Dark Energy Is Real, Despite Claim to the Contrary

The galaxy cluster Abell 1689 is famous for the way it bends light in a phenomenon called gravitational lensing. Study of the cluster has revealed secrets about how dark energy shapes the universe.
(Image: © NASA, ESA, E. Jullo (JPL/LAM), P. Natarajan (Yale) and J-P. Kneib (LAM))
A new study suggests that dark energy might not be real after all. But other scientists have found major flaws with this bold claim.

Dark energy is a mysterious and hypothetical form of energy that is used to explain the accelerating expansion of our universe. One way that scientists have provided evidence of dark energy and its influence on the universe comes from measuring the redshift (a phenomenon in which the light coming from objects moving away from us appears red) of type Ia supernovas (SN Ia).

In other words, by measuring how the light that these supernovas emit changes as they move away from us, scientists can show how far they are and therefore how the universe is “pushing out” or expanding over time. This evidence depends on the assumption that supernova luminosity, or brightness, doesn’t evolve with redshift, or vary over cosmic time.

If dark energy is real, as many scientists expect it to be, the universe will continue to expand faster and faster. But, if it turns out that dark energy doesn’t exist after all, the expansion of the universe will eventually slow down and the universe could even start shrinking.

In a new study, published to the pre-print server arXiv and accepted for publication in The Astrophysical Journal, researchers from Yonsei University in Seoul, South Korea, along with collaborators at Lyon University and the Korea and Space Science Institute claim that they have found proof that dark energy might not exist at all. They studied a small sample of galaxies hosting about 30 type Ia supernovas and claim to have disproven the assumption that supernova luminosity evolves.

“Quoting Carl Sagan, extraordinary claims require extraordinary evidence, but I am not sure we have such extraordinary evidence for dark energy. Our result illustrates that dark energy from SN cosmology, which led to the 2011 Nobel Prize in Physics, might be an artifact of a fragile and false assumption,” professor Young-Wook Lee of Yonsei University, who led the study, said in a statement.

“Taken at face values, our result suggests that ~100% of the evidence for dark energy simply goes away. This will be confirmed by future observations,” Lee and co-author Yijung Kang told Space.com in an email.

To come to such a bold conclusion, the researchers observed the spectra — bands of colors that can be produced when matter interacts with or emits electromagnetic radiation — of the stars in nearby galaxies that host these supernovas. Studying the light coming from these galaxies helped them to determine the ages of the stars in those galaxies.

The team found what they reported as a significant correlation between the luminosity of these supernovas and the ages of the stars in these galaxies. They found that supernovas in younger galaxies are fainter than in older galaxies, which would upend the assumption that supernova luminosity doesn’t evolve over cosmic time. So, because they found fault with one of the main pieces of evidence for dark energy, they concluded that there is a likelihood that dark energy may not exist at all.

Taking this study at face value, it seems probable that, if the researchers’ work is correct, it could throw a huge wrench into our understanding of dark energy. However, in speaking with Adam Riess, a professor of physics and astronomy at Johns Hopkins University in Baltimore, and looking a bit closer at the study, it became clear that this study likely does not discredit the existence of dark energy.

“I think that it’s flawed,” Riess said about Lee’s study. The findings from Lee’s team are “at odds with what’s been seen with larger samples of supernovae,” he added.

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