytime there is no perceptible contrast, whatever the color of the environment. So, is it then surprising that our retina is always active, even in darkness? But then, if retinal cells react not only to colors, but also to darkness, then the dark spots of the so-called interference patterns are impinging on discrete elements on our retina, and since waves would be much too "chaotic" to render visual scenes with the degree of precision needed and impinge on individual cells, we would have to assume that somehow light waves have transformed themselves into rays on the way to our retina. But isn't that what we were always asked to believe, that light was either wave or particle at its own convenience, and ours?
In this case individual colors would create the necessary sensation of black in our perception, and the interference patterns would appear in all their glory.
Such an interpretation is of course not without its problems. Are the dark spots the result of the absorption of all light frequencies by the object or screen, or the result of a combination of activated retinal cells?
One way or another, we have to be able to perceive them, and that is only possible if individual cells, and neurons, are excited in definite, discrete, patterns.

One thing seems certain to me: if interference is a real phenomenon, there is no reason why particles should not be able to interfere with each other, and if they cannot, there is no reason why waves should be able to do so.

Light: The First Frontier
The concept of Wavelength and its Fallacies
Imagine a water wave with a certain wavelength. Let us say, 10 cm. That is the distance between two crests or two troughs. The water has to go through the slit whatever the distance between the two moments. Whether the wavelength is 10 or 100 cm, its frequency will determine the quantity of water passing through the slit.
I could understand the amplitude playing a crucial role. If the wave is too high, it will be stopped by the (lower) slit, unless of course the slit is an open gap and not a hole. But how could the wavelength play the interference role it is supposed to play?
Secondary waves? Alright, but still, what does it have to do with wavelength? 
Once again, I understand the idea that a wide gap would have more chance of leaving places dry or in the dark. Something like a river creating its own bedding. There is a limit to the width water will expand in on both sides of a gap. Instead of expanding indefinitely on both sides, a powerful stream will dig itself in and create its own prison path. Still, make the underground hard enough, and you will get a very wide river. The wavelength, as a factor of velocity and volume, certainly plays a role in all this, but no more than the amplitude or the frequency of the wave. In fact, the same wavelength with a different amplitude and frequency would have a very different effect on how a wave reacts to a gap.
Last but not least, the concept of wavelength is quite ambiguous when it comes to light (or sound). Imagine yourself standing on a boat and watching the waves rolling towards the shore. The wavelength would be measured along the y-axis, from crest to crest or trough to trough. Suddenly, when the waves hit the shore, or a screen, wavelength becomes something that is measured along the x-axis. No explanation is ever given for this radical change of perspective. It is this change though that justifies the whole argumentation. A large wavelength makes it plausible that it will be hampered by a smaller gap, while the reverse, a small wavelength and a large gap, would have the opposite or different effects. But that only makes sense if waves entered the gaps sideways, only then could we say that the distance between two crests/troughs and the width of the gap have a direct influence on each other.

Listen to what John Gribbin has to say: "Imagine a nice set of plane waves progressing across our tank of water and coming up to, not an obstruction surrounded by water but a complete wall across their path, with a gap in the middle. If the gap is much larger than the wavelength of the disturbance, just the portion of the wave that is lined up with the gap gets through, spreading out slightly but leaving most of the water on the other side of the barrier undisturbed—like the waves arriving at the entrance to a harbor wall. " ("In Search of Schrödinger's Cat", 1984, p.15).
If you can make sense of these affirmations, please let me know.

How come nobody sees such a blatant fallacy? I think it comes because everybody is concentrated on the end result, the interference patterns, for which no reasonable explanation besides wave interference has been found. The problem is now that if wavelengths play no role in the behavior of waves going through a gap, then it becomes really difficult to explain why they suddenly should get such a central place in the overall model.