The cosmological principle 8

The cosmological principle and the speed of light

 

It is known that the speed of light does not depend on the system of reference (invariance). This invariance is a conceptual basis of the special theory of relativity. Light is an electromagnetic wave and the theory of relativity is based on electromagnetism. Is there any relationship between the speed of light and the expansion of the universe and the cosmological principle?

Based on the special theory of relativity, we know that there is an upper limit of speed - a material body cannot move faster than the limit speed. The speed of light is the limit. But it's not just about electromagnetism. It turns out that the speed of light is the upper limit of the speed of each particle, even if it does not participate in the electromagnetic interaction. Indeed, the matter must be approached from a broader perspective. "But why is this velocity also not dependent on the system of reference, why is it invariant?" [In special relativity it is only assumed that the speed of light is invariant (as a postulate). However, there is no answer to the question: "Why?"] We know that motion is relative - it is impossible to clearly define the speed of the body (due to the existence of different frames of reference). But the speed of light is absolute.

"Invariance of the speed of light" is a postulate, an assumption by Albert Einstein, not directly based on observational facts. However, the conclusions of the theory are confirmed by the experiment. But we still don't know "why the speed of light is invariant." Is it possible to explain invariance? We will soon see that it is.

In the previous article, we built a model (preferred in our eyes) in which the relative velocity of celestial bodies is proportional to the distance (in a set of various objects). According to this model, more distant objects move at a higher radial speed. But we already know that there is a maximum speed equal to the speed of light. Therefore, the speeds of the farthest objects should be close to the speed of light and cannot be greater than it (even equal).

What's the conclusion? It is very possible that the dimensions of the universe are limited. The boundary of the universe (horizon) is determined by an object that moves at the speed of light. Based on this, the speed of the expansion of the universe can be determined. It's the speed of light, of course. The size (radius) of the universe is obviously defined as the distance at which there are objects that move away at the speed of light. [It should be noted here that modern cosmology uses the concept of the tempo of expansion, which is defined by the Hubble factor H. This will be discussed later.]

This limiting speed (speed of expansion) does not depend on the direction of observation, that is, according to the cosmological principle. Thus, it is invariable - it does not depend on the system of reference, because regardless of the direction of observation - the same maximum speed. In summary, the speed of light does not depend on a system of reference, as it is the expansion speed of the universe. This is the secret of the existence of invariant speed. We have here confirmation of the validity of the cosmological principle. The speed of light is not relative, it is not local. Also, the universe as a whole is not local because it is all that exists (materially). [A local object is one whose location can be determined because there are other, external objects.]

The size of the universe ("radius") is determined by the distance of the most distant objects because their velocity tends to c. They represent matter that existed at a very early stage of expansion, about 15 billion years ago. Back then, the universe was very small, so it was auto-coordinated in terms of features and phenomena, and so it also expanded in any direction at the same speed c. It is acceptable that even today the universe is completely auto-coordinated. [So we have a cosmological principle. Here the circle closes.] It is obvious that you cannot see what was at the very beginning, even with the best telescopes. It is not possible. After all, in the first moments, there was no electromagnetic radiation (light). However, our model is in line with what we already see.

The opinion that there are objects faster than light - "they cannot be seen because they are beyond the horizon" is not the conclusion from the observation (for understandable reasons). There is no observational fact that confirms this opinion even indirectly. This judgment is based solely on the theory, or more precisely on the interpretation of general relativity. In the model of the universe built on this theory, light does not run in a straight line, but along geodetic lines - this gives the possibility of a speed greater than light. The idea that there are objects beyond the horizon defined by the speed of light is consistent with the inflation hypothesis. But that's not proof; it's just a hypothetical option, not necessarily the right one.

    For the sake of completeness, it is worth adding that there is an option of moving faster than light. But what would move like that? Perhaps some particles - rather not galaxies.