The Webb telescope could help settle one of the biggest controversies in modern astronomy: the dispute about the expansion rate of the universe.
On Christmas morning of 2021, astronomers watched their new, greatest tool successfully blast off into space. Now the James Webb Space Telescope is fully deployed and has arrived at its deep-space destination, a quiet locale 1.5 million kilometers beyond Earth.
Measurements of the universe’s expansion rate, known as the Hubble constant, currently cluster around two figures: 67 and 73. Each number is an expression of the same thing—the kilometers-per-second rate of cosmic expansion per every megaparsec of space. Although seemingly slight, the difference between these figures is enormous in comparison with the high-precision agreement that exists for other cosmological measurements. Simply put, something is not adding up.
The first camp gathers data from the very early universe. These researchers rely on the cosmic microwave background, a residual glow of radiation from roughly 400,000 years after the big bang. By taking measurements from the cosmic microwave background and extrapolating them into the present using our best physical models, astronomers in this camp can reach an estimate for the expansion rate of the universe today. Their calculations indicate that the Hubble constant is around 67.
Astronomers have found a few ways to gauge such celestial distances. Most of them rely on “standard candles,” astronomical objects of known brightness. By comparing such an object’s actual, intrinsic brightness with its apparent brightness through a telescope, observers can reliably determine its distance from Earth.
This is a much bigger range than the measurements out of the early-universe camp. Likewise, local studies tend to have greater “error bars” than studies that use early-universe data. So what would it mean if local studies again cluster around 73 but this time with even greater precision? According to Treu, that would imply the Hubble tension is a real discrepancy and not just the result of study error.
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James Webb Space Telescope arrives at new home in spaceChelsea “Foxanne” Gohd joined Space.com in 2018 and is now a Senior Writer, writing about everything from climate change to planetary science and human spaceflight in both articles and on-camera in videos. With a degree in Public Health and biological sciences, Chelsea has written and worked for institutions including the American Museum of Natural History, Scientific American, Discover Magazine Blog, Astronomy Magazine and Live Science. When not writing, editing or filming something space-y, Chelsea 'Foxanne' Gohd is writing music and performing as Foxanne, even launching a song to space in 2021 with Inspiration4. You can follow her on Twitter chelsea_gohd and foxannemusic.
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