“For the moment we might very well can them DUNNOS (for Dark Unknown Nonreflective Nondetectable Objects Somewhere).” -Bill Bryson

The Sun makes up 99.8% the mass of our Solar System, yet stars account for only about 10-20% of the matter that protons, neutrons and electrons make up. Protons, neutrons and electrons — along with all the other particles known to exist, represented by the Standard Model and what it builds — make up only about 15% of the observed matter. The remainder must be something different that doesn’t interact with electromagnetism or light: dark matter.

Image credit: Stefania.deluca of Wikimedia Commons.

Image credit: Stefania.deluca of Wikimedia Commons.

That’s the conventional picture. But must that be the case? Is it possible, as an alternative, that we’ve simply got an incomplete theory of gravity, and that there’s no such thing as dark matter after all? While there’s one piece of evidence that supports that possibility, there are a great many other lines of evidence that completely discount it, leaving dark matter as the only viable alternative thus far.

A massive, distant galaxy cluster as imaged by Hubble, showcasing a number of phenomena supported by dark matter. Image credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Blakeslee (NRC Herzberg Astrophysics Program, Dominion Astrophysical Observatory), and H. Ford (JHU).

A massive, distant galaxy cluster as imaged by Hubble, showcasing a number of phenomena supported by dark matter. Image credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Blakeslee (NRC Herzberg Astrophysics Program, Dominion Astrophysical Observatory), and H. Ford (JHU).

Come get the whole story over on Forbes!

Comments

  1. #1 Denier
    United States
    March 24, 2016

    Does there need to be a common solution? Is it possible that as in the case with the problems of Uranus and Mercury that both solutions are correct, each in their own place?

  2. #2 Michael Kelsey
    SLAC National Accelerator Laboratory
    March 24, 2016

    @Denier #1: The problem is a bit more complex than that. CDM is part of a theory about the large scale structure of the universe. Starting from the assumption of conventional gravity, we can use the observed gravitational effects of CDM (what we “presume” to be CDM) to directly calculate the missing mass density. That calculated density can then be turned around and used to predict effects on different length scales, such as the solar system. If you work through the relatively straightforward math, you discover that local effects are unobservably small. So we can’t directly confirm CDM on sub-galactic scales, but observing larger visible effects (which we don’t) would be a fairly convincing refutation.

    Conversely, MOND alone does fit galaxy rotation curves better than CDM by itself, but because it is meant to be a generic theory of gravity, it can also (and *MUST* also) be applied to all other gravitating systems, including galaxy clusters, lensing systems, the solar system, and so on. It fails on two different counts: first, at solar-system or subgalactic scales, MOND makes predictions which are at variance with the observed behaviour of both planetary objects and spacecraft. On larger scales, MOND predictions are at variance with observed cluster motions and with gravitational lensing, unless additional (dark!) matter is included.

    So the problem isn’t just “different domains” (which is a not unreasonable hypothesis to make). It’s that MOND in particular is cast as a general theory of gravity, and its predictions fail outside of the specific domain for which it was tuned.

  3. #3 Denier
    United States
    March 24, 2016

    @Michael Kelsey #2

    Thank you for the clarification. I have no problem with the influence of CDM in all the places that it fits, but have issues with the core/cusp problem, and the required perfect distribution throughout the universe to make sure each galaxy has the perfect amount to make the rotations look like they are MOND effected. It is like tripping with a Jenga box and having all the pieces fly through the air only to land in the configuration of a perfect tower. It is technically possible, but it is so implausible that even if you witnessed it you’d have a hard time believing it. It would be fun to find out that CDM didn’t fit the galactic rotation issue because the effect was due to two phenomena instead of one.

  4. #4 s.a.top
    nl
    March 24, 2016

    Yes, current common “scientific” understanding of gravity is indeed very limited to say the least, and possibly wrong to in some respects.

    That’s why stupid projects like ligo get funded.

  5. #5 Michael Kelsey
    SLAC National Accelerator Laboratory
    March 24, 2016

    @Denier #3: I think you’ve got cause and effect reversed 🙂 Our current understanding (LCDM supported by large scale, high-resolution simulations), is that the dark matter is what forms structure in the first place, and the visible galaxies effectively “condense” within the nodules of dark matter.

    Under those conditions, it should be fairly obvious that different galaxies will have different rotation curves depending upon the local DM environment (size and density) in which they formed. This is an effect predicted by the simulations (and *NOT* an effect put into them by hand).

    The observational difficulty, and a likely source of your interpretation, is that we don’t actually get to _see_ the DM structure directly. All we’ve got are the visible galaxies and clusters, and we have to infer the DM distribution from what we can see. That makes the model look much more like ad hoc tuning than natural variation of an underlying pattern.

  6. #6 Patrick Sweetman
    New Zealand
    March 24, 2016

    This seems very very familiar. Is it a reprint?

  7. #7 Michael Hutson
    United States
    March 31, 2016

    If CDM was perfectly homogeneous in distribution throughout the observable universe, it would be indistinguishable from the gravitational constant having a different value than it does. So it must clump at least some; how do we get the degree of clumping consistent with observations?

  8. #8 Stephen Stillwell
    Fresno, TX
    April 1, 2016

    What if our observed universe is the space between protons/neutrons?

    Would the energy produced by gravity and the repulsive force be sufficient to spontaneously convert to matter, that is pulled by gravity toward the nearest super mass, accelerates to, or beyond light speed, reconverts to energy and passes through the super mass as a wave to a quantum distance, where it slows and reconverts to matter?

    …possibly at that quantum distance and the point of origin simultaneously?

  9. #9 Michael Kelsey
    SLAC National Accelerator Laboratory
    April 1, 2016

    @Michael Hutson #7: Because gravity is strictly attractive, any variation in density will eventually lead to clumping. Ethan has written multiple posts on the origin of large-scale structure by this process, and our observational evidence for it in the CMB and galaxy distributions.

  10. #10 wow
    April 2, 2016

    “What if our observed universe is the space between protons/neutrons?”

    Well, given our universe consists of many protons and neutrons, this would be impossible. Just like you can’t walk about in a universe that you’re carrying around in a pocket.

    So the “what if” does not apply. Ever.

    Even if it did, why would your claim follow on from it? Might as well proclaim that chocolate milkshake will therefore be the main constituent of all incandescent stars.

    • #11 Stephen
      April 2, 2016

      My use of proton/neutron in this context is a matter of scale.

      When black holes get big enough, they may well act like protons, attracting all mass, and repelling other similarly charged black holes.

      If three of these objects were large enough to contain our universe between them, the gravity would be sufficient to pull everything out of the interstitial space, and the confluence of gravity and the repulsive force could concentrate enough energy to spontaneously convert to matter.

      I’m obviously not familiar enough to do the requisite calculations, but unless you are, and can demonstrate that, please refrain from dickishness, thanks though, for your attention.

      And if so, the actions of other particles may be explained by the fact that they are parts of stable sized particles.

  11. #12 Kasim Muflahi
    United Kingdom
    April 2, 2016

    People assume that GR is correct all the time. Take for example time dilation: the proof given is the survival of short-lived muons to sea level from the upper atmosphere where they’re produced. The GR implies that time for the muons slows down because they’re travelling at close to the speed of light so they survive to sea level.

    My contention is that muons also gain relativistic mass so the have more mass to lose and that’s why they survive to sea level.

    GPS satellite clocks run faster in regions of low gravity – gravitational time delay – the clocks at sea level. I’d agree that it’s the clocks that run faster because of the low gravity. But Einstein claims that it’s time that progresses more quickly for the satellites. If that’s true then they should move into the future and we wouldn’t be able to see them.

    That means GR is wrong; so why are we being asked to replicate GR’s alleged successes?

    I also believe that the Higgs field and Boson are false which means that scientists have given experimental evidence for something that doesn’t exist. The Higgs mechanism was based on “what if the fundamental particles are massless?” I mean what if they’re not?

    How can massless energy give rise to mass? It seems that a lot of things proposed by Einstein are wrong?

  12. #13 Michael Kelsey
    SLAC National Accelerator Laboratory
    April 2, 2016

    @Kasim Muflahi #12: Your personal incredulity is not a falsification of GR; it is rather a fallacious argument. Each of your points is individually fairly straightforward to demonstrate as being wrong, but basically, “I believe” simply isn’t a scientific argument. If you have actual evidence, published in the peer-reviewed literature, please feel free to cite ti.

    • #14 Kasim Muflahi
      United Kingdom
      April 5, 2016

      @Michael Kelsey#13: aw you got me. I’m neither a scientist nor a mathematician. I don’t need factual evidence as I’m not proposing a theory – I’m simply using Einstein’s relativistic mass gain to prove that time dilation doesn’t happen as the muons gain mass so that they last longer as there’s more mass to decay. At least muon decay cannot be used to prove time dilation.

      On the gravitational time dilation front, GPS satellites should move into the future as time passes more quickly for them and this is according to GR by Einstein himself – I don’t need any proof. Einstein and other scientists talk about time travel without proof and you’re asking me a non-scientist for factual evidence of a theory I’m not proposing.

      Interstellar is wrong; Matthew McConnaughy wouldn’t age at all. When he came to earth, he and his daughter should’ve been a year older. I haven’t got any factual evidence for this but then neither do established scientists; they just give us flawed data as evidence.

      You claim that you can demonstrate that all my points are wrong without giving a point by point demonstration. Please demonstrate my points as being wrong.

  13. #15 Stephen
    April 2, 2016

    How much mass, where, would cause the universe expansion just with it’s gravity?

  14. #16 Michael Kelsey
    SLAC National Accelerator Laboratory
    April 5, 2016

    @Kasim #14:

    (1) There is no such thing as “relativistic mass gain.” That is a popular misconception. Mass is a scalar, frame independent quantity, and is an intrinsic property of an object. The relativistic formula for energy, E = (gamma)mc^2, includes the kinematic factor (gamma) for the motion of the object in the observer’s frame, and the intrinsic mass “m” of the object.

    (2) “Decay takes longer because there’s more mass to decay.” A stunningly transparent demonstration of utter and complete ignorance. Particle lifetimes depend on the interactions involved in the decay (so that weak interaction decays, like radioactive beta decay, are much slower than comparable electromagnetic/radiative decays, which in turn are much slower than strong/nuclear decays), and depend inversely on the available phase space for the final state(s). The more mass available to decay, the more phase space available to final states, and therefore the _shorter_ the lifetime.

    Gravitation time dilation has nothing whatever to do with time travel. Just like time dilation in special relativity, it tells you about how clocks tick in two different reference frames. If a remote clock ticks faster, then the number of ticks you count coming from that clock will be more than the same number of ticks from your local clock. That doesn’t mean the remote clock is “travelling to the future.” It means the remote clock is ticking faster.

    The fact that you draw an incorrect conclusion starting from incorrect premises merely demonstrates that your premises are wrong.

  15. #17 Wow
    April 6, 2016

    Moreover, to a rough explanation, decays depend on the difference between masses in the rest frame of the decay of the orignator and the constituents of decay.

    Inversely.

    So a massive particle like the Pion decays quickly because the weight of the decay products are much lower than the mass of the particle.

    So not the masses, but the DIFFERENCES in them.

    Of course, the method of decay has a massive effect on the rate, but within the same mechanism, the above holds true.

  16. #18 Wow
    April 6, 2016

    “My use of proton/neutron in this context is a matter of scale.”

    Then the words you’re using are meaningless and no information is possible to impart with them.

    Learn the language, including what the words mean BEFORE writing them down, and then try again. Because your follow up is either likewise ridiculously wrong or so hopelessly malformed as to be worthless to consider.

    • #19 Stephen
      April 6, 2016

      The current view seems to accept that beyond our perceived universe there is void, when it is just as likely that beyond our perceived universe there is super mass.

      If a unified theory recognizes a fractal nature to the whole universe, then the atomic structure should be expected on a much larger scale. Further, that scale would need to be larger than the difference between atoms and galaxies, because galaxies do not act like atoms.

      If a fractal model holds, then some super massive objects vastly larger than our perceived universe exist beyond our view. Since these objects have no name, it is appropriate to use the name of their analog.

      Much effort is expended trying to conceive of a force that affects the accelerated expansion of the universe. If only we had some force that affects acceleration to consider as cause, like gravity.

  17. #20 Wow
    April 11, 2016

    “The current view seems to accept that beyond our perceived universe there is void,”

    That isn’t what the current view is, therefore the seeming is in question.

    There is nothing beyond the universe in the current theory, and the perceptible universe is liable to be many times larger than the visible (if this is what you mean by “perceived”) universe, therefore what is beyond the “perceived” universe is more of the same universe, just one that is beyond our ability to perceive.

    Given your seeming seems to be only a creation of your own ignorance, you will need to recalibrate your thoughts on the subject before proclaiming more on them.

  18. #21 Yaniv Stern
    April 28, 2016

    W against T, reference required. #conspiracyofscience

  19. #22 Stephen Stillwell
    April 28, 2016

    What source is appropriate to find the difference between void and nothing?

    Since no observed reality exists, why should we not consider the possibility that much of space beyond our view is supermassive

  20. #23 Tololo
    Chile
    November 28, 2016

    La materia oscura es el eter del siglo XXI ; realmente no existe.
    Sus propiedades gravitatorias no se muestran en el sistema Solar y si en las Galaxias ¿Como es posible’

New comments have been disabled.