New Paper on 'MOND' Argues That Gravity Changes At Very Low Accelerations (phys.org) 81
porkchop_d_clown (Slashdot reader #39,923) writes:
MOND — MOdified Newtonian Dynamics is a hypothesis that Newton's law of gravity is incorrect under some conditions. Now a paper claims that a study does indeed show that pairs of widely separated binary stars do show a deviation from Newton's Second Law, arguing that, at very low levels, gravity is stronger than the law predicts.
Phys.org writes that the study "reinforces the evidence for modified gravity that was previously reported in 2023 from an analysis of the orbital motions of gravitationally bound, widely separated (or long-period) binary stars, known as wide binaries."
But RockDoctor (Slashdot reader #15,477) calls the hypothesis "very much disputed." YouTubing-astrophysicist Dr Becky considered this report a couple of months ago (2023-Nov-09), under the title "HUGE blow for alternate theory of gravity MOND". At the very least, astrophysicists and cosmologists are deeply undecided whether this data supports or discourages MOND. (Shortened comment because verification problem.)
Last week, I updated my annual count of MOND and other "alternative gravity" publications. While research on MOND (and others) continues, and any "suppression" the tin-foil-hat brigade want to scream about is ineffective, it remains an unpopular (not-equal-to "suppressed") field. Generally, astronomical publication counts are increasing, and MOND sticks with that trend. If anything is becoming more popular, it's the "MOG" type of "MOdified Gravity".
Phys.org writes that the study "reinforces the evidence for modified gravity that was previously reported in 2023 from an analysis of the orbital motions of gravitationally bound, widely separated (or long-period) binary stars, known as wide binaries."
But RockDoctor (Slashdot reader #15,477) calls the hypothesis "very much disputed." YouTubing-astrophysicist Dr Becky considered this report a couple of months ago (2023-Nov-09), under the title "HUGE blow for alternate theory of gravity MOND". At the very least, astrophysicists and cosmologists are deeply undecided whether this data supports or discourages MOND. (Shortened comment because verification problem.)
Last week, I updated my annual count of MOND and other "alternative gravity" publications. While research on MOND (and others) continues, and any "suppression" the tin-foil-hat brigade want to scream about is ineffective, it remains an unpopular (not-equal-to "suppressed") field. Generally, astronomical publication counts are increasing, and MOND sticks with that trend. If anything is becoming more popular, it's the "MOG" type of "MOdified Gravity".
Lol /. idiots like me (Score:1)
Re: (Score:2)
Oh, yeah, I'm big-time into 'corns. So magical, right? You know, they're the most lethal animal on the planet.
(That's a quote from the movie "Central Intelligence")
Re: (Score:1)
Too may people's paychecks depend on Dark Matter for a useful public discussion.
Many people get highly emotional *immediately*.
I find the sociology of science as interesting as the astrophysics.
Some very PhD people throw the Philosophy of Science out the window as soon as someone gets near their nut cache.
Yet insist on being called experts.
Re:Lol /. idiots like me (Score:5, Insightful)
There is no Big Dark Matter handing out grants and influencing scientific newsletters and pressuring lawmakers. Because there is no business case in Dark Matter. You don't gain anything if Dark Matter exists, and you don't lose anything if it doesn't. Either way, Dark Matter does not interact with anything on Earth, may it be because it does not exist at all, or it exists, but does not interact with Electromagnetism.
That's like claiming that too many people's paycheck were depending on Light Ether back in the late 19th century, hence it took an outside to come up with Special Relativity. That's how Little Johnny imagines Science to be, but it is not science.
Dark Matter is nothing else than a nickname for the difference in observation of mass in the Universe by the amount of radiation the mass emits and the observation of mass according to its gravitational effects. The name was coined by Fritz Zwicky in the mid-1930ies and was meant quite literally. If you read his 1936 paper, you find it directly described as "the mass Mr. Edwin Hubble did not observe because it does not send out light".
There are two main ideas how to resolve the difference, either by postulating that there is a huge amount of mass, which does not interact with electromagnetic radiation, or by postulating that our way to calculate gravitational effects is flawed. Both ideas have their problems, and as the ways to test them require quite different methods, you have different specialists working on them. But every astrophysicists will be able to calculate the main aspects of both non-baryonic Dark Matter and the different Modified Gravity models.
Re: (Score:2)
There is no Big Dark Matter handing out grants and influencing scientific newsletters and pressuring lawmakers.
Not sat on many grant panels, have you?
It's not an active conspiracy, but when one area starts to dominate the field, they also dominate the grant panels, and tend to be much more keen on awarding grants to people who are doing things not wrong (i.e. not the competing area). The same problem exists in HEP: string theory has utterly dominated research and grant allocations for decades and continues
Re: (Score:2)
Re: (Score:2)
Sorry, I didn't mean this to be about the relative merits of MOND vs dark matter, but how grant panels work. In some cases there is actual science versus let's say fringe theories which are basically wrong. Obviously grant panels consisting of scientists are going to fund the real science not the garbage.
The trouble is there's a smooth continuation from there to where we ended up with string theory. String theory looked to be the way forward and exploded. Naturally people don't work on what they think is wr
Re: (Score:2)
Have you discussed astronomy with any foreign scholars on work visas? They seem very eager, indeed, to study a field with endless opportunities for simply inventing new theories from the same original measurements.
Grad students are, generally, quite willing to pursue whatever research their advisor directs in the hope of working on their own topic of interest. And "dark matter" is what the "luminiferous aether" used to be to optical physics.
Re: (Score:2)
And "dark matter" is what the "luminiferous aether" used to be to optical physics.
"Dark Matter" might also be what neutrinos were to the mass deficit in the Beta decay, first just a postulate to save an old theory, several decades later proven to be real. You just don't know. Maybe Dark Matter proves to be unnecessary in the end. Maybe not. And that's why it is important to delve into several theoretical models and know their strengths and flaws and the predictions that arise from them. One thing is clear: to use derogatory terms for one of the possible solutions is not helping in sortin
Re: (Score:2)
You've a point. The original meaning of the phrase "dark matter" referred to mass that was inferred from gravitational effects, but doesn't show up with optical or radio astronomy. However, the "luminiferous ether" metaphor is well earned. The variety of speculative and mutually inconsistent requirements for the many speculative forms of what is collectively and confusingly called "dark matter" has earned considerable skepticism. And let's be honest about the progress of science, mockery is part of the test
Re: (Score:3, Insightful)
Too may people's paychecks depend on Dark Matter for a useful public discussion.
Ah, yes! The grand conspiracy. Scientists made something up in order to bilk the public out of endless funding. And they're *all* in on it - no one will screw the pooch by fessing up. We wouldn't know about it at all if clever laymen hadn't seen through the deception.
Same thing with global warming - just ask anyone who doesn't want to believe it. And evolution, except that creationists are rather vague about what scientists are getting out of the scam.
Please, if you don't like or believe a hypothesis,
Re:Lol /. idiots like me (Score:4, Informative)
It's definitely true that MOND is "highly disputed". This is very different from saying that it is either correct or wrong. (FWIW, I don't feel informed enough in that area to have a reasonable opinion. But "highly disputed" is definitely correct.)
Re: (Score:2)
The counter claims are direct evidence to. And this is a counter-counter-claim, which ALSO has direct evidence! And they're all highly significant.
Any signal is deep down in the noise so it all depends on which data you include. And since everybody's claim is super significant, there's either some very motivated data cleaning going on or the methods being used are poop.
The problem is (Score:5, Insightful)
There's no good reason to accept this claim.
"Gravity's just different according to this fudge factor we put into the calculations to make our other observations make sense" is a reason to keep investigating, but it's not a reason to claim the fudge factor is actually a thing.
"Gravity is stronger at low accelerations" would indicate there's some equivalent of static friction to overcome before you can move freely in the three spatial dimensions, and there are just so many other things we know with extreme accuracy and precision that would break.
Re: (Score:3)
Re: (Score:3)
There's enough evidence to see that gravity follows linear law instead of quadratic below a0. We can't know why. N
It's just the simulationists using the equivalent of the small-angle approximation for sine.
Can we falsify theory of dark matter? Mostly? (Score:2)
Interesting idea that you can't falsify a theory of dark matter. Never thought of that.
And I think you're right, no matter what, you could come up with some distribution of dark matter that would fit any observation.
That said, I think such distributions would come to resemble the epicycles which were once used to explain the motion of the solar system, and would be come increasingly unlikely and implausible.
I did a bit of searching, and some theories of dark matter are falsifiable and have already been fal
Re: (Score:2)
Re: (Score:2)
What do you mean, "we can't falsify a theory of dark matter"? Of course we can, we do, and we design and perform experiments to test a number of hypotheses.
Re: (Score:2)
Wasn't my claim, it was the guy I was responding to.
That said, if I claim there's a thing there that you can't see, can't touch, and can't detect in any other way, you've got no way to falsify this "theory".
The hypothesis that there's some kind of gravitionally active, but otherwise undetectable substance that is affecting galactic rotation, is also hard to falsify. I point out that we have falsified hypotheses that some particular particles are dark matter, but they can just move the goalposts and say it'
Re: (Score:1)
Re: (Score:2)
My post is bothering me; it looks like I got the math wrong at a very basic level.
The underlying point of "don't tell me the fudge factor is real until you have a proper explanation" stands, but I got the sign wrong. If gravity is stronger at low accelerations then that would be a claim of something like a negative equivalent of static friction.
Anyway, tell me the strength curve with distance doesn't quite seem to be scaling exactly with the square of the distance and there are possibilities to discuss. V
Check in with the flat earthers next? (Score:5, Insightful)
MOND isn't taken seriously anymore and has never been more likely to be right than wrong. Why is this trash being pushed on /.?
Re: (Score:3)
While your statement is generally true, that's not an argument either that MOND is correct or that it is false. AFAIKT most of those denying it haven't examined the data, and most of those believing it don't have the skill to examine the data. But there are a few who do appear to have the skill and intention, and they disagree. (Note that MOND is not a theory, it's a family of theories. Proving one of them wrong doesn't necessarily show anything about the other variations. And the supporters disagree
Re:Check in with the flat earthers next? (Score:5, Insightful)
MOND variants are neither "correct" nor "false". They are just exercises in curve fitting on a small subset of all data available on the phenomenon of the so-called "dark matter".
For example of a spectacular failure of all MOND, look at the behavior of matter in the "bullet cluster". https://en.wikipedia.org/wiki/... [wikipedia.org]
MOND's biggest problem (beside the fact that it fails to explain all data) is that there is no physics behind it. At all. It is an exercise in math, and while you may tell me that the quantum hypothesis also arose from a mathematical exercise, I'll point out that unlike it, MOND is neither consistent with data, nor with itself.
Re: (Score:1)
Is science really just about arbitrary, fickle human popularity, not reality?
Floating point error (Score:2)
As long as no repeatable experiment is proposed... (Score:2)
Re:As long as no repeatable experiment is proposed (Score:4, Insightful)
MOND fails on everything that dark matter explains except rotation curves, and even then you have to parameterize it for each galaxy. E.g., it doesn't do anything at all in galaxies that other scientists say are devoid of dark matter.
It's almost as if MOND depends on the presence or absence of something in the galaxy.
"Very low levels" (Score:2)
Then lab experiments should be able to measure it. Run a Cavendish experiment with different masses.
Re: (Score:2)
I think there might be problems with isolation for that suggestion. However, there are asteroids with moons that should be good testbeds. They're already there, all you need to do is observe them precisely enough.
Re: (Score:1)
ISTM that that MOND says that gravity doesn't always work like we thought it did, and that therefore general relativity shouldn't always work like we think it does. Maybe some boffin can come up with a feasible experiment where MOND and GR make different predictions. Precession of parahelia? Gravitational time dilation? It seems that some effect should be there, and someone with more clue than me should be able to think of it.
Re: (Score:2)
Why would isolation matter? Earth's gravity is at right angles to the torsion balance and static anyway. But if you really want you could do it in freefall in orbit.
Re: (Score:2)
Re: (Score:2)
The force (sorry, Dr. Einstein, I shouldn't call it that) between two solid balls in a lab is very low in any reference frame. https://en.wikipedia.org/wiki/... [wikipedia.org]
Fun topic to hear about. (Score:2)
At what point is the failure to find what you're predicting evidence that it's not there? The whole concept of dark matter just seems Aristotlean. If stuff in the sky moves weird, let's just keep assuming the Earth is at the center and make everything else move in increasingly absurd ways to explain it instead of reexamining assumptions.
Re: (Score:2)
You're not the only one. The more ways they try to detect Dark Matter and fail, the more the theoretical physicists have to dance around trying to explain just what it is and how it works. At this point, they're almost down to the point of saying that it's something that can't be detected in any way except by it's gravity. My personal opinion is that when we finally find out just what's going on it will turn out not to require any actual mass and Dark Matter will
Re: (Score:2)
Re: (Score:3)
At this point, they're almost down to the point of saying that it's something that can't be detected in any way except by it's gravity.
So what? We know that humans are electromagnetic force chauvinists, because that's how all of our innate senses work. If we can't somehow make a physical phenomenon interact directly or indirectly with the electromagnetic field, than we don't believe that it exists.
However, there's no fundamental reason why there can't be a particle that simply doesn't interact by any means other than gravity. Maybe we should just learn to accept that possibility and move on.
Re:Fun topic to hear about. (Score:4, Informative)
Currently our understanding is this:
1. There is a phenomenon which behaves like there is a lot of mass, which we don't see.
2. We only see electromagnetic stuff directly, and three more kinds of stuff indirectly through EM
3. We know that there are things (neutrino) that are coupled very weakly to EM (that is, a brazzilion of them pass through, one reacts)
4. It isn't outlandish to suppose there is stuff that totally does not react via the known (Standard Model) mechanisms
5. But it is okay if we see them through gravity - it isn't part of SM anyways
6. All other evidence is also consistent with the existence of such particles.
therefore
7. It is our working hypothesis, until evidence to the contrary appears
Re: (Score:2)
Re: (Score:3)
but it seems like they were proposed theoretically before they were observed
Yes, but do you know why?
Because there was "missing mass" in the observed spectra of beta decay electrons, a true piece of "dark matter". In the absence of a neutrino, people expected to see electron spectra that looked like the optical ones - discrete spikes with a definite energy. Instead, people saw a wide, smooth distribution like this one [1] that ended where the spike should have been.
A smart guy named Pauli proposed that the "missing" momentum was carried away by an "invisible" particle, which he ini
Re: (Score:2)
Re: (Score:2)
The observations of the "missing matter" that became neutrino happened in the 20s. The theory was developed in the 30s. Discovery happened in the late 40s. Note, however, that the probability of neutrino reacting is at least orders of magnitude higher than that of dark matter. In fact, it is possible dark matter may not react with standard model matter at all, in which case we will not see it in the way we see neutrino, at least with the current detector technologies.
Another illuminating experiment involvin
Re: (Score:2)
We're also discovering that there are far more rogue planets in interstellar space than previously thought, discovering them only as our optical telescopes improve enough to detect such cold, unilluminated objects within optical range. If they're more prevalent than previously expected, especially in the vast reaches of intergalactic space, they could easily be a considerable percent of the matter in our universe yet be undetectable to remote or to radio based astronomy.
Re: (Score:2)
Hardly. Planets lack mass to explain the effects of DM.
The better candidate was the MACHO-massive compact halo object hypothesis ( https://en.wikipedia.org/wiki/... [wikipedia.org] ), which has been tested extensively by detection of macrolensing, with negative results.
Re: (Score:2)
"Planets lack mass".... How many planets. If they're more common than realized in interstellar space, which is consistent with the numbers being found as our telescopes improve, there is plenty of space between stars to hold stellar masses worth of rogue planets. If they exist in even modest numbers in inter-galactic space, they'd be impossible to detect with current tools except by... let me think, what was it we were talking about??? Oh, yes, gravitational effects, which in no way require non-baryonic m
Re: (Score:2)
Ok, I'll try. Let's take the Solar system. It has the Sun, 9 planets and a lot of asteroid junk, my beltalowda.
The Sun contains 99.86% of the mass of the Solar system. How do we know? We've measured it.
The estimated (see virial theorem) mass of the dark matter in the Universe is approximately 4.5 times MORE than ALL visible matter in the universe - stars, gas, black holes - everything that we can see.
So, if the Solar system is typical, which it pretty much is, you'll need AT LEAST 3208.5 times more mass in
Re: (Score:2)
Fortunately, interstellar space is vast. The solar system is far, far less than the available space between stars. Sol is about 22 light hours across. The nearest star is roughly 4 light years away. The relevant "empty" volume is roughly ... 3000 * 3000 or roughly 10 million times the space of the solar system, even if we neglect "virtal" space. If we include the third dimension, it's roughly 3000 * 3000 * 3000 or roughly 30,000,000,000 times the space. It doesn't take a high density of cold, congealed matt
Re: (Score:2)
Get a book on mechanics and work through the problems. Feinman's vol. 1 is available online with the solutions manual.
Re: (Score:2)
It isn't outlandish to suppose there is stuff that totally does not react via the known (Standard Model) mechanisms
It really kind of is outlandish. I would even say it is the definition of outlandish. It is possible, so it shouldn't be ignored, but it definitely is outlandish.
Re: (Score:2)
that's, like, your opinion, man.
Re:Fun topic to hear about. (Score:5, Informative)
We don't have "kinks in kinematics." Newton had this bright idea that your theory had to be mathy and explanatory and stuff, you see, and a bunch of other nogoodniks came up with other things that a theory should be like "consistent."
In modern physics there are two ways to solve a problem like this. You can add a fermion or you can add a boson. Dark matter is a fermion (thus the "matter" part). Modified gravity is a boson, i.e. another force. You can't just make gravity 1/r^2 except not quite. There are very fundamental reasons gravity should be 1/r^2, and it definitely shouldn't just switch to something else at some distance or acceleration or whatever. So you have to add another force to existing gravity to "modify" it.
The nice thing about adding fermions is that you can look at what the distribution needs to be to solve the problem and see if it's reasonable. Adding bosons is much less flexible, so it turns out you can't make it work. So the solution comes down to: new fermion or new boson AND new fermion.
Dark matter is the simple solution, barring some out their possibilities about observational issues. Modified gravity is very complicated.
Re: (Score:2)
Re: (Score:2)
The motivation for relativity wasn't explaining astronomical observations. If it had only been Mercury's orbit, an extra planet too close to the sun to detect is (and was) a much simpler explanation than special relativity. The motivation for special relativity was reconciling an apparent inconsistency in Maxwell's electromagnetism, and the invariance of the speed of light observed by experiments like Michaelson and Morely. Relativity famously *also* explained the anomalous orbit of Mercury. Relativity expl
Re: (Score:2)
Re: (Score:2)
The science media seems to have figured out that stories about "ghostly matter nobody can detect" get a lot of clicks. Never mind that "ghostly" just means uncharged and perfectly ordinary things like sand are reasonable dark matter candidates (most of which have been excluded over the years for other reasons). The distinction between dark matter and modified gravity can be pretty fuzzy too. One proposal is that there's a new particle (a boson, like modified gravity) that has mass (like dark matter) but is
Re: (Score:2)
Re: (Score:1)
At what point is the failure to find what you're predicting evidence that it's not there?
Never. When you hypothesize that something exists there's not a game show host that starts a timer and makes you retract if you don't figure out the details before the bell rings.
That's just not how empirical knowledge acquisition works. Stuff existed almost 14 gigayears before our species came around to detect any of it. There's probably stuff out there that we will *never* detect.
DM may be an incorrect hypothesis, but not figuring it out yet is not an argument against it.
Re: (Score:2)
Re: (Score:1)
There is no "empirical knowledge" of dark matter. It's a hypothesis to explain observations of galactic motion.
I agree. But you're misinterpreting what I said. We are trying to obtain empirical knowledge of that hypothetical substance, but we haven't found it yet. What I said is that there isn't a deadline for finding it before you have to reject the hypothesis.
Re: (Score:2)
There is empirical knowledge, and it isn't only the galactic rotational curves. The existence of the phenomenon has been confirmed by gravitational lensing, by its impact on the distribution of visible matter, and by the negative results of many attempts to explain it away by means of "dim matter", that is, things that are part of the SM, but are too weak to be detected.
This is a lot of empirical evidence.
Re: (Score:2)
Re: (Score:2)
Re: (Score:2)
As we discussed it later somewhere up-thread - https://slashdot.org/comments.... [slashdot.org] - we observed neutrinos as "missing matter" nearly a decade BEFORE the theory appeared.
In general, since physics is a science, it has no "theories" that develop before observations. Modern physics, which started with Galileo or thereabouts, needs observations or other experimental evidence to develop and validate its theories.
At times, the experiments may be thought experiments, but they are based in a physical reality and requ
Re: (Score:2)
Re: (Score:2)
Not that I can handle an actual technical discussion of cosmology, but dark matter has always bugged me on a conceptual level. I get "Occam violation" vibes from it.
Not if you compare it to MOND.
A silly question (Score:2)
If this theory claims that Newtonian law of gravity is incorrect, then why is it called MOND instead of MONG (Modified Newtonian Gravity)?
Re: (Score:2)
Because a journalist wrote the article.
Yes, the claim is that Newton's gravity is wrong, and that's why you need to modify it. The problem is getting it to fit in with relativity and quantum mechanics. (Well, and with various observations, like of galaxies that have suffered a collision, where it *appears* that the dark matter component went one way and the observable matter went another.)
Re: (Score:3)
Nope, the claim is that the second principle of Newton is incomplete, and journos are just quoting.
Instead of
F = dp/dt = mdv/dt = m.a from your physics textbook,
MOND postulates (or, rather, MONDs postulate) that
F = mk(a,..)a,
where k(a,...) is a free parameter taking the form of a function which looks like whatever pleases a specific data set most, but depends on the magnitude of the acceleration.
Re: (Score:2)
It is called "dynamics" because it doesn't propose modification of the law of gravity, but an extension to the second principle of Newton, remember, F = dp/dt.
Re: (Score:2)
MOND is not a modification of gravity. It's an addition to gravity that causes different acceleration (dynamics) at low accelerations.
The other side of the coin (Score:1)
Here's a story I submitted a bit over a month ago. It's about another paper that looked at wide binaries, and came to the exact opposite conclusion.
It's also interesting because of the phenomenal number of sigmas the author offers for his result.
A new article analyzing the orbits of wide-binaries appears to be fatal to MOND — iff the results are confirmed.
Here [universetoday.com]'s a high-level summary at universetoday.com
Here [arxiv.org]'s the paper on arxiv.org (If, like me, you are not an astronomer you might want to skip down to the Conclusions section, which I fond pretty lay-accessible.)
From that paper's conclusion:
[certain observations are] consistent with Newtonian gravitation and MOG at 19[\sigma] confidence and rules out MOND at 16[\sigma] confidence
[...]
If these results obtained from the Gaia DR3 data continue in future investigations to exclude MOND as a correct description of the wide binary systems, then this can mark the end of MOND as a purely acceleration dependent modification of gravity.
But this certainly won't be the last word on it.
Note that he's decent enough to recognize that his results need to be duplicated.