Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Is there an alternative theory to dark matter?

  1. Aug 5, 2017 #1
    My physics teacher, who dislikes the idea of dark matter, told me that a physicist created an alternative explanation to the phenomena caused by dark matter.

    Is there something I missed on the news?

    What is the alternative theory to dark matter and how does it explain 'things' ?
  2. jcsd
  3. Aug 5, 2017 #2


    User Avatar
    Gold Member

    Its called modified gravity which is actually an umbrella term for any attempt to modify general relativity at large scales. Right now experimental evidence is not enough to favor one approach over the other.
  4. Aug 5, 2017 #3

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    Sure there is. Look at the number of dark matter publications vs. modified gravity publications. The fact of the matter is that there is no theory of modified gravity consistent with all the data.
  5. Aug 5, 2017 #4


    User Avatar
    Science Advisor

    Publications reporting direct experimental detection of actual dark matter are rather less numerous. :confused:
  6. Aug 5, 2017 #5


    User Avatar
    Science Advisor

    Of course this is true. But, as Vanadium50 pointed out, the dark matter hypothesis is consistent with the experimental data, while there is no modified gravity theory which is consistent with the data.
  7. Aug 5, 2017 #6
    Nobody likes the idea of dark matter, but no point in complaining unless there is a better idea.
  8. Oct 21, 2017 #7
    Yes I can: no dark matter is a better idea since it saves the embarrassment of not finding it. Having reviewed most of the supposed evidence for dark matter, not one of these is unchallenged; contrary to what the dark matter fraternity try to imply.
  9. Oct 21, 2017 #8
    Dark matter isn't really a theory.
    It's a placeholder name for "something which has observable gravitational effect, similar to matter, but which cannot be detected by other means".
    Originally there were three plausible explanations.
    1. Something is wrong with our understanding of gravity. (Modified gravity).
    2. It's ordinary matter, but we don't have a way of seeing it (MACHO's).
    3. It's an as yet undiscovered kind of massive particle which barely interacts at all with anything else except through gravity. (WIMPS).

    While we still don't know what it is, 1 and 2 now seem less likely.
    So currently the effort is on detecting WIMPS. - Looking for the vary rare interactions of those particles using detectors deep underground where background noise is mostly eliminated.
    Last edited: Oct 21, 2017
  10. Oct 21, 2017 #9


    User Avatar
    2017 Award

    Staff: Mentor

    You prefer something in complete disagreement with observations over something with just unusually small cross sections?
    Challenged, but not refuted, unlike all other approaches that can’t get a consistent picture combining all observations.

    The models of dark matter are not perfect, but they are the best we have so far.
  11. Oct 22, 2017 #10
    There is a 4 which it is possible to use the physics we have to explain most of the anomalies, and certainly for the galaxy rotation problem. I believe we have been looking at the rotation problem the wrong way and I have found several published papers pointing to alternatives but because of the hold the dark matter paradigm has on current thinking, these alternatives are either not viewed or ignored. For example: i) Jalocha, J., Bratek, L. and Kutschera1, M. (2008). ‘Is Dark Matter Present in NGC 4736? An Iterative Spectral Method for Finding Mass Distribution in Spiral Galaxies.’ Astrophysical Journal, vol 679, pp 373–378.
    ii) J. D. Carrick and F. I. Cooperstock. ‘General relativistic dynamics applied to the rotation curves of galaxies.’ Department of Physics and Astronomy, University of Victoria P.O. Box 3055, Victoria, B.C. V8W 3P6 (Canada): arXiv:1101.3224v1.
  12. Oct 22, 2017 #11
    Definitely not something in complete disagreement with observations I class myself as a scientist after all. Though the issue of small cross sections is interesting because is there a lower limit! I know I am paraphrasing Prof Stacy McGaugh here but if there is no lower limit, then theoretically there is no end to this search for a WIMP. Good news for tenure but I am not sure about physics.
  13. Oct 22, 2017 #12
    I'm not sure the dark matter hypothesis is experimentally falsifiable. Once you have the observation that observable matter cannot account for observable gravitational effects, you can posit some arbitrary distribution of unobservable matter in any way you want to account for the additional gravity.

    But what observation could then falsify the hypothesis?

    Sure, one might envision proposing alternate hypotheses (new models of how gravity works), but all these are constrained in their distribution of matter by the matter being observable through other means. In the "dark matter" hypothesis, one is free to distribute the dark matter however one pleases.
  14. Oct 22, 2017 #13


    User Avatar
    2017 Award

    Staff: Mentor

    What is your alternative proposal that is internally consistent both for weak and strong gravitational fields and consistent with all measurements at the same time?
    I'm not aware of theoretical limits. The neutrino background will make improved experimental searches very difficult after DARWIN or maybe its successor.
    Of course it is. We have multiple independent measurements of its overall mass density. They wouldn't have to agree - but they do. We have multiple independent measurements of the distribution within galaxies. They wouldn't have to agree - but they do. All these tests could have ruled out dark matter but did not.
  15. Oct 22, 2017 #14
    Are these measurements really independent of the stellar velocities? The same stellar velocities will give the same mass distributions if one assumes dark matter as an explanation. This does not mean the dark matter hypothesis is falsifiable, only that the stellar velocity measurements are consistent.

    And if the stellar velocity measurements are consistent (the same with different methods), the assumption of dark matter will always lead to the same inferences regarding dark matter densities. But this is a circular argument, not a failure to falsify the dark matter hypothesis. It is merely a confidence boost for the different methods for determining stellar velocities.
  16. Oct 22, 2017 #15
    Yes it is - see my response to rootone above. Since my position is that existing physics can explain the galaxy rotation problem, I am by default consistent with any accepted theory. In fact since one of my references (J. D. Carrick and F. I. Cooperstock. ‘General relativistic dynamics applied to the rotation curves of galaxies.’ Department of Physics and Astronomy, University of Victoria P.O. Box 3055, Victoria, B.C. V8W 3P6 (Canada): arXiv:1101.3224v1) uses General Relativity I am entirely consistent with gravitational field theories.
  17. Oct 22, 2017 #16


    User Avatar
    2017 Award

    Staff: Mentor

    Which measurements?
    CMB measurements? Sure.
    Gravitational lensing measurements? Sure.
    Submitted to arXiv 2010. Where is the publication? If that would be a solid result clearly they would have tried to publish it? Why didn't it get published?
    And where do they discuss the dark matter measured with other methods? The CMB and lensing are briefly mentioned as evidence for dark matter in the introduction but then they are ignored.
    That is a measurement of a single galaxy. That doesn't explain anything else, like the amount of dark matter inferred from cosmology and so on.

    That is not special about these two references, it is a general pattern. "Oh, we if do this, we can explain this single observation without dark matter" - while ignoring all the others. I asked for something compatible with all observations, exactly for this reason.

    By the way: There is a high mortality rate for modified gravity due to the gravitational waves from the binary neutron star merger.
  18. Oct 23, 2017 #17
    Based on my experience both in physics and another scientific area that I am professionally involved in, the problem is that if your paper does not fit the prevailing paradigm then it often doesn’t get published. So it is a little disingenuous to use this argument as absence of scientific value.

    Yes I will concede that using a limited data set is questionable. However, there are larger data sets and published studies, questioning the dark matter paradigm:

    1) Magain, P. and Chantry, V. (2013). ‘Gravitational lensing evidence against extended dark matter halos.’ Institut d’Astrophysique et de Géophysique, Université de Liège, Liège Belgium.

    2) Lu et al (2010). ‘Large-scale structure and dynamics of the most X-ray luminous galaxy cluster known – RX J1347−1145’. Mon. Not. R. Astron. Soc. 403, 1787–1800.
  19. Oct 23, 2017 #18
    This is not really true. A number of colleagues and I stopped trying to publish many of our papers beyond arXiv several years ago. If none of the co-authors "need" the paper on their CVs, we often just post to arXiv, because this reaches our intended audience and avoids the extra time (and politics) of submitting to the print journals and encountering editors and referees who want to change our work without even a careful reading to properly understand it.

    Cooperstock and his colleagues are well established enough in their fields that I don't think it is reasonable to conclude the paper is flawed because it was only published at arXiv. Many of their other papers in the field are published in peer-reviewed journals, and the paper in question ( arXiv:1101.3224v1 ) has been cited 21 times. By the time a paper has been cited over 20 times, it is being taken seriously, and one should not knock it because it only appears at arXiv.

    Lots of disciplines are "old boy networks" where the peer-review process works pretty hard to protect the prevailing paradigm. Publishing at arXiv can be an effective work-around, establishing priority, putting the ideas before the intended audience, generating widespread discussion, etc. It is disingenuous to suggest that a paper is unworthy of discussion because it only appears at arXiv.
  20. Oct 23, 2017 #19


    User Avatar
    2017 Award

    Staff: Mentor

    You know how that sounds, and how that argument can be (and is) abused.
    I totally understand that for typical results, but if you make extraordinary claims?
    It has been cited 21 times, we would have to see how many authors agree with the conclusions and how many do not. I picked one at random:
  21. Oct 23, 2017 #20


    User Avatar
    Gold Member

    The fact of the matter is that there is no theory of dark matter consistent with all the data.

    Every outstanding dark matter theory is contradicted by some very solid piece of empirical data. The following 36 citations set forth some of the highlights of the current crisis in dark matter theory.

    There are lots of dark matter publications, but those publications are overwhelmingly ruling out variations of dark matter theory, sometimes huge classes of them such as pretty much all MACHOs, all WIMPS, all collisionless dark matter, all cold dark matter theories, and all self-interacting dark matter theories. Warm dark matter is very close to being over constrained (and general exclusions of collisionless dark matter are the nail in the coffin), and many forms of axion dark matter are ruled out.

    One common theme is that it isn't possible to devise a dark matter model that simultaneously fits lamdaCDM model constraints and the tight fix of inferred dark matter distributions to baryonic matter distributions (something that modified gravity models do naturally).

    * Exclusions from the LHC. https://arxiv.org/abs/1709.02304 and https://arxiv.org/abs/1510.01516

    * Dark matter can't have any significant coupling to Standard Model matter. https://arxiv.org/abs/1501.00907 This is a problem because "collisionless" dark matter that does not interact with Standard Model matter is pretty much ruled out per other citations below.

    * Exclusions from Xenon-100 https://arxiv.org/abs/1709.02222

    * Exclusions of Charming Dark Matter theories. https://arxiv.org/abs/1709.01930

    * Theodorus Maria Nieuwenhuizen "Subjecting dark matter candidates to the cluster test" (October 3, 2017):

    A variety of searches for sterile neutrinos have also ruled out this possibility in the relevant mass range. See, e.g., https://arxiv.org/abs/1710.06488 and http://iopscience.iop.org/article/10.1088/1742-6596/718/3/032008/pdf

    * Exclusions for Axion Dark Matter: Renée Hlozek, David J. E. Marsh, Daniel Grin "Using the Full Power of the Cosmic Microwave Background to Probe Axion Dark Matter" (August 18, 2017).

    * Combined direct dark matter detection exclusions. https://arxiv.org/abs/1708.04630 and https://arxiv.org/abs/1707.01632

    * Exclusions based on non-detection of annihilations in dwarf galaxies. https://arxiv.org/abs/1708.04858

    * Primordial black hole exclusions. https://arxiv.org/abs/1301.4984

    * Daniele Gaggero, et al., "Searching for Primordial Black Holes in the radio and X-ray sky" (Pre-Print December 1, 2016). Abstract:

    * Tight Warm Dark Matter parameter exclusions. https://arxiv.org/pdf/1704.01832.pdf

    * More Warm Dark Matter parameters exclusions: Simon Birrer, Adam Amara, and Alexandre Refregier, "Lensing substructure quantification in RXJ1131-1231: A 2 keV lower bound on dark matter thermal relict mass" (January 31, 2017).

    * Lin Wang, Da-Ming Chen, Ran Li "The total density profile of DM halos fitted from strong lensing" (July 31, 2017). Abstract:

    As the body text explains:

    * Paolo Salucci and Nicola Turini, "Evidences for Collisional Dark Matter In Galaxies?" (July 4, 2017). Abstract:

    * Dark matter distributions have to closely track baryon distributions, even though there is no viable mechanism to do so: Edo van Uitert, et al., "Halo ellipticity of GAMA galaxy groups from KiDS weak lensing" (October 13, 2016).

    * One of the more successful recent efforts to reproduce the baryonic Tully-Fischer relation with CDM models is L.V. Sales, et al., "The low-mass end of the baryonic Tully-Fisher relation" (February 5, 2016). It explains:

    The paper manages to simulate the Tully-Fisher relation only with a model that has sixteen parameters carefully "calibrated to match the observed galaxy stellar mass function and the sizes of galaxies at z = 0" and "chosen to resemble the surroundings of the Local Group of Galaxies", however, and still struggles to reproduce the one parameter fits of the MOND toy-model from three decades ago. Any data set can be described by almost any model so long as it has enough adjustable parameters.

    * Dark matter can't explain bulge formation in galaxies: Alyson M. Brooks, Charlotte R. Christensen, "Bulge Formation via Mergers in Cosmological Simulations" (12 Nov 2015).

    * Baryon effects can't save cold dark matter models. https://arxiv.org/abs/1706.03324

    * Cold dark matter models don't explain the astronomy data. https://arxiv.org/pdf/1305.7452v2.pdf

    * As of 2014, a review article ruled out rule out pretty much all cold dark matter models except "warm dark matter" (WDM) (at a keV scale mass that is at the bottom of the range permitted by the lamdaCDM model) and "self-interacting dark matter" (SIDM) (which escapes problems that otherwise plague cold dark matter models with a fifth force that only acts between dark matter particles requiring at least a beyond the Standard Model fermion and a beyond the Standard Model force carried by a new massive boson with a mass on the order of 1-100 MeV). Alyson Brooks, "Re-Examining Astrophysical Constraints on the Dark Matter Model" (July 28, 2014). As other more recent links cited here note, collisionless WDM and pretty much all SIDM models have since been ruled out.

    * Dark matter annihilation has largely been ruled out as a source of FERMI signals attributed to dark matter annihilation. Samuel K. Lee, Mariangela Lisanti, Benjamin R. Safdi, Tracy R. Slatyer, and Wei Xue. "Evidence for unresolved gamma-ray point sources in the Inner Galaxy." Phys. Rev. Lett. (February 3, 2016). Millisecond pulsars were the source.

    * Proposed warm dark matter annihilation signals also turned out to be false alarms. https://arxiv.org/abs/1408.1699 and https://arxiv.org/abs/1408.4115

    * The bounds on the minimum dark matter mean lifetime of 3.57*10^24 seconds. This is roughly 10^17 years. By comparison the age of the universe is roughly 1.38 * 10^9 years. This means that dark matter (if it exists) is at least as stable as anything other than a proton, which has an experimentally determined mean lifetime of at least 10^33 years. https://arxiv.org/abs/1504.01195 This means that all dark matter candidates that are not perfectly stable or at least metastable are ruled out. Decaying dark matter and dark matter with any significant annihilation cross section are inconsistent with observation.

    * Torsten Bringmann, et al., "Strong constraints on self-interacting dark matter with light mediators" (December 2, 2016). Abstract:

    The conclusion of the paper notes that:

    * Dark photon parameter space (the carrier boson of the SIDM models) is also tightly constrained and all but ruled out. Yet, the properties a dark photon has to have, if there is one, are tightly experimentally established based upon cluster dynamics. https://arxiv.org/abs/1504.06576

    * The Bullet Cluster is a huge problem for DM. Jounghun Lee, Eiichiro Komatsu, "Bullet Cluster: A Challenge to LCDM Cosmology" (May 22, 2010). Later published in Astrophysical Journal 718 (2010) 60-65. Abstract:

    and also

    Garry W. Angus and Stacy S. McGaugh, "The collision velocity of the bullet cluster in conventional and modified dynamics" (September 2, 2007) published at MNRAS.

    * El Gordo poses similar problems for dark matter models. Sandor M. Molnar, Tom Broadhurst. "A HYDRODYNAMICAL SOLUTION FOR THE “TWIN-TAILED” COLLIDING GALAXY CLUSTER “EL GORDO”. The Astrophysical Journal, 2015; 800 (1): 37 DOI: 10.1088/0004-637X/800/1/37

    * Axion fuzzy dark matter ruled out: Vid Iršič, Matteo Viel, Martin G. Haehnelt, James S. Bolton, George D. Becker. "First Constraints on Fuzzy Dark Matter from Lyman-α Forest Data and Hydrodynamical Simulations." Physical Review Letters, 2017; 119 (3) DOI: 10.1103/PhysRevLett.119.031302
    Last edited: Oct 23, 2017
  22. Oct 23, 2017 #21


    User Avatar
    Gold Member

    Cooperstock (2011) was published, but the arXiv entry was never updated. https://link.springer.com/article/10.1007/s10509-011-0854-z

    A previous pre-print by Cooperstock was published and reached the same conclusion as https://arxiv.org/abs/1101.3224

    General relativistic velocity: the alternative to dark matter
    F.I. Cooperstock, S. Tieu
    (Submitted on 30 Nov 2007)
    We consider the gravitational collapse of a spherically symmetric ball of dust in the general relativistic weak gravity regime. The velocity of the matter as viewed by external observers is compared to the velocity gauged by local observers. While the comparison in the case of very strong gravity is seen to follow the pattern familiar from studies of test particles falling towards a concentrated mass, the case of weak gravity is very different. The velocity of the dust that is witnessed by external observers is derived for the critically open case and is seen to differ markedly from the expectations based upon Newtonian gravity theory. Viewed as an idealized model for a cluster of galaxies, we find that with the general relativistic velocity expression, the higher-than-expected constituent velocities observed can be readily correlated with the solely baryonic measure of the mass, obviating the need to introduce extraneous dark matter. Hitherto unexplained and subject-to-reinterpretation astrophysical phenomena could also be considered within this context. It is suggested that an attempt be made to formulate an experimental design at smaller scales simulating or realizing a collapse with the aim of implementing a new test of general relativity.
    Comments: 12 pages, 2 figures
    Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
    Journal reference: Mod.Phys.Lett.A23:1745-1755,2008
    DOI: 10.1142/S0217732308027163

    There have also been at least three published papers subsequent to the 2011 paper for which pre-prints have not been posted:

    N. S. Magalhaes, F. I. Cooperstock. (2017) Mass density and size estimates for spiral galaxies using general relativity. Astrophysics and Space Science 362:11. [Crossref]

    Rotation curves of spiral galaxies reveal a physical phenomenon that has been seen to lack a satisfactory scientific explanation: velocities of stars far from the nucleus are high and approximately constant. In the context of Newtonian dynamics, the existence of a new kind of matter (dark matter) is assumed, which, when added to the usual observed matter, would account for the phenomenon; however, the nature of such dark matter is unknown and it was never detected. There are other ongoing investigations of the phenomenon, such as MOND and emergent gravity. In this work we present new results from another approach, in which general relativity is employed to approximate a galaxy by an axially-symmetric, pressure-less fluid in stationary rotation, yielding an expression for its rotation curve and mass density. We apply this model to data of four galaxies: NGC 2403, NGC 2903, NGC 5055 and the Milky Way. We obtain mass density contours of these galaxies which we compare to observational data, a procedure that could open a new window for investigating galactic structure. In our Solar neighborhood, we found a mass density and density fall-off fitting observational data satisfactorily, addressing a critique to the model by Fuchs and Phleps. Using a threshold density apparently related to the observed optical zone of a galaxy, the model had already indicated that the Milky Way could be larger than had been believed to be the case. To our knowledge, this was the only such existing theoretical indication ever presented. Recent observational results by Xu et al. have confirmed that theoretical prediction, which we fortify here using a large set of observational data. Galactic masses are seen to be higher than the baryonic mass determined from observations but lower than those deduced from the approaches relying upon dark matter in a Newtonian context. We also calculate the non-luminous fraction of matter for our sample of galaxies and present possible general relativistic explanations for this. The evidence points to general relativity playing a significant role in the explanation of the phenomenon.

    F. I. Cooperstock. (2016) The power of weak-field GR gravity. International Journal of Modern Physics D 25:12. Online publication date: 1-Oct-2016. [Abstract | PDF (153 KB) | PDF Plus (159 KB)]

    The power of weak-field GR gravity

    Received: 7 June 2016
    Accepted: 5 September 2016
    Published: 6 October 2016

    While general relativity (GR) is our premier theory of gravity, galactic dynamics from the outset has been studied with Newtonian gravity (NG), guided by the long-held belief in the idea of the “Newtonian-limit” of GR. This maintains that when the gravitational field is weak and the velocities are nonrelativistic, NG is the appropriate theory, apart from small corrections at best (such as in GPS tracking). However, there are simple examples of phenomena where there is no NG counterpart. We present a particularly simple new example of the stark difference that NG and weak-field GR exhibit for a modified van Stockum source, which speaks to the flat galactic rotation curve problem. We note that the linear GR compatibility equation in the literature is incomplete. Its completion is vital for our case, leading to a stark contrast between GR and NG for totally flat van Stockum rotation curves.

    F. I. Cooperstock. (2016) Weak-field general relativistic dynamics and the Newtonian limit. Modern Physics Letters A 31:05. Online publication date: 20-Feb-2016. [Abstract | PDF (293 KB) | PDF Plus (305 KB)]

    Weak-field general relativistic dynamics and the Newtonian limit
    F. I. Cooperstock1 orcid.png
    1Department of Physics and Astronomy, University of Victoria, P. O. Box 3055, Victoria, B.C. V8W 3P6, Canada

    Dedicated to the memory of W. B. Bonnor

    Received: 27 August 2015
    Revised: 16 November 2015
    Accepted: 17 December 2015
    Published: 25 January 2016

    We show that the generally held view that the gravity of weak-field nonrelativistic-velocity sources being invariably almost equivalent to Newtonian gravity (NG) (the “Newtonian limit” approach) is in some instances misleading and in other cases incorrect. A particularly transparent example is provided by comparing the Newtonian and general relativistic analyses of a simple variant of van Stockum’s infinite rotating dust cylinder. We show that some very recent criticisms of our work that had been motivated by the Newtonian limit approach were incorrect and note that no specific errors in our work were found in the critique. In the process, we underline some problems that arise from inappropriate coordinate transformations. As further support for our methodology, we note that our weak-field general relativistic treatment of a model galaxy was vindicated recently by the observations of Xu et al. regarding our prediction that the Milky Way was 19–21 kpc in radius as opposed to the commonly held view that the radius was 15 kpc.
    Last edited: Oct 23, 2017
  23. Oct 23, 2017 #22


    User Avatar
    Gold Member

    You are mistaken. The dark matter hypothesis is not consistent with the experimental data. See the citations at post #20 in this thread.

    While the dark matter hypothesis does a decent job of explaining the cosmological evolution of the overall universe as demonstrated in CMB data, for example, it does a poor job of explaining phenomena at the galactic cluster and cluster level, there has been no direct detection of it, it has not been observed at the LHC, every hint of dark matter annihilation has subsequently been ruled out, and there is no dark matter theory that can explain why inferred dark matter quantities and distributions are so intimately and exactly correlated with baryonic matter distributions. Simulations of how dark matter should behave contradict what is observed unless models are highly tuned (with sixteen parameters!) to the data sets that it is supposed to be predicting.

    Also, the best extant modified gravity theories perform as well as better as the best extant dark matter theories.
    Last edited: Oct 24, 2017
  24. Oct 23, 2017 #23


    User Avatar
    Gold Member

    Another series of articles (the first two published, the latter just released as a pre-print last month) which like Cooperstock argue that one can fit a basically GR analysis to reproduce the data as opposed to the Newtonian one commonly used in practice, but from a quantum gravity rather than a classical GR perspective is as follows:

    * A. Deur, "A possible explanation for dark matter and dark energy consistent with the Standard Model of particle physics and General Relativity" (September 7, 2017). Abstract:

    * A. Deur, "Self-interacting scalar fields in their strong regime" (November 17, 2016). Abstract:

    * Alexandre Deur, "A correlation between the amount of dark matter in elliptical galaxies and their shape" (July 28, 2014). Abstract:

    At the back of napkin level, at least, this approach solves all dark matter and dark energy problems, although I would be the first to acknowledge that these promising theories need more rigorous and thorough investigation by other authors with more data.
    Last edited: Oct 24, 2017
  25. Oct 24, 2017 #24
    I'm not exactly sure what your point is but I agree that publication is a measure of quality but not necessarily that the reverse is true. What is true is a lot of registered but not published papers will be of less merit. However, rather than get involved in a hypothetical discourse I would be more interested in a response to my other comment in post 17 which I did reference.
  26. Oct 24, 2017 #25


    User Avatar
    Science Advisor
    Gold Member

    No you can't. It is observable via gravity, specifically lensing. It is easy to imagine a scenario (that hasn't happened) whereby placement needed to explain dynamics is contradicted by lensing observations. Then you would be pretty much forced to look at modified gravity of some sort.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted