Do We Really Need Dark Matter?

Hubble mosaic of massive galaxy cluster MACS J0717.5+3745, thought to be connected by a filament of dark matter. Credit: NASA, ESA, Harald Ebeling (University of Hawaii at Manoa) & Jean-Paul Kneib (LAM)

Even though teams of scientists around the world are at this very moment hot on the trail of dark matter — the “other stuff” that the Universe is made of and supposedly accounts for nearly 80% of the mass that we can’t directly observe (yet) —  and trying to quantify exactly how so-called “dark energy” drives its ever-accelerating expansion, perhaps one answer to these ongoing mysteries is maybe they don’t exist at all.

This is precisely what one astronomer is suggesting in a recent paper, submitted Dec. 3 to Astrophysical Journal Letters.

In a paper titled “An expanding universe without dark matter and dark energy” (arXiv:1212.1110) Pierre Magain, a professor at Belgium’s Institut d’Astrophysique et de Géophysique, proposes that the expansion of the Universe could be explained without the need for enigmatic material and energy that, to date, has yet to be directly measured.

In addition, Magain’s proposal puts a higher age to the Universe than what’s currently accepted. With a model that shows a slower expansion rate during the early Universe than today, Magain’s calculations estimate its age to be closer to 15.4 – 16.5 billion years old, adding a couple billion more candles to the cosmic birthday cake.

The benefit to a slightly older Universe, Magain posits, is that it’s not so uncannily close to the apparent age of the most distant galaxies recently found — such as MACS0647-JD, which is 13.3 billion light-years away and thus (based on current estimates, see graphic at right) must have formed when the Universe was a mere 420 million years old.

Read more: Now Even Further: Ancient Galaxy is Latest Candidate for Most Distant

Using accepted physics of how time behaves based on Einstein’s theory of general relativity — namely, how the passage of time is relative to the position and velocity of the viewer (as well as the intensity of the gravitational field the viewer is within) — Magain’s model allows for an observer located within the Universe to potentially be experiencing a different rate of time than a hypothetical viewer located outside the Universe. Not to be so metaphysical as to presume that there are external observers of our Universe but merely to say that an external point would be a fixed one against which one could benchmark a varying passage of time inside the Universe, Magain calls this universal relativity.

A viewer experiencing universal relativity would, Magain claims, always measure the curvature of the Universe to be equal to zero. This is what’s currently observed, a “flatness problem” that Magain insinuates is strangely coincidental.

By attributing an expanding Universe to dark energy and the high velocities of stars along the edges of galaxies (as well as the motions of galaxy clusters themselves) to dark matter, we may be introducing ad hoc elements to the Universe, says Magain. Instead, he proposes his “more economical” model — which uses universal relativity — explains these apparently accelerating, increasingly expanding behaviors… and gives a bigger margin of time between the Big Bang and the formation of the first galactic structures.

Read more: First Images in a New Hunt for Dark Energy

There’s quite a bit of math involved, and since I never claimed to understand physics equations you can check out the original paper here.

While intriguing, the bottom line is that dark energy and dark matter have still managed to elude science, existing just outside the borders of what can be observed (although the gravitational lensing effects of what’s thought to be dark matter filaments have been observed by Hubble) and Magain’s paper is merely putting another idea onto the table — one that, while he recognizes needs further testing and relies upon very specific singular parameters, doesn’t depend upon invisible, unobservable and mysteriously dark “stuff”. Whether it belongs on the table or not will be up to other astrophysicists to decide.

Prof. Magain’s research was supported by ESA and the Belgian Science Policy Office.

At right: Artist’s impression of dark matter (h/t to Steve Nerlich)

Note: this is “just” a submitted paper and has not been selected for publication yet. Any hypotheses proposed are those of the author and are not endorsed by this site. (Personally I like dark matter. It’s fascinating stuff… even if we can’t see it. Want an astrophysicist’s viewpoint on the existence of dark matter? Check out Ethan Siegel’s blog response here.)

35 Replies to “Do We Really Need Dark Matter?”

  1. I’m on the fence on dark matter. Oh, I’m not saying it’s flim-flam – it could very well exist. There’s been some great stuff on the subject. However there’s still the chance of other reasons for the mass discrepancy.

    Fact is we just don’t know what effect the outside of the universe has on us if any, and the added effects of all the tiny events on the whole. All of the frenzied calculating the mass of the universe is based merely on what we know right now – and that’s fine, it’s science – but I think we know less of the larger universe than we think we do. I think what we’re seeing now with dark matter is like how people were trying to figure out how the sun could keep burning before we understood atoms – learned scientists pointed out that a mass couldn’t “burn” (like fire) so long – until fusion was figured out. When it comes to the universe we know a lot of stuff, but we’re probably still “trying to figure out how it burns”.

    1. There is _always_ a risk of other reasons. But as soon as they are pushed below the mutually agreed quality threshold, and there is no competing theory, considering such risks is beyond reasonable doubt.

      It isn’t very social to be unreasonable in any group. For one, people stops listening.

      1. “We already know the laws underlying everyday physics completely..” and we still don’t know how life came into existence.

  2. I’d love anyone who knows about relativity to look at this paper. Is it an interesting insight or completely bogus? From the little I know of special relativity, I wonder about the sentence “According to Einstein’s special relativity, an observer moving at high velocity with respect to an external observer will measure time flowing at a slower pace than the outside observer.”. Doesn’t each observer measure time flowing more slowly in the other’s frame of reference?

    Also, the paper says “The higher than expected velocities of stars in the outskirts of spiral galaxies gave rise to the hypothesis that these galaxies are embedded in dark matter halos … Even more dramatically, the velocities of individual galaxies in galaxy clusters led to postulate that, for these clusters to remain bound, an even larger fraction of their mass must be dark”, but the prediction he later gives is only for “To test this, we have simulated simple galaxy clusters dynamics. Galaxies are approximated by point masses”. So he raises the question of velocities of stars in a single galaxy, but then ignores it.

    So I’m leaning towards bogosity, but I’d love to know for sure.

    1. “According to Einstein’s special relativity, an observer moving at high velocity with respect to an external observer will measure time flowing at a slower pace than the outside observer.”

      Thanks. I think your find shows exactly what I just wrote above, to look further is a meaningless waste of time. As you surmise, that isn’t doable in relativity, it enforces a symmetry here and that is its basic rationale to boot (besides that this simplification works).

  3. News flash from the near future? “The James Webb Space Telescope pinpoints the furthest galaxy seen to date at some 20 billion light years!”

    Now wouldn’t THAT burn your toast? LOL! Back to the calcs!

  4. I’d love to hear what Torjborn and lcrowell think of the linked paper? I’ve always thought that the FTL early inflation period didn’t sound quite right. I assume the greater age for the universe eliminates the need for this? It would also explain the mass of the most distant galaxies that shouldn’t have been as large or developed as what we have observed.

    1. Done, at least for my part.

      Inflation doesn’t go ftl, that is a misconception.

      Inflation is a mechanism for local spacetime expansion, an expansion that we see today from other mechanisms. Local expansion can add up over cosmological distances to seem ftl. Locally nothing goes ftl.

      If seeming to go ftl was a problem, apparent superluminal motion would be a deal breaker for astronomical jets.

      1. Thank you! I was tired when I wrote that, I should have pointed out that it doesn’t matter [sic!?] for spacetime anyway.

        But even so, the ftl claim is probably erroneous from the beginning. Usually it is the observable horizon that is the ftl limit. Of course inflation moved spacetime volumes outside the horizon, but we are talking local effects.

        I’ll admit I haven’t studied general relativity (though I have some differential geometry so I could probably try it), so I can’t really tell. I’m not sure how to formulate the problem so we can look at it locally, except in terms of the horizon. And having horizon at all times seems to say that there is a local volume which is observable (not ftl).

        Hence the “what I know”, I have never seen it explicitly spelled out. It is a question to ask lcrowell perhaps.

      2. I understand what you are saying. No point actually goes FTL, even if two points can wind up separated by a distance which would sugguest superluminal velocities.

        It still doesn’t sit right why would everything expand at or above the speed of light, slow down drastically, then speed up again only at a much reduced yet increasing rate? It just makes no sense! It’s like firing a bullet that comes out of a gun @ 1900 fps, slows to 800 fps (with out hitting anything) then resumes acceleration gaining at +50 fps thereafter.

  5. afaik dark matter and dark energy are the X and Y in a formula according to observed data.

    So any math that can’t handle X and Y already is flawed. Wether X and Y is a compounded statement of known “stuff” or not.

    Just like G is just as much an unknown variable which happens to be a constant by observation. Although no doubt its a scalar vectored radial volume strength

  6. There is something odd about this paper . The metric for the FLRW spacetime for a cosmology is

    ds^2 = dt^2 – a(t)^2[dr^2 – r^2d?^2].

    The term a(t) is the scale factor for the universe. The time variable t is a coordinate variable, which is set to the Hubble frame of comoving coordinates. The proper time is on the left, the variable s with ds an infinitesimal element. It is not hard to see that ?s/?t = 1. So I am not sure what Magain means by proper time here, but this is not the standard definition of proper time. This appears to be some additional definition of time. For this reason this paper is on my “suspect list” for the moment. I might have to ponder this a bit further to see if there is some reasoning behind this.


  7. Betteridge’s law of headlines strikes again!

    But in all seriousness, these kind of theories was what the WMAP team to great care to exclude. Yes, there is always a maybe at the 3-4 sigma standard cosmology is tested against, some parts of a percent risk perhaps. But a theoretical paper is not the extraordinary evidence needed to test an extraordinary claim.

    And of course you can’t reinterpret general relativity to mean what Magain suggest it means. That’s pure arxiv crackpottery.

  8. If this guys is right, which is probably a long shot, we have to find another explanation for the gravitational lensing effect of dark matter.

  9. This paper doesn’t seem to offer any explanation for stellar velocities or gravitational lensing. While the author seems to be making a case that his theory is more parsimonp It explains less than dark matter does, thus requiring a significant increase

  10. The author of this paper seems to be making a case that his theory is the more parsimonious in that it does not require DM.  But his theory fails to explain the velocities of stars within galaxies or the gravitational lensing we have observed being caused by unseen matter, so he’s really done nothing to reduce the number of new assumptions required to explain our observations.  If anything, he’s multiplied them, since eliminating DM will require two separate additional explanations for these two phenomena.

  11. Seems very unlikely. but I would prefer it especially to dark energy. Yet facts seem to be against this – the indirect observation of dark matter through it’s gravitational effect, the hints of dark matter particle decay from PAMELA and Fermi – so the less attractive dark matter plus dark energy seem to be on a firm ground.

  12. From my perspective – looking at both the micro and macro worlds human being are endowed with 5 basic PROVEN senses that enable physical observation and thereby discovery. All other observations require other external support to validate suppositions by implications or assumed certification established by observed repeatable unique events.

    Despite centuries of ever increasing complex external physical scaffolding we still rely on the same 5 basic biological senses for all sensory input into our minds, which in turn constructs all that we know and ultimately determine to be the reality of life.

    In fact another complete universe of unknown forces and events could be unfolding just beyond the crook of our elbows, and without the experience of suitable sensory detection far more differentiated than our standard 5 senses such a new reality could not exist even in our imagination.

    1. Funny, people cannot see x-rays, so the tumor that are on these x-ray images don’t exist because the human senses cannot detect x-rays?

      That GPS satellite does not exist because people cannot see the GPS satellite?

      The radio station does not exist because humans cannot detect radio waves?

      1. Obviously you missed my second sentence above, so I will repeat here for your clarification. Please read it carefully.

        “All other observations require other external support to validate suppositions by implications or assumed certification established by observed repeatable unique events.”

      2. Then please specify what you indented to state?
        Your eyes are just measuring instruments just like all other measuring methods. They are not SPECIAL and can be completely faulty and unreliable.

  13. Is dark matter as it’s name implies simply rock, ice, and gasses that don’t emit energy in the cosmos? That is hardly exotic. Why do scientists insist on finding somthing new out there when our own solar system contains probably 99.9% of all the different elements. We are a part of the same universe that we are looking at. As for the expansion of the universe, does anyone calculate the momentum of the mass in this expansion (from the singularity); I assume that is the reason there is expansion.

    1. You appear to mix a lot of different topics in this one post.

      The scientists know that there is dark matter because they see the gravitational effects on it. Dark matter is actually a general name, for something that we can not see except through gravitational interaction.

      Why do we explore the rest of the universe while we have still much to do left in our own solar system? Why not? It is not that we have only one scientist that has to do everything. We have thousands of scientists, why would we limit them to only look at the solar system? An in addition, exploring the universe also gives us other knowledge that can be used at the quantum scale en therefore you might even use it in your electronics or cancer treatment.

      I am pretty sure that momentum is one of the first things that scientists did take into account.

    2. Scientists aren’t “insisting on finding something new out there”; they’re drawing conclusions from their observations — namely that there is a significant quantity of matter in the Universe that we just can’t see. While some of this unseen matter is surely standard baryonic matter made of the same protons, neutrons an electrons that we are, scientists have calculated that solid matter such as rock and ice cannot account for more than a few percent of the unseen matter. Perhaps more importantly, we have observed that the dark matter in colliding galaxies does not behave as a gas would: it does not interact electromagnetically. Scientists have therefore concluded that most “dark matter” must be in the form of collisionless or near-collisionless particles. The first, most obvious candidate, was the neutrino; but we just don’t observe enough neutrinos to account for much of the missing dark matter. There must be something else out there.

  14. “Do we really need dark matter?”

    The case isn’t do we need it or not. It is if its existence can be fully traced. it will significantly help us to recognize the cosmos or the Universe. Even we can prove whether current most trusting theory true or not.

  15. Hah – thanks Jason. That joke never gets old.

    Not sure about this idea though. The language used with respect to benchmarks and proper time imply the existence of a priviledged and absolute frame of reference that is then affected/changed over time by universal expansion.
    This conflicts with a fundamental assumption of relativity – i.e. that there is no absolute frame of reference, motion can only be described relatively to specified frames of reference – none of which can be considered as ‘absolute’.
    It is good that the authors raise the flatness problem as an issue. It is well worth thinking more about this. How is it that the universe still remains geometrically flat despite undergoing ongoing accelerating expansion?

  16. I have hypothesized many times on the myth of. or the lack of, dark matter. My layman’s theory of this unexplained “mass” is that it isn’t mass at all .. but energy– energy waives from all directions, some more intense than others, that (relatively) creeps upon us –and throughout the entire universe(s), delivering dwindling shock waves of energy, being absorbed by what little mass there is (including planets to micro particles) floating in the vastness of space.
    Where do these shock waves come from? They come from everywhere, and from all times tables, created by the constant re-beginnings of new constellations, from time ever backwards.

  17. Dark matter plays extremely significant role in “Cloud & rain model” of Universe structure.

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