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

Dark Matter, On the Ropes?

  1. May 15, 2010 #1
    What comes next if the dark matter hypothesis fails? A hypothesis that is fundamentally incorrect blocks any progress. The entire effort is trying to make a round peg fit in a square hole as opposed to looking for the correct mechanism. What theorist and modeler do is try to change the free parameters to make the model fit what is observed. If the fundamental mechanisms are correct the process has meaning and value. The purpose also of comparing simulations to observations is to kill off incorrect mechanisms.

    Computer simulations of galaxy formation with Dark Matter do not match how galaxies are observed to form and do not match the observed properties of galaxies.

    The simulations for example have half the observed angular momentum as compared to observations of spiral galaxies and the galaxies that form in simulation are significantly smaller than observed. The problem is dark matter thermalizes the motion of the gas clouds which causes them to clump earlier before forming large galaxies and reducing the angular momentum of the resultant galaxy. In addition the thermalization causes in the simulations a larger galaxy bulge than is observed.

    A third problem is how the angular momentum (rotational velocity) changes as one approaches the center of the simulated galaxy as compared to observational data. The computer simulations show dark matter should clump at the galaxy's center which should reduce the total angular momentum (rotational velocity) at the center of the galaxy. This is not observed. The spiral galaxy continues to rotate as one moves to the center of the spiral. This clumping of dark matter in the center of galaxy's also breaks up the bars in spiral galaxy in simulations, which makes it difficult to even form bar, which does not make sense as the observational data indicates spiral bars form and have a long lifetime.

    The dark matter detection experiments have not been able to detect dark matter. The point of the dark matter detection is to determine if dark matter does or does not exist.

    It is telling that there multiple very fundamental observations that dark matter cannot explain and no one has been able to detect dark matter.

    There is currently no viable alternative (MOND has at least as many problems as dark matter) to dark matter, which is curious as there is observational evidence that provides a clue as to what is causing the observational anomalies which dark matter does not in computer simulation explain.

    To use an analogy, think of the logical methodology that is used to solve crimes. When there is repeating peculiar evidence at multiple murder scenes, the investigators look for a serial criminal as they expect independent murders to have not have the same peculiar evidence.

    This next paper shows eight spiral galaxy properties are interrelate including angular momentum, non random. This is likely a clue to what is really the physical cause of the angular momentum and related anomalies, such the large scale structure anomalies, and the large scale velocity anomalies. (Velocities are higher than the would be expected based on the estimated masses.)

    As the authors of the paper note when dark matter was hypothesized there was not large survey data available to test the dark matter hypothesis.



    Last edited: May 15, 2010
  2. jcsd
  3. May 15, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    I think the main problems is that simulating galaxy formation is very hard. There's lots of complex physics involved, we don't quite know how to handle it.

    I mean, we also don't know how to simulate star formation, but that doesn't mean there's a problem with Hydrogen.
  4. May 15, 2010 #3
    Of course we know hydrogen exists and that fusion (hydrogen to helium) creates a great deal of energy. What is the connection with hydrogen and stellar fusion to dark matter and the rotational anomaly of spiral galaxies?

    What I have said in my comment is consistent with published papers.

    Based on two decades of observation (the more recent and more accurate observational data and computer analysis continues to support the earlier findings) searching for direct evidence of the "dark matter particle" and computer simulations and analysis of what is predicted, to what is observed, is not in agreement. The analysis and the observation supports the assertion that dark matter does not physically exist and if dark matter did exist it could not explain the evolution and morphology of galaxies.

    Dark matter appears based on observations and theoretical analysis, in published papers to be an incorrect mechanism.

    A failed hypothesis should be treated as a failed hypothesis. Physics has moved on from phlogiston. Physics should and will move on from "Dark Matter". The first step in that process is public criticism of the mechanism in question.
  5. May 15, 2010 #4


    User Avatar
    Science Advisor
    Homework Helper

    Please find a citation for me from a published paper on what constraints, from not directly detecting dark matter particles, can be placed. From my understanding, the constraints aren't very significant.

    Edit: My point, and I know that a lot of people agree, is that computer simulations that show that galaxy formation with dark matter doesn't work isn't evidence against dark matter, it just shows that we don't know how to simulate galaxy formation.
    Last edited: May 15, 2010
  6. May 15, 2010 #5
    Dark matter has not passed the first hurdle which is that it physically exists. Dark matter requires the creation of a particle that has the necessary properties which simulations indicate unfortunately is not possible.

    The observational tests with increasingly sophisticated experimental apparatus does not support the assertion that dark matter exists. The computer simulation results are irrelevant if the "dark matter" particle does exist.

    Primarily Zeon100 results are negative for the detection of dark matter.



    As numerous people have stated the first group to find the dark matter particle will be awarded a Nobel prize. However, if the dark matter particle does not exists how does one prove it does not exist? Will the first team that proves the dark matter particle does not exist be awarded a Nobel Prize?

    A competing team are arguing that the ZEON100 finding is not definitive. The competing team of course erroneously announced that they had found evidence of dark matter's existence which was not supported by other teams and which was not replicated.

  7. May 15, 2010 #6


    User Avatar
    Science Advisor
    Homework Helper

    "and hence exclude spin-independent WIMP-nucleon elastic scattering cross-sections above 3.4 x 10^-44 cm^2 for 55 GeV/c^2 WIMPs at 90% confidence level"

    Isn't nearly convincing enough to conclude that dark matter is a failed hypothesis, as you say.
  8. May 15, 2010 #7
    As I said, the simulations with dark matter produce galaxies with half the angular momentum of real physical galaxies and galaxies that are an order of magnitude smaller than observed galaxies.

    The authors of this paper acknowledge the problem and then propose unrealistic heating and unrealistic lack of cooling of the massive gas clouds to try to rectify the problem. What they are proposing does not agree with observations and analysis of how intergalactic gas cools. As they note in the paper that theoretical toy model assumption creates other problems which does not agree with observations.


  9. May 15, 2010 #8
    If "Dark Matter" does not exist and even if dark matter did exist it could not explain the observations, at what point does astrophysics abandon the dark matter mechanism?

    The galaxy rotational anomaly, the galaxy velocity anomaly, the spiral galaxy morophological anomalies (there are obvious unexplained patterns and processes going on) has a physical explanation. What is interesting is the physical explanation for those anomalies appears based on published papers to not be dark matter and is not MOND.


  10. May 15, 2010 #9
    The direct detection attempts to find evidence that dark matter exist have been negative.

    Even if dark matter exists, it cannot explain galaxy formation. It seems logically that dark matter does not exist based on the negative results to observe it.

    If dark matter existed galaxies would be an order of magnitude smaller and would have half the angular momentum than this universe and its galaxies. As this is not observed, it appears "dark matter" does not exist.


  11. May 16, 2010 #10


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Unfortunately, galaxy formation is extremely difficult to simulate and the failure to simulate a galaxy from first principles cannot be automatically blamed on the dark matter hypothesis. This isn't because the dark matter itself is difficult to simulate (this part is quite easy), but rather because of uncertainties in the baryonic physics. In a dark-matter dominated universe, we expect galaxies to form in a bottom-up fashion, meaning that little things merge together to form bigger things. To simulate the formation of, for example, the Milky Way, we need to simulate the gas physics, star formation, and AGN and stellar feedback of these little things as they merge together to form bigger things. This means that we need to start our simulations on very small scales and run the simulation until the little things merge together to form the present-day Milky Way (which will be hundreds or thousands of times larger than its original components). Such simulations take tremendous computational resources and even then require us to make a great many approximations.

    Direct detection experiments are a more promising avenue for examining the dark matter problem, but unfortunately, we've explored only a very small subset of the parameter space of possible dark matter particles. Even if the dark matter hypothesis is wrong, it will be difficult to rule it out as a possibility anytime in the near future. However, physicists continue to examine possible alternative theories of gravity. If one of these theories were to make a successful prediction that ran contrary to most conventional dark matter theories, I think the community would take notice. Unless that happens, astronomers will continue to work within the dark matter paradigm.

    Admittedly, dark matter is difficult to falsify, but that doesn't make it wrong. Rest assured, however, that we are working hard on this problem and you will know as soon as we have hard evidence one way or the other.
  12. May 16, 2010 #11


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I don't see that anywhere in Julio's paper. Where are you quoting from?
  13. May 16, 2010 #12


    User Avatar
    Science Advisor
    Gold Member

    It took decades to detect neutrinos after Pauli hypothesized their existence, so, it is unsurprising it is taking time to detect dark matter - a much more difficult endeavor. The evidence in favor of dark matter is overwhelming [e.g., bullet cluster] in the minds of most mainstream scientists. Disney has a history of flamboyant opposition to mainstream ideas, so I would suggest a grain of salt when reading his papers.
  14. May 16, 2010 #13


    User Avatar

    Same happens with the Tooth Fairy. Rest assured though we are working hard on it.
  15. May 16, 2010 #14


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Might I suggest putting a camera in your bedroom. :smile:
  16. May 16, 2010 #15
    Spiral galaxies show indicates of patterns which indicates they were not formed from many mergers.

    A second problem with the many mergers hypothesis is that simulations indicate multiple mergers of spiral with spiral produces an elliptical galaxy. Observationally that is not observed. The number of spiral galaxies stays roughly constant with redshift at 70%.

    It should be noted that the paradox between simulation properties and observed properties are fundamental properties of the spiral. Angular momentum and change in angular momentum as one moves towards the core of the galaxy for example.

    Saul: My error, I copied and quoted one of my own comments. That specific comment is the issue.



    Galaxies appear (my comment Non random) simpler than expected

    Last edited by a moderator: May 4, 2017
  17. May 16, 2010 #16


    User Avatar

    You got me there :smile:
  18. May 16, 2010 #17
    As noted in my above comments, the dark matter hypothesis does not explain spiral galaxy morphology or evolution. There are multiple specific significant gaps between observation and simulation. For example the simulation spiral galaxies have half the angular momentum and are smaller than physical spiral galaxies.

    The claim that there is a gap between simulation and observation due to the complexity of the of performing a many body simulation, misses the issue or more appropriate the problem situation. The observational data is pointing to a difficult physical cause.

    A different observational problem that I noted in my above comment, is mergers of spiral galaxies with spiral galaxies should produce an elliptical galaxy. The observation that the percentage of spiral galaxies does not vary with redshift and remains at 70% is interesting as it is a clue to what causing the rotational anomaly in spiral galaxies and the systematic morphology changes in spiral galaxies. A second related question is what is causing the difference between spiral and elliptical galaxies? (i.e. What is causing the two very different galaxy types to form.)

    An elliptical galaxy's stars do not all rotate about the galaxy's gravitational center in the same direction. That observational fact makes sense based on conservation of angular momentum and the random direction of merging galaxies. What one would expect, if elliptical galaxies formed from multiple mergers of gas clouds or other galaxies is the elliptical would have a small net rotation (its stars rotate in both directions and hence the angular momentum cancels) and should have multiple rotational axises which is what is observed.

    The reason that there has been no theoretical progress to explain the spiral galaxy observations is the initial proposed hypothesis "dark matter" was proposed at a time when there has not very accurate survey data showing how galaxies evolve with redshift.


  19. May 16, 2010 #18


    User Avatar

    Saul do you have any working hypothesis that might substitute the "dark matter" hypothesis for the shape of the spiral galaxies?
  20. May 16, 2010 #19
    From a theoretical standpoint, the neutrino is required from energy/mass balance. (i.e. The point is there is a clear unequivocal theoretical requirement which indicate that the "neutrino" must exist.)

    It does not follow from the fact there is a clear theoretical requirement that neutrinos exist and that the neutrino was found that there is a theoretical requirement for "dark matter" and that the "dark matter" exists.

    Science is the proof and disproof of hypotheses. For example science move beyond phlogiston.


    There are degrees of certainty concerning different hypotheses.

    The fact that no one has been able to detect dark matter using the most sophisticated detection apparatus and that there are multiple fundamental observations which the dark matter hypothesis cannot explain, justify the criticism of the theory.

    Dark matter has specific predicted theoretical affects on rotational speeds, galaxy formation, and galaxy morphology.

    As noted above those specific dark matter theoretical predictions have been shown to not be correct. In the normal process of science we would agree the theory has been falsified and the field is in a crisis. (i.e. There are multiple fundamental observations that have no explanation and the observations in question appear to be connected.)

    In other fields of science the participants would not propose changing the laws of physics or to create a new particle to explain observations.
  21. May 16, 2010 #20

    Jonathan Scott

    User Avatar
    Gold Member

    As I see it, the evidence for Dark Matter consists entirely of the fact that matter on scales larger than the solar system gravitates more strongly than predicted by GR, which means that if we accept GR any extra gravitation must therefore be caused by invisible matter. The evidence is therefore equivalent to the evidence that GR is correct in this regime.

    That evidence in turn consists mainly of the fact that GR is a neat and self-consistent theory and that it passes solar system experimental tests accurately, where many proposed alternatives, often more complex, have failed to do so.

    However, I personally don't think GR is completely right, both on theoretical and experimental grounds. I think it's probably a very accurate local weak-field approximation to a different theory which gives very different results on a larger scale. I'm looking forward to seeing more experimental results to help give clues as to the nature of that theory. Unfortunately, these forums are not the place to speculate about such things.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Dark Matter, On the Ropes?
  1. Dark matter? (Replies: 2)

  2. Dark Matter (Replies: 2)

  3. On Dark Matter (Replies: 5)

  4. Dark matter (Replies: 2)

  5. Dark matter (Replies: 28)