![]() ![]() ![]() All other measurements of the CMB, like those by the Atacama Cosmology Telescope (ACT) in Chile and the Wilkinson Microwave Anisotropy Probe, are consistent with flatness. ![]() But aside from this data, there isn’t the slightest reason to doubt the universe is flat. If true, it would overturn decades of astronomical findings. He and his co-authors deemed it a “cosmological crisis.” “Once you assume a closed universe it’s a bit of a catastrophe,” he says, “because there are many data sets that start to be in tension with. He also recognizes the implications of that statement. His point isn’t that the universe is closed, per se, only that this inconsistency may be telling us something important. Melchiorri admits he’s “playing a bit of the devil’s advocate,” but he does believe scientists should remain humble and not dismiss the Planck data outright. “If you get a big dataset and you look for weirdnesses,” Lewis says, “you’re bound to find it.” He, like most researchers, attributes the discrepancy to a statistical fluke. “It’s something you can live with quite easily,” says Antony Lewis, a cosmologist at the University of Sussex in Brighton, England, and a member of the Planck team. The Planck collaboration (of which Melchiorri is a part) also detected a lensing anomaly but didn’t find it as significant. If you remove the assumption of a flat universe, instead of “trying to fit the data to the wrong model,” he says, the deviation disappears. They analyzed the amount of gravitational lensing - how much the light from the CMB has been deflected by the gravity of matter in its path - and found a figure higher than predicted by the ΛCDM model. ( Λ is the Greek letter for lambda, denoting dark energy.) But, in late 2019, Alessandro Melchiorri of the Sapienza University of Rome and his colleagues published a paper concluding that CMB measurements by the Planck space observatory indicate a closed universe. Over the past few decades, scientists have repeatedly measured temperature fluctuations in the CMB - essentially performing trigonometry at the largest scale possible - and found almost no curvature at all.Ī flat universe is a key piece of the standard cosmological model, also known as the Lambda cold dark matter (ΛCDM) model. The best clues to the shape of the universe are embedded in the cosmic microwave background (CMB), the afterglow of the Big Bang that radiates toward us from every direction. And in a negatively curved, open universe, the rockets will separate and never cross paths again. This is unlike a closed universe, in which the paths of these two rockets will diverge, trek along the curvature of space, and eventually loop around to meet where they started. If you're (understandably) still confused, here's another example: In a flat universe, two rockets flying next to each other will always remain parallel. In the flat universe example, it took four turns to get back to where you started, but only three in the closed universe example. Turn 90 degrees once more and walk back to your starting point. Then, turn 90 degrees and walk back to the equator. This time, start at Earth's equator and walk to the North Pole. This is the standard Euclidean geometry that we all learned in high school, and if you add one more dimension you get a flat universe.īut conducting this experiment on a positively curved space that's representative of a closed universe would create a different outcome. Do this twice more and you’ll find yourself back where you started - you’ve completed a square. Walk another 10 feet and turn 90 degrees again. Walk 10 feet along the wall to the next corner, then turn 90 degrees. Say you’re standing in one corner of a square room. What does a flat universe mean, though? This flatness isn’t the two-dimensional kind we often encounter in everyday life, but you can envision it with a few analogies. (Perhaps this will come as some consolation to anyone disappointed by our planet’s roundness.) Flat in 3D Most cosmological evidence points to the universe's density as being just right - the equivalent of around six protons per 1.3 cubic yards - and that it expands in every direction without curving positively or negatively. There's also a Goldilocks scenario for the universe, which scientists say is the most plausible. ![]()
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