Quote:
Originally Posted by Van Rijn
The Andromeda and Milky Way galaxies are heading towards each other, it isn't a "collapse."
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Look, don't mince words.
If there was nothing beyond 5 Mpc, but otherwise everyting looked the same up to 5 Mpc, we would say, "The universe is 5 Mpc across and contracting." (According to GR as currently formulated, the universe must do one or the other: expand or contract.) It is not until we look beyong 5 Mpc that we observe expansion. So we say, "The universe is expanding."
But this is incorrect. It is
not doing one or the other; it is doing
both at the same time: contracting locally/expanding non-locally.
Quote:
Originally Posted by Van Rijn
But in any event, at the shorter scales, gravity dominates over cosmological expansion. If it didn't, we wouldn't exist. This quantitative issue certainly isn't ignored, and in fact, there is the idea of the Big Rip where, if validated, there could come a time in the distant future when galaxies and even planets and living creatures would be ripped apart. |
Duality, as you point jout, is observable. "The Big Rip" is pure speculation. Speculation does nothing to invalidate what is observed.