Send Link mailing list submissions to
[email protected]
To subscribe or unsubscribe via the World Wide Web, visit
https://mailman.anu.edu.au/mailman/listinfo/link
or, via email, send a message with subject or body 'help' to
[email protected]
You can reach the person managing the list at
[email protected]
When replying, please edit your Subject line so it is more specific
than "Re: Contents of Link digest..."
Today's Topics:
1. The Hubble Tension (Stephen Loosley)
----------------------------------------------------------------------
Message: 1
Date: Sun, 07 Dec 2025 22:20:10 +1030
From: Stephen Loosley <[email protected]>
To: "link" <[email protected]>
Subject: [LINK] The Hubble Tension
Message-ID: <[email protected]>
Content-Type: text/plain; charset="UTF-8"
This Telescope?s Final Data Release Just Killed 30 Cosmological Theories
The Atacama Cosmology Telescope in Chile not only confirmed one of the greatest
mysteries in the universe?it also ruled out dozens of models that attempted to
solve it.
By Ellyn Lapointe Published December 5, 2025
https://gizmodo.com/this-telescopes-final-data-release-just-killed-30-cosmological-theories-2000696247
{Map Caption: A map showing polarization vectors overlaid on a total intensity
map of the cosmic microwave background, created using observations by the
Atacama Cosmology Telescope ? The Atacama Cosmology Telescope collaboration]
Comments (19)
The Atacama Cosmology Telescope (ACT) in Chile spent nearly two decades
studying how the universe began, what it?s made of, and how it evolved to its
current state. The observatory was decommissioned in 2022, but its last batch
of data is still sending shockwaves through the cosmological community.
A recent study published in the Journal of Cosmology and Astroparticle Physics
used this data to test about 30 ?extended? models of the universe?s
evolution?alternatives to the standard model of cosmology.
These alternatives attempt to explain certain cosmological phenomena that the
standard model can?t, such as the Hubble tension, a discrepancy between
different measurements of the universe?s expansion rate.
The researchers ruled out every extended model they tested. Alongside another
JCAP-published study that used ACT?s final data to confirm the Hubble tension,
the findings deepen this cosmological mystery, leaving experts with even more
questions about what?s driving the expansion of the universe.
?We assessed them completely independently,? Erminia Calabrese, a Cardiff
University cosmologist and co-author of the study that tested the extended
models, said in a statement. ?We weren?t trying to knock them down, only to
study them. And the result is clear: The new observations, at new scales and in
polarization, have virtually removed the scope for this kind of exercise. It
does shrink the theoretical ?playground? a bit.?
A deepening cosmological mystery
There are two main ways to measure the universe?s expansion rate, also known as
the Hubble constant. One method involves looking at the radiation leftover from
the Big Bang (the cosmic microwave background), and the other looks at galaxies
and supernovae in the local universe.
According to the standard model of cosmology, both methods should produce the
same value. The problem is, they don?t. This, in essence, is the Hubble tension.
Researchers have spent years trying to explain this discrepancy, and they?ve
come up with many interesting hypotheses. Others have found evidence to suggest
the Hubble tension may not actually exist. The latest ACT data strengthen the
case for this cosmological conundrum but bring experts no closer to resolving
it.
More questions, but a clearer path to answers
So, ?What?s the big deal?? you ask. Well, for one thing, confirming the Hubble
tension with ACT?s observations means we can be pretty darn sure this problem
is real.
The telescope measured the cosmic microwave background with unprecedented
precision, producing polarization maps that complement the temperature maps
created by the European Space Agency?s Planck spacecraft. By comparison, the
ACT maps?published in a third JCAP study?have much higher resolution than
Planck?s. This is largely owed to the fact that ACT?s primary mirror is much
larger than Planck?s, with a diameter of about 20 feet (6 meters).
?When we compare [the maps], it?s a bit like cleaning your glasses,? Calabrese
said. As such, the ACT data fill several gaps in our understanding of the CMB.
?Our new results demonstrate that the Hubble constant inferred from the ACT CMB
data agrees with that from Planck?not only from the temperature data, but also
from the polarization, making the Hubble discrepancy even more robust,? Colin
Hill, a cosmologist at Columbia University and co-author of the study that used
ACT data to confirm the Hubble tension, said in the statement.
ACT?s observations also allowed Calabrese and her colleagues to rule out many
of the extended models that attempt to explain the Hubble tension. While this
narrows the range of possibilities, it provides a clear path forward. If these
models are dead ends, it?s time to stop pursuing them and look for answers
elsewhere.
ACT?s operational lifespan may be over, but its final data release marks a new
beginning for cosmologists working to resolve the Hubble tension. Experts will
continue using the data for years to come, inching their way closer to a better
understanding of our expanding universe.
--
------------------------------
Subject: Digest Footer
_______________________________________________
Link mailing list
[email protected]
https://mailman.anu.edu.au/mailman/listinfo/link
------------------------------
End of Link Digest, Vol 397, Issue 3
************************************
