You can't prove those measurements are not refraction of light on a surface. The wavelength of light changes when it passes through anything.

In other words, even background radiation and redshift are not provable as NOT being caused by, for instance, the surface of a bubble refracting light in a closed system. That would also explain why there is light going in every direction, aka "everything is moving away from each other" heat death religion.

That's not science, but guesswork built on basic assumptions that are not provable, it's all measurements in a void. If the universe was proven to be a closed system, all that science and your whole cosmology goes in the bin.

Here's the great part: nobody else has to prove it's "not refraction of light on a surface", whatever that means in this context.

We got models. They work pretty good as far as we can measure. That some other model could potentially explain the same measurements doesn't change that fact.

If someone proposes some other model that explains something better, ie with same or better accuracy and/or with less assumptions, then great!

You say that while letting the modelers of your cosmology get away with the most egregious science man ever witnessed. The models do wonders for technology on earth, but they do not produce any meaning out of the sky, only fantasies built on mathematical aberrations. On the contrary, and contrary to your favorite Razor, these models only make the wildest claims about the universe possible.

Occam's Razors says your cosmology is wrong. It's too convoluted, it has to explain the craziest singularities, which are not observable, yet it cannot explain real observations, like missing energy sources and background radiation. No math changes these facts. It's all in your head.