Our perception of light says at least as much about us as it does about light.
We perceive light behaving the way it does because of what and where we are while perceiving it.
I am going to make the assumption that light actually exists. This is not a radical assumption on the face of it, but I have just stated that from the point of view of light itself--which ought to be an important point of view--light doesn’t exist, never has existed, never will exist, and doesn’t/neverhas/neverwill even have a universe to exist in.
Something is wrong with my understanding of existence.
Existence requires space, time, mass, and motion. In a word, existence requires momentum.
Let’s back up, way back, to a point of view that is impossible, but, for simple purposes, can be modeled. Let’s look at the universe as a whole.
What is the total momentum of the universe?
It’s a closed system. Its total momentum is zero. For every part moving one direction there is an equal part moving the opposite direction that cancels out the overall momentum.
This would indicate the universe doesn’t exist.
Assuming that it does, the problem is clear. Existence depends on local characteristics. It’s local momentum that matters. As long as our corner and all the other corners of the universe have measurable momentum, we’re all real, even if we all add up to nothing.
How can this help us with light? Does light have parts?
The wave theory helps again. Yes, there are parts. Light is made of alternating electric and magnetic fields. And they don’t move at the speed of light. As one field grows, the other decays. The field that grows begins to create the next field and then decays as the new one grows. It’s the front edge of this constantly self-creating, self-destroying pair of fields that moves at the speed of light. The fields themselves, like the waving flag on the flagpole, don’t really move in the direction of travel of the light.
The momentum of the light beam lies in the energy of these fields. When light hits something other than a vacuum, these fields give up some or all of their energy to whatever that something is. But the particular fields that hit that something are NOT the fields that started the light beam. Those never went anywhere at any speed. The final fields are created shortly (very shortly!) before the impact and all they do is try to transfer their energy to another set of fields but something in the way prevents the next set from being created. Their energy has to go somewhere, so it goes into the something in whatever form that something is structured to handle, but it’s no longer light. And, though the energy was transported at light speed, no mass actually moved from the beginning point to the ending point.
The alternating E and B (B for magnetic…I know, just accept it) fields do move. They oscillate at right angles to the direction of travel of the light they create. Just like the waving flag moves back and forth but not at all in the direction of the waves in it.
The difference again with light is that there is no flag. Light propagates in a vacuum. And it propagates in all directions. This is because there is nothing keeping the two alternating fields in one plane, so they go all over the place in every existing dimension. The rate of dissipation (in a vacuum) would be 1/r^2 in three dimensions, 1/r^3 in four dimensions, etc.
Since we observe a dissipation of 1/r^2, we can conclude that light and we exist in three spacial dimensions and one of time as we perceive light. This jives with Relativity theory and seems to answer out initial question about dimensions. The extra ones proposed in current physical models would be so small as to not be able to be detected, non-zero, but small. They would have noticeable magnitudes only under extreme conditions, like the birth of the universe.
Our perception of light says that we are three dimensional, lower than light speed creatures in a four dimensional, light speed defined universe. Light is the lines and boundaries of the universe. It shows us how the universe is shaped. Remember, when a light beam bends near massive objects, it isn’t being bent at all. That’s just how the universe is shaped. It has curves in it—sort of like a straight road in West Texas (and that’s straight!) that actually bends slightly around the curvature of the earth.
I’m getting close to the end of this line of thought. Just a couple more blogs.
And still, where does momentum come from? Oh, yes there’s that thing, Quantum Mechanics. Could that help?