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Does Modified Newtonian Dynamics Negate the Need for Dark Matter?
Does Dark Matter really exist? Or is it a figment of our imagination? The ultra-diffuse galaxy NGC1052-DF2, despite its small size, finds itself at the center of a big debate over the correct laws of gravity. This fuzzy-looking galaxy is so diffuse that astronomers call it a “see-through” galaxy because they can clearly see distant galaxies behind it. The ghostly object doesn’t have a noticeable central region or even spiral arms and a disk, typical features of a spiral galaxy. But it doesn’t look like an elliptical galaxy either. Even its globular clusters are oddballs -- They are twice as large as typical stellar groupings seen in other galaxies. All of these oddities pale in comparison to the weirdest aspect of this galaxy -- NGC 1052-DF2 is missing most, if not all, of its Dark Matter. Now a new study based on Modified Newtonian Dynamics (MOND), which relies on data from NGC1052-DF2, provides a very viable explanation for why Dark Matter does not really exist in any galaxy. This image was taken by the Advanced Camera for Surveys on the Hubble Space Telescope. (Image Credit: NASA, ESA, and P. van Dokkum - Yale University)
Does Modified Newtonian Dynamics Negate the Need for Dark Matter?
Galaxies rotate so quickly that they should fly apart according to the existing laws of physics. Two current theories attempt to explain this anomaly – the first places a halo of an imaginary and as of yet undetected substance called “Dark Matter” around every galaxy. The second, Modified Newtonian Dynamics (MOND) does this by applying a mathematical compensation to Newtonian physics that strengthens the visible material’s gravity, but only where it gets very weak. Otherwise, gravity follows Newton’s conventional laws, as in our Solar System.
Recently, an international group of astrophysicists from the University of Bonn in Germany and the University of St Andrews in the UK re-examined a previously published paper in the journal Nature that attempted to debunk MOND. The original paper claimed that MOND couldn’t be true because the internal motions were too slow within dwarf galaxy NGC1052-DF2, a small galaxy comprising about 200 million stars. This latest study, however, also in Nature, shows that the earlier work neglected a subtle environmental effect and MOND provides a very viable explanation for why dark mater does not exist. It is remarkable that MOND continues to make such successful predictions based on equations written down 35 years ago.
History provides us with many examples where scientists have simply invented ideas out of thin air to help explain away things that are just not understood. In some ways, Dark Matter and Dark Energy bring to mind another imaginary concept -- the so called "Aether Wind" of the 1800s. Back then, everybody just "knew" that space was filled with an "Aether Wind." The problem was that no one had ever seen it or measured it.
In 1887, Albert Michelson and Edward Morley set out to prove the existence of Aether Wind once and for all. Their experiment failed spectacularly in its attempt to detect any Aether Wind, but in the process they showed that the whole concept of Aether Wind, which most scientists at the time simply accepted as fact, was flawed -- There was no such thing.
Albert Michelson eventually won the Nobel Prize in Physics in 1907 for this work and became the first American to do so.
Will the concepts of Dark Matter and Dark Energy meet the same fate as the Aether Wind of the 19th century? Time will tell.
For close on a century, researchers have hypothesized that the Universe contains more matter than can be directly observed and have named it Dark Matter. They have also posited the existence of a Dark Energy that is more powerful than gravitational attraction. These two hypotheses, it has been argued, account for the movement of stars in galaxies and for the accelerating expansion of the universe, respectively.
Various theories have been put forward to explain what holds galaxies together and debate rages over which is right. A recent paper published in Nature claimed that MOND was dead. However, this latest study – also published in Nature – shows that the earlier work neglected a subtle environmental effect that shows just the opposite.
The new research argues that the previous work did not consider that the influence of the gravitational environment around the dwarf galaxy could affect motions within it. In other words, if the dwarf galaxy were close to a massive galaxy – which is the case here – then the motions within the dwarf would be slower.
Lead author Pavel Kroupa, Professor at the University of Bonn and Charles University in Prague, said: “There have been many premature claims on the death of MOND in very influential journals. So far, none stand up to detailed scrutiny.”
Dr. Indranil Banik of the School of Physics and Astronomy at the University of St Andrews, and soon to be of Bonn University, said: “It is remarkable that MOND still makes such successful predictions based on equations written down 35 years ago.”
Dr. Hongsheng Zhao, of the School of Physics and Astronomy at the University of St Andrews, said: “Our modelling of the MOND environmental effect was later confirmed by another group.”
Hosein Haghi, Professor of Physics at the Institute for Advanced Studies in Basic Sciences, in Iran, said: “This effect has been known for a long time. These Nature authors were unaware of our papers on how to include it.”
Have the Imaginary Concepts of Dark Matter and Dark Energy Finally Run Their Course?
In separate research, a University of Geneva researcher has also concluded that the accelerating expansion of the Universe and the movement of the stars in galaxies can be explained without drawing on the concepts of Dark Matter and Dark Energy... And the work is pointing to a very inconvenient conclusion -- These two entities may not actually exist.
According to researchers at the University of Geneva (UNIGE) in Switzerland, these concepts of Dark Matter and Dark Energy may no longer be valid. Their work shows that the phenomena they are supposed to describe can be demonstrated without them. This research, which was published in The Astrophysical Journal, exploits a new theoretical model based on the scale invariance of empty space, and potentially solves two of astronomy's greatest mysteries.
In 1933, the Swiss astronomer Fritz Zwicky made a discovery that left the scientific world speechless. There was, claimed Zwicky, substantially more matter in the universe than we could actually see. Astronomers called this unknown matter "Dark matter," a concept that was to take on yet more importance in the 1970s, when the US astronomer Vera Rubin called on this enigmatic matter to explain the movements and speed of the stars.
Scientists have subsequently devoted considerable resources to detecting Dark Matter -- in space, on the ground, and even at CERN -- but without success. In 1998 there was a second thunderclap. A team of Australian and US astrophysicists discovered the acceleration of the expansion of the Universe, earning them the Nobel Prize for physics in 2011.
However, in spite of the enormous resources that have been implemented, no theory or observation has been able to define this Dark Energy that is allegedly stronger than Newton's gravitational attraction. In short, Dark Matter and Dark Energy are two mysteries that have had astronomers stumped for over 80 years and 20 years, respectively.
The generally accepted way we represent the Universe and its history are described by Einstein's equations of general relativity, Newton's universal laws of gravitation, and quantum mechanics. The consensus model of the Universe at present is that of a Big Bang followed by an expansion.
"In this model, there is a starting hypothesis that hasn't been taken into account, in my opinion," says Andre Maeder, honorary professor in the Department of Astronomy in UNIGE's Faculty of Science. "By that I mean the scale invariance of the empty space. In other words, the empty space and its properties do not change following a dilatation or contraction."
Empty space plays a primordial role in Einstein's equations as it operates in a quantity known as a "Cosmological Constant," and the resulting Universe model depends on it. Based on this hypothesis, Maeder is now re-examining the model of the Universe, pointing out that the scale invariance of the empty space is also present in the fundamental theory of electromagnetism.
Do we finally have an explanation for the expansion of the universe and the speed of the galaxies?
When Maeder carried out cosmological tests on his new model, he found that it matched the observations. He also found that the model predicts the accelerated expansion of the Universe without having to factor in any particle or Dark Energy. In short, it appears that Dark Energy may not actually exist since the acceleration of the expansion is contained in the equations of the physics.
In a second stage, Maeder focused on Newton's law, a specific instance of the equations of general relativity. The law is also slightly modified when the model incorporates Maeder's new hypothesis. Indeed, it contains a very small outward acceleration term, which is particularly significant at low densities. This amended law, when applied to clusters of galaxies, leads to masses of clusters in line with that of visible matter (contrary to what Zwicky argued in 1933).
This means that no Dark Matter is needed to explain the high speeds of the galaxies in the clusters. A second test demonstrated that this law also predicts the high speeds reached by the stars in the outer regions of the galaxies (as Rubin had observed), without having to turn to Dark Matter to describe them.
Finally, a third test looked at the dispersion of the speeds of the stars oscillating around the plane of the Milky Way. This dispersion, which increases with the age of the relevant stars, can be explained very well using the invariant empty space hypothesis, while there was before no agreement on the origin of this effect.
Maeder's discovery paves the way for a new concept in astronomy -- One that will certainly raise questions and generate controversy. "The announcement of this model, which at last solves two of astronomy's greatest mysteries, remains true to the spirit of science -- Nothing can ever be taken for granted, not in terms of experience, observation, or the reasoning of human beings," concludes Andre Maeder.
So, Does Dark Matter Really Exist? Or is it a Figment of Our Imagination?
An international team of astronomers, led by Michele Cappellari from the University of Oxford in the UK has used data gathered by the W.M. Keck Observatory in Hawaii to analyze the motions of stars in the outer parts of elliptical galaxies. The team discovered surprising gravitational similarities between spiral and elliptical galaxies, implying the influence of hidden forces.
The scientists from the US, Australia, and Europe used the powerful DEIMOS spectrograph installed on the world's largest optical telescope at Keck Observatory to conduct a major survey of nearby galaxies, which mapped out the speeds of their stars. The team then applied Newton's law of gravity to translate these speed measurements into the amounts of matter distributed within the galaxies.
"The DEIMOS spectrograph was crucial for this discovery since it can take in data from an entire giant galaxy all at once, while at the same time sampling the speeds of its stars at a hundred separate locations with exquisite accuracy," said Aaron Romanowsky, of San Jose State University in California.
One of the most important scientific discoveries of the 20th century was that the spectacular spiral galaxies, such as our own Milky Way, rotate much faster than expected, powered by an extra invisible gravitational force. For lack of a better term (coupled with a lack of better understanding), this mysterious force has been dubbed "Dark Matter." Since this discovery 40 years ago, we have learned that dark matter, which is probably an exotic elementary particle, makes up about 85 percent of the mass in the Universe, leaving only 15 percent for the ordinary stuff encountered in our everyday lives. Dark matter is central to our understanding of how galaxies form and evolve and is ultimately one of the reasons for the existence of life on Earth. Yet we know almost nothing about it.
"The surprising finding of our study was that elliptical galaxies maintain a remarkably constant circular speed out to large distances from their centers, in the same way that spiral galaxies are already known to do," said Cappellari. "This means that in these very different types of galaxies, stars and dark matter conspire to redistribute themselves to produce this effect, with stars dominating in the inner regions of the galaxies, and a gradual shift in the outer regions to dark matter dominance."
However, the conspiracy does not come out naturally from models of dark matter, and some disturbing fine-tuning is required to explain the observations. For this reason, the conspiracy even led some scientists to suggest that, rather than being due to dark matter, it may be due to Newton's law of gravity becoming progressively less accurate at large distances. Remarkably, decades after it was proposed, this alternative theory (a universe without dark matter) still cannot be conclusively ruled out.
Spiral galaxies only constitute less than half of the stellar mass in the universe, which is dominated by elliptical and lenticular galaxies, and which have puffier configurations of stars and lack the flat disks of gas that spirals have. In these galaxies, it has been very difficult technically to measure their masses and to find out how much dark matter they have, and how it is distributed -- until now.
Because the elliptical galaxies have different shapes and formation histories than spiral galaxies, the newly discovered findings are even more profound and will lead experts in dark matter and galaxy formation to carefully re-think some aspects of their theory.
"This question is particularly timely in this period when physicists at CERN are about to restart the Large Hadron Collider (LHC) to try to directly detect the same elusive dark matter particle, which makes galaxies rotate fast -- if it really exists" said Professor Jean Brodie, principal investigator of the survey.
Maybe it is Time to Discard the Whole Dark Matter Contrivance
In the late 1970s, astronomers Vera Rubin and Albert Bosma independently found that spiral galaxies rotate at a nearly constant speed – That is, the velocity of stars and gas inside a galaxy does not decrease with radius, as one would expect from Newton's laws and the distribution of visible matter. Such "flat rotation curves" have generally been attributed to an invisible dark matter surrounding galaxies, providing additional gravitational attraction.
A team led by Case Western Reserve University researchers has found a significant new relationship in spiral and irregular galaxies -- The acceleration observed in rotation curves tightly correlates with the gravitational acceleration expected from the visible mass only. This work challenges the current understanding (and possibly the existence) of dark matter.
"If you measure the distribution of star light, you know the rotation curve, and vice versa," said Stacy McGaugh, chair of the Department of Astronomy at Case Western Reserve and lead author of the research.
The finding is consistent among 153 spiral and irregular galaxies, ranging from giant to dwarf, including those with massive central bulges or none at all. It is also consistent among those galaxies comprised of mostly stars or mostly gas.
McGaugh and co-authors Federico Lelli, an astronomy postdoctoral scholar at Case Western Reserve, and James M. Schombert, astronomy professor at the University of Oregon, argue that the relation they've found is tantamount to a new natural law.
An astrophysicist who reviewed the study said the findings may lead to a new understanding of internal dynamics of galaxies.
"Galaxy rotation curves have traditionally been explained via an ad hoc hypothesis -- that galaxies are surrounded by dark matter," said David Merritt, professor of physics and astronomy at the Rochester Institute of Technology, who was not involved in the research. "The relation discovered by McGaugh et al. is a serious, and possibly fatal, challenge to this hypothesis, since it shows that rotation curves are precisely determined by the distribution of the normal matter alone. Nothing in the standard cosmological model predicts this, and it is almost impossible to imagine how that model could be modified to explain it, without discarding the dark matter hypothesis completely."
McGaugh and Schombert have been working on this research for a decade and with Lelli the last three years. Near-infrared images collected by NASA's Spitzer Space Telescope during the last five years allowed them to establish the relation and that it persists for all 153 galaxies.
The key is that near-infrared light emitted by stars is far more reliable than optical light for converting light to mass, Lelli said.
The researchers plotted the radial acceleration observed in rotation curves published by a host of astronomers over the last 30 years against the acceleration predicted from the observed distribution of ordinary matter now in the "Spitzer Photometry and Accurate Rotation Curves Database" that McGaugh's team created. The two measurements showed a single, extremely tight correlation, even when dark matter is supposed to dominate the gravity.
"There is no intrinsic scatter, which is how far the data differ on average from the mean when plotted on a graph," McGaugh said. "What little scatter is found is consistent with stellar mass-to-light ratios that vary a little from galaxy to galaxy."
Lelli compared the relation to a long used natural law. "It's like Kepler's third law for the solar system. If you measure the distance of each planet from the sun, you get the orbital period or vice versa" he said. "Here we have something similar for galaxies, with about 3000 data points."
"In our case, we find a relation between what you see in normal matter in galaxies and what you get in their gravity," McGaugh said. "This is important because it is telling us something fundamental about how galaxies work."
Arthur Kosowsky, professor of physics and astronomy at the University of Pittsburgh, was not involved but reviewed the research.
"The standard model of cosmology is remarkably successful at explaining just about everything we observe in the universe," Kosowsky said. "But if there is a single observation which keeps me awake at night worrying that we might have something essentially wrong, this is it."
He said McGaugh and collaborators have steadily refined the spiral galaxy scaling relation for years and called this latest work a significant advance, reducing uncertainty in the mass in normal matter by exploiting infrared observations.
"The result is a scaling relation in the data with no adjustable parameters," Kosowky said. "Throughout the history of physics, unexplained regularities in data have often pointed the way towards new discoveries."
McGaugh and his team are not pressing any theoretical interpretation of their empirical relation at this point.
"The natural inference is that this law stems from a universal force such as a modification of gravity like MOND, the hypothesis of Modified Newtonian Dynamics proposed by Israeli physicist Moti Milgrom. But it could also be something in the nature of dark matter like the superfluid dark matter proposed by Justin Khoury," McGaugh said. "Most importantly, whatever theory you want to build has to reproduce this."
While We’re At It, Is It Time to Discard the Whole Dark Energy Contrivance Too?
So what is Dark Energy? Well, the simple answer is that we don't know. It seems to contradict much of our understanding about the way the Universe works.
We all know that light waves (a form of radiation) carry energy. You feel that energy the moment you step outside on a hot summer day.
Also, Einstein's famous equation, E = mc^2 teaches us that matter and energy are interchangeable -- merely different forms of the same thing. We have a giant example of that in our daytime sky: the Sun. The Sun is powered by the conversion of mass to energy.
However, energy is supposed to have a source -- either matter or radiation. But the idea behind "Dark Energy" is that space, even when devoid of all matter and radiation, has a residual energy. And this "energy of space," when considered on a cosmic scale, leads to a force that increases the expansion of the universe -- At least, that's according to the current conventional wisdom.
Perhaps Dark Energy results from weird behavior on scales smaller than atoms. The physics of the very small, called Quantum Mechanics, allows energy and matter to appear out of nothingness, although only for the tiniest instances. The constant brief appearance and disappearance of matter could be giving energy to otherwise empty space.
It could also be that Dark Energy creates a new, fundamental force in the universe -- something that only starts to show an effect when the universe reaches a certain size. Scientific theories allow for the possibility of such forces as well. The force might even be temporary, causing the universe to accelerate for some billions of years before it weakens and essentially disappears.
Or perhaps the answer lies within another longstanding unsolved problem -- how to reconcile the physics of the large with the physics of the very small. Einstein's theory of gravity (as described in General Relativity) can explain everything from the movements of planets to the physics of black holes, but it simply doesn't seem to apply on the scale of the particles that make up atoms. To predict how these small particles behave, we need the theory of Quantum Mechanics. Quantum Mechanics explains the way small particles function, but it simply doesn't apply on any scale larger than an atom. The elusive solution for combining the two theories might yield a natural explanation for Dark Energy, but we just don't know.
We do, however, know this -- Since space is everywhere, this so-called Dark Energy force appears to be everywhere, and its effects increase as space expands. In contrast, gravity's force is stronger when things are close together and weaker when they are far apart. Because gravity weakens with the expansion of space, it is believed that Dark Energy now makes up about 68 percent of all of the energy in the universe.
It sounds rather strange that we have no firm idea about what makes up 68 percent of the universe. It's as though we had explored all the land on the planet Earth and never in all our travels encountered an ocean. But now that we think we've caught sight of the waves, we want to know what this huge, strange, powerful entity really is.
The strangeness of Dark Energy is perplexing. It shows us that there is a gap in our knowledge that needs to be filled. We have before us the apparent evidence that the cosmos may be configured vastly differently than we imagine. Dark Energy signals that we still have a great deal to learn and shows us that we stand poised for another great leap in our understanding of the universe.
But what if there is an alternative explanation for this enigmatic Dark Energy? What if it does not exist at all? That is what a Hungarian-American team of researchers is starting to conclude. The researchers believe that today's standard models of the universe fail to take account of its changing structure. Once that is done the need for Dark Energy disappears.
Our universe was formed in the Big Bang, 13.8 billion years ago and has been expanding ever since. The key piece of evidence for this expansion is Hubble's law, based on observations of galaxies, which states that on average, the speed with which a galaxy moves away from us is proportional to its distance.
Astronomers measure this velocity of recession by looking at lines in the spectrum of a galaxy, which shift more towards red the faster the galaxy is moving away. From the 1920s, mapping the velocities of galaxies led scientists to conclude that the whole universe is expanding, and that it began life as a vanishingly small point.
In the second half of the twentieth century, astronomers found evidence for unseen Dark Matter by observing that something extra was needed to explain the motion of stars within galaxies. Dark Matter is now thought to make up 27 percent of the content of universe (In contrast, ordinary matter amounts to only 5 percent).
Observations of the explosions of white dwarf stars in binary systems, so-called Type Ia supernovae, in the 1990s then led scientists to the conclusion that ordinary and Dark Matter were accompanied by a third component, Dark Energy, which made up 68 percent of the cosmos and was responsible for driving an acceleration in the expansion of the universe.
In their new work, the researchers (Gabor Racz and Laszlo Dobos of Eotvos Lorand University in Hungary and Robert Beck, Istvan Szapudi, and Istvan Csabai of the University of Hawaii) question the existence of Dark Energy and suggest an alternative explanation. They argue that conventional models of cosmology rely on approximations that ignore its structure and where matter is assumed to have a uniform density.
"Einstein's equations of General Relativity that describe the expansion of the universe are so complex mathematically, that for a hundred years no solutions accounting for the effect of cosmic structures have been found. We know from very precise supernova observations that the universe is accelerating, but at the same time we rely on coarse approximations to Einstein's equations, which may introduce serious side effects, such as the need for Dark Energy, in the models designed to fit the observational data." explains Dr. Laszlo Dobos at Eotvos Lorand University.
In practice, ordinary and Dark Matter appear to fill the universe with a foam-like structure, where galaxies are located on the thin walls between bubbles and are grouped into super-clusters. The insides of the bubbles are in contrast almost empty of both kinds of matter.
Using a computer simulation to model the effect of gravity on the distribution of millions of particles of Dark Matter, the scientists reconstructed the evolution of the universe, including the early clumping of matter and the formation of large scale structure.
Unlike conventional simulations with a smoothly expanding universe, taking the structure into account led to a model where different regions of the cosmos expand at different rates. The average expansion rate though is consistent with present observations, which suggest an overall acceleration.
Dr. Dobos adds "The theory of General Relativity is fundamental in understanding the way the universe evolves. We do not question its validity. We question the validity of the approximate solutions. Our findings rely on a mathematical conjecture which permits the differential expansion of space, consistent with General Relativity, and they show how the formation of complex structures of matter affects the expansion. These issues were previously swept under the rug, but taking them into account can explain the acceleration without the need for Dark Energy."
If their findings are upheld, it could have a significant impact on the direction of future research in physics. For the past 20 years, astronomers and theoretical physicists have speculated on the nature of Dark Energy, but it remains an unsolved mystery. With the new model, this team of researchers expect at the very least to start a lively debate.
Dark Matter and Dark Energy Lead to Revamped Gravitational Field Equations
Two mathematicians -- one from Indiana University and the other from Sichuan University in China -- have proposed a unified theory of Dark Matter and Dark Energy that alters Einstein's equations describing the fundamentals of gravity.
Shouhong Wang, a professor in the IU College of Arts and Science Department of Mathematics, and Tian Ma, a professor at Sichuan University, suggest the law of energy and momentum conservation in spacetime is valid only when normal matter, dark matter, and dark energy are all taken into account. For normal matter alone, energy and momentum are no longer conserved, they argue.
While still employing the metric of curved spacetime that Einstein used in his field equations, the researchers argue the presence of dark matter and dark energy -- which scientists believe accounts for at least 95 percent of the universe -- requires a new set of gravitational field equations that take into account a new type of energy caused by the non-uniform distribution of matter in the universe. This new energy can be both positive and negative, and the total over spacetime is conserved, Wang said.
It is curved spacetime, along with a new scalar potential field representing the new energy density, and the interactions between the two that form the foundation for the new gravitational field equations.
"Many people have come up with different theories for dark energy," Wang said. "Unfortunately, the mystery remains, and in fact, the nature of dark energy is now perhaps the most profound mystery in cosmology and astrophysics. It is considered the most outstanding problem in theoretical physics.
"The other great mystery concerning our universe is that it contains much more matter than can be accounted for in our visible stars. The missing mass is termed as dark matter, and despite many attempts at detecting dark matter, the mystery remains and even deepens."
The researchers postulate that the energy-momentum tensor of normal matter is no longer conserved and that new gravitational field equations follow from Einstein's principles of equivalence and general relativity, and the principle of Lagrangian dynamics, just as Einstein derived his field equations. Wang said the new equations were the unique outcome of the non-conservation of the energy-momentum tensor of normal matter.
When Einstein developed his theory, dark energy and dark matter had not yet been discovered, so it was natural for him to start his theory using the conservation law of energy and momentum of normal matter, Wang added.
"The difference between the new field equations and Einstein's equations is the addition of a second-order covariant derivative of a scalar potential field," he said. "Gravity theory is fundamentally changed and is now described by the metric of the curved spacetime, the new scalar potential field and their interactions."
Tensors provide a concise framework for solving general relativity problems and the energy-momentum tensor quantifies the density and current of energy and momentum in spacetime. The second-order covariant derivative would be the geometric analog of a second order derivative in calculus which measures how the rate of change of a quantity is itself changing.
Associated with the scalar field is a scalar potential energy density consisting of positive and negative energies and representing a new type of energy caused by the non-uniform distribution of matter in the universe. The scalar potential energy density varies as the galaxies move and matter redistributes, affecting every part of the universe as a field.
Wang said negative energy produces attraction while the positive energy produces a repelling force fundamentally different from the four forces -- gravity, electromagnetism, the weak interaction and the strong interaction -- recognized in physics today.
"Most importantly, this new energy and the new field equations offer a unified theory for both dark energy and dark matter, which until now have been considered as two totally different beasts sharing only 'dark' in name," he said. "Both dark matter and dark energy can now be represented by the sum of the new scalar potential energy density and the coupling energy between the energy-momentum tensor and the scalar potential field."
The negative part of this sum represents the dark matter, which produces attraction, and the positive part represents the dark energy, which drives the acceleration of expanding galaxies, he said.
"In a nutshell, we believe that new gravity theory will change our view on energy, gravitational interactions, and the structure and formation of our universe," Wang said.
Kevin Zumbrun, chair of the Department of Mathematics at IU Bloomington, said the new unified theory looked sound in principle.
"It is speculative at the cosmological level, since one must match with experiment, but the math is solid," he said. "It's a new and elegant angle on things, and if this does match experiment, it is a huge discovery. Quite exciting!"
Wang said the new field equations also lead to a modified Newtonian gravitational force formula, which shows that dark matter plays a more important role in a galactic scale at about 1,000 to 100,000 light years, but is less important in the larger scale, where dark energy will be significant (more than 10 million light years).
"This unified theory is consistent with general characterizations of dark energy and dark matter, and further tests of the theory up to measured precisions of cosmic observations are certainly crucial for an eventual validation of the theory," Wang added.
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