The going theory among cosmologists is that the universe will eventually rip itself to shreds owing to its ever-accelerating rate of expansion. Not so, say a pair of physicists who have just taken it upon themselves to reformulate an integral facet of general relativity: the cosmological constant.
Albert Einstein had to add the idea of the cosmological constant (i.e. the value of the uniform energy density that permeates the vacuum of space) to his theory of general relativity as a way to explain why the universe wasn't collapsing in on itself and why it appeared to be static. More recently, because the universe appears to be expanding, the cosmological constant had to be given a non-zero value.
The problem, say Nemanja Kaloper and Antonio Padilla, is that this "non-zero" value is very, very far from zero and that it's unreasonably huge. What's more, resulting "tuning" rationalizations, like the notion that the energy comes from a Higgs-like particle, are too unstable. Michael Schirber from the American Physical Society explains:
Because the cosmological constant is, by definition, constant throughout time and space, it's natural to associate it with the energy of the vacuum. Unfortunately, if one calculates the vacuum energy density from quantum zero-point fluctuations (i.e., when particles pop in and out of existence), the result is a factor of 10120 higher than the value deduced from astronomical observations.
To address this problem, Kaloper and Padilla have slightly reformulated general relativity such that the cosmological constant is the historical average of the matter energy density in the universe, thus canceling out the input from quantum fluctuations.
The result is a relatively small cosmological constant — one which suggests that the universe's current rate of expansion will stop in the future and reverse direction, leading to the Big Crunch.
Top image: Computer simulation of the formation of large-scale structures in the universe, showing a patch of 100 million light-years and the resulting coherent motions of galaxies flowing toward the highest mass concentration in the center. Credit: ESO.