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Today's Topics:
1. New evidence supports a "timescape" model of cosmic expansion
(Stephen Loosley)
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Message: 1
Date: Sun, 22 Dec 2024 23:03:19 +1030
From: Stephen Loosley <[email protected]>
To: "link" <[email protected]>
Subject: [LINK] New evidence supports a "timescape" model of cosmic
expansion
Message-ID: <[email protected]>
Content-Type: text/plain; charset="UTF-8"
Dark energy 'doesn't exist' so can't be pushing 'lumpy' Universe apart
"The new evidence supports the "timescape" model of cosmic expansion, which
doesn't have a need for dark energy because the differences in stretching light
aren't the result of an accelerating Universe but instead a consequence of how
we calibrate time and distance."
Date: December 20, 2024
Source: Royal Astronomical Society
Summary:
One of the biggest mysteries in science -- dark energy -- doesn't actually
exist, according to researchers looking to solve the riddle of how the Universe
is expanding. For the past 100 years, physicists have generally assumed that
the cosmos is growing equally in all directions. They employed the concept of
dark energy as a placeholder to explain unknown physics they couldn't
understand, but the contentious theory has always had its problems. Now a team
of physicists and astronomers are challenging the status quo, using improved
analysis of supernovae light curves to show that the Universe is expanding in a
more varied, 'lumpier' way.
Share:
https://ras.ac.uk/news-and-press/research-highlights/dark-energy-doesnt-exist-so-cant-be-pushing-lumpy-universe-apart
and
https://www.sciencedaily.com/releases/2024/12/241220133038.htm
FULL STORY
One of the biggest mysteries in science -- dark energy -- doesn't actually
exist, according to researchers looking to solve the riddle of how the Universe
is expanding.
For the past 100 years, physicists have generally assumed that the cosmos is
growing equally in all directions. They employed the concept of dark energy as
a placeholder to explain unknown physics they couldn't understand, but the
contentious theory has always had its problems.
Now a team of physicists and astronomers at the University of Canterbury in
Christchurch, New Zealand are challenging the status quo, using improved
analysis of supernovae light curves to show that the Universe is expanding in a
more varied, "lumpier" way.
The new evidence supports the "timescape" model of cosmic expansion, which
doesn't have a need for dark energy because the differences in stretching light
aren't the result of an accelerating Universe but instead a consequence of how
we calibrate time and distance.
It takes into account that gravity slows time, so an ideal clock in empty space
ticks faster than inside a galaxy.
The model suggests that a clock in the Milky Way would be about 35 per cent
slower than the same one at an average position in large cosmic voids, meaning
billions more years would have passed in voids. This would in turn allow more
expansion of space, making it seem like the expansion is getting faster when
such vast empty voids grow to dominate the Universe.
Professor David Wiltshire, who led the study, said: "Our findings show that we
do not need dark energy to explain why the Universe appears to expand at an
accelerating rate.
"Dark energy is a misidentification of variations in the kinetic energy of
expansion, which is not uniform in a Universe as lumpy as the one we actually
live in."
He added: "The research provides compelling evidence that may resolve some of
the key questions around the quirks of our expanding cosmos.
"With new data, the Universe's biggest mystery could be settled by the end of
the decade."
The new analysis has been published in the journal Monthly Notices of the Royal
Astronomical Society Letters.
Dark energy is commonly thought to be a weak anti-gravity force which acts
independently of matter and makes up around two thirds of the mass-energy
density of the Universe.
The standard Lambda Cold Dark Matter (?CDM) model of the Universe requires dark
energy to explain the observed acceleration in the rate at which the cosmos is
expanding.
Scientists base this conclusion on measurements of the distances to supernova
explosions in distant galaxies, which appear to be farther away than they
should be if the Universe's expansion were not accelerating.
However, the present expansion rate of the Universe is increasingly being
challenged by new observations.
Firstly, evidence from the afterglow of the Big Bang -- known as the Cosmic
Microwave Background (CMB) -- shows the expansion of the early Universe is at
odds with current expansion, an anomaly known as the "Hubble tension."
In addition, recent analysis of new high precision data by the Dark Energy
Spectroscopic Instrument (DESI) has found that the ?CDM model does not fit as
well as models in which dark energy is "evolving" over time, rather than
remaining constant.
Both the Hubble tension and the surprises revealed by DESI are difficult to
resolve in models which use a simplified 100-year-old cosmic expansion law --
Friedmann's equation.
This assumes that, on average, the Universe expands uniformly -- as if all
cosmic structures could be put through a blender to make a featureless soup,
with no complicating structure. However, the present Universe actually contains
a complex cosmic web of galaxy clusters in sheets and filaments that surround
and thread vast empty voids.
Professor Wiltshire added: "We now have so much data that in the 21st century
we can finally answer the question -- how and why does a simple average
expansion law emerge from complexity?
"A simple expansion law consistent with Einstein's general relativity does not
have to obey Friedmann's equation."
The researchers say that the European Space Agency's Euclid satellite, which
was launched in July 2023, has the power to test and distinguish the Friedmann
equation from the timescape alternative. However, this will require at least
1,000 independent high quality supernovae observations.
When the proposed timescape model was last tested in 2017 the analysis
suggested it was only a slightly better fit than the ?CDM as an explanation for
cosmic expansion, so the Christchurch team worked closely with the Pantheon+
collaboration team who had painstakingly produced a catalogue of 1,535 distinct
supernovae.
They say the new data now provides "very strong evidence" for timescape. It may
also point to a compelling resolution of the Hubble tension and other anomalies
related to the expansion of the Universe.
Further observations from Euclid and the Nancy Grace Roman Space Telescope are
needed to bolster support for the timescape model, the researchers say, with
the race now on to use this wealth of new data to reveal the true nature of
cosmic expansion and dark energy.
Story Source:
Materials provided by Royal Astronomical Society. Note: Content may be edited
for style and length.
Related Multimedia:
Graphic offers glimpse of history of the Universe
Journal Reference:
Zachary G Lane, Antonia Seifert, Ryan Ridden-Harper, David L Wiltshire.
Cosmological foundations revisited with Pantheon+. Monthly Notices of the Royal
Astronomical Society, 2024; DOI: 10.1093/mnras/stae2437
Cite This Page:
Royal Astronomical Society. "Dark energy 'doesn't exist' so can't be pushing
'lumpy' Universe apart."
&
ScienceDaily, 20 December 2024.
<www.sciencedaily.com/releases/2024/12/241220133038.htm>.
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