James Webb telescope confirms there is something seriously wrong with our
understanding of the universe
By Ben Turner published March 14, 2024
Depending on where we look, the universe is expanding at different rates.
Now, scientists using the James Webb and Hubble space telescopes have
confirmed that the observation is not down to a measurement error.
Astronomers have used the James Webb and Hubble space telescopes to
confirm one of the most troubling conundrums in all of physics — that the
universe appears to be expanding at bafflingly different speeds depending
on where we look.
This problem, known as the Hubble Tension, has the potential to alter or even
upend cosmology altogether. In 2019, measurements by the Hubble Space
Telescope confirmed the puzzle was real; in 2023, even more precise
measurements from the James Webb Space Telescope (JWST) cemented
the discrepancy.
Now, a triple-check by both telescopes working together appears to have put
the possibility of any measurement error to bed for good. The study,
published February 6 in the Astrophysical Journal Letters, suggests that
there may be something seriously wrong with our understanding of the
universe.
"With measurement errors negated, what remains is the real and exciting
possibility we have misunderstood the universe," lead study author Adam
Riess, professor of physics and astronomy at Johns Hopkins University, said
in a statement.
Reiss, Saul Perlmutter and Brian P. Schmidt won the 2011 Nobel Prize in
physics for their 1998 discovery of dark energy, the mysterious force behind
the universe's accelerating expansion.
Currently, there are two "gold-standard" methods for figuring out the Hubble
constant, a value that describes the expansion rate of the universe. The first
involves poring over tiny fluctuations in the cosmic microwave background
(CMB) — an ancient relic of the universe's first light produced just 380,000
years after the Big Bang.
JWST's infrared cameras allow it to look at the universe in more precise
detail than any telescope before it. (Image credit: NASA, ESA, CSA, J. Diego
(Instituto de Física de Cantabria), B. Frye (University of Arizona), P.
Kamieneski (Arizona State University), T. Carleton (Arizona State University),
and R. Windhorst (University of Arizona), A. Pagan (STScI), J. Summers
(Arizona State University), J. D’Silva (University of Western Australia), A.
Koekemoer (STScI), A. Robotham (University of Western Australia), and R.
Windhorst (University of Arizona))
Between 2009 and 2013, astronomers mapped out this microwave fuzz
using the European Space Agency's Planck satellite to infer a Hubble
constant of roughly 46,200 mph per million light-years, or roughly 67
kilometers per second per megaparsec (km/s/Mpc).
The second method uses pulsating stars called Cepheid variables. Cepheid
stars are dying, and their outer layers of helium gas grow and shrink as they
absorb and release the star's radiation, making them periodically flicker like
distant signal lamps.
As Cepheids get brighter, they pulsate more slowly, giving astronomers a
means to measure their absolute brightness. By comparing this brightness to
their observed brightness, astronomers can chain Cepheids into a "cosmic
distance ladder" to peer ever deeper into the universe's past. With this
ladder in place, astronomers can find a precise number for its expansion from
how the Cepheids' light has been stretched out, or red-shifted.
Related: Mysterious 'unparticles' may be pushing the universe apart, new
theoretical study suggests
But this is where the mystery begins. According to Cepheid variable
measurements taken by Riess and his colleagues, the universe's expansion
rate is around 74 km/s/Mpc: an impossibly high value when compared to
Planck's measurements. Cosmology had been hurled into uncharted
territory.
"We wouldn't call it a tension or problem, but rather a crisis," David Gross, a
Nobel Prize-winning astronomer, said at a 2019 conference at the Kavli
Institute for Theoretical Physics (KITP) in California.
Initially, some scientists thought that the disparity could be a result of a
measurement error caused by the blending of Cepheids with other stars in
Hubble's aperture. But in 2023, the researchers used the more accurate
JWST to confirm that, for the first few "rungs" of the cosmic ladder, their
Hubble measurements were right. Nevertheless, the possibility of crowding
further back in the universe's past remained.
To resolve this issue, Riess and his colleagues built on their previous
measurements, observing 1,000 more Cepheid stars in five host galaxies as
remote as 130 million light-years from Earth. After comparing their data to
Hubble's, the astronomers confirmed their past measurements of the Hubble
constant.
"We've now spanned the whole range of what Hubble observed, and we can
rule out a measurement error as the cause of the Hubble Tension with very
high confidence," Riess said. "Combining Webb and Hubble gives us the
best of both worlds. We find that the Hubble measurements remain reliable
as we climb farther along the cosmic distance ladder."
In other words: the tension at the heart of cosmology is here to stay.
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