Physicists may need to come up with a new theory for how the universe works, after a dark energy experiment produced confounding results. An international team of scientists has released a "3D map of the universe", built on data from the Dark Energy Spectroscopic Instrument (DESI). The map contains information about more than 14 million galaxies, gathered by the DESI device at the Mayall Telescope in Arizona. The results suggest dark energy, a mysterious phenomenon thought to be behind the acceleration of the Universe after the Big Bang, is slowing down. So what is it saying, and how likely is it we'll need to rewrite the physics textbooks? Do we need to rethink Einstein's theories of the universe? The data still supports Einstein's theory of relativity but it's starting to question the make-up of the universe that came after the Big Bang. The current model — known as the Lambda-CDM model — posits the universe has been expanding due to a "cosmological constant", which governs dark energy. Rossana Ruggeri, a researcher at Queensland University of Technology and collaborator on the DESI project, said the Lambda-CDM model is the "backbone" of our understanding of the universe. What researchers are currently calling into question is the idea that dark energy is constant. The DESI experiment has started to hint that dark energy may not be a constant at all, but changing over time. "We have doubled the volume and the data, this has really sharpened the precision of the measurements that we can make," Dr Ruggeri said. "We're still finding these hints that there might be something a bit more complex than just the cosmological constant permeating space." Tamara Davis, an astrophysicist at the University of Queensland, said other large astronomy projects, such as the Dark Energy Survey, had started to point towards this idea too. "This new set of data is pushing even further in that direction," she said. How sure are they that dark energy is getting weaker? Scientists from around the world have cross checked data collected by DESI against information from other telescopes on the cosmic microwave background (the light left over from the Big Bang), supernovae, and the way gravity from galaxies can warp light. While the researchers have been extremely careful checking and re-checking their results, they're still not entirely confident their findings haven't happened by accident. Physicists use a statistical measure to judge how strong their theories are. At the moment, the DESI results, in combination with all this other information, sit at "4.2 sigma" at their highest. Dr Ruggeri said that a measure of 5 sigma means there's an extremely low probability that the results have happened by accident. "It's usually standard to assume that once you find 5 sigma tension … you say you found new physics," she said. That 4.2 sigma number comes from comparing DESI's data to data from other telescope surveys. More DESI data, and more information from other sources, should help the team get up to the magic 5 number. Professor Davis said that, despite how hard the team has worked on checking and verifying the data, there's still a chance the findings don't pan out. "I still think that there is a very strong chance there's a statistical fluctuation or a small systematic [error] in our data that's causing this," she said. If the current model is wrong, what happened after the Big Bang? If the results are, however, correct and dark energy isn't constant, scientists will need a new theory to explain the role it plays in the universe. But Dr Ruggeri said this new theory was still in question. "Once we open up the possibility of dark energy not being a cosmological constant, we have so many different models that theoretical physicists have been building up." There are some potential frontrunners — including one called quintessence theory — that might finally be able to tie the theory of relativity to the other great pillar of modern physics: quantum science. But Professor Davis said theorists will need to go back to the drawing board to come up with something new that fits all the data. What's next? DESI has only completed a fraction of its intended run so far: it has observed 14 million galaxies out of a total goal of 40 million. Those 40 million galaxies may provide physicists with enough information to dismantle the standard model of the universe — or they may not. Other telescopes, like the ESA's Euclid telescope that has also just released a trove of data on hundreds of thousands of galaxies it has captured, may help to support a new model of the universe. But whether or not DESI is able to toss out the standard model, it will be able to yield other information about the universe. Dr Ruggeri said the collaboration has research coming down the pipeline on mysterious neutrino particles, for instance. Another, which looks at gravity, may eventually actually challenge Einstein's theory of relativity — but more research is required to confirm this. Professor Davis is excited by the speed and size of the DESI experiment. It can complete observations in a single night that has taken other, older telescopes years to finish. It, and other newer projects, can also capture very fine data about the history of the universe. "When this light started travelling towards us, the Sun hadn't turned into a star yet — it was just a cloud of gas," Professor Davis said. "We're watching history unfold as we look at this really old light that's been travelling through the universe, and the first thing it's hit is the mirror of our telescopes."