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.
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and second we have this:
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:
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.
Fascinating stuff
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