Although the answer to this ancient question is still unknown, there are strong observational hints toward a clear outcome. And, that, in and of itself, would have surprised most astronomers who thought about the subject during the past 85 years.

For most of recorded history, the answer was simple: The universe has always existed and always will. Few people challenged the dogma or even suspected it might not be true.

That started to change in the 1910s with the publication of Albert Einstein’s general theory of relativity. The first models developed from Einstein’s equations showed that the universe does not have to be static and unchanging, but it can evolve.

In the 1920s, Belgian priest and astronomer Georges Lemaître developed the concept of the Big Bang. Coupled with Edwin Hubble’s observations of an expanding universe, astronomers were coming around to the idea that the universe had a beginning — and could have an end.

It wasn’t until the 1960s that strong observational evidence supported the Big Bang. The two breakthroughs were the discovery of the cosmic microwave background radiation by radio astronomers Arno Penzias and Robert Wilson, and the realization that active galaxies existed preferentially in the distant universe, which meant they existed when the cosmos was much younger than it is today, and so the universe has been evolving.

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By the 1980s, most astronomers were convinced that the universe began with a bang, but they had little clue how it would end. There were basically three scenarios, all based on how much matter the universe contained. If the cosmos had less than a certain critical density, the universe was “open” and would expand forever; if the density were above the critical value, the universe was “closed” and the expansion ultimately would stop and then reverse, leading to a “Big Crunch”; if the universe were at the critical density, it was “flat” and expansion would continue forever, but the rate would eventually slow to zero.

Observations seemed to favor an open universe, with astronomers finding only about 1 percent of the matter needed to halt expansion. But scientists knew that a lot of dark matter — nonluminous material that nevertheless has gravitational pull — existed. Would it be enough to stop the expansion? No one knew.