A new theory claims the universe might not be expanding as quickly as was previously thought.

Scientists at the University of Arizona recently found that the supernovae used to measure distances in the universe, Type Ia supernovae, have irregularities from one to the next.

"We found that the differences are not random, but lead to separating Ia supernovae into two groups, where the group that is in the minority near us are in the majority at large distances -- and thus when the universe was younger," Peter A. Milne, an associate astronomer, said in a statement. "There are different populations out there, and they have not been recognized. The big assumption has been that as you go from near to far, type Ia supernovae are the same. That doesn't appear to be the case."

Since Ia supernovae vary in brightness, because of different levels of dark energy, the idea that the universe is expanding at an accelerating rate may not be true. That theory has been based on the fact supernovae look fainter the farther away they are, which could just have to do with how they naturally differ.

The study is published in The Astophysical Journal.