Question

there is a theory that gravity could pull galaxies back together, causing a reverse big bang. which observation makes this theory less likely than the idea that the universe may continue to expand? background radiation is present. galaxies exist outside of the milky way. the expansion of the universe is accelerating. gas giants form farther from the sun, where temperatures are cooler.

Explanation:

The accelerating expansion of the universe suggests that there is a force (dark energy) overpowering gravity's pull. This makes the idea of gravity pulling galaxies back together for a reverse big - bang less likely. Background radiation is evidence for the Big Bang but not relevant to ruling out a reverse big - bang. The existence of galaxies outside the Milky Way has no bearing on the universe's expansion or contraction. The formation of gas giants is a solar - system related phenomenon and not related to the overall expansion or contraction of the universe.

Answer:

The expansion of the universe is accelerating