Mysterious results in an experiment may be due to dark energy

Shane McGlaun - Sep 16, 2021, 

One of the most mysterious subjects that scientists around the world are studying is called dark energy. Scientists believe dark energy is the mysterious force that leads to acceleration in the universe. A team of researchers from the University of Cambridge has published a study that suggests unexplained results obtained from an experiment conducted in Italy called XENON1T could have been caused by dark energy.

Interestingly, the experiment was designed to detect dark matter, but Cambridge scientists believe dark energy could account for the mysterious and unexplained results from the experiment. In the study, physical models were constructed in an attempt to explain the experiment results. Study researchers believe the experiment results could have been caused by dark energy particles in a region of the sun dominated by strong magnetic fields.

Unfortunately, additional experiments will be required to confirm their theory. Nevertheless, scientists are excited at the possibility of the discovery of dark energy. Currently, estimates predict that everything we can see with our eyes in the universe accounts for less than five percent of what’s there. Most of the material in the universe is dark, and theories suggest 27 percent of the entire universe is dark matter.

Dark matter is described as a force that holds galaxies and the cosmos itself together. Scientists also believe that 68 percent of the universe is made up of dark energy causing the universe to expand and accelerate. Since both dark matter and dark energy are invisible, little is known about them.

The presence of dark matter was first theorized in the 1920s, but dark energy wasn’t discovered until 1998. Scientists say that while the experiment was intended to detect dark matter, detecting dark energy is even more difficult. The study comes after the XEON1T experiment discovered an unexpected signal about a year ago that was higher than the expected background. Researchers on this study decided to explore a model where the unexpected signal was attributed to dark energy rather than dark matter. Scientists admit they are still far from understanding dark energy, and additional experiments are needed.

Have we detected dark energy? Scientists say it's a possibility

by University of Cambridge

Credit: CC0 Public Domain

A new study, led by researchers at the University of Cambridge and reported in the journal Physical Review D, suggests that some unexplained results from the XENON1T experiment in Italy may have been caused by dark energy, and not the dark matter the experiment was designed to detect.

They constructed a physical model to help explain the results, which may have originated from dark energy particles produced in a region of the Sun with strong magnetic fields, although future experiments will be required to confirm this explanation. The researchers say their study could be an important step toward the direct detection of dark energy.

Everything our eyes can see in the skies and in our everyday world—from tiny moons to massive galaxies, from ants to blue whales—makes up less than five percent of the universe. The rest is dark. About 27% is dark matter—the invisible force holding galaxies and the cosmic web together—while 68% is dark energy, which causes the universe to expand at an accelerated rate.

"Despite both components being invisible, we know a lot more about dark matter, since its existence was suggested as early as the 1920s, while dark energy wasn't discovered until 1998," said Dr. Sunny Vagnozzi from Cambridge's Kavli Institute for Cosmology, the paper's first author. "Large-scale experiments like XENON1T have been designed to directly detect dark matter, by searching for signs of dark matter 'hitting' ordinary matter, but dark energy is even more elusive."

To detect dark energy, scientists generally look for gravitational interactions: the way gravity pulls objects around. And on the largest scales, the gravitational effect of dark energy is repulsive, pulling things away from each other and making the Universe's expansion accelerate.

About a year ago, the XENON1T experiment reported an unexpected signal, or excess, over the expected background. "These sorts of excesses are often flukes, but once in a while they can also lead to fundamental discoveries," said Dr. Luca Visinelli, a researcher at Frascati National Laboratories in Italy, a co-author of the study. "We explored a model in which this signal could be attributable to dark energy, rather than the dark matter the experiment was originally devised to detect."

At the time, the most popular explanation for the excess were axions—hypothetical, extremely light particles—produced in the Sun. However, this explanation does not stand up to observations, since the amount of axions that would be required to explain the XENON1T signal would drastically alter the evolution of stars much heavier than the Sun, in conflict with what we observe.

We are far from fully understanding what dark energy is, but most physical models for dark energy would lead to the existence of a so-called fifth force. There are four fundamental forces in the universe, and anything that can't be explained by one of these forces is sometimes referred to as the result of an unknown fifth force.

However, we know that Einstein's theory of gravity works extremely well in the local universe. Therefore, any fifth force associated to dark energy is unwanted and must be 'hidden' or 'screened' when it comes to small scales, and can only operate on the largest scales where Einstein's theory of gravity fails to explain the acceleration of the Universe. To hide the fifth force, many models for dark energy are equipped with so-called screening mechanisms, which dynamically hide the fifth force.

Vagnozzi and his co-authors constructed a physical model, which used a type of screening mechanism known as chameleon screening, to show that dark energy particles produced in the Sun's strong magnetic fields could explain the XENON1T excess.

"Our chameleon screening shuts down the production of dark energy particles in very dense objects, avoiding the problems faced by solar axions," said Vagnozzi. "It also allows us to decouple what happens in the local very dense Universe from what happens on the largest scales, where the density is extremely low."

The researchers used their model to show what would happen in the detector if the dark energy was produced in a particular region of the Sun, called the tachocline, where the magnetic fields are particularly strong.

"It was really surprising that this excess could in principle have been caused by dark energy rather than dark matter," said Vagnozzi. "When things click together like that, it's really special."

Their calculations suggest that experiments like XENON1T, which are designed to detect dark matter, could also be used to detect dark energy. However, the original excess still needs to be convincingly confirmed. "We first need to know that this wasn't simply a fluke," said Visinelli. "If XENON1T actually saw something, you'd expect to see a similar excess again in future experiments, but this time with a much stronger signal."

If the excess was the result of dark energy, upcoming upgrades to the XENON1T experiment, as well as experiments pursuing similar goals such as LUX-Zeplin and PandaX-xT, mean that it could be possible to directly detect dark energy within the next decade.

New study sows doubt about the composition of 70 percent of our universe

More information: Sunny Vagnozzi et al, Direct detection of dark energy: The XENON1T excess and future prospects, Physical Review D (2021). DOI: 10.1103/PhysRevD.104.063023

Journal information: Physical Review D 

Provided by University of Cambridge 

Dark Energy Could Be Responsible for Mysterious Experiment Signals, Researchers Say

What if a bunch of liquid xenon under the Apennine Mountains found 68% of the universe?

By
Isaac Schultz
Friday 3:03PM

The XENON1T Time Projection Chamber TPC in a clean room.

Photo: XENON1T / Purdue University

A team of physicists at the University of Cambridge suspects that dark energy may have muddled results from the XENON1T experiment, a series of underground vats of xenon that are being used to search for dark matter.


Dark matter and dark energy are two of the most discussed quandaries of contemporary physics. The two darks are placeholder names for mysterious somethings that seem to be affecting the behavior of the universe and the stuff in it. Dark matter refers to the seemingly invisible mass that only makes itself known through its gravitational effects. Dark energy refers to the as-yet unexplained reason for the universe’s accelerating expansion. Dark matter is thought to make up about 27% of the universe, while dark energy is 68%, according to NASA.

Physicists have some ideas to explain dark matter: axions, WIMPs, SIMPs, and primordial black holes, to name a few. But dark energy is a lot more enigmatic, and now a group of researchers working on XENON1T data says an unexpected excess of activity could be due to that unknown force, rather than any dark matter candidate. The team’s research was published this week in Physical Review D.

The XENON1T experiment, buried below Italy’s Apennine Mountains, is set up to be as far away from any noise as possible. It consists of vats of liquid xenon that will light up if interacted with by a passing particle. As previously reported by Gizmodo, in June 2020 the XENON1T team reported that the project was seeing more interactions than it ought to be under the Standard Model of physics, meaning that it could be detecting theorized subatomic particles like axions—or something could be screwy with the experiment.

“These sorts of excesses are often flukes, but once in a while they can also lead to fundamental discoveries,” said Luca Visinelli, a researcher at Frascati National Laboratories in Italy and a co-author of the study, in a University of Cambridge release. “We explored a model in which this signal could be attributable to dark energy, rather than the dark matter the experiment was originally devised to detect.”

“We first need to know that this wasn’t simply a fluke,” Visinelli added. “If XENON1T actually saw something, you’d expect to see a similar excess again in future experiments, but this time with a much stronger signal.”


Despite constituting so much of the universe, dark energy has not yet been identified. Many models suggest that there may be some fifth force besides the known four known fundamental forces in the universe, one that is hidden until you get to some of the largest-scale phenomena, like the universe’s ever-faster expansion.

Axions shooting out of the Sun seemed a possible explanation for the excess signal, but there were holes in that idea, as it would require a re-think of what we know about stars. “Even our Sun would not agree with the best theoretical models and experiments as well as it does now,” one researcher told Gizmodo last year.

Part of the problem with looking for dark energy are “chameleon particles” (also known as solar axions or solar chameleons), so-called for their theorized ability to vary in mass based on the amount of matter around them. That would make the particles’ mass larger when passing through a dense object like Earth and would make their force on surrounding masses smaller, as New Atlas explained in 2019. The recent research team built a model that uses chameleon screening to probe how dark energy behaves on scales well beyond that of the dense local universe.

“Our chameleon screening shuts down the production of dark energy particles in very dense objects, avoiding the problems faced by solar axions,” said lead author Sunny Vagnozzi, a cosmologist at Cambridge’s Kavli Institute for Cosmology, in a university release. “It also allows us to decouple what happens in the local very dense Universe from what happens on the largest scales, where the density is extremely low.”

The model allowed the team to understand how XENON1T would behave if the dark energy were produced in a magnetically strong region of the Sun. Their calculations indicated that dark energy could be detected with XENON1T.

Since the excess was first discovered, ​​the XENON1T team “tried in any way to destroy it,” as one researcher told The New York Times. The signal’s obstinacy is as perplexing as it is thrilling.

“The authors propose an exciting and interesting possibility to expand the scope of the dark matter detection experiments towards the direct detection of dark energy,” Zara Bagdasarian, a physicist at UC Berkeley who was unaffiliated with the recent paper, told Gizmodo in an email. “The case study of XENON1T excess is definitely not conclusive, and we have to wait for more data from more experiments to test the validity of the solar chameleons idea.”

The next generation of XENON1T, called XENONnT, is slated to have its first experimental runs later this year. Upgrades to the experiment will hopefully seal out any noise and help physicists home in on what exactly is messing with the subterranean detector.

  

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Mysterious new dark energy could be driving expansion of the universe: Study

Albert Einstein was the first person to theorise that space is not empty and that it is possible for more space to come into existence.

India Today Web Desk New DelhiSeptember 22, 2021


The Atacama Cosmology Telescope in Chile. (File Photo)

One of the biggest questions surrounding cosmology and astronomy is how the universe began. We know a lot about the evolution of the planet and the human species, however, the understanding of the origins of the universe and what drives this massive force, remains little. Cosmologists have now stumbled upon a unique phenomenon, which could be driving the expansion of the universe.

Cosmologists speculate that this unique energy may have existed just after the Big Bang happened, barely 3,00,000 years after the explosion. In a series of studies published in preprint, researchers identify it as Early Dark Energy which has been detected in data from the Atacama Cosmology Telescope in Chile.

This data was collected between 2013 and 2016, and if confirmed, it could shed light on the early universe. However, researchers also maintain that it's not definitive proof and more research is required in the area. Researchers believe that this early dark energy was not as strong as today's to accelerate the expansion and would have caused the plasma that emerged from the Big Bang to cool down faster.

Cosmologists speculate that interpreting the observations from the telescope on the basis of this early dark energy may put the universe to be 12.4 billion years old, which is 11 per cent younger than 13.8 billion years calculated by initial observations.


Early dark energy was not as strong as today's to accelerate the expansion. (Representative Photo)

“If this really is true — if the early Universe really did feature early dark energy — then we should see a strong signal," Colin Hill, a co-author of the ACT paper, told Nature. He added that the current expansion would be about 5 per cent faster than the standard model predicts — closer to what astronomers calculate today.

What is Dark Energy?

It was initially believed that the Universe was expanding. However, astronomers thought that gravity was certain to slow the expansion. But observations from the Hubble Space Telescope showed that the expansion was not slowing due to gravity and instead has been accelerating, researchers knew a mysterious force was driving this expansion, which later came to be known as Dark Energy.

Albert Einstein was the first person to theorise that space is not empty and that it is possible for more space to come into existence and his gravity theory proposed that space can possess its own energy. "Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear."

According to Nasa, we know how much dark energy there is because we know how it affects the universe's expansion. "Other than that, it is a complete mystery," the agency said, adding that roughly 68 per cent of the universe is dark energy. Dark matter makes up about 27 per cent. The rest — everything on Earth, everything ever observed with all of our instruments, all normal matter — adds up to less than 5 per cent of the universe.

IT'S ETHER

Dark energy might be neither particle nor field

Everything else in the universe is either a particle or field. Dark energy behaves as neither, and it may be a property inherent to space itself.

There is a large suite of scientific evidence that supports the picture of the expanding Universe and the Big Bang, complete with dark energy. The late-time accelerated expansion doesn’t strictly conserve energy, but the presence of a new component to the Universe, known as dark energy, is required to explain what we observe

. (Credit: NASA / GSFC)

KEY TAKEAWAYS


Dark energy dominates the energy content of the universe, making up more than 2/3rds of all that's out there.


But while everything else clumps or clusters together, dark energy remains uniform throughout space and time.


Instead of being a particle or field, it could be a property inherent to space itself, with alternatives creating more problems than they solve.

What is it, at a fundamental level, that makes up the universe? When we ask this question, we typically think about starting with things that we directly observe — things like stars, planets, humans, gas, dust, plasma, and other forms of the matter we know — and dividing them up until you reach something that is indivisible. Although we originally thought that atoms would be these “uncuttable” things, we soon discovered they could be further divided: into electrons and atomic nuclei, which themselves are composed of quarks and gluons.

As we mastered the laws of physics and began to manipulate these subatomic particles, we gained the ability to accelerate and collide them, enabling the creation of a wide slew of particles and antiparticles: everything described by the Standard Model of particle physics. And yet, if we add up the sum total of all of these forms of matter, including photons, neutrinos, and everything that does not compose atoms, we fall far short of what is needed to describe our universe. Two additional components are necessary: dark matter and dark energy. Moreover, although we fully expect there to be a particle responsible for dark matter, that is not the case at all for dark energy. Here’s why.

The particles and antiparticles of the Standard Model obey all sorts of conservation laws, with fundamental differences between fermionic particles and antiparticles and bosonic ones. Each set of particles possesses its own unique quantum numbers, but no particles here can explain dark matter or dark energy. (Credit: E. Siegel / Beyond the Galaxy)

Particles, at least as we know them, all have a few things in common. They have a set of “quantum numbers,” or properties that are inherent to them that determine their masses, spins, and various charges. All particles of the same type — electrons, down quarks, Z-bosons, etc. — have identical properties to one another, and you could replace any one of them with any other identical particle and everything would remain the same. The only things that differ between them are either random, like their decay lifetime (if they are unstable), or situational: things like their momentum, orbital angular momentum, or energy levels within a bound system.

But there is another way to break these various particles up: into massive and massless categories. Massive particles slow down as the universe expands and cools during the hot Big Bang and eventually gravitationally clump together, as every mass universally attracts every other mass. Massless particles, however, simply travel through curved space at the only permissible speed, the speed of light, until they interact with another particle in their path. Massive (matter) and massless (radiation) particles evolve in fundamentally different ways with respect to the expanding universe.

While matter and radiation become less dense as the universe expands owing to its increasing volume, dark energy is a form of energy inherent to space itself. As new space gets created in the expanding universe, the dark energy density remains constant. (Credit: E. Siegel / Beyond the Galaxy)

Astrophysically, when we survey the universe in all the different ways we know of, it reveals a variety of aspects of the cosmic story. By observing how abundant the lightest elements and their isotopes are, we can determine how much normal matter, total, makes up our universe. By measuring how galaxies clump and cluster together, as well as their large-scale distribution and individual, internal properties, we can determine how much total “stuff” there is that behaves as though it is made of massive particles. And when we look at the details embedded in the leftover glow from the Big Bang — the cosmic microwave background — it tells us that the universe is spatially flat, telling us how much total “stuff” is present in the universe, overall.

From this information, we learn that all of the normal, Standard Model material in our universe comes out to just 5 percent of the total. Another ~27 percent is dark matter, which cannot behave like any of the known particles. It clumps and gravitates like normal matter but appears to have zero cross-section — i.e., doesn’t collide — with normal matter, light, or other dark matter particles. Although we can only detect dark matter’s presence through its gravitational influence, it is immediately apparent that dark matter is distributed far more diffusely than normal matter; it isn’t as clumpy, particularly on small cosmic scales. Unfortunately, all attempts at direct detection experiments have failed to yield a robust, positive signal. Its true nature remains mysterious.

Light may be emitted at a particular wavelength, but the expansion of the universe will stretch it as it travels. Light emitted in the ultraviolet will be shifted all the way into the infrared when considering a galaxy whose light arrives from 13.4 billion years ago. The more the expansion of the universe accelerates, the greater the light from distant objects will be redshifted and the fainter it will appear. 

(Credit: Larry McNish / RASC Calgary)

Even with normal matter and dark matter combined, though, we haven’t gotten close to finding everything. The remaining ~68 percent of the universe is unaccounted for, and our big clue toward what that “stuff” is first came in the 1990s, when observations of distant supernovae appeared fainter than our models of the universe were predicting. It was as though something else beyond what we expected — various forms of matter and radiation — was contributing to the universe. As the evidence poured in, bolstered by the cosmic microwave background and large-scale clustering data, we realized that a wholly novel form of energy, inconsistent with the properties of any form of matter or radiation, must be present: what we call dark energy today.

What is remarkable about the evidence for dark energy is how perfectly uniform it is. There is no evidence that there’s more or less dark energy in the space occupied by rich galaxy clusters than in the voids of empty space. There is no evidence that dark energy correlates with density, direction, location, or epoch of the universe. It appears to be perfectly uniform, perfectly homogeneous, and perfectly constant: unchanging throughout space and time. And yet, despite its simplicity, it behaves fundamentally differently from all other known forms of energy.

Various components of and contributors to the universe’s energy density, and when they might dominate. Note that radiation is dominant over matter for roughly the first 9,000 years, then matter dominates, and finally, a cosmological constant emerges. (The others do not exist in appreciable amounts.) However, dark energy may not be a cosmological constant, exactly. (Credit: E. Siegel / Beyond the Galaxy)

Every form of matter and radiation in the universe is linked to quantum particles in some way. Normal matter is made up of subatomic particles: particles of which there are a finite number. As the universe expands, the number of particles stays the same while the volume increases, hence matter gets less dense as time marches forward. Similarly, radiation is quantized into particles as well (even, theoretically, gravitational radiation, which should be quantized into gravitons), but these particles are massless. As the universe expands, not only does the number of particles remain the same while the volume increases, but the energy of each individual particle decreases as the universe expands.

Still, both of these descriptions fall apart for dark energy. As the volume of the universe increases — as it expands — the energy density does not change; it remains constant. It’s as though there is something present through all of space that isn’t dependent on anything else: matter density, radiation density, temperature, changes in volume, etc. Although we can measure and quantify its effects on the universe, we cannot say that we understand dark energy’s nature. It could be a

particle of some type,

a field that permeates the universe,

or even a property inherent to the fabric of space itself.

A universe with dark energy (red), a universe with large inhomogeneity energy (blue), and a critical, dark energy-free universe (green). Note that the blue line behaves differently from dark energy. New ideas should make different, observably testable predictions from the other leading ideas. And ideas which have failed those observational tests should be abandoned once they reach the point of absurdity. 

(Credit: Gabor Racz et al., 2017)

Of course, each of these scenarios leads to a vastly different conception of the universe and what is present within it. If dark energy is a particle, then either new particles must constantly be created to keep the energy density constant, or the behavior of these particles must evolve with time to keep their effects on the universe constant. If dark energy is a field that permeates the universe, then it is permitted to evolve in either space or time or both, and any observed evidence (we have none) of such a variation would point in this direction; models of quintessence fall into this category.

But if we follow the observations, there is no evidence that dark energy is anything other than the most basic entity imaginable: a property that is uniformly inherent to space everywhere and at all times. This can come about in one of two different ways very easily:
The universe can possess a positive, non-zero cosmological constant, a term perfectly allowable in general relativity. It has to be very, very small, but when you put it in everywhere over the whole universe, it eventually comes to dominate.
It could be a quantum property of space: the zero-point energy of all the fields in the vacuum of space is not required to be zero but could take on some positive, non-zero value. What we often interpret as quantum fluctuations, or particle-antiparticle pairs popping in and out of existence, could be the cause behind dark energy.

Visualization of a quantum field theory calculation showing virtual particles in the quantum vacuum (specifically, for the strong interactions). Even in empty space, this vacuum energy is non-zero. (Credit: Derek Leinweber)

From a theoretical perspective, it is important to keep in mind that until we understand the nature of dark energy, which is to say that we acquire some sort of evidence that points toward one possibility over another, we have to keep all of these options in mind. Dark energy could be linked to the inflationary epoch that set up and gave rise to the Big Bang; dark energy could have been important and impactful early on in the universe’s history before decaying to its present, low-density state; dark energy could be slowly evolving or inhomogeneous, or could have a slightly higher or lower density dependent on what else is around. Theoretically, all options remain on the table.

But that is also why we don’t simply base our conclusions on theory alone. The whole idea of science is based on the notion that the way we find out information about the universe is by putting the universe itself to the test: through measurement, experiment, and observation. As we study:

the cosmic microwave background down to smaller and smaller scales, in more wavelength bands and with polarization included;

the large-scale structure of the universe out to greater distances, fainter objects, and larger areas on the sky;

and individually luminous objects, out to greater precision and greater distances,

we gain the ability to see whether there is any indication that dark energy is anything other than a pure constant, and whether it shows evidence for any evolution or inhomogeneities in time and/or space.

This snippet from a structure-formation simulation, with the expansion of the universe scaled out, represents billions of years of gravitational growth in a dark matter-rich universe. Even though the universe is expanding, the individual, bound objects within it no longer expand. Their sizes, however, may be impacted by the expansion; we do not know for certain. 

(Credit: Ralf Kahler and Tom Abel (KIPAC) / Oliver Hahn)

Of course, it hasn’t. Fifteen years ago, we were able to constrain that dark energy was a constant to a precision of ±30 percent or so. Today, that has improved to a precision of ±7 percent or so, with the next generation of space-based and ground-based observatories — particularly ESA’s Euclid, NSF’s Vera Rubin observatory, and NASA’s Nancy Roman telescope — poised to take us to a precision of just ±1 percent. If there are any imperfections, inhomogeneities, or evolutionary effects that occur in the dark energy sector, these upcoming surveys will be our best bet at uncovering them.

However, there are other methods that could reveal some more exotic interpretations. Recently, the XENON experiment claimed to see an excess of events over the anticipated background, beyond what conventional sources could explain. There are three main interpretations on the table, at present:

the result is an experimental fluke that will go away with better statistics, which is within the realm of possibility;

that this is our first evidence of an unexpected type of dark matter, whose explanations would require additional contortions over what was theorized previously; 

or

a new source of background that hasn’t been included in the analysis (such as tritium in the water) is causing it.

Of these explanations, most physicists favor the last one. But, as we said earlier, all possibilities, no matter how exotic or strange, have to be kept in mind.

The XENON1T detector, with its low-background cryostat, is installed in the centre of a large water shield to protect the instrument against cosmic ray backgrounds. This setup enables the scientists working on the XENON1T experiment to greatly reduce their background noise and more confidently discover the signals from processes that they are attempting to study. XENON is not only searching for heavy, WIMP-like dark matter but other forms of potential dark matter and dark energy. 

(Credit: XENON1T Collaboration)

That is where, as was recently shown by a small team of scientists, the idea of chameleon dark energy comes into play. If dark energy is actually a very specific, exotic type of particle that has its clumping and density restricted in the most matter-rich regions of space, it could have potentially created the signal seen by the XENON experiment. With some additional theoretical contortions, the team was able to conclude, at the ~95 percent confidence level, that this interpretation is favored over the null hypothesis: that the result is a mere fluke.

Of course, what most people do not realize is that this is precisely what most ideas in theoretical physics look like: you add in one or two new free parameters to explain one or two new phenomena. Most ideas like this are not new, but rather are variations on an old idea, and most ideas in this vein are colossally bad: they are ill-motivated and are considered only because experiments are nearing the precision necessary to rule them out, either wholly or at least in part. In physics, as well, a signal at ~95 percent confidence is barely worth a second look; this idea of chameleon dark energy particles likely will never rear its head again in any experimental setting.

Constraints on the total matter content (normal + dark, x-axis) and dark energy density (y-axis) from three independent sources: supernovae, the CMB (cosmic microwave background), and BAO (which is a wiggly feature seen in the correlations of large-scale structure). Note that even without supernovae, we would need dark energy for certain, and also that there are uncertainties and degeneracies between the amount of dark matter and dark energy that we would need to accurately describe our universe. 

(Credit: Supernova Cosmology Project, Amanullah et al., ApJ, 2010.)

When you take away wishful thinking and look only at the evidence that we have, the story the universe tells is very simple, albeit counterintuitive. The stuff that we thoroughly understand — the matter and radiation composed of all the known particles of the Standard Model plus gravitational waves — makes up only 5 percent of the total of what’s out there. There is another form of mass, dark matter, that makes up an additional ~27 percent or so. But the majority of what is present, the ~68 percent of the universe that is dark energy, doesn’t appear to either be a particle or change with time. It behaves neither as a particle nor as a field, but rather as a property that is inherent to space itself.

Although it is a fun exercise to consider what might happen under a variety of exotic conditions, particularly when experiments or observations are reaching the sensitivities necessary to probe them, it is vital to treat them as the fringe hypotheses that they are. The default, working hypothesis of what dark energy is doesn’t include extra couplings, clumpiness, time-or-space evolution, or anything else beyond a simple constant in space. It is time to take seriously the idea that dark energy might simply be a property inherent to the very fabric of space. Until we learn how to calculate the zero-point energy of empty space itself, or gain some bizarre, surprising, and unanticipated evidence, this will remain one of the biggest existential questions in all the universe.

Ethan Siegel
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SPACE/COSMOS

Dark energy seems to be changing, rattling our view of universe

AETHYR BY ANY OTHER NAME 

By AFP
March 19, 2025


What if dark energy is not what we thought it was? This strange force could be weakening over time, observations suggest 

- Copyright AFP JOHN WESSELS

Bénédicte Rey and Daniel Lawler

Dark energy, the mysterious force thought to be driving the ever-faster expansion of the universe, appears to be changing over time, according to new observations released Wednesday.

If dark energy is in fact weakening, it would likely mean that science’s understanding of how the universe works will need to be rewritten.

The new findings come from the Dark Energy Spectroscopic Instrument (DESI), which sits on a telescope at the Kitt Peak National Observatory in the US state of Arizona.

“What we are seeing is deeply intriguing,” said Alexie Leauthaud-Harnett, a spokesperson for the DESI collaboration which brings together 70 institutions across the world.

“It is exciting to think that we may be on the cusp of a major discovery about dark energy and the fundamental nature of our universe,” she said in a statement.

The DESI instrument’s thin optical fibres can simultaneously observe 5,000 galaxies or quasars — blazing monsters with a black hole at their heart — for 20 minutes.

This allows scientists to calculate the age and distance of these objects, and create a map of the universe so they can detect patterns and trace its history.



– ‘Tensions’ emerging –



Scientists have known for a century that the universe is expanding, because massive clusters of galaxies have been observed moving away from each other.

In the late 1990s, scientists shocked the field by discovering that the universe’s expansion has been speeding up over time.

The name dark energy was given to the phenomenon driving this acceleration, the effects of which seem to be partially offset by ordinary matter — and an also unknown thing called dark matter.

The universe is thought to be made of 70 percent dark energy, 25 percent dark matter — and just five percent normal matter.

Science’s best understanding of how the universe works, which is called the standard cosmological model, refers to dark energy as being constant — meaning it does not change.

The idea was first introduced by Albert Einstein in his theory of relativity.

Arnaud de Mattia, a French physicist involved in analysing the DESI data, told AFP that the standard model is “satisfactory” but some “tensions” are emerging between observations.

There are several different ways of measuring the expansion of the universe, including looking at the lingering radiation from after the Big Bang, exploding stars called supernovae and how gravity distorts the light of galaxies.

When the DESI team combined their new data with other measurements, they found “signs that the impact of dark energy may be weakening over time”, according to a statement.

“When we combine all the cosmological data, it favours that the universe’s expansion was accelerating at a slightly higher rate around seven billion years ago,” de Mattia said.

But for the moment there is “absolutely not certainty” about this, he added.



– ‘Inflection point’ –



French physicist Etienne Burtin was confident that “we should have a clearer picture within five years”.

This is because there is loads of new data expected from DESI, Europe’s Euclid space telescope, NASA’s upcoming Nancy Grace Roman space telescope and the Vera Rubin Observatory in Chile.

“This new generation of surveys — in the next few years — will nail this,” Joshua Frieman, a theoretical astrophysicist at the University of Chicago, told AFP.

But for now, “we’re at this interesting inflection point”, added Frieman, a dark energy expert and former DESI member.

Burtin said confirming the “evolving dark energy” theory would be a “revolution on the level of the discovery of accelerated expansion”, which itself was the subject of a physics Nobel.

“The standard cosmological model would have to be different,” he added.

The DESI research, which involved three years’ worth of observations of 15 million galaxies and quasars, was presented at a conference of the American Physical Society in California.

What is dark energy? One of science’s great mysteries, explained


By AFP
March 20, 2025


The truth is out there: Scientists hope to crack the case of dark energy in the next few years - Copyright AFP/File NICHOLAS KAMM, Handout

Daniel Lawler

Dark energy makes up roughly 70 percent of the universe, yet we know nothing about it.

Around 25 percent of the universe is the equally mysterious dark matter, leaving just five percent for everything that we can see and touch — matter made up of atoms.

Dark energy is the placeholder name scientists have given to the unknown force causing the universe to expand faster and faster over time.

But some recent cosmic clues have been chipping away at the leading theory for this phenomenon, which could eventually mean humanity will have to rethink our understanding of the universe.

And with several new telescopes taking aim at the problem, scientists hope to have some concrete answers soon.

Here is what you need to know about what many scientists have called the greatest mystery in the universe.

– So what is dark energy exactly? –

No one knows. It is invisible and it does not interact with matter or light.

And it may not even exist.

This story begins — like everything else — at the Big Bang around 13.8 billion years ago, when the universe first started expanding.

Since then, there has been “cosmic tug-of-war” between two mysterious forces, Joshua Frieman, a theoretical astrophysicist at the University of Chicago, told AFP.

Dark matter is thought to pull galaxies together, while dark energy pushes them apart.

During the first nine or so billion years of the universe, “dark matter was winning,” forming galaxies and everything else, Frieman said.

Then dark energy gained the upper hand, starting to speed up the expansion of the universe.

However for most of history, scientists had little idea this almighty tussle was going on. They thought that the expansion of the universe would simply start to slow down because of gravity.

Everything changed in 1998, when two separate groups of astronomers noticed that distant exploding stars called supernovae were farther away than they ought to be.

This led to the discovery that the universe is not just expanding — it is do so faster and faster.

So what could be causing this acceleration? They gave this strange force a name: dark energy.

– What are the main theories? –

The leading theory has long been that empty space itself produces dark energy.

Think of a cup of coffee, Frieman said.

“If I remove all the particles from the cup of coffee, there is still energy in there due to what we call the quantum vacuum,” he said.

This energy of empty space is known as the cosmological constant. It is the theory used in the standard model of cosmology, Lambda-CDM, which is our best guess for how the universe works.

But in recent years, several scientific results have appeared to support a rival theory — called evolving dark energy — which has brought the standard model into question.

On Wednesday, new results from the Dark Energy Spectroscopic Instrument provided the latest signs that dark energy could actually be weakening over time.

However the scientists behind the research emphasise there is not yet definitive proof.

If proven right, this would rule out that dark energy is a cosmological constant.

It could not be “the energy of empty space — because empty space doesn’t change,” explained Frieman, a leading proponent of the theory.

For dark matter to change, it would likely require the existence of some incredibly light, as-yet-unknown particle.

Another possibility is that there is something wrong with our calculations — or our understanding of gravity.

Einstein’s theory of relativity has withstood an incredible amount of scientific scrutiny over the last century, and has been proven right again and again.

There is no evidence that Einstein was wrong, but there is “a little bit of room” to change his theory when it comes to the largest scales of the universe, Frieman said.

– When could we know more? –

Soon. The best way to understand dark energy is to look at a vast swathe of sky, taking in as many galaxies with as much data as possible.

And a bunch of new telescopes are working to do just that.

On Wednesday, Europe’s Euclid space telescope released its first astronomical data since launching in 2023 — but any dark energy results are a couple of years away.

NASA’s Nancy Grace Roman space telescope, planned for launch in 2027, and the under-construction Vera Rubin Observatory in Chile will also take aim at the problem.

It is an exciting time for dark energy, Frieman said, adding that he expected a “definitive answer” in the next couple of years.

There is no time to waste, Frieman said.

“Every minute we wait, galaxies are disappearing from view.”

 LA REVUE GAUCHE - Left Comment: Search results for DARK MATTER 

LA REVUE GAUCHE - Left Comment: Search results for AETHYR 

LA REVUE GAUCHE - Left Comment: Search results for ETHER 

LA REVUE GAUCHE - Left Comment: Search results for DARK ENERGY

Oxygen discovered in most distant known galaxy

ESO

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image: 

This image shows the precise location in the night sky of the galaxy JADES-GS-z14-0, an extremely tiny dot in the Fornax constellation. As of today, this is the most distant confirmed galaxy we know of. Its light took 13.4 billion years to reach us and shows the conditions of the Universe when it was only 300 million years old. The inset of the image shows a close-up of this primordial galaxy as seen with the Atacama Large Millimeter/submillimeter Array (ALMA). The inset is overlaid on an image taken with the NASA/ESA/CSA James Webb Space Telescope.

When two research teams studied this galaxy with ALMA, operated by ESO and its international partners, they uncovered something unexpected: the spectrum of the galaxy indicated the presence of oxygen. This is the most distant detection of oxygen ever, and it defies what we knew about galaxy formation in the early Universe. The presence of heavy elements like oxygen suggest that these early galaxies evolved more rapidly than we thought. It is like finding an adolescent where you would only expect babies. 

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Credit: ALMA (ESO/NAOJ/NRAO)/S. Carniani et al./S. Schouws et al/JWST: NASA, ESA, CSA, STScI, Brant Robertson (UC Santa Cruz), Ben Johnson (CfA), Sandro Tacchella (Cambridge), Phill Cargile (CfA)

Two different teams of astronomers have detected oxygen in the most distant known galaxy, JADES-GS-z14-0. The discovery, reported in two separate studies, was made possible thanks to the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner. This record-breaking detection is making astronomers rethink how quickly galaxies formed in the early Universe.

Discovered last year, JADES-GS-z14-0 is the most distant confirmed galaxy ever found: it is so far away, its light took 13.4 billion years to reach us, meaning we see it as it was when the Universe was less than 300 million years old, about 2% of its present age. The new oxygen detection with ALMA, a telescope array in Chile’s Atacama Desert, suggests the galaxy is much more chemically mature than expected.

“It is like finding an adolescent where you would only expect babies,” says Sander Schouws, a PhD candidate at Leiden Observatory, the Netherlands, and first author of the Dutch-led study, now accepted for publication in The Astrophysical Journal. “The results show the galaxy has formed very rapidly and is also maturing rapidly, adding to a growing body of evidence that the formation of galaxies happens much faster than was expected." 

Galaxies usually start their lives full of young stars, which are made mostly of light elements like hydrogen and helium. As stars evolve, they create heavier elements like oxygen, which get dispersed through their host galaxy after they die. Researchers had thought that, at 300 million years old, the Universe was still too young to have galaxies ripe with heavy elements. However, the two ALMA studies indicate JADES-GS-z14-0 has about 10 times more heavy elements than expected.

“I was astonished by the unexpected results because they opened a new view on the first phases of galaxy evolution,” says Stefano Carniani, of the Scuola Normale Superiore of Pisa, Italy, and lead author on the paper now accepted for publication in Astronomy & Astrophysics. “The evidence that a galaxy is already mature in the infant Universe raises questions about when and how galaxies formed.”

The oxygen detection has also allowed astronomers to make their distance measurements to JADES-GS-z14-0 much more accurate. “The ALMA detection offers an extraordinarily precise measurement of the galaxy’s distance down to an uncertainty of just 0.005 percent. This level of precision — analogous to being accurate within 5 cm over a distance of 1 km — helps refine our understanding of distant galaxy properties,” adds Eleonora Parlanti, a PhD student at the Scuola Normale Superiore of Pisa and author on the Astronomy & Astrophysics study [1].

“While the galaxy was originally discovered with the James Webb Space Telescope, it took ALMA to confirm and precisely determine its enormous distance,” [2] says Associate Professor Rychard Bouwens, a member of the team at Leiden Observatory. “This shows the amazing synergy between ALMA and JWST to reveal the formation and evolution of the first galaxies.”

Gergö Popping, an ESO astronomer at the European ALMA Regional Centre who did not take part in the studies, says: "I was really surprised by this clear detection of oxygen in JADES-GS-z14-0. It suggests galaxies can form more rapidly after the Big Bang than had previously been thought. This result showcases the important role ALMA plays in unraveling the conditions under which the first galaxies in our Universe formed."

Notes

[1] Astronomers use a measurement known as redshift to determine the distance to extremely distant objects. Previous measurements indicated that the galaxy JADES-GS-z-14-0 was at a redshift between about 14.12 and 14.4. With their oxygen detections, both teams have now narrowed this down to a redshift around 14.18.

[2] The James Webb Space Telescope is a joint project of NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA).

More information

This research was presented in two papers to appear in Astronomy & Astrophysics (https://aanda.org/10.1051/0004-6361/202452451) and The Astrophysical Journal.

The teams are composed of:

Italian-led, Astronomy & Astrophysics paper: Stefano Carniani (Scuola Normale Superiore, Pisa, Italy [SNS]), Francesco D’Eugenio (Kavli Institute for Cosmology, University of Cambridge, Cambridge, UK [CAM-KIC]; Cavendish Laboratory, University of Cambridge, Cambridge, UK [CAM-CavL] and INAF – Osservatorio Astronomico di Brera, Milano, Italy), Xihan Ji (CAM-KIC and CAM-CavL), Eleonora Parlanti (SNS), Jan Scholtz (CAM-KIC and CAM-CavL), Fengwu Sun (Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA [CfA]), Giacomo Venturi (SNS), Tom J. L. C. Bakx (Department of Space, Earth, & Environment, Chalmers University of Technology, Gothenburg, Sweden), Mirko Curti (European Southern Observatory, Garching bei München, Germany), Roberto Maiolino (CAM-KIC, CAM-CavL and Department of Physics and Astronomy, University College London, London, UK [UCL]), Sandro Tacchella (CAM-KIC and CAM-CavL), Jorge A. Zavala (National Astronomical Observatory of Japan, Tokyo, Japan), Kevin Hainline (Steward Observatory, University of Arizona, Tucson, USA [UArizona-SO]), Joris Witstok (Cosmic Dawn Center, Copenhagen, Denmark [DAWN] and CAM-CavL), Benjamin D. Johnson [CfA], Stacey Alberts [UArizona-SO], Andrew J. Bunker (Department of Physics, University of Oxford, Oxford, UK [Oxford]), Stéphane Charlot (Sorbonne Université, CNRS, Institut d’Astrophysique de Paris, Paris, France), Daniel J. Eisenstein (CfA), Jakob M. Helton (UArizona-SO), Peter Jakobsen (DAWN and Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark), Nimisha Kumari (Space Telescope Science Institute, Baltimore, USA), Brant Robertson (Department of Astronomy and Astrophysics University of California, Santa Cruz, USA), Aayush Saxena (Oxford and UCL), Hannah Übler (CAM-KIC and CAM-CavL), Christina C. Williams (NSF NOIRLab, Tucson, USA), Christopher N. A. Willmer (UArizona-SO) and Chris Willott (NRC Herzberg, Victoria, Canada).

Dutch-led, The Astrophysical Journal paper: Sander Schouws (Leiden Observatory, Leiden University, Leiden, the Netherlands [Leiden]), Rychard J. Bouwens (Leiden), Katherine Ormerod (Astrophysics Research Institute, Liverpool John Moores University, Liverpool, United Kingdom [LJMU]), Renske Smit (LJMU), Hiddo Algera (Hiroshima Astrophysical Science Center, Hiroshima University, Hiroshima, Japan and National Astronomical Observatory of Japan, Tokyo, Japan), Laura Sommovigo (Center for Computational Astrophysics, Flatiron Institute, New York, USA), Jacqueline Hodge (Leiden), Andrea Ferrara (Scuola Normale Superiore, Pisa, Italy), Pascal A. Oesch (Département d’Astronomie, Université de Genève, Versoix, Switzerland; Cosmic Dawn Center, Copenhagen, Denmark and Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark), Lucie E. Rowland (Leiden), Ivana van Leeuwen (Leiden), Mauro Stefanon (Leiden), Thomas Herard-Demanche (Leiden), Yoshinobu Fudamoto (Center for Frontier Science, Chiba University, Chiba, Japan), Huub Rottgering (Leiden) and Paul van der Werf (Leiden).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA. 

The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration for astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, Czechia, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as survey telescopes such as VISTA. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates ALMA on Chajnantor, a facility that observes the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society. 

Links

• Research paper (Carniani et al.)
• Research paper (Schouws et al.)
• Photos of ALMA 
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Journal

Astronomy and Astrophysics

DOI

10.1051/0004-6361/202452451 

 

NRL's narrow field imager launches on NASA's PUNCH mission

Naval Research Laboratory

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WASHINGTON, D.C. — The U.S. Naval Research Laboratory’s (NRL) Narrow Field Imager (NFI) was launched into space aboard a SpaceX Falcon 9 rocket as a part of NASA’s Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission on March 11 and deployed from Falcon 9 on March 12.

PUNCH is a four-satellite constellation, collecting observations in low Earth orbit. It will conduct global, 3D observations of the inner heliosphere to investigate the solar corona's evolution into the solar wind. The mission is scheduled to conduct science for the next two years, following a 90-day commissioning period.

The NRL-developed NFI, sponsored by NASA, is a compact, externally occulted coronagraph. The external occulter blocks direct sunlight from entering the main optical aperture, which views the corona and starfield around the Sun using a compound lens system. Polarization is resolved using a polarizing filter wheel and the image is digitized using a CCD camera with a 2K x 2K active detector area.

NFI will image the transition of the Sun’s atmosphere to the solar wind to understand how the Sun generates the space plasma environment.

"The launch and deployment of NRL's Narrow Field Imager aboard the PUNCH mission marks a significant step forward in our ability to understand the dynamic processes that drive space weather," said NRL Coronal and Heliospheric Physics Section Head Robin Colaninno, Ph.D. "By imaging the transition of the Sun's atmosphere to the solar wind, we're gaining crucial insights that will ultimately improve our ability to predict and mitigate the impacts of these powerful events on Earth and in space."

Predicting the impact of space weather, from minor fluctuations to major coronal mass ejections (CMEs) and corotating interaction regions (CIRs), requires a comprehensive understanding of the solar wind. While originating at the Sun, these events evolve significantly on their journey to Earth, especially within the sparsely imaged region between the solar corona and inner heliosphere, posing a significant scientific challenge.

By capturing the evolution of coronal mass ejections (CMEs), PUNCH will provide scientists new data on their formation and propagation. This is essential for understanding and predicting these events, which can cause significant disruptions on Earth, including satellite damage, radio communication blackouts, and power grid failures. Enhanced predictions will also safeguard robotic explorers operating in interplanetary space.

 

About the U.S. Naval Research Laboratory

NRL is a scientific and engineering command dedicated to research that drives innovative advances for the U.S. Navy and Marine Corps from the seafloor to space and in the information domain. NRL, located in Washington, D.C. with major field sites in Stennis Space Center, Mississippi; Key West, Florida; Monterey, California, and employs approximately 3,000 civilian scientists, engineers and support personnel.

For more information, contact NRL Corporate Communications at (202) 480-3746 or nrlpao@nrl.navy.mil. Please reference package number at top of press release.

 

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