Consensus is the universe was created in a colossal bang — called the Big Bang — roughly 13.8 billion years ago, and then began expanding. All signs suggest the universe is continuing to stretch out in every direction like an ever-expanding balloon.
However, agreement among physicists on the birth and life of the universe hits a snag beyond this point. The expansion rate of the universe appears to differ depending on how it's measured.
The way we measure universal expansion could be wrong, or something could be happening in the universe that physicists have yet to uncover — throwing their models off.
The latter might be so, according to a recent study published in the journal Physical Review D. In the study the authors propose a new kind of dark energy in the universe. When this new type is included in calculations of the expansion of the universe, you get results with more in common than before — reducing the schism in consensus.
A new kind of dark energy might explain the expansion of the universe
"A new type of dark energy can solve the problem of the conflicting calculations," said Professor of Cosmology Martin S. Sloth of the University of Southern Denmark (SDU), in a Science Daily report.
When physicists try to calculate the rate of the universe's expansion, they assume the universe is made up of three parts: dark matter, dark energy, and ordinary matter. Until recently, every kind of observation worked with this model of the universe's composition of energy and matter — but this might no longer be the case.
Varying results in the calculation of the universe's expansion happen when physicists look at the latest data from measurements of supernovae or cosmic microwave background radiation. The two methods just have different output expansion rates.
"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," said Sloth.
"We 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," explained Sloth. "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."
Positing a dark energy 'phase shift' could strengthen consensus on the universe's rate of expansion
Sloth and post-doctoral researcher Florian Niedermann — a colleague of Sloth's at SDU — said their calculations work, provided you imagine dark energy experienced a phase transition caused 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," said Sloth. "On a cosmic scale, it is a very violent quantum mechanical process."
As of writing, we know what roughly 20% of the universe's matter consists of. This is ordinary matter, which composes all of us, the planets, stars, and galaxies. But the universe also contains dark matter — which so far has evaded all empirical study.
The third ingredient — dark energy — is the energy thought to drive the universe's expansion — making up roughly 70% of the universe's energy density. While the universe is not lacking in mysteries, building better consensus in our calculations about what it's made of, how it works, and when dark energy underwent a phase shift could bring us closer to a cohesive understanding of the rate of cosmic expansion.