2 related articles appeared last week:
First we had this:
Astronomers may have got dark energy all
wrong. It’s great news for the universe
By Dennis Overbye
April 5, 2024 — 3.30pm
New York: On Thursday, astronomers who are
conducting what they describe as the biggest and most precise survey yet of the
history of the universe announced that they might have discovered a major flaw
in their understanding of dark energy, the mysterious force that is
accelerating the expansion of the cosmos.
Dark energy was assumed to be a constant
force in the universe, both currently and throughout cosmic history. But the
new data suggest that it may be more changeable, growing stronger or weaker
over time, reversing or even fading away.
“As [Joe] Biden would say, it’s a BFD,” said
Adam Riess, an astronomer at Johns Hopkins University and the Space Telescope
Science Institute in Baltimore, referring to the US president’s “big f-—ng
deal” expression. Riess shared the 2011 Nobel Prize in physics with two other
astronomers for the discovery of dark energy, but was not involved in this new
study. “It may be the first real clue we have gotten about the nature of dark
energy in 25 years,” he said.
That conclusion, if confirmed, could
liberate astronomers – and the rest of us – from a long-standing, grim
prediction about the fate of the universe. If the work of dark energy were
constant over time, it would eventually push all the stars and galaxies so far
apart that even atoms would be torn asunder, sapping the universe of all life,
light, energy and thought, and condemning it to an everlasting case of the
cosmic blahs. Instead, it seems, dark energy is capable of changing course and
pointing the cosmos towards a richer future.
The keywords are “might” and “could”. The
new finding has about a 1-in-400 chance of being a statistical fluke, a degree
of uncertainty called three sigma, which is far short of the gold standard for
a discovery, called five sigma: 1 chance in 1.7 million. In the history of
physics, even five-sigma events have evaporated when more data or better
interpretations of the data emerged.
This news comes in the first progress
report, published as a series of papers, by a large international collaboration
called the Dark Energy Spectroscopic Instrument, or DESI. The group has just
begun a five-year effort to create a 3D map of the positions and velocities of
40 million galaxies across 11 billion years of cosmic time. Its initial map,
based on the first year of observations, includes just 6 million galaxies. The
results were released on Thursday at a meeting of the American Physical Society
in Sacramento, California, and at the Rencontres de Moriond conference in
Italy.
“So far we’re seeing basic agreement with
our best model of the universe, but we’re also seeing some potentially
interesting differences that could indicate that dark energy is evolving with
time,” Michael Levi, the director of DESI, said in a statement issued by the
Lawrence Berkeley National Laboratory, which manages the project.
The DESI team had not expected to hit pay
dirt so soon, Nathalie Palanque-Delabrouille, an astrophysicist at the Lawrence
Berkeley lab and a spokesperson for the project, said in an interview. The
first year of results were designed to simply confirm what was already known,
she said: “We thought that we would basically validate the standard model.”
But the unknown leaped out at them.
When the scientists combined their map with
other cosmological data, they were surprised to find that it did not quite
agree with the otherwise reliable standard model of the universe, which assumes
that dark energy is constant and unchanging. A varying dark energy fit the data
points better.
“It’s certainly more than a curiosity,”
Palanque-Delabrouille said. “I would call it a hint. Yeah, it’s not yet
evidence, but it’s interesting.”
But cosmologists are taking this hint very
seriously.
Wendy Freedman, an astrophysicist at the
University of Chicago who has led efforts to measure the expansion of the
universe, praised the new survey as “superb data”. The results, she said, “open
the potential for a new window into understanding dark energy, the dominant
component of the universe, which remains the biggest mystery in cosmology.
Pretty exciting.”
Michael Turner, an emeritus professor at the
University of Chicago who coined the term “dark energy,” said in an email:
“While combining data sets is tricky, and these are early results from DESI,
the possible evidence that dark energy is not constant is the best news I have
heard since cosmic acceleration was firmly established 20-plus years ago.”
Dark energy entered the conversation in
1998, when two competing groups of astronomers, including Riess, discovered
that the expansion of the universe was speeding up rather than slowing, as most
astronomers had expected. The initial observations seemed to suggest that this
dark energy was acting just like a famous fudge factor – denoted by the Greek
letter Lambda – that Albert Einstein had inserted into his equations to explain
why the universe didn’t collapse from its own gravity. He later called it his worst
blunder.
But perhaps he spoke too soon. As formulated
by Einstein, Lambda was a property of space itself: The more space there was as
the universe expanded, the more dark energy there was, pushing ever harder and
eventually leading to a runaway, lightless future.
Dark energy took its place in the standard
model of the universe known as LCDM, composed of 70 per cent dark energy
(Lambda), 25 per cent cold dark matter (an assortment of slow-moving exotic
particles) and 5 per cent atomic matter. So far that model has been bruised but
not broken by the new James Webb Space Telescope. But what if dark energy were
not constant as the cosmological model assumed?
At issue is a parameter called w, which is a
measure of the density, or vehemence, of the dark energy. In Einstein’s version
of dark energy, this number remains constant, with a value of -1, throughout
the life of the universe. Cosmologists have been using this value in their
models for the past 25 years.
But this version of dark energy is merely
the simplest one. “With DESI we now have achieved a precision that allows us to
go beyond that simple model,” Palanque-Delabrouille said, “to see if the
density of dark energy is constant over time, or if it has some fluctuations
and evolution with time”.
The DESI project, 14 years in the making,
was designed to test the constancy of dark energy by measuring how fast the
universe was expanding at various times in the past. To do that, scientists
outfitted a telescope at Kitt Peak National Observatory with 5000 fibre-optic
detectors that could conduct spectroscopy on that many galaxies simultaneously
and find out how fast they were moving away from Earth.
As a measure of distance, the researchers
used bumps in the cosmic distribution of galaxies, known as baryon acoustic
oscillations. These bumps were imprinted on the cosmos by sound waves in the
hot plasma that filled the universe when it was just 380,000 years old. Back
then, the bumps were 500,000-light-years across. Now, 13.5 billion years later,
the universe has expanded a thousandfold, and the bumps – which are now
500-million-light-years across – serve as convenient cosmic measuring sticks.
The DESI scientists divided the past 11
billion years of cosmic history into seven spans of time. (The universe is 13.8
billion years old.) For each, they measured the size of these bumps and how
fast the galaxies in them were speeding away from us and from each other.
When the researchers put it all together,
they found that the usual assumption – a constant dark energy – didn’t work to
describe the expansion of the universe. Galaxies in the three most recent
epochs appeared closer than they should have been, suggesting that dark energy
could be evolving with time.
“And we do see, indeed, a hint that the
properties of dark energy would not correspond to a simple cosmological
constant” but instead may “have some deviations,” Palanque-Delabrouille said.
“And this is the first time we have that.” But, she emphasised again, “I
wouldn’t call it evidence yet. It’s too, too weak.”
Time and more data will tell the fate of
dark energy, and of cosmologists’ battle-tested model of the universe.
“LCDM is being put through its paces by
precision tests coming at it from every direction,” Turner said. “And it is
doing well. But, when everything is taken together, it is beginning to appear
that something isn’t right or something is missing. Things don’t fit together
perfectly. And DESI is the latest indication.”
Riess of Johns Hopkins, who had an early
look at the DESI results, noted that the “hint,” if validated, could pull the
rug out from other cosmological measurements, such as the age or size of the
universe. “This result is very interesting and we should take it seriously,” he
wrote in his email. “Otherwise why else do we do these experiments?”
This article originally appeared in The New York Times.
Here is the
link:
https://www.smh.com.au/world/north-america/astronomers-may-have-got-dark-energy-all-wrong-it-s-great-news-for-the-universe-20240405-p5fhq0.html
and second we have this:
Space
New 3D cosmic map raises questions over future
of universe, scientists say
Researchers say findings from map with three
times more galaxies than previous efforts could challenge standard idea of dark
energy
Nicola Davis
Science correspondent
Fri 5 Apr 2024 02.00 AEDTLast modified on
Fri 5 Apr 2024 07.07 AEDT
The biggest ever 3D map of the universe,
featuring more than 6m galaxies, has been revealed by scientists who said it
raised questions about the nature of dark energy and the future of the
universe.
The map is based on data collected by the
Dark Energy Spectroscopic Instrument (Desi) in Arizona and contains three times
as many galaxies as previous efforts, with many having their distances measured
for the first time.
Researchers said that by using this map,
they have been able measure how fast the universe has been expanding at
different times in the past with unprecedented accuracy.
The results confirm that the expansion of
the universe is speeding up, they added. However, the findings have also raised
the tantalising possibility that dark energy – a mysterious, repulsive force
that drives the process – is not constant throughout time as has previously
been suggested.
Dr Seshadri Nadathur, a co-author of the
work and senior research fellow at the University of Portsmouth’s Institute of
Cosmology and Gravitation, said: “What we are seeing are some hints that it has
actually been changing over time, which is quite exciting because it is not
what the standard model of a cosmological constant dark energy would look
like.”
Prof Carlos Frenk, from Durham University
and a co-author of the research, said that if dark energy was indeed constant
in time, the future of the universe was simple: it would expand on and on, for
ever. But if the hints found in the map stood up, that would be called into
question.
“Now all of that goes out the window and
essentially we have to start from scratch, and that means revising our
understanding of basic physics, our understanding of the big bang itself, and
our understanding of the long-range forecast for the universe,” he said, adding
that the new hints left open the possibility that the universe might undergo a
“big crunch”.
The research, which has been published in a series of preprints
– meaning it has yet to be peer-reviewed – reveals how the team first created
the 3D map, then measured patterns in the distribution of galaxies that relate
to sound waves that occurred in the early universe, known as baryon acoustic
oscillations.
As the size of these patterns is known to be
regular, the team was able to calibrate the distances to different galaxies in
the map, allowing them to work out how fast the universe has been growing over
the last 11bn years, with a precision better than 0.5% over all times, and
better than 1% between 8bn and 11bn years ago.
Frenk said the precision itself of the
measurements was notable given that galaxies could be billions of light years
away, and billions of years old. “It’s mind-boggling that we can measure
anything to a precision of 1%, which is precision you get in the laboratory in
physics for high-precision measurements,” he said.
Andrew Pontzen, professor of cosmology at
University College London and author of the book The Universe in a Box, who was
not involved in the work, said Desi was one of a slew of exciting new
astronomical surveys cataloguing the night sky, with one of the primary goals
being to measure the rate at which our expanding universe has speeded up.
“Like measuring the acceleration of a car,
charting the universe’s expansion tells us about the ‘engine’ powering cosmic
acceleration. That engine is known as dark energy,” he said.
However, Pontzen noted that our knowledge of
how dark energy operates was limited. “The new data, when combined with
existing measurements, would seem to contradict the simplest possible
explanations for dark energy,” he said.
“At face value, that’s an exciting step
forward. But as the team themselves caution, there is a huge amount still to
understand about this data and early results should be taken with a healthy
grain of salt.”
Here is the
link:
https://www.theguardian.com/science/2024/apr/04/biggest-ever-3d-map-universe-dark-energy-data-scientists
I think Joe Biden is right that what
we a dealing with here is a Big F…king Deal as it really goes to our
understanding (or not) of the history and fabric of the cosmos. Doesn’t matter
for tonight’s dinner but for where, over time, our overall understanding of the universe
winds up!
All we can do is sit back and watch
as the story unfolds, and keep our sense of awe and wonder alive.
David.
