The Universe is 13.77 billion years old.
That’s the conclusion from a team of astronomers working 17,030 ft./5,190 meters above Chile’s Atacama Desert using a telescope to detect the oldest light in the Universe.
Give or take 40 million years, that is.
The European Space Agency’s Planck satellite measured remnants of the Big Bang from 2009 through 2013 and came up with the same number—13.77 billion years.
So who is right? Why do different methods of measuring the expansion of the Universe give different results?
This new measurement, made using the National Science Foundation’s Atacama Cosmology Telescope (ACT), may appear to confirm Planck’s calculation.
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However, it may suggest that astronomers are on the verge of a new discovery in cosmology that could change our understanding of how the Universe works.
Why? Let’s look at what’s been discovered—and how.
Published in the Journal of Cosmology and Astroparticle Physics, this new research re-asserts the figure of 13.77 billion years. “Now we’ve come up with an answer where Planck and ACT agree,” said Simone Aiola, a researcher at the Flatiron Institute’s Center for Computational Astrophysics and first author of one of two papers. “It speaks to the fact that these difficult measurements are reliable.”
Calculating the age of the Universe requires working out how fast it’s expanding.
That figure is known as the Hubble Constant, named after American astronomer Edwin Hubble’s observation in the 1920s that galaxies are moving away from the Earth.
To work out how fast that’s happening requires selecting anchors of light in the night sky, such as stars, galaxies and globular clusters. This is known as the cosmic distance ladder—you begin close by and move further out into the Universe, though you’re only ever looking at objects that came into being billions of years after the Universe itself.
These are so-called local Universe measurements.
These local measurements tend to result in calculations of a larger Hubble Constant—and that means a faster moving, and therefore a younger, Universe.
The new study—and that by Planck—measures light from the distant Universe. The leftover radiation from the Big Bang—nature’s oldest light—is termed the cosmic microwave background (CMB).
The CMB is a faint glow of light—very long wavelength microwave radiation—that fills the Universe, and is strong evidence for the Big Bang theory.
It’s so much closer to the origin of the Universe than stars and galaxies.
By resolving the CMB in a higher resolution than ever, the astronomers involved in this latest study were able to carefully study variations in the polarization of its light. They used the spacing between these variations to calculate how far light from the CMB traveled to reach Earth—and thus to calculate a new estimate for the Universe’s age.
The study’s figure for the Hubble Constant suggest that an object 1 megaparsec (around 3.26 million light-years) from Earth is moving away from us at 67.6 kilometers per second. Planck found the Hubble Constant to be a very similar 67.4 km/s/Mpc in 2018, whereas the 2019 figure— inferred from measurements of Cepheid variable stars—was 74 km/s/Mpc. Another 2019 study using red giant stars found the Hubble Constant to be 69.8 km/s/Mpc.
A larger Hubble Constant means a faster moving, and therefore a younger, Universe.
“We find an expansion rate that is right on the estimate by the Planck satellite team. This gives us more confidence in measurements of the Universe’s oldest light,” said Choi, who expressed no preference for any specific value. “It was going to be interesting one way or another,” he added.
This is the first time that two independent CMB measurements have found consistently lower Hubble constants than local Universe measurements.
The discrepancies between estimates for the Universe’s expansion rate—and therefore its age—suggest that astronomers may need a new interpretation of the Universe’s fundamental properties.
“The growing tension between these distant versus local measurements of the Hubble constant suggests that we may be on the verge of a new discovery in cosmology that could change our understanding of how the Universe works,” said Michael Niemack, associate professor of physics and astronomy, and co-author on the two preliminary papers.
It could be that measurements of both the CMB and local objects merely need more accuracy.
The ACT, a six-meter diameter telescope on Cerro Toco in the Atacama Desert of northern Chile, will continue making ever-higher resolution measurements of the CMB.
Meanwhile, NASA’s upcoming mission, the Wide Field Infrared Survey Telescope (WFIRST), scheduled to launch in the mid-2020s, will better explore the value of the Hubble constant across cosmic time by collecting more data on new Type Ia supernovae, Cepheid variables, and red giant stars to fundamentally improve distance measurements to galaxies near and far.
Wishing you clear skies and wide eyes.