Or the reason I think that an infinite universe exists outside of our Big Bang is because we can see the effects of all that extra gravity in the behavior of our own big bang galaxies, not to mention that the JWT has actually seen galaxies older than our big bang and hence born from BBNs outside of our big bang.
That a "fictitious" illusion of dark matter can arise from actual real very-far-away matter has been calculated in the work of A. Carati et al. (2009)
https://astronomy.com/news/2023/04/einstein-rings-inch-us-closer-to-solving-dark-matter-debate
Proving the Relativistic Energy-Momentum relation, the hard way and the easier way.
This adds the proof for the relativistic mass effects from motion, proving that gravity causes it.
Two reference frames in motions are not symmetrical. A system at rest on the surface of a planet moves faster in time than a moving system. This is not the case using just Special Relativity. This is proven just using the gravitational metric field in General Relativity.
