It is crucial to pay close attention to new data, and observational astrophysicist Prof Stacy McGaugh has a habit, like John Anderson, of writing nicely concise analyses of new data that are easy to test against. McGaugh, Lelli and Schombert have just published a paper comparing the data from 153 different galaxies across a large range of scales from dwarfs to large disc galaxies, looking at two things 1) the acceleration within them as predicted using standard dynamics from their baryonic (visible) mass only (g_bar, x axis in the Figure), and the actual acceleration as determined from the observed motion of their stars (g_obs, y axis). The result is shown on a log-log plot here (from McGaugh and Lelli, 2016):
If Newton or Einstein's general relativity were right (without the crutch of dark matter) then you would expect the data to lie along the faint straight diagonal line, so that the predicted acceleration would equal that observed. It does not. As you can see the data lifts from the straight line on the left hand side because for lower accelerations the stars' orbital speed, and therefore acceleration, is greater than expected. This is the famous galaxy rotation problem noticed by Zwicky (1933) and Rubin & Ford (1980). The majority of astrophysicists fix this by adding dark matter to the galaxies where it's needed, but that is an ad hoc solution that no-one should have to resort to in a scientific age. In the paper, McGaugh and Lelli fit a curve to this data using this formula
and show it predicts well if the fitting parameter 'gt' is set to the value 1.2x10^-10 m/s^2 and both McGaugh and Lelli, and Milgrom in a note published soon after, say this looks like some of the possible variants of MoND (Modified Newtonian dynamics). Milgrom in his note even says 'nothing else can give this behaviour' but this is simply not true. MiHsC / quantised inertia also predicts this behaviour far more plausibly and simply than MoND, and without any adjustment at all. The MiHsC formula can be found in McCulloch (2012) (see Eq. 6 in the ref below, and note the comments on a' therein. The Eq. I showed before is based on Eq. 7 and is less general). The MiHsC formula (note, only strictly valid at a galaxy's edge) is
This formula is based on a specific physical model (MiHsC: Unruh waves harmonise with horizons and cause inertia) unlike MoND which is just an empirical relation with no physical model. It is obviously much simpler than McGaugh & Lelli's formula, and crucially there are no fitting parameters in MiHsC/quantised inertia at all! Its predictions of g_obs are exactly right see Figure below and are predicted from just the known quantities of the speed of light (c) and the size of the observable universe (Theta=8.8x10^26 m):
I do feel a bit like a broken record going on about this, but it's necessary because it has not yet been widely appreciated that a theory that predicts real data without any fitting parameters, like MiHsC does, is like a diamond in the mine. Like special relativity, it is a sign of something fundamental.
(Note: MoND is a bit like the early twin patchwork formulas of Wien & Rayleigh-Jeans for blackbody radiation, whereas MiHsC/QI is like the quantum mechanics of Planck et al. which predicted it more concisely with a shocking new assumption).
(Note: MoND is a bit like the early twin patchwork formulas of Wien & Rayleigh-Jeans for blackbody radiation, whereas MiHsC/QI is like the quantum mechanics of Planck et al. which predicted it more concisely with a shocking new assumption).
References
McGaugh, S.S, F. Lelli, J. Schombert, 2016. The radial acceleration relation in rotationally supported galaxies. Phys. Rev. Lett. (to be published). Preprint.
McCulloch, M.E., 2012. Testing quantised inertia on galactic scales. Astrophysics and Space Science, 342, 342-575. Preprint
18 comments:
Can you show the curve MiHsC would suggest as an overlay to the Figure?
I've emailed McGaugh to ask for the raw galaxy data from their Fig 3, & I will then plot MiHsC with it..
Best 'don't [mess] with us' abstract I've read in ages! 'The dark matter contribution is fully specified by that of the baryons' - such a politically correct way of saying 'This hypothetical non-interacting 'dark' matter is clearly a figment' :)
It's not about political correctness, it's the most that can be concluded from the data, for now. Though I do wonder sometimes, if MOND was written in giant letters across the sky, whether some dark matter adherents would still try to compute the probability that this was just a fluke.
Getting back to actual observations, this kind of work doesn't easily allow to disprove dark matter, but it does make it look very contrived. I've done some work on the Local Group where the Milky Way and Andromeda may have interacted in the past. You could use Local Group data to make statements like galaxies can't have substantial amounts of mass in large halos around them. I explain a bit about this towards the end of this lecture I gave, summarising a lot of the evidence for MOND:
https://www.youtube.com/watch?v=PYVC0VtmpDg
I published my work in the Monthly Notices of the Royal Astronomical Society (459, 2237). Only a week later, it won the (international) Duncombe Prize of the American Astronomical Society, allowing me to present it to their members. You can see a summary of the work and links to the paper here:
https://darkmattercrisis.wordpress.com/
Much of the evidence for MOND could be read as evidence for a similar-behaving modified gravity theory. After all, MOND itself is empirical, so could do with a more fundamental understanding of why Newtonian dynamics doesn't work all the way down to zero acceleration.
It is important to think what might be definitive proof of MOND. Maybe a laboratory experiment where the inverse square law doesn't work (but it'd have to be done about a light year away to avoid the gravity of the Sun raising the total gravity above the low a_0 threshold). There might be some other tests. But rotation curves of galaxies aren't quite in that league of definiteness, even though they are very important contributions.
The way I think about it, people have been wondering how gravity works for centuries, so we only expect to make a small amount of progress each year with each publication. And MOND itself may seem like a fancy new idea to some, but is over 30 years old.
Indranil: Yes, MoND is better than dark matter and was a step forward, but the point of my blog is that MoND is an suggestive empirical relation that needs an adjustable parameter, a0. It has no reason behind it, as you yourself said. Quantised inertia (MiHsC) is a coherent model that predicts all these galaxies from just the size of the cosmos and the speed of light! No fudge needed. It explains why MoND works, and it is a fundamental theory (MiHsC: Unruh radiation is tuned by horizons). MoND is a bit like the early formulas of Wien & Rayleigh-Jeans for blackbody radiation, whereas MiHsC/Qi is like the quantum mechanics of Planck et al. which predicted it more concisely from a shocking new assumption.
The existence of dark matter filaments and dark galaxies indicates, that the presence/distribution of dark matter can be independent of INTRINSIC presence/distribution of visible matter.
a0 can be estimated as a product of Hubble constant and speed of light, therefore the MoND doesn't differ from MiHsC so much - they're both based on quantification of quantum correction of gravity with Hubble red shift, which has also origin in scattering of light with quantum fluctuations. They're fine models, but they do apply only to dark matter distributed around visible matter in symmetric way.
/* MiHsC does, is like a diamond in the mine. Like special relativity, it is a sign of something fundamental */
And it of course is, but it also indicates, that these theories aren't fundamental. What is fundamental here is the common shielding geometry of gravity field and dark matter formation.
/* MoND is better than dark matter */
Dark matter is phenomenological description for effect, which MoND/MOD/MiHsC are both trying to describe. This doesn't imply, that the dark matter is or is not actually a matter in common sense (what is the "matter", anyway? Space-time curvature gradients, no matter how subtle they are? After then dark matter fits the matter definition without problem). None of these theories actually explains it.
Zephir: Your comments on filaments are interesting, I have not got around to looking at them yet, but MiHsC predicts dark galaxies well (it works well on Dragonfly 44 for example). I appreciate MoND as being an empirical clue, but it never had an underlying reason, so it was sterile and was not unable to be applied elsewhere. MiHsC/QI has an underlying reason (inertia's caused by Unruh waves resonating with information horizons) and with this understanding it is possible to apply MiHsC to galaxies, the cosmos, flybys, emdrives, atoms and an infinity of other experiments.
http://www.nature.com/nature/journal/v537/n7622_supp/full/537S194a.html
What do you think? :-)
Jacob: I'm very confident in MiHsC/quantised inertia now, since I can predict disc galaxies exactly with no 'tuning' at all, and many other phenomena. Dark matter, as a solution to large scale dynamics, is dead, but the detectors they have built will probably be useful for some other purpose.
Mike - I noticed that Brian Koberlein, over at the One Universe At A Time blog, had posted about the McGaugh et. al. paper as well. ( briankoberlein.com/2016/09/29/galactic-motion-challenges-dark-matter/ ) I left a comment including a link to your post here. Hopefully this will get some discussion going.
Thanks for all your efforts!
Andrew: Back in April I read one of Brian Koberlein's blogs discussing my paper on MiHsC/QI and emdrive, and it stood out by being objective and balanced. I hope he replies.
https://www.theguardian.com/science/life-and-physics/2016/oct/02/dark-matter-did-we-just-hear-the-most-exciting-phrase-in-science?CMP=twt_a-science_b-gdnscience
The Guardian relaying McGaugh paper.
If any of you has a guardian account... worth a comment about MiHsC imo.
Hi Mike,
Might be the beginning of the "maybe we're missing something key here..." moment in galactic physics, causing re-examination of your idea.
I hope so. There's a good chance they'll pay attention to MiHsC/QI now, because it is very difficult to ignore something that predicts the data with such simplicity.
Congrats on a great fit before-the-fact, seems like very strong confirmation.
Thank you. Now writing a paper on it..
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