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dark matter research paper

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Breaking new ground in the search for dark matter

By: Ana Lopes

7 AUGUST, 2020 · Voir en français

Our fourth story in the LHC Physics at Ten series discusses the LHC’s hunt for the hypothetical particle that may make up dark matter

The Large Hadron Collider (LHC) is renowned for the hunt for and discovery of the Higgs boson, but in the 10 years since the machine collided protons at an energy higher than previously achieved at a particle accelerator , researchers have been using it to try to hunt down an equally exciting particle: the hypothetical particle that may make up an invisible form of matter called dark matter , which is five times more prevalent than ordinary matter and without which there would be no universe as we know it. The LHC dark-matter searches have so far come up empty handed, as have non-collider searches, but the incredible work and skill put by the LHC researchers into finding it has led them to narrow down many of the regions where the particle may lie hidden – necessary milestones on the path to a discovery.

“Before the LHC, the space of possibilities for dark matter was much wider than it is today,” says dark-matter theorist Tim Tait of UC Irvine and theory co-convener of the LHC Dark Matter Working Group.

“The LHC has really broken new ground in the search for dark matter in the form of weakly interacting massive particles, by covering a wide array of potential signals predicted by either production of dark matter, or production of the particles mediating its interactions with ordinary matter. All of the observed results have been consistent with models that don’t include dark matter, and give us important information as to what kinds of particles can no longer explain it. The results have both pointed experimentalists in new directions for how to search for dark matter, and prompted theorists to rethink existing ideas for what dark matter could be – and in some cases to come up with new ones.”

Simulation of the dark-matter distribution in the universe

Make it, break it and shake it

To look for dark matter, experiments essentially “make it, break it or shake it”. The LHC has been trying to make it by colliding beams of protons. Some experiments are using telescopes in space and on the ground to look for indirect signals of dark-matter particles as they collide and break themselves out in space. Others still are chasing these elusive particles directly by searching for the kicks, or “shakes”, they give to atomic nuclei in underground detectors.

The make-it approach is complementary to the break-it and shake-it experiments, and if the LHC detects a potential dark-matter particle, it will require confirmation from the other experiments to prove that it is indeed a dark-matter particle. By contrast, if the direct and indirect experiments detect a signal from a dark-matter particle interaction, experiments at the LHC could be designed to study the details of such an interaction.

Missing-momentum signal and bump hunting

Proton Collisions,Event Displays,Physics,ATLAS

So how has the LHC been looking for signs of dark-matter production in proton collisions? The main signature of the presence of a dark-matter particle in such collisions is the so-called missing transverse momentum. To look for this signature, researchers add up the momenta of the particles that the LHC detectors can see – more precisely the momenta at right angles to the colliding beams of protons – and identify any missing momentum needed to reach the total momentum before the collision. The total momentum should be zero because the protons travel along the direction of the beams before they collide. But if the total momentum after the collision is not zero, the missing momentum needed to make it zero could have been carried away by an undetected dark-matter particle.

Missing momentum is the basis for two main types of search at the LHC. One type is guided by so-called complete new physics models, such as supersymmetry (SUSY) models. In SUSY models, the known particles described by the Standard Model of particle physics have a supersymmetric partner particle with a quantum property called spin that differs from that of its counterpart by half of a unit. In addition, in many SUSY models, the lightest supersymmetric particle is a weakly interacting massive particle (WIMP). WIMPs are one of the most captivating candidates for a dark-matter particle because they could generate the current abundance of dark matter in the cosmos. Searches targeting SUSY WIMPs look for missing momentum from a pair of dark-matter particles plus a spray, or “jet”, of particles and/or particles called leptons.

Another type of search involving the missing-momentum signature is guided by simplified models that include a WIMP-like dark-matter particle and a mediator particle that would interact with the known ordinary particles. The mediator can be either a known particle, such as the Z boson or the Higgs boson, or an unknown particle. These models have gained significant traction in recent years because they are very simple yet general in nature (complete models are specific and thus narrower in scope) and they can be used as benchmarks for comparisons between results from the LHC and from non-collider dark-matter experiments. In addition to missing momentum from a pair of dark-matter particles, this second type of search looks for at least one highly energetic object such as a jet of particles or a photon.

In the context of simplified models, there’s an alternative to missing-momentum searches, which is to look not for the dark-matter particle but for the mediator particle through its transformation, or “decay”, into ordinary particles. This approach looks for a bump over a smooth background of events in the collision data, such as a bump in the mass distribution of events with two jets or two leptons.

Narrowing down the WIMP territory

What results have the LHC experiments achieved from these WIMP searches? The short answer is that they haven’t yet found signs of WIMP dark matter. The longer answer is that they have ruled out large chunks of the theoretical WIMP territory and put strong limits on the allowed values of the properties of both the dark-matter particle and the mediator particle, such as their masses and interaction strengths with other particles. Summarising the results from the LHC experiments, ATLAS experiment collaboration member Caterina Doglioni says “We have completed a large number of dedicated searches for invisible particles and visible particles that would occur in processes involving dark matter, and we have interpreted the results of these searches in terms of many different WIMP dark-matter scenarios, from simplified models to SUSY models. This work benefitted from the collaboration between experimentalists and theorists, for example on discussion platforms such as the LHC Dark Matter Working Group , which includes theorists and representatives from the ATLAS, CMS and LHCb collaborations. Placing the LHC results in the context of the global WIMP search that includes direct- and indirect-detection experiments has also been a focus of discussion in the dark-matter community, and the discussion continues to date on how to best exploit synergies between different experiments that have the same scientific goal of finding dark matter.”

Giving a specific example of a result obtained with data from the ATLAS experiment, Priscilla Pani, ATLAS experiment co-convener of the LHC Dark Matter Working Group, highlights how the collaboration has recently searched the full LHC dataset from the machine’s second run (Run 2), collected between 2015 and 2018, to look for instances in which the Higgs boson might decay into dark-matter particles . “We found no instances of this decay but we were able to set the strongest limits to date on the likelihood that it occurs,” says Pani.

Phil Harris, CMS experiment co-convener of the LHC Dark Matter Working Group, highlights searches for a dark-matter mediator decaying into two jets, such as a recent CMS search based on Run 2 data.

“These so-called dijet searches are very powerful because they can probe a large range of mediator masses and interaction strengths,” says Harris.

Xabier Cid Vidal, LHCb experiment co-convener of the LHC Dark Matter Working Group, in turn notes how data from Run 1 and Run 2 on the decay of a particle known as the B s meson has allowed the LHCb collaboration to place strong limits on SUSY models that include WIMPs. “The decay of the B s meson into two muons is very sensitive to SUSY particles, such as SUSY WIMPs, because the frequency with which the decay occurs can be very different from that predicted by the Standard Model if SUSY particles, even if their masses are too high to be directly detected at the LHC, interfere with the decay,” says Cid Vidal.

Casting a wider net

“10 years ago, experiments (at the LHC and beyond) were searching for dark-matter particles with masses above the proton mass (1 GeV) and below a few TeV.  That is, they were targeting classical WIMPs such as those predicted by SUSY. Fast forward 10 years and dark-matter experiments are now searching for WIMP-like particles with masses as low as around 1 MeV and as high as 100 TeV,” says Tait. “And the null results from searches, such as at the LHC, have inspired many other possible explanations for the nature of dark matter, from fuzzy dark matter made of particles with masses as low as 10 −22 eV to primordial black holes with masses equivalent to several suns. In light of this, the dark-matter community has begun to cast a wider net to explore a larger landscape of possibilities.”

Diagram showing the possible explanations for the nature of dark matter

On the collider front, the LHC researchers have begun to investigate some of these new possibilities. For example, they have started looking at the hypothesis that dark matter is part of a larger dark sector with several new types of dark particles. These dark-sector particles could include a dark-matter equivalent of the photon, the dark photon, which would interact with the other dark-sector particles as well as the known particles, and long-lived particles, which are also predicted by SUSY models.

“Dark-sector scenarios provide a new set of experimental signatures, and this is a new playground for LHC physicists,” says Doglioni.

“We are now expanding upon the experimental methods that we are familiar with, so we can try to catch rare and unusual signals buried in large backgrounds. Moreover, many other current and planned experiments are also targeting dark sectors and particles interacting more feebly than WIMPs. Some of these experiments, such as the newly approved FASER experiment , are sharing knowledge, technology and even accelerator complex with the main LHC experiments, and they will complement the reach of LHC searches for non-WIMP dark matter, as shown by the CERN Physics Beyond Colliders initiative .”

Finally, the LHC researchers are still working on data from Run 2, and the data gathered so far, from Run 1 and Run 2, is only about 5% of the total that the experiments will record. Given this, as well as the immense knowledge gained from the many LHC analyses thus far conducted, there’s perhaps a fighting chance that the LHC will discover a dark-matter particle in the next 10 years. “It’s the fact we haven’t found it yet and the possibility that we may find it in the not-so-distant future that keeps me excited about my job,” says Harris. “The last 10 years have shown us that dark matter might be different from what we had initially thought, but that doesn’t mean it is not there for us to find,” says Cid Vidal.

“We will leave no stone unturned, no matter how big or small and how long it will take us,” says Pani.

Further reading: A new era in the search for dark matter Searching for Dark Matter with the ATLAS detector

Hero header image: NASA, ESA, H.Teplitz and M.Rafelski (IPAC/Caltech), 
A. Koekemoer (STScI), R. Windhorst (ASU), Z. Levay (STScI)

Don't miss the next articles of our series, which will cover the Standard Model, the early universe and more.

Entering Uncharted Waters

The higgs boson: what makes it special, the higgs boson: revealing nature’s secrets, breaking new ground in the search for dark ma..., recreating big bang matter on earth, welcome to the precision era, standard model surprises at high energies, searching for the unknown.

Dark matter is darker

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  • Published: 13 June 2023
  • Volume 34 , article number  81 , ( 2023 )

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dark matter research paper

  • Yang Bai   ORCID: orcid.org/0000-0002-2957-7319 1  

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New results for directly searching for dark matter electromagnetic interactions have been reported by the PandaX Collaboration. The study reveals the most stringent upper limits on dark matter charge radius, millicharge, magnetic dipole moment, electric dipole moment, and anapole moment to date. These findings demonstrate that dark matter is significantly darker than previously anticipated.

Dark matter’s existence in the universe has been established through various observations, including galaxy rotation curves, galaxy distributions, and cosmic microwave background radiation [ 1 ]. Although astrophysicist Fritz Zwicky first pointed out its existence nearly a century ago [ 2 ], the true nature of dark matter particles remains unidentified. As a candidate for dark matter, it is generally assumed that the particles have no interaction with photons. Indeed, if dark matter particles had a similar electric charge to electrons, many observed properties of dark matter in the early and current universe would contradict observations.  Footnote 1

On the other hand, dark matter could possess a suppressed interaction with photons, similar to neutrons, which are electrically neutral but still exhibit electromagnetic interactions such as charge radius, magnetic dipole, and anapole moments. This scenario arises in a wide range of models, particularly when dark matter is considered a composite state comprised of charged constituents with a totally neutral charge [ 3 ]. Discovering these interactions of dark matter would not only establish the microscopic particle identity of dark matter but also enable measurement of the dark matter composite scale.

In a recent publication in Nature  [ 4 ], the PandaX Collaboration conducted a search for electromagnetic interactions of dark matter using the 0.63-tonne-year exposure during the PandaX-4T commissioning run. The PandaX-4T experiment features a large detector with 3.7 tonnes of liquid xenon and is situated within the China Jinping Underground Laboratory, the world’s most well-shielded underground facility, located approximately 2400 ms underground. Due to the weak interactions between dark matter and ordinary matter, dark matter particles can traverse the detector and scatter off charged particles such as nuclei and electrons through potential photon-mediated interactions.

During this scattering process, some nuclei acquire recoil energy, typically on the order of 10 keV for a 100 GeV dark matter mass, derived from the kinetic energy of the dark matter particles. This recoil energy is then converted into prompt scintillation photons (S1). Simultaneously, the surrounding electrons are ionized, drift towards the detector’s surface, and generate delayed electroluminescence photons (S2). An illustration of this photon-mediated scattering process and the corresponding dual-phase signature is shown in Fig.  1 .

figure 1

(Color online) An illustrative plot for the PandaX-4T experiment to search for dark matter (taken from Ref. [ 4 ]). A dark matter particle interacts with a xenon (Xe) nucleus through photon-mediated interactions, resulting in a distinctive dual-phase signature within the liquid xenon medium. This signature is characterized by the production of prompt scintillation photons (S1) and delayed electroluminescence photons (S2)

Thanks to the distinctive dual-phase signature, the PandaX Collaboration is able to utilize the two-dimensional distribution of S1 and S2 photon counts to discern between signal and background events. Owing to the reduced capability of nuclear recoils to induce ionizations, the signal events generated by dark matter exhibit smaller S2 signals compared to background events. The two dominant backgrounds, namely flat ER (including \(\beta\) decay of radon, \(^{85}\text{ Kr }\) , etc.) and tritium, exhibit higher S2 signals. To effectively mitigate background events, the collaboration employs the S2/S1 ratio as a selection variable, leading to a reduction in background events by two orders of magnitude. In the region of interest, there are 1058 events, which aligns with the expected background event count of \(1037\pm 45\) .

While the PandaX-4T experiment has not yet discovered dark matter particles, its results contribute significantly to our understanding of dark matter properties and shed light on the question of “how dark is dark matter?” This article investigates five different photon-mediated interactions of dark matter, including charge radius, millicharge, magnetic dipole moment, electric dipole moment, and anapole moment. Each interaction exhibits distinct Lorentz-invariant forms and differential event rates as a function of nuclear recoil energy \(E_\textrm{R}\) . For example, the millicharge interaction follows a \(1/E_\textrm{R}^2\) spectrum, while both the magnetic and electric dipole moments follow a \(1/E_\textrm{R}\) spectrum. The authors individually examine each dark matter–photon interaction, employing a two-sided profile likelihood ratio to test the signal hypothesis. However, no significant signals above the background are observed. Consequently, upper limits are established on the interaction strengths between dark matter and photons for all five interactions, as presented in Table  1 . Additionally, Table  1 includes constraints on the electromagnetic interactions of neutrinos for comparison. Notably, the limits on dark matter’s charge radius and electric dipole moment surpass those for neutrinos. This result is particularly remarkable, considering that we have less knowledge about dark matter compared to neutrinos.

Knowledge of the constraints on dark matter’s electromagnetic interactions can provide insights into the composite scale of dark matter or the mass scale of other charged states within the dark sector. Taking the example of the magnetic dipole moment for a Dirac fermion \(\chi\) (the dark matter particle), its relativistic interaction with a photon can be expressed as \(\frac{e}{2\Lambda }\,\overline{\chi }\,\sigma ^{\mu \nu } \chi \,F_{\mu \nu }\) , where \(\Lambda\) represents the dark matter composite scale. The constraint on the dark matter’s magnetic moment, which is less than \(4.8\times 10^{-10}\) times the Bohr magneton \(\mu _\textrm{B}\) , can be translated into a lower bound on \(\Lambda\) of \(\Lambda > 1.1 \times 10^6\) GeV. Consequently, if dark matter is a composite particle composed of electrically charged constituents, the dynamical scale required for the formation of the dark matter state is approximately \(10^6\) GeV. This scale is relatively high and lies beyond the reach of other experiments such as the Large Hadron Collider.

In addition to composite dark matter models, electromagnetic interactions of dark matter can also emerge in weakly interacting models like supersymmetry or other dark matter portal models. For instance, in the lepton portal dark matter model [ 5 ], the magnetic dipole moment operator takes the form \(\frac{e\,\lambda ^2\,m_\chi }{16\pi ^2\,M^2}\,\overline{\chi }\,\sigma ^{\mu \nu } \chi \, F_{\mu \nu }\) , where M represents the mass of the charged state in the dark sector and \(\lambda\) denotes a Yukawa coupling among the dark matter, the charged lepton, and the charged dark state. Choosing the dark matter mass \(m_\chi = 40\) GeV and \(\lambda \sim 1\) , the constraint on the dark matter magnetic dipole moment from the PandaX-4T experiment can be translated into a lower bound on M of \(M \gtrsim 6\times 10^4\) GeV. This requirement also surpasses the capabilities of colliders in probing dark matter with masses above one GeV.

In addition to the five dark matter electromagnetic interactions explored in this article, the PandaX Collaboration has the potential to search for other interactions such as dipole transition or Rayleigh interactions [ 6 ]. In summary, the publication in Nature by the PandaX Collaboration [ 4 ] showcases the impressive capabilities of the PandaX-4T experiment in the search for dark matter particles. Even with just the data collected during the commissioning run, the experiment has achieved the most stringent constraints on dark matter electromagnetic interactions to date. Undoubtedly, when the collaboration completes their full-scheduled science run in the near future, we can anticipate even more significant advancements in our understanding of dark matter.

There is one exceptional situation for superheavy dark matter, where the charge per mass ratio is significantly smaller than that of an electron. In this report and the accompanying paper, the mass of dark matter is assumed to be below a few TeV.

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Bai, Y. Dark matter is darker. NUCL SCI TECH 34 , 81 (2023). https://doi.org/10.1007/s41365-023-01249-5

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Published : 13 June 2023

DOI : https://doi.org/10.1007/s41365-023-01249-5

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Dark Energy and Dark Matter

All the atoms and light in the universe together make up less than five percent of the total contents of the cosmos. The rest is composed of dark matter and dark energy, which are invisible but dominate the structure and evolution of the universe. Dark matter makes up most of the mass of galaxies and galaxy clusters, and is responsible for the way galaxies are organized on grand scales. Dark energy, meanwhile, is the name we give the mysterious influence driving the accelerated expansion of the universe. What these substances are and how they work are some of the major challenges facing modern astronomers.

Center for Astrophysics | Harvard & Smithsonian scientists study dark matter and dark energy in multiple ways:

Observing galaxies to measure the effects of dark matter on their structure and evolution. The next-generation Giant Magellan Telescope (GMT) will provide new details in large galaxies, and detect dwarf galaxies too faint to see using current instruments. Since dark matter models predict many more dwarf galaxies than we observe, surveys of this type are very important. Mapping Dark Matter

Creating theoretical models of dark matter behavior from observational data. Since we don’t have direct measurements of dark matter behavior, researchers have to infer what the particles might be like from indirect evidence. Does Some Dark Matter Carry an Electric Charge?

  • Measuring cosmic acceleration by mapping the position of tens of thousands of galaxies. The Baryon Oscillation Spectroscopic Survey (BOSS) is an ongoing astronomical project that has provided some of the best observational data on dark energy. A One-Percent Measure of Galaxies Half the Universe Away

Invisible Glue

Dark matter isn’t simply dark: it’s invisible. Light of all types seems to pass through as though it’s completely transparent. However, dark matter does have mass, which we see by its gravitational influence.

Studies of galaxies show stars and gas moving as though there’s a lot more mass than we can see pulling them along. Based on the motion of what we can observe, galactic dark matter resides in a “halo” surrounding the ordinary matter of the galaxy. Astronomers also study dwarf galaxies, which are less bright and therefore harder to observe, but which contain a higher fraction of dark matter than their larger cousins.

Galaxy clusters can contain hundreds or thousands of galaxies, each of which have their own dark matter halo. However, the cluster has its own dark matter, which outweighs everything else put together. This dark matter influences how individual galaxies and hot gas move inside the cluster. Astronomers can measure how much invisible mass is inside a cluster by the motion of the visible material, much as they do with galaxies. Researchers can also determine the amount of cluster dark matter by the way its gravity affects light. This effect is called gravitational lensing , and it provides an independent measure of how much mass is in a cluster and where it resides.

One particular galaxy cluster, known as the Bullet Cluster, provides some of the best evidence we have for the existence of dark matter. This cluster is made up of two smaller clusters that collided sometime in the past. During this collision, the hot gas interacted to produce a shock wave, similar to that made by a bullet. However, gravitational lensing shows that most of the mass of the combined cluster is collected around the galaxies, not in the center where the gas is. That provides us with the first independent measurement of how much gas and dark matter are in a galaxy cluster, where in most clusters the plasma and dark matter occupy the same regions.

Using fluctuations in the cosmic microwave background ( CMB ), astronomers determined that dark matter is about 27% of the contents of the universe, in terms of its overall contribution to the total mass and energy content of the cosmos.

representation of the evolution of the universe over 13.8 billion years

A timeline of the universe from the Big Bang at the left to modern times at the right. For much of that time, dark matter has governed the cosmos, forming galaxies and galaxy clusters; dark energy dominates the future, pushing galaxies ever farther apart.

Faster and Faster

In the 1920s, astronomers including Edwin Hubble discovered that galaxies seem to be moving away from us, and the farther they are, the faster they recede. Combined with Einstein’s general theory of relativity, researchers concluded that the universe is expanding, carrying galaxies along with it.

Then in 1998, two independent groups of researchers announced they had measured cosmic expansion to a higher degree of precision, and found that it was getting faster. This acceleration implies some unknown force is counteracting gravity to make the universe expand at a greater rate.

We call that mysterious force “dark energy”. Despite the name, dark energy isn’t like dark matter, except that they’re both invisible. Dark matter pulls galaxies together, while dark energy pushes them apart.

Astronomers measure the expansion of the universe using the explosions of white dwarfs , called type Ia supernovas, which led to the discovery of dark energy in 1998. They also use thousands of galaxies to map sound waves called baryon acoustic oscillations (BAO) produced when the universe was young, which stretch as the universe expands. In addition, CMB measurements show dark energy contributes about 68% of the total energy content of the universe.

  • What happened in the early universe?
  • What is the universe made of?
  • Extragalactic Astronomy
  • Theoretical Astrophysics
  • Computational Astrophysics
  • Optical and Infrared Astronomy

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dark matter research paper

Adjunct professor, Physics, L’Université d’Ottawa/University of Ottawa

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Rajendra Gupta receives unconditional research funding from Macronix Research Corporation. He is affiliated with the American Physical Society, Royal Astronomical Society, European Astronomical Society, and CASCA.

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Do constants of nature — the numbers that determine how things behave, like the speed of light — change over time as the universe expands ? Does light get a little tired travelling vast cosmic distances? It was believed that dark matter and dark energy explained these cosmological phenomena, but recent research indicates that our universe has been expanding without dark matter or dark energy.

Doing away with dark matter and dark energy resolves the “ impossible early galaxy problem ,” that arises when trying to account for galaxies that do not adhere to expectations regarding to size and age. Finding an alternative to dark matter and energy that complies with existing cosmological observations, including galaxy distribution , is possible.

Read more: How old is the universe exactly? A new theory suggests that it's been around for twice as long as believed

  • Dark matter

Dark matter is a hypothetical form of matter that does not interact with ordinary matter in any way except through gravity. It was proposed as a theoretical way to explain our astrophysical and cosmological observations. Ordinary matter can travel through the dark matter without any resistance and vice versa.

In space, gravitational pull determines the speed at which an object orbits. A higher speed than expected from surrounding orbiting objects is attributed to the existence and gravitational pull of dark matter .

The gravitational pull of dark matter can also bend light rays, causing a gravitational lensing effect just like normal matter. This allows for the measurement of dark matter in the object causing the bending, such as in galaxies and clusters of galaxies.

The most robust support for the existence of dark matter comes from the tiny variations observed in the cosmic microwave background radiation (remnant radiation from the big bang), measured with increasingly high precision .

Another argument for the existence of dark matter is that large-scale structures of the universe, such as galaxies, would not be able to form without the dark matter within the limited age of the universe.

a fiery orange swirl against a dark background

Alternative theories

There are alternatives to dark matter that account for many astrophysical observations. The oldest and most popular theory is modified Newtonian dynamic (MoND), which suggests that the Newtonian inverse square law of gravitational attraction force is a simplified version of a complete force that becomes perceptible only at very large distances when Newtonian force becomes negligible.

Another alternative is a version of MoND that includes Einstein’s relativistic effects and explains observations where MoND is limited, such as cosmic microwave background radiation . Then there is the proposed theory of retarded gravity that also claims to comply with such observations.

Astronomers are surprised to learn that many observations show a complete absence of dark matter or dark matter-deficient structures . This leads one to question its existence.

One then has to find an explanation of what might have created the problem, such as tidal forces exerted by the passing of nearby galaxies stripping away dark matter . Even the mass of the Milky Way has recently been determined to be much smaller than expected from cosmology .

Does dark matter exist?

Recent discoveries create doubt around the existence of dark matter. Despite extensive research and billions of dollars in investment, there has been no direct detection of any dark matter.

The dark energy theory negates the gravitational pull of matter, causing the universe to expand faster with time, as observed. The interrelated variation of constants of nature, dubbed covarying coupling constants (CCC), achieve the same effect by weakening the gravitational pull and other forces of nature with time, eliminating the need for dark energy.

Combined with the tired light (TL) effect which posits that light slows down as a result of energy loss, such a cosmological model has no room for dark matter . The CCC approach could also replace the dark energy-like constant considered responsible for the extremely rapid expansion of the universe following the Big Bang, called inflation .

The age of the universe is determined from the historical expansion rate of the universe, and can vary depending on the model used for the expansion. Measuring the redshift of exploding stars, called supernovae type 1a, and their observed brightness can determine the expansion rate.

Redshift is the lowering of spectral line frequencies depending on the recessional speed of the emitting object, similar to the frequency of a receding ambulance siren. By allowing the redshift due to the tired light effect to coexist with the expansion redshift, the universe’s expansion rate is reduced, and age of the universe increases.

an image of a galaxy showing white flecks on a dark background with an inset showing a reddish-purple elongated blob

This new model predicts the universe is older than we think it is — 26.7 billion years in the CCC cosmology compared to 13.8 in the standard cosmology — and allows galaxies and their clusters to form without dark matter. The increase in the age of the universe in early times when structures started forming was up to 100 times larger in the new model.

The absence of dark matter that reduces the gravitational force and increases the time for collapsing the matter to form structures is greatly overcompensated by increased age in the CCC model.

Slowing time

The expansion of the universe causes time to appear slowed down when observing distant galaxies . The CCC+TL model complies with observations showing a time dilation effect that appears to slow down the clock in distant objects.

Emerging criticisms of the CCC+TL model rely on flawed hypotheses, such as the deficiencies presented by the tired light concept, or incorrect analyses, including redshift analysis of cosmic microwave background temperatures . A single free parameter in the CCC cosmology determines the variation of all constants that asymptotically approach their respective constant values. As in the standard cosmology, CCC cosmology has only two free parameters. Adding tired light to CCC does not require any additional free parameter.

The standard cosmology model requires dark matter to fit observations, such as accounting for redshift when measuring the brightness of supernovae. Dark matter is also used to explain physical processes such as galaxy rotation curves, galaxy clusters or gravitational lensing. Using CCC+TL cosmology means that we must seriously consider alternative physical processes to account for astrophysical observations that had previously been attributed to dark matter.

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We need to consider alternatives to dark matter that better explain cosmological observations

by Rajendra Gupta, The Conversation

We need to consider alternatives to dark matter that better explain cosmological observations

Do constants of nature—the numbers that determine how things behave, like the speed of light—change over time as the universe expands ? Does light get a little tired traveling vast cosmic distances? It was believed that dark matter and dark energy explained these cosmological phenomena, but recent research indicates that our universe has been expanding without dark matter or dark energy.

Doing away with dark matter and dark energy resolves the " impossible early galaxy problem ," that arises when trying to account for galaxies that do not adhere to expectations regarding to size and age. Finding an alternative to dark matter and energy that complies with existing cosmological observations , including galaxy distribution , is possible.

Dark matter

Dark matter is a hypothetical form of matter that does not interact with ordinary matter in any way except through gravity. It was proposed as a theoretical way to explain our astrophysical and cosmological observations. Ordinary matter can travel through the dark matter without any resistance and vice versa.

In space, gravitational pull determines the speed at which an object orbits. A higher speed than expected from surrounding orbiting objects is attributed to the existence and gravitational pull of dark matter .

The gravitational pull of dark matter can also bend light rays, causing a gravitational lensing effect just like normal matter. This allows for the measurement of dark matter in the object causing the bending, such as in galaxies and clusters of galaxies.

The most robust support for the existence of dark matter comes from the tiny variations observed in the cosmic microwave background radiation (remnant radiation from the big bang), measured with increasingly high precision .

Another argument for the existence of dark matter is that large-scale structures of the universe, such as galaxies, would not be able to form without the dark matter within the limited age of the universe.

We need to consider alternatives to dark matter that better explain cosmological observations

Alternative theories

There are alternatives to dark matter that account for many astrophysical observations. The oldest and most popular theory is modified Newtonian dynamic (MoND), which suggests that the Newtonian inverse square law of gravitational attraction force is a simplified version of a complete force that becomes perceptible only at very large distances when Newtonian force becomes negligible.

Another alternative is a version of MoND that includes Einstein's relativistic effects and explains observations where MoND is limited, such as cosmic microwave background radiation . Then there is the proposed theory of retarded gravity that also claims to comply with such observations.

Astronomers are surprised to learn that many observations show a complete absence of dark matter or dark matter-deficient structures . This leads one to question its existence.

One then has to find an explanation of what might have created the problem, such as tidal forces exerted by the passing of nearby galaxies stripping away dark matter . Even the mass of the Milky Way has recently been determined to be much smaller than expected from cosmology .

Does dark matter exist?

Recent discoveries create doubt around the existence of dark matter. Despite extensive research and billions of dollars in investment, there has been no direct detection of any dark matter.

The dark energy theory negates the gravitational pull of matter, causing the universe to expand faster with time, as observed. The interrelated variation of constants of nature, dubbed covarying coupling constants (CCC), achieve the same effect by weakening the gravitational pull and other forces of nature with time, eliminating the need for dark energy.

Combined with the tired light (TL) effect which posits that light slows down as a result of energy loss, such a cosmological model has no room for dark matter . The CCC approach could also replace the dark energy -like constant considered responsible for the extremely rapid expansion of the universe following the Big Bang, called inflation .

The age of the universe is determined from the historical expansion rate of the universe, and can vary depending on the model used for the expansion. Measuring the redshift of exploding stars, called supernovae type 1a, and their observed brightness can determine the expansion rate.

Redshift is the lowering of spectral line frequencies depending on the recessional speed of the emitting object, similar to the frequency of a receding ambulance siren. By allowing the redshift due to the tired light effect to coexist with the expansion redshift, the universe's expansion rate is reduced, and age of the universe increases.

We need to consider alternatives to dark matter that better explain cosmological observations

This new model predicts the universe is older than we think it is— 26.7 billion years in the CCC cosmology compared to 13.8 in the standard cosmology—and allows galaxies and their clusters to form without dark matter. The increase in the age of the universe in early times when structures started forming was up to 100 times larger in the new model.

The absence of dark matter that reduces the gravitational force and increases the time for collapsing the matter to form structures is greatly overcompensated by increased age in the CCC model.

Slowing time

The expansion of the universe causes time to appear slowed down when observing distant galaxies . The CCC+TL model complies with observations showing a time dilation effect that appears to slow down the clock in distant objects.

Emerging criticisms of the CCC+TL model rely on flawed hypotheses, such as the deficiencies presented by the tired light concept, or incorrect analyses, including redshift analysis of cosmic microwave background temperatures . A single free parameter in the CCC cosmology determines the variation of all constants that asymptotically approach their respective constant values. As in the standard cosmology, CCC cosmology has only two free parameters. Adding tired light to CCC does not require any additional free parameter.

The standard cosmology model requires dark matter to fit observations, such as accounting for redshift when measuring the brightness of supernovae. Dark matter is also used to explain physical processes such as galaxy rotation curves, galaxy clusters or gravitational lensing. Using CCC+TL cosmology means that we must seriously consider alternative physical processes to account for astrophysical observations that had previously been attributed to dark matter .

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Physics > General Physics

Title: a unifying theory of dark energy and dark matter: negative masses and matter creation within a modified $λ$cdm framework.

Abstract: Dark energy and dark matter constitute 95% of the observable Universe. Yet the physical nature of these two phenomena remains a mystery. Einstein suggested a long-forgotten solution: gravitationally repulsive negative masses, which drive cosmic expansion and cannot coalesce into light-emitting structures. However, contemporary cosmological results are derived upon the reasonable assumption that the Universe only contains positive masses. By reconsidering this assumption, I have constructed a toy model which suggests that both dark phenomena can be unified into a single negative mass fluid. The model is a modified $\Lambda$CDM cosmology, and indicates that continuously-created negative masses can resemble the cosmological constant and can flatten the rotation curves of galaxies. The model leads to a cyclic universe with a time-variable Hubble parameter, potentially providing compatibility with the current tension that is emerging in cosmological measurements. In the first three-dimensional N-body simulations of negative mass matter in the scientific literature, this exotic material naturally forms haloes around galaxies that extend to several galactic radii. These haloes are not cuspy. The proposed cosmological model is therefore able to predict the observed distribution of dark matter in galaxies from first principles. The model makes several testable predictions and seems to have the potential to be consistent with observational evidence from distant supernovae, the cosmic microwave background, and galaxy clusters. These findings may imply that negative masses are a real and physical aspect of our Universe, or alternatively may imply the existence of a superseding theory that in some limit can be modelled by effective negative masses. Both cases lead to the surprising conclusion that the compelling puzzle of the dark Universe may have been due to a simple sign error.
Comments: Accepted for publication in Astronomy and Astrophysics (A&A). Videos of the simulations are available online at:
Subjects: General Physics (physics.gen-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc)
Cite as: [physics.gen-ph]
  (or [physics.gen-ph] for this version)
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Journal reference: A&A 620, A92 (2018)
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Science News

Strange observations of galaxies challenge ideas about dark matter.

A new look at how light bends in the universe could point to an alternative theory of gravity

Streaks around the galaxy cluster Abell 370 reveal more distant galaxies whose light has been bent and distorted by an effect called gravitational lensing.

As seen by the Hubble Space Telescope, the galaxy cluster Abell 370 reveals telltale streaks of light from more distant galaxies that have had their light bent and distorted by an effect called gravitational lensing.

NASA, ESA, and J. Lotz and the HFF Team/STScI

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By Adam Mann

July 5, 2024 at 10:30 am

Head-scratching observations of distant galaxies are challenging cosmologists’ dominant ideas about the universe, potentially leading to the implication that the strange substance called dark matter doesn’t exist.

That’s one possible conclusion from a new study published June 20 in The Astrophysical Journal Letters . The finding “raises questions of an extraordinarily fundamental nature,” says Richard Brent Tully, an astronomer at the University of Hawaii at Manoa who was not involved in the work.

Astronomers suspect dark matter exists because of the way stars and other visible material at a galaxy’s visible edge rotate. The rotation speeds of objects far from a galactic center are much higher than they should be given the amount of luminous stuff seen in telescopes. Under physicists’ current understanding of gravity, this implies that a massive reservoir of invisible matter must be tugging on those stars.

The new results rely on the fact that massive objects warp the fabric of space and time. Galaxies are made from enormous amounts of visible stars, gas and dust, as well as — the theory goes — a huge halo of invisible dark matter. This means that light will be bent and distorted as it travels past a galaxy, an effect known as gravitational lensing. 

Knowing this, astronomer Tobias Mistele of Case Western Reserve University in Cleveland and colleagues decided to hunt for signs of gravitational lensing around multiple galaxies as a way to probe the galaxies’ contents. The team looked at a catalog of roughly 130,000 galaxies imaged by the VLT Survey Telescope at the European Southern Observatory’s Paranal Observatory in Chile, searching for telltale streaks that indicated the presence of more distant galaxies whose light had been bent and distorted by the intervening objects.

An image of the VLT Survey Telescope, located in the high desert of Paranal in Chile, which was used for the gravitational lensing observations in this study.

The amount of lensing provides a proxy for the masses of the foreground galaxies, including both their luminous matter and, presumably, the much larger quantity of dark matter that surrounds each galaxy. The team then calculated the mass at various distances from each galaxy’s center and used that to infer the speed at which a star would orbit at those distances.

Under the prevailing model of cosmology, called Lambda CDM , dark matter clumps up into enormous globs in the cosmos, and the gravitational attraction of these globs draws in visible matter, which goes on to form a galaxy ( SN: 4/4/24 ). Previous observations have established that these halo-like clumps extend out to at least 300,000 light-years from a galaxy’s center. Beyond that edge, stars’ rotation rates should start to slow down.

Yet using their gravitational lensing data, Mistele and his colleagues calculated that a star placed a million light-years from each galaxy’s center, and potentially up to 3 billion light-years away, would still be rotating far too fast given both the visible and dark matter believed to be present in the galaxy.

Does that mean that there’s even more invisible material than previously thought? Perhaps not.

A rival theory to Lambda CDM, known as modified Newtonian dynamics , or MOND, does away with the concept of dark matter entirely and instead suggests that gravity behaves differently on the scale of galaxies ( SN: 3/28/18 ). Long championed by Mistele’s coauthor Stacy McGaugh, also of Case Western, MOND specifically predicts the types of observations found in the study.

But Lambda CDM isn’t down for the count quite yet.

“I think it’s a real stretch to say that one can do away with dark matter, because the lines of evidence [for it] are so numerous,” says Bhuvnesh Jain, a cosmologist at the University of Pennsylvania.

For instance, the growth of large-scale structures in the universe since the Big Bang is far better explained by Lambda CDM than MOND. Jain suggests that perhaps there are even more exotic ideas in mathematical models of gravity, inspired by the higher-dimensional thinking found in string theory, that could account for the current large-scale structure of the universe. Certain variations of such ideas might be able to explain Mistele and his colleagues’ data while also revising the role of dark matter.

Observations from the European Space Agency’s Euclid satellite, which launched last year, will soon provide researchers with much better gravitational lensing data, potentially helping untangle what’s going on with this odd mystery.

More Stories from Science News on Cosmology

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The universe may have a complex geometry — like a doughnut

Web-like structures are visible in a map of the universe.

The largest 3-D map of the universe reveals hints of dark energy’s secrets

An image showing enormous numbers of galaxies taken by NASA's James Webb Space Telescope

Did the James Webb telescope ‘break the universe’? Maybe not

spiral galaxy NGC 5584

New JWST images suggest our understanding of the cosmos is flawed

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JWST’s hunt for distant galaxies keeps turning up surprises

A montage of images from the James Webb Space Telescope showing a wide collection of stars.

The James Webb telescope may have spotted stars powered by dark matter

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Centuries on, Newton’s gravitational constant still can’t be pinned down

A simulation image of filaments and clusters shown in blue lines and pink dots.

Astronomers spotted shock waves shaking the web of the universe for the first time

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  • BOOKS AND ARTS
  • 03 September 2019

Deciphering dark matter: the remarkable life of Fritz Zwicky

  • Jaco de Swart 0

Jaco de Swart is a historian of science at the University of Amsterdam. He works on the history of the dark-matter problem and has co-authored a review titled ‘ How dark matter came to matter ’.

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Fritz Zwicky using the 18-inch Schmidt telescope at Palomar Observatory in the 1930s.

Fritz Zwicky at the Schmidt telescope at Palomar Observatory, California, in the 1930s. Credit: Palomar Observatory/Caltech

Zwicky: The Outcast Genius Who Unmasked the Universe John Johnson Harvard (2019)

Fritz Zwicky advanced astronomy over much of the twentieth century, pioneering findings on constituents of the cosmos from supernovae and neutron stars to dark matter and compact galaxies. He worked at two of the world’s most historically important observatories: Mount Wilson and Palomar in California. He was an early innovator in jet-engine design. Yet the Swiss astronomer is a somewhat elusive figure in the history of science. Science journalist John Johnson seeks to rectify that in his spirited biography, Zwicky .

As Johnson reveals, the very boldness and ingenuity of Zwicky’s discoveries could work against him: many were viewed as unconventional, and were confirmed only years after he made them. Zwicky also had a reputation for abrasiveness. For instance, he reportedly called some of his colleagues at the California Institute of Technology (Caltech) in Pasadena “spherical bastards” (meaning, from whichever angle you looked at them). Johnson’s book unravels these two sides of Zwicky — the brilliance and the ire — by framing him as an “outcast genius”. But can this portrayal help to change perceptions of the prolific astrophysicist?

Zwicky trained in physics and mathematics at the Swiss Federal Institute of Technology in Zurich. In 1925, the Rockefeller Foundation in New York City offered him a fellowship to study the physics of crystals at Caltech with the Nobel-prizewinning experimental physicist Robert Millikan. Two years later, he shifted fields. He began to research galaxies at Mount Wilson alongside Edwin Hubble, the astronomer who would find evidence for the expansion of the Universe in 1929. Zwicky himself soon produced a series of intriguing theories and observations.

dark matter research paper

Astronomy: The great unseen

Zwicky is celebrated mainly as the ‘father of dark matter’. In the early 1930s, while studying Hubble’s observations of the Coma Cluster of galaxies, he noted an anomaly. According to the measure of visible mass, single galaxies were moving too fast for the cluster to remain bound together. Zwicky posited that an as-yet unobserved type of mass, dunkle Materie (dark matter) might explain it, and in 1933 he presented his findings in the journal of the Swiss Physical Society. However, it took another three decades for the phenomenon to be observed widely. And only after Zwicky’s death, in 1974, was dark matter accepted as part of the cosmological canon, through the work of radio astronomers, cosmologists and particle physicists.

Zwicky’s star soon rose. In 1934, he and Walter Baade identified the existence of supernovae, the explosive final stage of a star’s life. Zwicky posited that novae launched a sea of particles into space that might account for cosmic rays, the then-unexplained phenomenon observed by Nobel laureate Victor Hess in 1912, during experiments conducted in a balloon. When the theory was made public, Zwicky’s career exploded, and he became “the darling of reporters everywhere”, Johnson writes.

Johnson touches on many other examples of Zwicky’s prescience during his Caltech years. Again with Baade in 1934, he predicted the existence of neutron stars, extremely dense bodies of neutrons left behind after a supernova. In 1937, he was the first to argue that galaxies, like stars, could act as gravitational lenses, bending light according to Albert Einstein’s general theory of relativity. And in the 1940s, his search with Milton Humason for white dwarfs — another class of dense stellar remnants — gave early hints of the highly energetic outbursts that came to be known as quasars. Johnson tells the story well, but does not delve much into the science behind the insights.

As a scientist, Zwicky went his own way, tending to study phenomena outside trends in stellar astrophysics. His professional animosities, however, were actively divisive. Johnson notes that Zwicky despised what he saw as unoriginal “grey thinking” in fellow researchers. He called theoretical physicist Richard Feynman a “spiritual coward”, and was contemptuous of astrophysicists who adhered to the theory of an expanding Universe. Johnson contends that after Zwicky’s retirement in 1968, he was barred from using the telescopes at Mount Wilson and Palomar, owing to a quarrel with Hubble’s protégé Allan Sandage.

dark matter research paper

Cosmology: Matter and mixology

Johnson reveals other facets of the astronomer. He points to Zwicky’s dedication to his family, and his determination to use science as a tool for human progress. Along with his extraordinary discoveries, Zwicky formulated schemes such as turning asteroids into habitable planets and — in another discerning moment — colonizing the Moon. Just as inventive was his methodology, which he dubbed “morphological analysis”. In essence, this is a problem-solving technique for exploring all possible solutions to any complex issue, from learning languages to computing astrophysical quantities. Although Johnson does not describe it in depth, Zwicky clearly found it essential to doing good, creative science.

For instance, in 1943, he used the method in researching and developing a jet engine at Aerojet, a rocket-manufacturing company that at the time was based in Pasadena, California. It worked. Zwicky became a force in US rocket science, and in 1945 he was the first to interview Werner von Braun — the engineer of the German V-2 rocket who became a crucial asset to the US space programme. Zwicky’s contributions to the US Air Force were considered so valuable that he received the Medal of Freedom from then-president Harry Truman in 1949.

Zwicky also wrote several books on his methodology. In the 1971 Jeder ein Genie (‘Everyone a Genius’), he argued for morphological analysis as a universal technique for developing intellectual prowess. However, genius is a slippery concept, and Johnson’s use of the term to describe Zwicky is risky. A genius is a person apart, a ‘wonder’ who evades explanation. The characterization is distancing, hindering our understanding of the person as a product of their era.

Readers seeking that understanding might find Johnson’s book too anecdotal, and lacking in the context needed for an integrated portrait. Zwicky was part of a new generation of early-twentieth-century astrophysicists, probing the cosmos beyond the Milky Way. And he was an émigré in a war-torn era. If Johnson had more thoroughly explored what linked the man and his work to these historical developments, what insights might have emerged?

To some degree, then, Zwicky remains elusive. Nevertheless, Johnson’s book is rich enough to inspire interesting meditations on research, idiosyncrasy — and reputation.

Nature 573 , 32-33 (2019)

doi: https://doi.org/10.1038/d41586-019-02603-7

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    Dark energy and dark matter refers to the unseen energy and matter components of the Universe. Dark matter is invisible, non-baryonic matter hypothesized to explain phenomena including ...

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    The current state of the search for dark-matter particles is reviewed, and a broader experimental and theoretical approach is proposed to solve the dark-matter problem.

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    Dark matter is one of the main puzzles in fundamental physics and the goal of a diverse, multi-pronged research programme. Underground and astrophysical searches look for dark matter particles in the cosmos, either by interacting directly or by searching for dark matter annihilation. Particle colliders, in contrast, might produce dark matter in ...

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  8. Progress of dark matter research

    Dark matter is new physics beyond the standard model with solid evidences. What is dark matter made of and how it interacts with the SM particle still elude us, which catalyze model building of dark matter and experimental research in the energy, intensity and cosmic frontiers. This paper briefly reviews recent dark matter theoretical studies and experimental researches progress. For theory ...

  9. Breaking new ground in the search for dark matter

    Phil Harris, CMS experiment co-convener of the LHC Dark Matter Working Group, highlights searches for a dark-matter mediator decaying into two jets, such as a recent CMS search based on Run 2 data. "These so-called dijet searches are very powerful because they can probe a large range of mediator masses and interaction strengths," says Harris.

  10. Dark matter universe

    Abstract. Most of the mass in the universe is in the form of dark matter—a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations—from the early observations of the large ...

  11. Brief review of recent advances in understanding dark matter and dark

    Abstract. Dark sector, constituting about 95% of the Universe, remains the subject of numerous studies. There are lots of models dealing with the cause of the effects assigned to "dark matter" and "dark energy". This brief review is devoted to the very recent theoretical advances in these areas: only to the advances achieved in the last ...

  12. [1006.2483] Dark Matter: A Primer

    Dark matter is one of the greatest unsolved mysteries in cosmology at the present time. About 80% of the universe's gravitating matter is non-luminous, and its nature and distribution are for the most part unknown. In this paper, we will outline the history, astrophysical evidence, candidates, and detection methods of dark matter, with the goal to give the reader an accessible but rigorous ...

  13. New research suggests that our universe has no dark matter

    The current theoretical model for the composition of the universe is that it's made of normal matter, dark energy and dark matter. A new University of Ottawa study challenges this.

  14. Constraining ultralight dark matter through an accelerated resonant

    Weak signal detection, as in the case for the search of Dark Matter, relies on the resonant effect, when many frequencies are scanner in search of the signal, but this is very time consuming. The ...

  15. Dark Matter, Dark Energy

    The purpose of the reportwas to discuss the existence of dark energy and dark matter, how scientists and researchers came to know about it's existence, the role of supernovas in the understanding ...

  16. Dark matter and the early Universe: a review

    Dark matter represents currently an outstanding problem in both cosmology and particle physics. In this review we discuss the possible explanations for dark matter and the experimental observables which can eventually lead to the discovery of dark matter and its nature, and demonstrate the close interplay between the cosmological properties of the early Universe and the observables used to ...

  17. Dark matter is darker

    These findings demonstrate that dark matter is significantly darker than previously anticipated. Dark matter's existence in the universe has been established through various observations, including galaxy rotation curves, galaxy distributions, and cosmic microwave background radiation [ 1 ]. Although astrophysicist Fritz Zwicky first pointed ...

  18. Dark Energy and Dark Matter

    Dark Energy and Dark Matter. All the atoms and light in the universe together make up less than five percent of the total contents of the cosmos. The rest is composed of dark matter and dark energy, which are invisible but dominate the structure and evolution of the universe. Dark matter makes up most of the mass of galaxies and galaxy clusters ...

  19. Scaling up the dark matter search

    Physicists are preparing for the next generation of dark-matter experiments. ... Get an overview of research at SLAC: X-ray and ultrafast science, particle and astrophysics, cosmology, particle accelerators, biology, energy and technology. X-ray & ultrafast science.

  20. PDF A unifying theory of dark energy and dark matter: Negative masses and

    Dark energy and dark matter constitute 95% of the observable Universe. Yet the physical nature of these two phenomena remains a mystery. Einstein suggested a long-forgotten solution: gravitationally repulsive negative masses, which drive cosmic expansion and cannot coalesce into light-emitting structures.

  21. How dark matter came to matter

    The acceptance of dark matter came slowly despite its abundance. Jaco de Swart and colleagues reconstruct the history of how dark matter brought astronomers to cosmology in their Review Article ...

  22. We need to consider alternatives to dark matter that better explain

    Cosmology does not need dark matter or dark energy in an expanding universe that allows the constants of nature to evolve, and light loses energy as it travels vast distances.

  23. We need to consider alternatives to dark matter that better explain

    It was believed that dark matter and dark energy explained these cosmological phenomena, but recent research indicates that our universe has been expanding without dark matter or dark energy.

  24. Brief Review of Recent Advances in Understanding Dark Matter and Dark

    Dark sector, constituting about 95% of the Universe, remains the subject of numerous studies. There are lots of models dealing with the cause of the effects assigned to "dark matter" and "dark energy". This brief review is devoted to the very recent theoretical advances in these areas: only to the advances achieved in the last few years. For example, in section devoted to particle dark ...

  25. What Is Dark Matter?

    For a theorist, an observer or an experimentalist, dark matter is a promising target for research. We know it exists, but we do not yet know what it is at a fundamental level.

  26. A Unifying Theory of Dark Energy and Dark Matter: Negative Masses and

    Dark energy and dark matter constitute 95% of the observable Universe. Yet the physical nature of these two phenomena remains a mystery. Einstein suggested a long-forgotten solution: gravitationally repulsive negative masses, which drive cosmic expansion and cannot coalesce into light-emitting structures. However, contemporary cosmological results are derived upon the reasonable assumption ...

  27. Strange observations of galaxies challenge ideas about dark matter

    Head-scratching observations of distant galaxies are challenging cosmologists' dominant ideas about the universe, potentially leading to the implication that the strange substance called dark ...

  28. Deciphering dark matter: the remarkable life of Fritz Zwicky

    Jaco de Swart enjoys a biography of the scientist who pioneered findings on dark matter and supernovae.