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<\/div>A slice of the largest 3D map of the universe showing the underlying structure of matter<\/p>\n
laire Lamman\/DESI collaboration; custom colormap package by cmastro<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
The largest 3D map of the universe ever created is providing hints about the evolution of the cosmos, and they suggest that we may be wrong about the behaviour of dark energy, which makes up most of the universe. It seems that this mysterious force may be weakening over time.<\/p>\n
\u201cIf it holds up, this is a very big deal,\u201d says Adam Riess<\/a> at Johns Hopkins University in Maryland, who found the first evidence for dark energy 25 years ago. That is because the standard model of cosmology, called lambda-CDM, suggests that the strength of dark energy should be static over time.<\/p>\n Dark energy is thought to cause the accelerating expansion of the cosmos \u2013 if it is not static, that could also have huge implications for our ideas about the beginning of the universe, its size and its ultimate fate. Reiss, who was not involved in the new work, says the implications could mean \u201cwe will have to do some serious soul-searching regarding [our understanding of] gravity and fields\u201d.<\/p>\n <\/p>\n The strange findings come from the Dark Energy Spectroscopic Instrument (DESI) in Arizona \u2013 and even DESI collaborators are not quite sure what to make of the fact that their data suggests dark energy may have recently gotten weaker. \u201cIt\u2019s all we\u2019ve been talking in the collaboration about for months\u2026 whether this is interesting or not,\u201d says DESI spokesperson Kyle Dawson<\/a> at the University of Utah.<\/p>\n DESI researchers examined the strength of dark energy by measuring the large-scale structure and distribution of galaxies in the cosmos, which illuminates how the universe has expanded over time. The researchers then combined this information with three sets of data on supernovae, which act as so-called \u201cstandard candles<\/a>\u201d to determine the distances to cosmic objects thanks to their predictable brightnesses.<\/p>\n Surprisingly, each of the three samples of supernovae yielded a different answer to the change in the universe\u2019s rate of expansion over time. All three suggested that the effects of dark energy may have decreased in recent aeons, but the strength of these suggestions varied, so researchers are not quite sure how to interpret the data.<\/p>\n \u201cTwo of the supernova samples disagree with each other, and they\u2019re very, very similar samples,\u201d says Dawson. \u201cI don\u2019t know which one\u2019s right, it\u2019s possible that the truth lies in between, but it really looks like the differences lie in the way [the supernova researchers] evaluated the data.\u201d<\/p>\n Discrepancies in models are denoted by a factor called sigma, which measures the likelihood that a similar clash could have happened by chance if the models did disagree with one another. \u201cAbout 3-sigma is the level we usually sit up and pay attention and call an \u2018indication\u2019 of something,\u201d says Riess. Anything lower than that would not generally be particularly exciting to researchers \u2013 it would be too likely to be a simple coincidence.<\/p>\n