Answer: 1. recollapsing universe
4. critical universe
3. coasting universe
2. accelerating universe
Explanation:
The universe is continually growing and galaxies are moving apart relative to one another.
These four models foresee the expansion and possible contraction of the universe.
Recollapsing universe: this model predicts that galaxies will stop growing apart and start getting closer to one another. It predicts that there is enough density to stop the growth of the universe in the future.
Critical universe: the universe has the same density as the critical density. This is the difference between the density the universe requires to stop and that of a universe with too little density to ever stop expanding
.
Coasting universe: has enough density to enable galaxies to keep growing apart
, in essence, less than the critical density.
Accelerating universe: this model explains that the distance of far-off galaxies is growing exponentially from an observer over time.
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