End of the Universe

While the fate of the universe is unkown, cosmologists have come up with many different theories on how the universe will end. One theory some cosmologists believe is that the expansion of the universe is slowing down. Gravity will overcome the outward expansion, and the universe will collapse in on itself becoming a singularity again. Then the universe will experience a Big Bang, restarting the cycle.

Other cosmologists disagree with this theory because they believe the expansion is accelerating. They believe the universe will continue to expand forever. As the universe expands, it will get cooler until it reaches a point where it is too cold for stars to form. Eventually, all stars will die, planets will decay, and even black holes will evaporate. Some cosmologists have studied supernovae, which are explosions of stars that are dying. They measure the distance to the star by measuring their brightness. When the supernovae is dimmer than expected, it reveals that the star is farther away, meaning that the universe's expansion is accelerating instead of slowing down. Cosmologists do not exactly know what is causing this acceleration, but they call it dark energy. Dark energy is a force that counters gravity. We do not really notice it because it is much weaker than gravity. There is still so much to learn about dark energy and what it means for the future of our universe.

Source:NASA’s WFIRST Will Help Uncover Universe’s Fate