How will we know if the universe stops expanding?

The idea that the universe should be expanding at a decreasing rate, which would be consistent with the theory that the universe recycles—that is, where there are alternating big bangs and big crushes where the universe is pulled back together—was tested in 1998 through an examination of quasars. This theory was consistent with the dominant belief that matter and energy are eternal.

The study's findings indicated that rather than the universe's rate of expansion slowing down, it was increasing. This is consistent with the empirical scientific evidence that the universe's rate of expansion will never slow down; consequently, matter and energy are not eternal and our observable universe will not recycle.

Through a variety of techniques, including the measurement of the redshift of distant galaxies and the analysis of cosmic microwave background radiation, scientists are able to measure the rate of cosmic expansion. In the event that the expansion were to cease, these indicators would cease to provide evidence of the increasing distances between celestial objects.