Astronomers Witness a Web of Dark Matter


We can’t see it, we can’t feel it, we can’t even interact with it… but dark matter may very well be one of the most fundamental physical components of our Universe. The sheer quantity of the stuff – whatever it is – is what physicists have suspected helps gives galaxies their mass, structure, and motion, and provides the “glue” that connects clusters of galaxies together in vast networks of cosmic webs.

Now, for the first time, this dark matter web has been directly observed.

An international team of astronomers, led by Dr. Catherine Heymans of the University of Edinburgh, Scotland, and Associate Professor Ludovic Van Waerbeke of the University of British Columbia, Vancouver, Canada, used data from the Canada-France-Hawaii Telescope Legacy Survey to map images of about 10 million galaxies and study how their light was bent by gravitational lensing caused by intervening dark matter.

Inside the dome of the Canada-France-Hawaii Telescope. (CFHT)

The images were gathered over a period of five years using CFHT’s 1×1-degree-field, 340-megapixel MegaCam. The galaxies observed in the survey are up to 6 billion light-years away… meaning their observed light was emitted when the Universe was only a little over half its present age.

The amount of distortion of the galaxies’ light provided the team with a visual map of a dark matter “web” spanning a billion light-years across.

“It is fascinating to be able to ‘see’ the dark matter using space-time distortion,” said Van Waerbeke. “It gives us privileged access to this mysterious mass in the Universe which cannot be observed otherwise. Knowing how dark matter is distributed is the very first step towards understanding its nature and how it fits within our current knowledge of physics.”

This is one giant leap toward unraveling the mystery of this massive-yet-invisible substance that pervades the Universe.

The densest regions of the dark matter cosmic web host massive clusters of galaxies. Credit: Van Waerbeke, Heymans, and CFHTLens collaboration.

“We hope that by mapping more dark matter than has been studied before, we are a step closer to understanding this material and its relationship with the galaxies in our Universe,” Dr. Heymans said.

The results were presented today at the American Astronomical Society meeting in Austin, Texas. Read the release here.

46 Replies to “Astronomers Witness a Web of Dark Matter”

  1. I would argue that inferring its location based on gravitational lensing still does not constitute a “direct” observation of dark matter.

    1. The irony is that we don’t actually observe anything. Our eyes only have certain chemical receptors of photons (rhodopsins) which generate action potentials which along with others assemblies of action potential constructs some sort of virtual image in the brain we observe. These photons may scatter off some object, or be emitted by that object and so forth, but we do not actually perceive that object as it is, just as a representation of that object according to how photons interact with the eye and then ultimately the brain. Much the same holds for sound, olfaction, taste and tactile perception: Our brains ultimately construct a representation based upon a cascade of physiological processes. That representation is then something which is manufactured in this larger representation (illusion) the brain generates of the self.

      Dark matter by virtue of its mass does interact gravitationally, and we pick up signatures of that by the deflection of images by photon geodesics in curved spacetime. In the above chain of observing as an object dark matter is only one more step removed relative to this chain in a representation in our conscious perception. The same hold for detecting elementary particles in experiments, or measuring some resonance of a system with input signal, or … . That is how science is done.


      1. Nice exposition!

        One could also add that we never observe here and now due to relativity. We can only observe and extrapolate or, better, theorize, while quantifying uncertainties.

      2. Let alone the time it takes our brains to process input from “here and now” – we’re constantly living in the past. =)

  2. Is dark matter all around us? I know (or think I know) that its mass is what keeps galaxies together but besides that matter and dark matter do not ‘interact’.

    But it seems from what I have read that dark matter’s effects are only seen on very very large scales (galactic). We never see the orbit of a planet or moon disturbed by dark matter.

    For something that make up an estimated 83% of the matter in the universe it certainly seems elusive.

    Can someone shed some light on dark matter??

    1. It if often suggested that dark matter is nothing more than ordinary matter, except that it doesn’t interact with ordinary matter in any way except through gravitation. But like you, I find it very curious that the effects of dark matter are only observed at the cosmic scale, whereas the effects of gravitation are observed at the planetary scale. Maybe such observations are forthcoming, or maybe our ideas of what this stuff is are completely wrong.

      1. I liken it to trying to get your head around relativistic conundrums like looking behind your close-to-light-speed ship or watching someone fall into a black hole. Because we expect matter to be …well, matter, it seems to fly in the face of logic that we can’t feel it or bottle it or cough when we get too much up our noses. If it’s “everywhere” (and I’m speaking from human experience) as in all around us, and we can’t feel it, because it goes right through us, there really is no other way to register its existence. It’s like trying to figure out relativity without math. From our own, earthbound experiences, most of what relativity postulates is just too much to take in!

    2. Matter and dark matter DO interact (that’s how we know the dark matter’s there) via gravity. What distinguishes them is the fact that dark matter interacts weakly (perhaps not at all) with electromagnetic energy (e.g. light)–in other words, photons are neither absorbed nor emitted by dark matter, and dark matter is not subject to the electromagnetic interaction. (While this may seem strange, consider that electrons are not subject to the strong nuclear force.) From a planet’s/moon’s perspective, dark matter is smoothly distributed as a halo surrounding the galaxy, and there’s as much in one direction as another (i.e. the planet’s/moon’s orbit is infinitesimal compared to the overall distribution of dark matter), so the effect on the orbit is negligible. It’s only when we consider the effect from one side of the galaxy to the other that the distribution/density of dark matter becomes significant.

      1. Canderson, I did state that dark matter affected normal matter. My second sentence I stated that dark matter’s mass (hence gravity) affects matter on the galactic scale.

        The question I have is how could dark matter be unformly distributed? If dark matter does have mass then gravity should affect it like it affects normal matter. Should we not see dark matter ‘clump’ like regular matter does.

        I guess what I am asking in a nut shell is why don’t we see the effects of dark matter planets orbiting the sun? I understand we would see them directly but we sure should see dark matter interacting with regular matter on a smaller scale than galactic.

      2. DM is not uniformly distributed. As mentioned in the articles, it is clumped together in a network of webs across the universe, which maybe helped to seed galaxies. It’s not that DM doesn’t interact with small scale objects (i.e. planets, moons, suns, etc…) – it still has a gravitational interaction with each of them. It is just that it is clumped around a galaxy in a halo such that it doesn’t differentially impact the various objects in our solar system. This might be compared to the impact the matter at the centre of our galaxy has on all the planets and moons and our sun, but they all feel a similar impact because they are all approximately the same distance from it.

      3. Kawarthajon,

        It does appear to be uniform within dwarf galaxies. In research published in The Astrophysical Journal scientists studied two of the most dark-matter dominated galaxies known and found a uniform distribution.

        University of Cambridge’s website reports the following from this link: )

        The standard cosmological model describes a universe dominated by dark energy and dark matter. Most astronomers assume that dark matter consists of “cold” (ie slow-moving) exotic particles that clump together gravitationally. Over time these dark matter clumps grow and attract normal matter, forming the galaxies we see today.

        Cosmologists use powerful computers to simulate this process. Their simulations show that dark matter should be densely packed in the centers of galaxies. Instead, new measurements of two dwarf galaxies show that they contain a smooth distribution of dark matter. This suggests that the standard cosmological model may be wrong.

        The lead author of the report said the following:

        “After completing this study, we know less about dark matter than we did before,” said lead author Matt Walker, who is now a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics in the USA. “We now have even more questions to answer – such as why the current cosmological paradigm fails to describe the distribution of dark matter in two of the most dark-matter dominated galaxies of the universe.”

      4. For myself, I have assumed that dark matter can not “clump” past a certain limit. As in, there is likely no dark sand, dark dust, dark rock or dark foam. It’s a gas or a wavelike form of matter that doesn’t even interact with itself other than having antipathy to being lonely. So it doesn’t surprise me that it’s of uniform density in any galaxy. You can’t compress that which will not press on itself.

      5. Yes of course. Sometimes, lots of loose hydrogen out there. However, you’re failing to recognize the “other” nature of dark matter. Hydrogen loves to interact ie: water. Dark matter acts totally unlike hydrogen, which is BTW, a singular. Its like you’re asking neutrinos to wake up and notice each other so they can start a big neutrino party. They’re loners and always will be.

      6. Ok, but the article that we’re commenting on talks about how DM clumps into these networks and webs, with galaxies in them. I was talking about DM clumping on a large scale. If DM is clumped into a dwarf galaxy, then my point is secure, even if the distribution of DM is smooth within the galaxy. My point was that DM’s gravity operates on a grand scale and doesn’t have differential effects on comparatively little objects like planets, moons and stars.

      7. Because it doesn’t interact electromagnetically, dark matter particles can’t easily slow down, so they just go on travelling round and round, in a halo.

      8. Dark matter (DM) can’t clump, no electromagnetic interactions so no charges and no chemistry. DM particles are loosely associated with other gravitational masses such as stars. But pass through them like neutrinos, just more massive and likely then less speedy.

        As it happens, late last year the last unconquered territory of DM was laid to its feet. The Eris simulation modeled a spiral galaxy successfully for the very first time. The crucial component was – DM!

        The significance was that while alternative hypotheses could explain some particulars of precisely galaxies they were not successful anywhere else. And now they are kicked out by a more parsimonious model over a wide variety of scales.

        Earlier that year another large simulation of the universe, the Bolshoi simulation, confirmed earlier DM models to even better resolution.

        DM models have always done well on gravitational lensing of galaxy clusters as well as their collisions.

        What the lower limit for DM structure formation is seems unclear.

        There are observational signs that they dominate dwarf galaxies. If they can repeat the Eris simulation for those, which will take another year at a guess, it would be interesting.

        Another recent observation is that they have managed to set a lower limit on DM particle mass from observation. I don’t remember the details right now, but they are still way off the scale where they expect to see them in detectors. But it is a start!

      9. Assuming dark matter is composed of particles (wimps), then it seems the particles are moving randomly, i.e. they have a temperature.

        They can not be very cold, or they would simply collapse gravitationally.
        They can not be very hot, or DM would not contract at all.
        They can have an effective temperature that allows it to contract some, but at that point it behaves like a cloud of gas in an approximate hydrodynamic equilibrium.

        Each time two ‘galaxies’ with much DM collide, the effective temperature of the DM would increase slightly, causing the new DM-cloud to reach equilibrium in a slightly large size. Over time, this cloud would spread symmetrically unless otherwise disturbed.

        In effect, if the above is the case, DM behaves like a very large but low density ‘cloud’. Collapse on smaller scales are prohibited by the effective temperature.

  3. It has not been observed in any way, shape or form, its existence so far has only been inferred. Dark matter, XXI-century science’s ether

    1. I believe you mean aether, which was its time’s phlogiston. Hypotheses soundly rejected with time.

      This is more like our neutrinos, hypotheses that successfully accrue tests and characteristics over time.

      Note that neutrinos are quite difficult to observe too! Yet we can manage.

  4. Wide-field weak lensing surveys like this one will be an important tool in our understanding of dark matter, as it gives us a way to directly map its distribution over a wide expanse of the cosmos.

  5. As for clumping, DM does not generally clump because it does not interact by electromagnetism which dissipates away energy by radiating photons. Assume you were some super-observer who had super technology and you grabbed every particle of DM by some means and brought them all to a dead stop relative to the galaxy. These particles would be mutual gravitation begin to fall towards some relative center and implode into a huge black hole. The rub is that you have no catcher’s mitt to stop them, and their status as “cold” DM reflects the fact these particles are in motion and are in free orbits that are conservative and do not lose energy..

    Do DM particles influence things like planets? We can do an estimate of this. DM constitutes about 4 times that of luminous matter in a galaxy. It extends out to about a million light years. So for a galaxy with 10^{11} stars this is a matter density of ? ~ 10^{12}x10^{30}kg/(10^6ly x 10^15}m/ly)^3 = 10^{-21}kg/m^3.

    This density may be used in the Poisson equation

    ?^2? = 4?G?,

    to compute the gravitational potential of the DM in a much smaller region, such as in a spherical volume that might encompass the solar system. The potential determines the acceleration A = -??, so we write

    ??A = -4?G?.

    Now let me integrate ??A over the volume of a sphere which encompasses the solar system

    ???A dv = ?F?da

    which is Stokes’ rule for the integration over the volume and bounding area of a sphere and this is

    ???A dv = ?A?da = -4?G??dv

    = 4? R^2A = -(4?)^2G?R^3/3.

    Now solve for A to get

    A = -(4?/3)G?R

    which is the force equation for a spring.

    Now input some numbers

    A =~ 4×6.67×10^{-11}N(m/kg)^2 x 10^{-21}kg/m^3 x R

    = 2.7×10^{-31}N/kg-m x R

    So input the radius for some planetary orbits. As a trial I can put R = 10^{12}m, to approximate a gas giant and you get a very small acceleration 2.7×10^{-19}N/kg. This is compared to the force/mass or acceleration the sun will exert

    A = GM/r^2 ~ 6.67×10^{-11}N(m/kg)^2x 2×10^{30}kg/10^{24}m^2 ~ 1.3×10^{-4}N/kg

    The difference is striking! The perturbing effect on the solar system is very small. Now input the orbit of a star at 100,000 ly in the galaxy and this up to 2.7×10^{-10}N/kg.


  6. How do they know how the light coming to us has been bent? Is there something in the spectral signature that says, I was aligned like that but since passing by a huge glob of nothing, I look like this instead.? What tells us that what we’re detecting is an “after” picture?

  7. How do they know how the light coming to us has been bent? Is there something in the spectral signature that says, I was aligned like that but since passing by a huge glob of nothing, I look like this instead.? What tells us that what we’re detecting is an “after” picture?

  8. How do they know how the light coming to us has been bent? Is there something in the spectral signature that says, I was aligned like that but since passing by a huge glob of nothing, I look like this instead.? What tells us that what we’re detecting is an “after” picture?

    1. The magic word here is “gravitational lenses”. We cannot infer it from “single” photons, but from distorted pictures of background galaxies.

      Since galaxies are not point sources their photons take a slightly different way into our telescopes depending on where they start in the galaxy. If there is no mass between the galaxy and us the photons travel on straight lines and the galaxy is seen as it is.
      However, if there is mass in between, then it becomes interesting. Now, it critically depends on the starting point how the way of the photon is affected by that mass. A photon from one side of the galaxy will be bent differently than a photon from the other side. In the end, the picture of the galaxy gets distorted and we may see it curved or shaped quite peculiarly. Since we can determine the galaxy’s redshift, we can determine its distance and with some calculations we can actually derive the mass distribution that is responsible for the distortion of the picture.

      1. Thanks, but I think you’re still suggesting that someone is making a value judgement about how “distorted” a galaxy might look. How do they quantify that level of distortion? Since we can’t see the galaxy from any other viewpoint, what have we to go on? There are lots of ACTUALLY distorted galaxies out there for which I would not want to be responsible to make that call.

      2. As with other high-resolution images we’ve all seen ( almost unbelievable to me ), that Image of Galaxy Cluster Abell 2218 reveals such extreme distortions, it leaves little doubt SOMETHING has altered the original light-picture of the background galaxies — or gravity-lensed them, as by some impossibly huge glass lens! On such a gargantuan scale, yet ( out on another limb I go ), basically the same effect one could demonstrate with a curved glass lens in hand. Simply amazing!

        I thought Peristoika’s questions were still good ones, as one off-stream observer of the grand planetarium show unfolding before us day by day, and week by week.

      3. This study (and others like it) employed weak gravitational lensing to discern the distribution of dark matter. Weak lensing produces subtle distortions in the shapes of galaxies which, when studied statistically, can be used to infer the distribution of mass (in this case, dark matter). Wikipedia has a good description of the methodology behind weak lensing studies:

        (btw, weak lensing rarely produces the long arcs and multiply-imaged galaxies as is seen in strong lensing, per Dr Flimmer’s awesome Abell 2218 image)

      4. I had considered to talk about the differences of strong and weak lenses, but I decided that the general picture should be enough to start with (and I would have needed to look up the details of weak lensing 😉 ).

  9. Gazing at the CFHT image, trying to picture it as a specially-dimensioned solid, its structure seems to have a familiar similarity to, mirror something seen in nature ( if true representation of how a solid version would appear ).

    No surprise would there be, though, as the mega-structure of galaxies in the Universe itself bears a remarkable resemblance to that of the inner human brain, and its neuron “web” – the folds within which intelligence is “fired”.

    These questions are more rhetorical, than anything else:

    Is “Dark Matter” matter? A quantifiable substance? That which “physicists have suspected helps gives galaxies their mass, structure, and motion, and provides the ‘glue’ that connects clusters of galaxies together in vast networks of cosmic webs.”

    10 million galaxies (!) strewn-back over a billion years of past cosmic time?

    So, if I understand, from the visible “gravity-lensing” effects, this invisible “Dark Matter” can be discerned, its counters through time seen, “visually mapped” – by tracing the “space-time distortion” along filaments of study?

    I still wonder ( perhaps for lack of in-depth knowledge or understanding ): If this “Dark Matter” really is “a mysterious MASS in the universe”? Is it really “dark”, or just invisible – materially undetectable?

    Could it be a force that imparts mass, shapes structure through time, and patterns matter in space, upholding its order, materialized energy in the folds of its fabric?

    Its “nature” is evident IN structure of time, but is it even bound by time? If so, it would have to be a matter of time (could not resist that)?

    Does DM really “fit” into “our current knowledge of physics”, or, perhaps, not unlike other avenues of inquiry ( related, but separate? ), is it something else? For example, could it be what frames the border, and encloses the values of those Universe-defining Laws of Physics? Elusive of clear definition, materially – yet powerful in fashioned filaments of luminous galaxy!

    Could it possibly be one facet view, thus far escaping any clear material definition, that is actually a part of a whole, one framing the motions and enclosing the forms, binding the very Laws of Physics?

    ( Does the velvet glove of DM slip over physics, or is physics woven-into very fabric of the DM glove? I may be inverted, or inside-out, here. )

    IMAGE: Scan the complex of facets over the surface of a clear diamond crystal ( elegant, beautiful ). As you turn it, and examine it under various lighting, colorful flashes will be seen, puzzling reflections discerned, mirroring interior dimensions, glinting insights externally visible from the different angles of view, when various planes of surface are looked through.

    Simply, is “Dark Matter” something non-physical – yet having dramatic material manifestation. And does it work in isolation, or is it part of a “Unified” whole, the fine details of which require high math computations, yet may have at its unseen heart, a simple elegant beauty of all-encompassing “field”, or integral force – a fine-cut diamond-like unity of geometry in or of Space?

    A “theory” ( unseen? ) may be emerging into reality – like brilliant reflections of subtle hues clearly seen in a mirror – through an array of lenses, of huge Telescopes atop the world’s summits, and small powerful lenses of Microscopes in Science labs, or from the light-burst of earth-embedded Accelerator results – is a single image of complex elements, blurry in areas, slowly coming into astonishing focus, to either dumbfound men ( leaving them perplexed? ) or – inspire them.

    Will it be of a rough diamond of natural formation? Or will it be of an exquisitely fashioned gem of the highest craftsmanship, precision-cut in every plane of facet, wonderfully symmetrical in surface-form of unified geometry?

    1. the overall structure of the Universe itself bears a remarkable resemblance to that of the inner human brain, and its neuron “web” – the folds within which intelligence is “fired”.

      Not even close, unless you mean superficial likeness for rhetorical purposes. The cortex is very differentiated and even layered, these structures not so much.

      A quantitative measure like a spatial FFT would testably show the difference.

      As for the rest of the “rhetorical” comment it is way too many questions. The baseline is that DM is accepted fruitful theory on its own, it is an indelible part of standard cosmology as well, and you can study what scientists claim for example here on UT or here.

      1. Sampling of images below ( a few main web-sites thereof ) that most closely support the comparison ( New York Times’ image comparison is a stunner! ): Surely, you cannot deny that some of the images of neurons, and “web” networks, along with others ( not all, to be sure ), do indeed resemble sections ( qualification – on a given scale, and in certain resolutions ) of the cosmic structure mapped-out by astronomers through super-computers: Filaments, intersecting knots ( absent sheets and walls, admittedly ) – neuron strands, cell junctures:

        You can almost picture the luminous galaxy-clusters strung along the “web”strands, around the “empty” inter-medium dark voids of the network –

        BRAIN STRUCTURE _________________________________________________

        [] “Normal Neurons in vitro” —–

        — >

        [] Nerve cell —–

        — >

        Neuron Network —–

        — >

        [] “The amazing picture in the New York Times shows, side-by-side, a picture of the CELLS in a mouse’s BRAIN, and a snap-shot of the INTERGALACTIC STRUCTURE OF THE UNIVERSE. Both pictures come from the very latest discoveries and technologies: and the two pictures are very similar.” (emphasis mine):

        — >

        — >

        — > ( Here is a clincher )

        [] Wired article: “Mapping the Most Complex Structure in the Universe: Your Brain”

        — >

        There are “100 BILLION neurons in the human brain” What a curious number!

        UNIVERSE STRUCTURE ________________________________________

        [] Millennium Simulation “shows galaxy distribution” – Main Page (note images)

        — >

        — >

        [] “This graphic represents a slice of the spider-web-like structure of the universe, called the ‘cosmic web.’ These great filaments are made largely of dark matter located in the space between galaxies. Credit: NASA, ESA, and E. Hallman (University of Colorado, Boulder)” – Main Page:

        — >

        — >

        [] Universe – “formation of the large-scale structure” —–

        — >

        [] “This — roughly — is what the matter in our Universe looks like on the largest scales. Great filaments of matter connect in a great cosmic web, and the intersections of the largest, strongest filaments correspond to the densest, richest collections of matter in our Universe today, such as clusters and superclusters of galaxies.” – Ethan Siegel, theoretical astrophysicist. – Main Page

        — >

        — >

        ( Typically, I somewhat re-edited my comment for greater clarity. )

      2. I am in the dark, lest I seek the light; so regarding link:

        [] “Remarkably, it turns out there is five times more material in clusters of galaxies than we would expect from the galaxies and hot gas we can see. Most of the stuff in clusters of galaxies is invisible and, since these are the largest structures in the Universe held together by gravity, scientists then conclude that most of the matter in the entire Universe is invisible. This invisible stuff is called ‘dark matter’, a term initially coined by Fritz Zwicky who discovered evidence for missing mass in galaxies in the 1930s.” – Goddard Space Flight Center on “Dark Matter” –

        [] “We believe that most of the matter in the universe is dark, i.e. cannot be detected from the light which it emits (or fails to emit). This is ‘stuff’ which cannot be seen directly — so what makes us think that it exists at all? ITS PRESENCE IS INFERRED INDIRECTLY from the motions of astronomical objects,… It is also required in order to enable gravity to amplify the small fluctuations in the Cosmic Microwave Background enough to form the large-scale structures that we see in the universe today.”
        – Martin White, Professor of Physics, Professor of Astronomy, UC Berkeley –

        (all emphasis mine)

        What is being detected cannot be explained by the visible mass: therefore, there is “matter” absent from the picture. But is it physical? Mass-like effects. My poor layman’s, math-impaired question remains: Could it be SOMETHING OTHER THAN “mass” ( in whatever “exotic particle” form that “substance” may yet be discovered to exist in )? Is there a widely held, very natural assumption here – “It must be mass.”

        What else could it be?

        I cannot help thinking ( if not subconscious memory of something read ) there might be some connection with “Dark Energy”. Maybe they are both stand-alone, but related “complexes”, or maybe they are two-dimensions of the same thing.

        [] “ …. Note that although the universe may be flat, that does not mean that matter makes up the critical density. In addition to dark matter there is dark energy, e.g. a cosmological constant, that needs to be included in the accounting.” – DW.

        [] “Hence we INFER that there is dark matter in the Universe.” (lost track of source) – man can only think in material terms, so the evident effects MOST be explainable by matter in SOME form.

        Well, 2012 may shed revealing light, one way or the other, from an underground accelerator – LHC.

        [] “Dark matter refers to non-luminous matter particles [ again, an assumption? ] whose presence is suggested because of the gravitational effects on the rotation rate of visible matter such [as] galaxies and the presence of clusters of galaxies..” Negev source, Israel, I presume.

        _____ CHANDRA

        Evidence for Dark Matter

        “Observations of the rotational speed of spiral galaxies, the confinement of hot gas in galaxies and clusters of galaxies, the random motions of galaxies in clusters, the gravitational lensing of background objects, and the observed fluctuations in the cosmic microwave background radiation require the presence of additional gravity, which can be explained by the existence of dark matter.”

        Does that necessarily follow, though. Of course, if more gravity than visibly explainable, then, yes, there must be “missing mass”, or non-light emitting matter. But, are they going further, and supposing that it IS a gravity effect? If it is, then so must it be. But if it is not gravity at work ( yet having gravity-like effects ), it might be something else altogether, an unknown active agency affecting matter – the working of its presence being readily detectable THROUGH matter.

        ( I may have tied myself into a Gordian Knot. )

        Alternatives to Dark Matter

        “One possibility, considered unlikely by most astrophysicists, is that a modification of the theory of gravity can explain the effect attributed to dark matter.”

        What is Dark Matter?

        “The nature of dark matter is UNKNOWN. A substantial body of evidence indicates that it CANNOT be baryonic matter, i.e., protons and neutrons. The favored model is that dark matter is mostly composed of exotic particles formed when the universe was a fraction of a second old. Such particles, which would require an extension of the so-called Standard Model of elementary particle physics,…[named]”

        The reason for my suspicion is here embedded. Baseless, it could turn out.

  10. Great amazing work by the CFHTLenS collaboration team, nice article Jason and some very interesting comments here too 🙂

    Especially like the discussion of clumping and action/interaction, lensing on galactic versus local scales….

    In the past I have been a sceptic of DM and DE feeling somehome cheated that I was being asked to believe something not directly observable… Something about scientific models, etc…

    However, I may be a sceptic but do not wish to be contrarian for the sake of it. I am now accepting (thanks in large part to these UT articles and comments) that DM and DE are important substantial place-holders at the very least and starting to accept the validity of the concept as more observations like this are reported.

    Thanks everyone.



    1. Great! Now if you only can drop the misplaced “place holder” metaphor*, you can embrace the Dark side.

      * We can observe DM by its characteristics of cold, particulate, mass and non-EM interaction, not so with theory place holders “insert remaining mass here”.

      1. Actually we go more light on the booze-ons (having them on the “darks”, as we may refer to the preferred mix).

        I dunno about the bad case of helmet hair. Of course, with no static clinging and less mechanisms to end up at the bottom of a gravity well you can have any hair style and it will look the same old burr. I never said there wasn’t disadvantages!

  11. If the Higgs mechanism is supposed to give rise to mass and normal baryonic matter seems to aggregate around dark matter clumps and filaments, is a connection possible?

    1. Mass is complicated. More generally it is a local conservation of energy (that gravity can feel as mass by its curving of spacetime), so it takes many forms.

      As for Higgs, 3 out of 4 different standard Higgs give mass to W & Z and hence themselves by such bootstrapping. But the remaining one gets its mass from symmetry breaking. Yet other different mechanisms makes Higgs give masses to matter and force particles.

      And the different cases continue to accrue as we look at additional mass contributions from conserved energies as we go to composite particles (say, nucleons, getting energies from both quarks and gluons), atoms (energies from electron shells), molecules (bonding energies), and so on.

      Surely though, the Higgs mechanism of matter particles is shared between baryonic and non-baryonic matter. And I seem to remember non-standard Higgs, i.e. more than those described above, as potential dark matter candidates.

      1. Thanks T.L. for your reply and ref. to the past article on the Higgs, I forgot about that. It’s getting harder to keep all the various proposals in my aged short term memory. I never really understood this Higgs thing anyway. Old school says energy gives rise to mass. Oh well, time for another Excedrin.

  12. What is inferred by gravitational lensing is intervening gravitating matter. Only due to the current fashion it is called dark matter!
    -Dilip G. Banhatti / Madurai (India)

    1. Well, dude, how do you account for the gravitational lensing observations that show the presence of considerably more mass than is indicated by the clusters’ light alone?

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