Synopsis: Cosmological Constant Redefined

A slight revision of general relativity can avoid an enormously large (and observationally inconsistent) cosmological constant, assuming that our Universe eventually collapses back on itself.
Synopsis figure
Adapted from an illustration by NASA/ESA/STScl

The cosmological constant refers to a uniform energy density that presumably could explain the accelerated expansion of the Universe. However, a straightforward calculation of this constant gives an impossibly large value. A new approach to this problem, detailed in Physical Review Letters, involves a slight reformulation of general relativity, in which the cosmological constant ends up being a historical average of the matter energy density in the Universe. Besides predicting a small cosmological constant, the theory foresees an eventual collapse of our Universe in a big crunch.

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.

Theorists have tried to “tune” the cosmological constant by assuming that the quantum vacuum energy is cancelled out by some additional energy (for example, coming from a Higgs-like particle). But these solutions have proven to be unstable. Nemanja Kaloper of the University of California, Davis, and Antonio Padilla of the University of Nottingham, UK, have devised a new strategy, in which they rewrite Einstein’s general relativity equations. The new equations effectively cancel out the input from quantum fluctuations, by treating the cosmological constant as an average of the matter contribution over all of space and time. This produces a relatively small cosmological constant, but it also predicts that our current accelerated expansion will somehow stop in the future and reverse direction. – Michael Schirber


Announcements

More Announcements »

Subject Areas

Cosmology

Previous Synopsis

Next Synopsis

Fluid Dynamics

Motion in the Ocean

Read More »

Related Articles

Synopsis: IceCube Neutrinos Pass Flavor Test
Particles and Fields

Synopsis: IceCube Neutrinos Pass Flavor Test

The highest energy neutrinos ever recorded have a flavor distribution of neutrinos that is consistent with the particles having a cosmic origin. Read More »

Viewpoint: Weighing Dark Matter Halos with the Cosmic Microwave Background
Astrophysics

Viewpoint: Weighing Dark Matter Halos with the Cosmic Microwave Background

Gravitational lensing by foreground dark matter halos leaves an observable imprint on the cosmic microwave background, which can be used to determine their masses Read More »

Viewpoint: A Clearer View of a Dusty Sky
Astrophysics

Viewpoint: A Clearer View of a Dusty Sky

A signal in the cosmic microwave background thought to be evidence of inflation in the early Universe can be explained by interstellar dust. Read More »

More Articles