According to current models of the universe and theoretical physics, the expansion of spacetime refers to increasing distances between objects in the universe over time. However, space-time expansion is not a process of creating the "illusion" of an expanding universe, but rather a natural growth of the universe itself.

According to the Standard Model of the modern universe, the expansion is thought to have begun about 13.8 billion years ago in an event known as the Big Bang. During this event, scientists believe that the universe was in a very dense and hot state, and since then it has been expanding and gradually cooling.

Space-time expansion is not an illusion, but rather a concept in cosmological physics based on strong evidence gathered from astronomical observations and measurements. The expansion of the universe involves increasing distances between astronomical objects, such as planets, stars, and galaxies, and as a result, astronomical objects appear to move further away from each other.

It should be noted that current models of the universe do not include the illusion of an actual expansion, but rather suggest a continuous expansion of the universe at a specific rate. This means that astronomical objects move away from each other over time, there is no ultimate limit to the expansion, but there is an expansion rate that changes over time.

However, it should be noted that these models and theories are subject to development and change as scientific research and discoveries advance, and understanding regarding the expansion of the universe may be updated and modified in the future.

Dear Mr. Elsayed,

Thank you for your contribution. However, I was not asking a question about the standard interpretation of the CMB. The hot big bang paradigm has fundamental problems, so it is not "law" but merely a consensus in a highly competitive field.

For example, see https://www.sciencedirect.com/science/article/abs/pii/S1355219816302039

Thank you again,

Rusty

"Could the CMB result from more distant galaxies than can be observed in optical wavelengths?"

- This idea has problems. Here are the two that stand out most for me. (1) The extreme uniformity in CMB temperature/spectrum (one blackbody temperature) could not be achieved by a thermally-diverse population of galaxies. (2) At high redshift (z > ~10-15), the only galaxies we see are "just-formed" from pristine H & He; beyond that there are no stars or galaxies yet formed...but somehow even further back in time and distance (z ~ 1100), there could suddenly be a wall of fully formed galaxies?! No, it just doesn't work.

If the CMB was due to the superposed light of many galaxies, it would significantly deviate from the perfect black-body spectrum that it has. Only a nearly uniformly hot opaque gas could do that. So regardless of how you want to imagine the creation of such a gas, it cannot be due to some random superposition of a multitude of galaxies' radiation. In any event, though your reply to previous answers doesn't seem to suggest that you are wedded to the idea of higher dimensions, we are incapable of observing them, so they would have nothing to do with what we observe.

Dear Courtney,

Your knowledge of the standard model of cosmology seems complete - much more complete than the model, itself. There are many options that get buried by politics, to wit:

https://charmingscience.com/expanding-universe-could-be-just-an-illusion-new-study-says/

And I still contend that curvature into higher dimensions could also create illusions because of the weird topologies that can arise. However, there are lots of other ideas, out there. I'm trying to get a copy of the CMB history of physics paper.

Cheers,

Rusy