Dark vitality is central to our trendy understanding of cosmology. In the usual mannequin, darkish vitality is what drives the enlargement of the Universe. In common relativity, it’s described by a cosmological fixed, making darkish vitality a part of the construction of area and time. But as we’ve gathered extra observational proof, there are a number of issues with our mannequin. For one, the speed of cosmic enlargement we observe is determined by the observational methodology we use, referred to as the Hubble pressure downside. For one other, whereas we assume darkish vitality is uniform all through the cosmos, there are some hints suggesting that may not be true. Now a brand new examine argues we’ve received the entire thing flawed. Dark vitality, the authors argue, doesn’t exist.
Let’s begin with what we all know. When we glance out throughout the billions of light-years of cosmic area, we see that matter is clumped into galaxies, and people galaxies are teams into clusters in order that the Universe has clumps of matter separated by nice voids. On a small scale, which means the distribution of matter is uneven. But as we go to bigger scales, say a billion light-years or so, the typical distribution of matter evens out. On a big scale, the cosmos is homogeneous and never biased in a selected course. This means we are able to broadly describe the Universe as the identical in every single place. This is called the precept of homogeneity. By making use of this precept to cosmic enlargement, we are able to mannequin the Universe by the Friedmann–Lemaître–Robertson–Walker (FLRW) metric, the place darkish vitality is a cosmological fixed.
Opponents of the usual mannequin argue that the precept can’t be utilized to cosmic enlargement. Some even argue that the essential ideas of common relativity can’t be utilized on cosmic scales. In one such mannequin, referred to as the Timescape mannequin, it’s argued that darkish vitality would violate the precept of equivalence. Since the precept equates inertial vitality and gravitational vitality, there isn’t any strategy to distinguish cosmic enlargement as an actual impact. Furthermore, since we all know that gravitational fields have an effect on the speed of time, the Timescape mannequin argues that the Universe can’t be homogeneous in time. Basically, the mannequin argues that inside the gravitational properly of a galactic cluster, clocks would run extra slowly than they might inside the huge empty cosmic voids. Over the billions of years of cosmic historical past, this distinction would construct up, making a variance of time all through the Universe. It is that this time divergence that may give the looks of cosmic enlargement.
In this newest examine, the authors use the Pantheon+ dataset of Type Ia supernovae to see if it higher matches the usual cosmological mannequin or the Timescape mannequin. The predominant distinction between the 2 fashions is that cosmic enlargement should be uniform in the usual mannequin, whereas within the Timescape mannequin, cosmic enlargement can’t be uniform. What the crew discovered was that whereas the Pantheon+ helps each fashions, the information is a barely higher match to the Timescape mannequin. In different phrases, the very best match of the information means that darkish vitality is an phantasm, however the match is just not sturdy sufficient to disprove the usual mannequin.
If future observations proceed to help the Timescape mannequin, it might revolutionize our understanding of the Universe. But there are causes to be cautious. To start with, the Timescape mannequin is just one of many proposed options to the usual mannequin, which this examine doesn’t tackle. The Timescape mannequin additionally has some inside problems with its personal that may have to be resolved to turn into the brand new cosmological mannequin. But it’s clear now that we are able to’t ignore the truth that the usual mannequin could also be flawed. We are getting into an thrilling interval of astronomy the place our information of the Universe will improve considerably within the close to future.
Reference: Seifert, Antonia, et al. “Supernovae proof for foundational change to cosmological fashions.” Monthly Notices of the Royal Astronomical Society: Letters 537.1 (2025): L55-L60.
Reference: Wiltshire, David L. “Cosmic clocks, cosmic variance and cosmic averages.” New Journal of Physics 9.10 (2007): 377.
