Dark energy has been a mysterious element of cosmological equation since it was proposed three decades ago, but new research says we can make the math of the universe’s expansion work without relying on it at all.
The standard cosmological model has a problem. We know that the universe is expanding, but rather than eventually slowing down due to gravity, this expansion seems to be speeding up. This implies the theoretical ‘dark energy’ as fuel for this acceleration.
In a new paper published last week in Proceedings of the Royal Society A, though, a team of researchers demonstrate how the problem of accelerated expansion might be more a matter of current cosmological models being based on instabilities that do not translate very well into observable reality.
“Unstable solutions in physics and science are considered not physical,” Blake Temple, the study’s co-author and a mathematician at University of California, Davis (UC Davis), said in a statement. “You’ll never observe them in nature.”
Temple and the UC Davis team instead explore an alternative model of expansion that is reportedly simpler and “based entirely within the framework of Einstein’s original theory” of general relativity.
When Albert Einstein first introduced the cosmological constant lambda (Λ), he did so with the assumption that the universe was static, an idea he later discarded when Edwin Hubble showed that it was actually expanding. Then in 1998, a Nobel-winning discovery found that the universe’s expansion rate was accelerating.
It was around this time that cosmologists revived lambda as a metric to characterize the universe’s accelerated expansion. Hence, the standard cosmological model came to be known as the lambda-cold dark matter model. The force driving this accelerated expansion was dubbed dark energy and is often associated with the cosmological constant.
A key component of the standard model is Friedmann spacetimes, which “describe a uniform three-dimensional universe of galaxies” that expand at a rate “determined by Einstein’s field equations,” according to the paper. But for the team, the math “didn’t add up.”
“Our first idea was that maybe the universe was expanding because there was a shockwave, and the anomalous acceleration was the expanding wave behind that shockwave,” Temple said.
Specifically, the team explored whether Friedmann spacetimes generated by the Big Bang’s instability could by themselves “account for the anomalous acceleration of the galaxies,” the authors noted in the study. They derived a self-similar version of Einstein’s field equation to evaluate the stability of Friedmann spacetimes during the “radiation epoch of the Big Bang,” Temple explained.
According to the team’s framework, Friedmann spacetimes were unstable both at small and large length scales at the Big Bang. What this means is that, even before dark energy comes anywhere near the equations, the “set of possible accelerations induced by the instability is rich enough to mimic the effects of dark energy at all orders, even consistent with a variable acceleration,” the paper noted.
That is, there’s a way to do the math to derive acceleration directly from the initial frameworks set forth by Einstein and Leonhard Euler. It’s too early to tell whether cosmologists will choose to adopt this alternative, but it’s an intriguing idea nonetheless.
Source: Gizmodo