Imagine a photon stretched in space along the direction of its motion from end to end of photon's world in range equal to the age of universe * c. In this way, each photon of background radiation is stretched, and such a photon passes through every point of space from each side. And what will happen to these photons, when the universe in their direction of motion, according to Hubble's law, stretches more than it is allowed by the limit of speed in Doppler formula, which must confirm their redshift? It's going to be the square root of the negative. There is no redshift of light, that cannot reach us because of the expansion speed v>c, but the velocity in Doppler equation that gives the redshift of CMB photons that are everywhere, this velocity doesn't know it and it's going to exceed c, resulting in a square root of negative and previously zero in the denominator for v=c.
If u care, read also my answer starting with "The speed we are talking about is the space expansion rate itself".
I'll happily admit, this may be above my lane, so ought to be answered by someone smarter than me. At least we can agree that the photon does not experience time, and thus does not experience distance either. Your question, I will need to ponder amidst my busy schedule.
In the meantime, I ask you a philosophical question; what's your stance on the mind-body problem? Do you have any more questions that I may be able to answer?
Space, that has been traversed by CMB photon does no longer exist, as well as the space that has been expanding behind it, moving away its emission place, as well as the space that has been expanding in front of it, lengthening its path. Current space, that separates us from the current position of the place of its emission, this space has a current metric, other than the metric of space traversed by the photon, other than the space that was expanding in front of it and behind it during its travel. In this current metric, our distance to the place of CMB photon emission is equal to the universe age * c. Former space no longer exists not only because of the changes of matter density in the expanding space traversed by the photon, but above all because the spacetime exists only for the time of its metric. What we have is current spacetime, photon travel time and its velocity. There's only one way to calculate the distance with this data. Until yesterday I myself was thinking of expansion as of creation of a new, additional space that adds to the existing one without vanishing the existing one - bullshit. It's replaced.
Something occurred to me. Even if the place of the source of CMB photons is currently moving away from us with 3.2 c, there was a time in the past, when it was moving away slower than c and the Doppler was applicable. And when it reached c, it was thrown in the garbage by modern astronomy. That's why I don't believe in 3.2 c and try to explain my reasoning.
I posted my question on Quora All 5 answers till now are the same: I can't use the Doppler, because the place of the source of CMB photons is currently 46 billion light years from us and moving away from us with 3.2 c. However, "The relativistic doppler shift can be applied to the cosmological redshift to get a speed of recession." So I'm asking: What is the mechanism that allows to use doppler formula for the recession velocity less than c and throws it in the garbage for velocity equal or greater than c? No answer. The same question to All of You. https://www.quora.com/Is-the-Doppler-formula-valid-for-the-redshift-of-the-microwave-background-radiation-If-so-can-the-velocity-from-this-formula-with-this-redshift-be-interpreted-as-the-speed-of-expansion-of-space-at-a-distance-equal
https://www.quora.com/What-is-the-mechanism-that-allows-to-use-Doppler-formula-for-the-recession-velocity-less-than-c-and-throws-it-in-the-garbage-for-velocity-equal-or-greater-than-c
It would be funny, if it was funny:
I believe this answer was deleted by author:
Meanwhile on Physics Stack Exchange:
Another idea of how CMB photon travels through the expanding space. In this vision it's literally embedded in a single, expanding cell. You could say that its motion is apparent. At the same time it always travels with v=c relative to the neighboring cells, but in a static, snapshot frame, like the ones in the drawing.
Thought experiment with an ant walking on stretched rubber band
I lay the long rubber band loose on the table and stretch the short one. Both have ants starting simultaneously from one end to the other, moving relative to the fabric of the rubber band with v=c. I stop stretching the short rubber band when it reaches the length of the long one, and exactly at that moment both ants reach the finish line. In both cases, they've traveled the ct distance. There is a catch. A short rubber band has a greater linear density (closer scale) at the start and it is in relation to this density/scale that the ant moves with v=c. After stretching the rubber band, its density decreases to the density of a long rubber band, their graduations coincide/overlap. And since the motion with v=c is relative to the density/scale, the varying rate of stretching loses its meaning because both ants always come together, so to speak, as long as I stretched the rubber band at a rate less than c, the speed of an ant. Otherwise, the rubber band breaks and the ant does not come. And that could even be nicely animated.
The scale coincides with the redshift or the wavelength of the CMB photon - it comes to the same thing.
That's why the changing rate of expansion - as long as its speed remains less than c - has no effect on the size of our visible universe. Its radius is always ct and that's why wikipedia is horribly wrong and probably half the astronomy with it.
You can crucify me now.
We're in the endgame now - https://media.tenor.com/-zSnftxJft8AAAAC/avengers-we-are-in-the-endgame-now.gif
They've deleted it. The same question to All of You. I've never been more serious in my life.
Very interesting information. Thank you, Marcin.