If you zoomed out on the universe, far beyond the level of planets, stars, or galaxies, you would end up seeing a large, evenly speckled expanse with no significant features. At least that was the conventional view.
The principle that everything everywhere looks the same is a fundamental pillar of the Standard Model of cosmology, which aims to explain the Big Bang and how the universe has evolved in the 13.7 billion years since.
But this week a meeting of some of the world’s leading cosmologists will gather at London’s Royal Society to ask the question: what if this basic assumption is wrong?
The meeting comes after a number of high-profile astronomical observations challenged the conventional view, according to Prof Subir Sarkar, a cosmologist at the University of Oxford and co-organiser of the meeting.
“We use in cosmology a model that was first formulated in 1922,” he said. “We have excellent data, but the theoretical basis is past its due date. More and more people are saying the same thing and they are respected astronomers.”
The conference brings together some of the scientists behind the recent anomalous findings. These include observations that suggest the universe is expanding faster in some regions than others, hints of megastructures in the night sky and evidence for cosmic flows – vast celestial rivers of material on a scale that cannot be easily accommodated within conventional theories .
Dr. Nathan Secrest, of the US Naval Observatory and a collaborator of Sarkar, presents findings that raise the possibility that the universe is slightly skewed. After analyzing a catalog of more than 1m quasars (extremely luminous galactic nuclei), the team found that one hemisphere of the sky appears to host about 0.5% more sources than the other.
This may not sound like a huge contradiction, but according to Sarkar, if confirmed, it would undermine the basis for dark energy, which is supposed to be the dominant component of the universe. “That would mean two-thirds of the universe has just disappeared,” Sarkar said.
Dr Konstantinos Migkas, from the University of Leiden, will share findings that the Hubble constant – the rate at which the universe is expanding – appears to vary across space. “Our results add another problematic piece to the puzzle,” Migkas said. On a local scale, at least, this suggests that observations do not match predictions from the standard model. “We can’t extrapolate that it’s wrong across the full universe,” he added.
Alexia Lopez, a PhD student at the University of Central Lancashire, has discovered what appear to be cosmic megastructures, called Big Ring and Giant Arc. These shapes, traced by galaxies and galaxy clusters, occur on a scale beyond which the universe should be smooth and effectively featureless.
“When we find a list of structures that exceed this scale, do they challenge this assumption that is so fundamental in cosmology?” said Lopez. “Perhaps there should be more of a critical analysis of our standard model.”
Sarkar suggests that belief in the standard model of cosmology is so deeply ingrained that it is treated as “the religion”. “Frankly, I find it annoying that this principle has not been checked,” he said, although not everyone agrees with this characterization.
Prof George Efstathiou, an astrophysicist at the University of Cambridge, presenting a more skeptical view at the conference, said it was not true that the model had not been questioned repeatedly. “People accuse me of defending the model,” he said. “But what they don’t realize is how much time I spent trying to disprove it. I totally disagree that there is some kind of groupthink.”
Efstathiou said that while interesting, none of the deviations presented were compelling enough to undermine standard theories. “The question is: how good is the data?” he said. The alleged skew of the universe, for example, could be due to the necessary use of multiple telescopes to observe different hemispheres of the sky, so sifting through data to look for patterns would inevitably turn up what appeared to be anomalies , he suggested. “I certainly don’t believe in the great circle in the sky,” he said.
Prof Wendy Freeman, presenting new findings from the James Webb Space Telescope, said: “There are all these tantalizing threads here at different levels of significance. We need more investigation into where, if at all, the standard model breaks down. I don’t think there is an obvious thing that will stand the test of time.”
This kind of robust debate is welcome at the conference. “I look forward to a vigorous discussion,” Sarkar said. “Let them do it with everything they’ve got.”
