Instructions: Given a text, write a compressed version of it in a single sentence.
Input: One way to explain a persistent accelerating expansion of a flat universe is to reintroduce Einstein's "cosmological constant" into the field equations of general relativity. A positive cosmological constant expresses itself as a repulsive force between masses that increases with the distance between those masses.
Output:
One way to explain an accelerating expansion of a flat universe is Einstein's "cosmological constant". A positive cosmological constant expresses itself as a repulsive force between masses that increases between those masses.