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Someday, the universe will end. As for how—be it the Big Freeze, the Big Rip, the Big Crunch, or even the Big Slurp—the possibilities are numerous and delightful. That said, the general consensus is that an accelerated expansion of the universe will end in a Big Freeze. And the latest research argues that a recent challenge to this understanding isn’t supported.
A study published yesterday in Monthly Notices of the Royal Astronomical Society (MNRAS) reinforces support for the theory that our universe’s expansion is still accelerating. The new results directly challenge a paper from November last year, published in the same journal, which argued that flaws in popular measurement methods mischaracterized the deceleration of the universe’s expansion. The latest work asserts that there is “no flaw in the widely accepted theory,” the team behind the new study said in a statement.
“The previous and well-accepted measurements were, in fact, fine, and our current understanding of the fate of the universe remains robust,” Phil Wiseman, the study’s lead author and an astrophysicist at the University of Southampton in the U.K., added.
This doesn’t mean we’ve decisively solved the many mysteries of the cosmos. Even if the universe’s expansion rate is accelerating, scientists have yet to fully understand the true nature of dark energy, the hypothetical force said to drive this expansion.
Some cosmic gripes
The pair of papers is actually the latest in a series of academic exchanges between research teams involving Young-Wook Lee and Adam Riess, astrophysicists at Yonsei University in South Korea and Johns Hopkins University, respectively. In the past five or so years, Lee’s team dug up evidence of age biases in measuring Type Ia supernovas, used as “standard candles” for measuring galactic distances. The argument was that astronomers misunderstood the maximum brightness of Type Ia supernovas, and, therefore, the speed of the universe’s expansion.
Almost every time, Riess and collaborators bounced back with rebuttals reinforcing the prevailing view—that the universe is expanding at an ever-accelerating rate. (Riess earned a Nobel Prize in 2011 for discovering this possibility). Last November’s challenge featured a larger dataset with a more nuanced approach; rather than suggesting dark energy doesn’t exist, Lee’s team argued that it wasn’t as constant as we believed. When the team corrected models for the proposed bias, it found the data aligned much more closely with independent findings from the first batch of Dark Energy Spectroscopic Instrument (DESI) observations.
Well, there’s that
The latest paper directly addresses these criticisms. The new analysis stated the South Korean team incorrectly assumed the age of relevant stars and didn’t account for the mass of host galaxies, which “captures known environmental dependencies that also correlate with stellar age,” the study noted. What’s more, the respective ages of the host galaxies aren’t interchangeable with those of the progenitors of Type Ia supernovae, as is implied in the November study.
Accordingly, for the new study, the researchers presented a reevaluation of relevant data that incorporates the missing factors. Doing so removed the alleged biases, which are “both accounted for and exaggerated,” they wrote in the paper.
“Extraordinary claims require especially careful testing,” Riess said in the statement. “What we find is that when we calibrate these supernovae, accounting for different host environments and populations, the evidence for cosmic acceleration remains remarkably consistent.”
To be continued?
When asked to comment, Lee told Gizmodo that his team had already prepared a counter-rebuttal to the rebuttal, which has been submitted to MNRAS and is currently available as a preprint on arXiv. In the preprint, Lee and colleagues argued that the “two main arguments advanced in their paper are either affected by serious errors or lead to conclusions that are internally inconsistent by their own logic.”
Specifically, Lee’s team points out that the corrections may be underestimating an important age-related trend. And while the age of a galaxy isn’t the same thing as the age of the star that exploded, the researchers say the two are more closely linked than the other team suggests.
So the debate continues. That said, it’s worth noting that the researchers involved in this back-and-forth call these processes “fundamental to science,” as per Mark Sullivan, the study’s co-author and an astrophysicist at the University of Southampton, in the statement. “This is how progress is made,” he said.
Again, there are still many outstanding mysteries we’ve yet to understand about the cosmos. For instance, astronomers believe it’s likely that dark energy drives the universe’s expansion but are becoming increasingly divided over whether dark energy is constant or fluctuating and, if so, what that would mean for the universe’s fate.
