Recent measurements of the expansion rate of the Universe have plunged the standard model of cosmology, the ΛCDM model, into a crisis. In a new paper published in the journal Physical Review D, a duo of physicists at the University of Southern Denmark proposes a simple resolution to this problem.
This artist’s impression shows the evolution of the Universe beginning with the Big Bang on the left followed by the appearance of the Cosmic Microwave Background. The formation of the first stars ends the cosmic dark ages, followed by the formation of galaxies. Image credit: M. Weiss / Harvard-Smithsonian Center for Astrophysics.
“Recent direct measurements of the expansion rate of the Universe using Type Ia supernovae as standard candles or strong gravitational lensing are in tension with the expansion rate inferred form the Cosmic Microwave Background when assuming the standard cosmological model,” said University of Southern Denmark’s Professor Martin Sloth and Dr. Florian Niedermannn.
“It is a hot subject of discussion whether unaccounted for systematical effects in astronomical distance measurements are responsible for this discrepancy or whether we have to refine our understanding of the history of the Universe by going beyond the ΛCDM model.”
“It could very well be the latter. A new type of dark energy can solve the problem of the conflicting calculations,” Professor Sloth added.
“In our model, we find that if there was a new type of extra dark energy in the early Universe, it would explain both the background radiation and the supernova measurements simultaneously and without contradiction.”
The researchers believe that in the early Universe, dark energy existed in a different phase.
“You can compare it to when water is cooled and it undergoes a phase transition to ice with a lower density,” Professor Sloth said.
“In the same way, dark energy in our model undergoes a transition to a new phase with a lower energy density, thereby changing the effect of the dark energy on the expansion of the Universe.”
According to the team’s paper, ‘early dark energy’ underwent a phase transition triggered by the expansion of the Universe.
“It is a phase transition where many bubbles of the new phase suddenly appear, and when these bubbles expand and collide, the phase transition is complete,” Professor Sloth said.
“On a cosmic scale, it is a very violent quantum mechanical process.”
Florian Niedermann & Martin S. Sloth. 2021. New early dark energy. Phys. Rev. D 103 (4): L041303; doi: 10.1103/PhysRevD.103.L041303