What we see
We see redshift, and we take it to mean the universe is expanding. It’s read like the Doppler effect: light from an object moving away from us is stretched to a longer wavelength, so it shifts toward the red.
Gravity and light
We know light is affected by gravity. It bends around a large mass. Climbing out of a gravity well, it is stretched to longer wavelengths, and seen from far away it is also slowed. Just outside a black hole’s event horizon, light seen from a distance slows almost to a stop and is stretched toward infinite redshift. Gravity slows and stretches light.
Galaxies are drawn by gravity, and light is affected by gravity. Both respond to masses inside and outside Our Universal Event Horizon (OUEH), the edge of our observable universe.
Two routes, both gravity
EGC doesn’t depend on which cause of redshift turns out to be right. There are two possibilities, and both come from gravity.
The first is expansion driven by gravity: an external pull on all mass, from masses inside and outside Our Universe, drawing galaxies apart.
The second is that the redshift we see is gravitational: light that has travelled for billions of years past masses and away from them, stretched along the way.
It may well be a combination of the two.