In Woody Allen’s 1977 classic, “Annie Hall,” a 9-year-old version of the protagonist is depressed.

When asked why he is upset, young Alvy says grimly, “The universe is expanding ... and if it’s expanding, someday it will break apart and that would be the end of everything!”

To this his frustrated mother replies: “What has the universe got to do with it? You’re here in Brooklyn! Brooklyn is not expanding!”

On Tuesday, three Harvard graduates were awarded the Nobel Prize in physics for their joint-discovery that the universe is not only expanding, but its rate of expansion is increasing—a discovery that shook the field of astronomy by overturning the common belief that the universe’s growth was slowing down.

Saul Perlmutter ’81, Adam G. Riess, and Brian P. Schmidt—the latter two each received both masters and Ph.D.s in astronomy from Harvard—worked in two teams in 1998 to study a special type of supernova known as the expanding star. They concluded separately that a mysterious force, referred to as “dark energy,” is pushing galaxies away from one another at a surprising rate.

The discovery enables scientists to predict what the universe may be like in the far future, specifically that it will be colder as light emitted from one galaxy will never reach another because they are traveling away from each other at a rapid speed.

The universe will keep expanding until there is no more energy in the universe, leading to an energy death, according to Abraham “Avi” Loeb, the chair of Harvard’s Astronomy Department.

Perlmutter and Schmidt led two separate teams that used a particular sub-category of supernova, or an exceptionally large explosion of a star, to gauge the expansion rate of the universe, which is 14 billion years old and has been expanding ever since the Big Bang.

The study seems to refute the thinking that the universe might implode, a theory which is popularly called the “Big Crunch.” The researchers were attempting to understand how quickly the universe was decelerating when they realized their calculations indicated acceleration.

Reiss said that he was “stunned, absolutely shocked” when he first saw the results and at first thought he was wrong.

“Anyone who has done scientific research or a chemistry lab in high school knows it is easy to make mistakes,” Reiss said in an interview. Only the fact that another group of researchers generated the same results stopped him from looking for the mistake he thought he must have made, he recalled.

Reiss said that his studies at Harvard’s Astronomy Department directly led to the basis of his discoveries and that the findings of Harvard Professor Robert P. Kirshner, who was Reiss’ thesis advisor, were important to the research.

Kirshner introduced Reiss to the idea of using exploding stars to calculate the expansion of the universe and was involved in the study that lead to the surprising results.

“The discovery that this expansion is accelerating is astounding,” the Royal Swedish Academy of Sciences, which awards the prize, said in a release. “The acceleration is thought to be driven by dark energy, but what that dark energy is remains an enigma—perhaps the greatest in physics today.”

Perlmutter, who lead the Supernova Cosmology Project, will receive half of the $1.4 million prize while the rest will be split between Schmidt, who lead the High-Z Supernova Search Team, and Reiss, who helped interpret the data for Schmidt and was the lead author of the 1998 paper in the Astronomical Journal where the results of the study were fist published.

The new discovery fitted very well with what Einstein considered his “greatest blunder.” In his general theory of relativity, Einstein needed an expanding universe but at that time the universe was thought to be more stable. Einstein introduced a constant that would help the numbers come together but then abandoned it, believing it to be a failure. An accelerating universe changes Einstein’s failure to brilliant foresight and for that Reiss and Schmidt were also awarded the Albert Einstein medal for furthering his research.

—Gautam S. Kumar and Caroline M. McKay contributed to the reporting of this article.