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.

  

SEE

LA REVUE GAUCHE - Left Comment: Search results for ETHER (plawiuk.blogspot.com)

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
Copy a link to the article entitled http://Dark%20energy%20might%20be%20neither%20particle%20nor%20field

 

A formula for life? New model calculates chances of intelligent beings in our Universe and beyond

Peer-Reviewed Publication

Royal Astronomical Society

 

image: 

How the same region of the Universe would look in terms of the amount of stars for different values of the dark energy density. Clockwise, from top left, no dark energy, same dark energy density as in our Universe, 30 and 10 times the dark energy density in our Universe. The images are generated from a suite of cosmological simulations.

view more 

Credit: Oscar Veenema

The chances of intelligent life emerging in our Universe – and in any hypothetical ones beyond it – can be estimated by a new theoretical model which has echoes of the famous Drake Equation.

This was the formula that American astronomer Dr Frank Drake came up with in the 1960s to calculate the number of detectable extraterrestrial civilisations in our Milky Way galaxy.

More than 60 years on, astrophysicists led by Durham University have produced a different model which instead focuses on the conditions created by the acceleration of the Universe's expansion and the amount of stars formed.

It is thought this expansion is being driven by a mysterious force called dark energy that makes up more than two thirds of the Universe.

What is the calculation?

Since stars are a precondition for the emergence of life as we know it, the model could therefore be used to estimate the probability of generating intelligent life in our Universe, and in a multiverse scenario of hypothetical different universes.

The new research does not attempt to calculate the absolute number of observers (i.e. intelligent life) in the universe but instead considers the relative probability of a randomly chosen observer inhabiting a universe with particular properties.

It concludes that a typical observer would expect to experience a substantially larger density of dark energy than is seen in our own Universe – suggesting the ingredients it possesses make it a rare and unusual case in the multiverse.

The approach presented in the paper involves calculating the fraction of ordinary matter converted into stars over the entire history of the Universe, for different dark energy densities.

The model predicts this fraction would be approximately 27 per cent in a universe that is most efficient at forming stars, compared to 23 per cent in our own Universe.

This means we don't live in the hypothetical universe with the highest odds of forming intelligent life forms. Or in other words, the value of dark energy density we observe in our Universe is not the one that would maximise the chances of life, according to the model.

Dark energy's impact on our existence

Lead researcher Dr Daniele Sorini, of Durham University's Institute for Computational Cosmology, said: "Understanding dark energy and the impact on our Universe is one of the biggest challenges in cosmology and fundamental physics.

"The parameters that govern our Universe, including the density of dark energy, could explain our own existence.

"Surprisingly, though, we found that even a significantly higher dark energy density would still be compatible with life, suggesting we may not live in the most likely of universes."

The new model could allow scientists to understand the effects of differing densities of dark energy on the formation of structures in the Universe and the conditions for life to develop in the cosmos.

Dark energy makes the Universe expand faster, balancing gravity's pull and creating a universe where both expansion and structure formation are possible.

However, for life to develop, there would need to be regions where matter can clump together to form stars and planets, and it would need to remain stable for billions of years to allow life to evolve.

Crucially, the research suggests that the astrophysics of star formation and the evolution of the large-scale structure of the Universe combine in a subtle way to determine the optimal value of the dark energy density needed for the generation of intelligent life.

Professor Lucas Lombriser, Université de Genève and co-author of the study, added: "It will be exciting to employ the model to explore the emergence of life across different universes and see whether some fundamental questions we ask ourselves about our own Universe must be reinterpreted."

Drake Equation explained

Dr Drake's equation was more of a guide for scientists on how to go about searching for life, rather than an estimating tool or serious attempt to determine an accurate result.

Its parameters included the rate of yearly star formation in the Milky Way, the fraction of stars with planets orbiting them and the number of worlds that could potentially support life.

By comparison, the new model connects the rate of yearly star formation in the Universe with its fundamental ingredients, such as the aforementioned dark energy density.

The study, which was funded by the European Research Council and also involved scientists at the University of Edinburgh and the Université de Genève, has been published today in Monthly Notices of the Royal Astronomical Society.

  

This Hubble Space Telescope image captures a triple-star system, which can host potentially-habitable planets. Our nearest stellar neighbour, the Alpha Centauri system, includes three stars.

Credit

NASA, ESA, G. Duchene (Universite de Grenoble I); Image Processing: Gladys Kober (NASA/Catholic University of America)

Images and captions

Stars in universes of different dark energy densities

Caption: How the same region of the Universe would look in terms of the amount of stars for different values of the dark energy density. Clockwise, from top left, no dark energy, same dark energy density as in our Universe, 30 and 10 times the dark energy density in our Universe. The images are generated from a suite of cosmological simulations.

Credit: Oscar Veenema

Note: The simulations were run on the Cosma@DiRAC supercomputer in Durham as part of the EAGLE project (J. Schaye et al., 2015, Monthly Notices of the Royal Astronomical society, Vol. 446, p. 521), and were first presented by L. A. Barnes et al. (2018) in Monthly Notices of the Royal Astronomical Society, Vol. 477, p. 3727.

A triple-star system

Caption: This Hubble Space Telescope image captures a triple-star system, which can host potentially-habitable planets. Our nearest stellar neighbour, the Alpha Centauri system, includes three stars.

Credit: NASA, ESA, G. Duchene (Universite de Grenoble I); Image Processing: Gladys Kober (NASA/Catholic University of America)

Drake Equation (revised)

Caption: The Drake Equation, a mathematical formula for the probability of finding life or advanced civilisations in the Universe, as revised by two University of Rochester researchers in 2016.

Credit: University of Rochester

Further information

The paper ‘The impact of the cosmological constant on past and future star formation’, by Daniele Sorini, John A. Peacock and Lucas Lombriser, will be published in Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stae2236. The link will go live when the embargo lifts. To view a copy of the study before this, email press@ras.ac.uk

 

The Drake Equation's parameters in full are:

R* = the rate of yearly star formation in the Galaxy

fp= the fraction of stars with planets orbiting them

fg= the fraction of stars that could support habitable planets

ne = the number of planets that can potentially support life (per star with planets)

fl = the fraction of planets that actually develop life at some point

fc= the fraction of civilisations that emit detectable signs of their presence

 

Notes for editors

About the Royal Astronomical Society

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

The RAS organises scientific meetings, publishes international research and review journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.

Keep up with the RAS on X, Facebook, LinkedIn and YouTube.

 

About Durham University

Durham University is a globally outstanding centre of teaching and research based in historic Durham City in the UK. We are a collegiate university committed to inspiring our people to do outstanding things at Durham and in the world.  
 
We conduct research that improves lives globally and we are ranked as a world top 100 university with an international reputation in research and education (QS World University Rankings 2024).  
 
We are a member of the Russell Group of leading research-intensive UK universities and we are consistently ranked as a top 10 university in national league tables (Times and Sunday Times Good University Guide, Guardian University Guide and The Complete University Guide).  
 
For more information about Durham University visit: www.durham.ac.uk/about/

---

DOI

10.1093/mnras/stae2236 

Article Title

The impact of the cosmological constant on past and future star formation

Article Publication Date

13-Nov-2024

Dark energy from supermassive black holes? Physicists spar over radical idea

New theory aims to account for one of the universe’s great mysteries

17 FEB 2023
BY ADAM MANN

An artist's impression of a supermassive black hole in the center of a galaxy. New reseach links these behemoths to the mysterious phenomenon called dark energy.NASA/JPL-CALTECH

Earlier this week, a study made headlines claiming that the mysterious “dark energy” cosmologists believe is accelerating the expansion of the universe could arise from supermassive black holes at the hearts of galaxies. If true, the connection would link two of the most mind-bending concepts in physics—black holes and dark energy—and suggest that the source of the latter has been under theorists’ noses for decades. However, some leading theorists are deeply skeptical of the idea.

“What they are proposing makes no sense to me,” says Robert Wald, a theoretical physicist at the University of Chicago who specializes in Albert Einstein’s general theory of relativity, the standard understanding of gravity. Other theorists were more receptive to the radical claim—even if it ends up being wrong. “I’m personally excited about it,” says astrophysicist Niayesh Afshordi of the Perimeter Institute for Theoretical Physics.

At first blush, black holes and dark energy seem to have nothing to do with each other. According to general relativity, a black hole is a pure gravitational field so strong that its own energy sustains its existence. Such peculiar beasts are thought to emerge when massive stars collapse to an infinitesimal point, leaving just their gravitational fields behind. Supermassive black holes having millions or billions of times the mass of our Sun are believed to lurk in the hearts of galaxies.

In contrast, dark energy is a mysterious phenomenon that literally stretches space and is accelerating the expansion of the universe. Theorists think dark energy could represent some new sort of field in space, a bit like an electric field, or it could be a fundamental property of empty space itself.

So how could the two be connected? Quantum mechanics suggests that the vacuum of empty space should contain a type of energy known as vacuum energy. This is thought to be spread throughout the universe and exert a force opposing gravity, making it a prime candidate for the identity of dark energy. In 1966, Soviet physicist Erast Gliner showed that Einstein’s equations could also produce objects that to outside observers look and behave exactly like a black hole—yet are, in fact, giant balls of vacuum energy.

If such objects were to exist, it would mean that rather than being uniformly spread throughout space, dark energy is actually confined to specific locations: the interiors of black holes. Even bound in these particular knots, dark energy would still exert its space-stretching effect on the universe.

One consequence of this idea—that supermassive black holes are the source of dark energy—is that they would be linked to the constant stretching of space and their mass should change as the universe expands, says astrophysicist Duncan Farrah of the University of Hawaii, Manoa. “If the volume of the universe doubles, so does the mass of the black hole,” he adds.

To test this possibility, Farrah and his colleagues studied elliptical galaxies, which contain black holes with millions or billions of times the Sun’s mass in their centers. They focused on galaxies with little gas or dust floating around between their stars, which would provide a reservoir of material that the central black hole could feed on. Such black holes wouldn’t be expected to change much over the course of cosmic history.

Yet by analyzing the properties of ellipticals over roughly 9 billion years, the team saw that black holes in the early universe were much smaller relative to their host galaxy than those in the modern universe, indicating they had grown by a factor of seven to 10 times in mass, Farrah and colleagues reported this month in the Astrophysical Journal.

The fact that the black holes swelled while the galaxies didn’t is the key, Farrah says. If the black holes had grown by feeding on nearby gas and dust, that material should have also generated many new stars in parts of the galaxy far from the black hole. But if black holes were made from dark energy, they would react to changes in the universe’s size in exactly the way that researchers observed in the centers of elliptical galaxies, Farrah’s team additionally reported this week in Astrophysical Journal Letters.

Wald is unpersuaded. He questions how an orb of pure dark energy could be stable. He also says the numbers don’t seem to add up: Dark energy is known to make up 70% of the mass-energy of the universe, whereas black holes are a mere fraction of the ordinary matter, which constitutes less than 5% of the universe. “I don't see how it is in any way conceivable that such objects could be relevant to the observed dark energy,” he says.

Others are taking a wait-and-see attitude. “At the moment, this is an interesting possibility,” says cosmologist Geraint Lewis of the University of Sydney, but “there would have to be a lot more evidence on the table if this is even a remotely plausible source of dark energy.”

Afshordi agrees. If black holes and dark energy are linked in this way, it would likely have other visible consequences in the universe, he says. At the moment, though, he’s unsure what those would be. Determining exactly how galaxies evolve over time is a tricky business, he adds, and there could be other mechanisms to grow black holes that the team hasn’t considered.

Nevertheless, Afshordi is supportive of efforts to rethink fundamental assumptions about the universe. “Most new theoretical ideas are dismissed by skepticism,” he says. “But if we dismiss all the new ideas then there won’t be anything left.”

SEE 

https://plawiuk.blogspot.com/2023/02/1st-observational-evidence-linking.html

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

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

LA REVUE GAUCHE - Left Comment: Search results for ETHER