This is literally straight out of 3 Body Problem - book 3 iirc written like 10 years ago

Basically creating a low density area next to a high density area will cause the high density to rush to low density to fill the void, ya know, like wind.

He explains it better in 3body

And even at the speed of light, we would never reach “The end of the cosmos,” because the universe is expanding at the speed of light.

Hense why as you go closer to the speed of light you experience time more slowly than an observer, because time is basically a by-product of this expansion. You would never even reach the next galaxy because we’re moving away from each other at the speed of light.

We would need a warp like in Event Horizon.

I’d prefer to avoid almost anything like in Event Horizon.