Dark Matter Doesn't Exist
iai.tv
iai.tv
* DM particle haven't yet been found.
* The current best theory of the structure formation and galaxy evolution involves dark matter and critically depend on it to reproduce observations.
* There is a broad variety of Dark matter models that are consistent with simulations.
* It is possible there is some theory that somehow explains everything without the need of dark matter, but it doesn't exist (now), and very likely it would work effectively like dark matter. Without such theory, claiming DM doesn't exist is simply stupid IMO.
* There are a few cases where you can find tensions with the existing DM based paradigm. I.e. the is test pointed in the article involving galactic bar in the paper "Fast galaxy bars continue to challenge standard cosmology". Note the toned down title. In this paper they just compared one specific feature of galactic disks in the simulations to the data and show that it doesn't match. I'd argue there are many reasons that could be the case that doesnt' involve killing DM. The same applies to other tensions.
* A final point. Even Modified Newtonian Dynamics theories require DM, because without it you cannot form enough structure early in the universe (as dark matter start to collapse earlier) and is essential to reproduce the amount of structure we see in the cosmic microwave background.
Dark matter models are fine-tuned to reproduce certain observations. These don't really count as evidence in favour of DM.
> * It is possible there is some theory that somehow explains everything without the need of dark matter, but it doesn't exist (now), and very likely it would work effectively like dark matter. Without such theory, claiming DM doesn't exist is simply stupid IMO.
MOND has more points in favour for it as a preferred theory than DM models. See [1].
> Even Modified Newtonian Dynamics theories require DM, because without it you cannot form enough structure early in the universe (as dark matter start to collapse earlier) and is essential to reproduce the amount of structure we see in the cosmic microwave background.
I'm not sure why I should find your claim that DM is "essential" as persuasive given MOND has received orders of magnitude less attention and less development than DM models. I would certainly not bet any money on MOND being incapable of reproducing these observations.
[1] From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
That's the definition of physics. Models are fine-tuned to match the observation and be predictive.
That's not what "fine-tuned" means. Epicycles can be fine-tuned to reproduce the motion we see from elliptical orbits. However, we should clearly prefer the theory of elliptical orbits because it reproduces observations without any extra parameters needed to fine-tune it.
I'm not an expert, but it seems like Dark Matter theories allow the DM distribution to be tuned. Is that the case? Can you say, "oh, there must be a clump of DM over here with mass X". If so, that would give you lots of parameters to tune per situation you're modelling. It may be that IS how the universe works. The problem is that the theory is hard to falsify if it has so much wiggle room to fit every situation.
Isn't MOND completely falsified by the discovery of galaxies without dark matter?
As for galaxies without DM, those observations are still being debated, but even if true, that doesn't entail MOND can't explain those results.
As long as a opposing theory can't replicate these simulations from initial state to known "now" state without the use of some form of "whatever" it is quite interesting to call out that there is nothing like "dark matter" (whatever this something may be).
But that is just my layman's take.
Whether it's a "shtick" or not, his basic point seems like one that is worthy of some kind of substantive counter argument, if one exists. His basic point is that small galaxies orbiting larger galaxies should experience Chandrasekhar dynamical friction if dark matter exists, but no such thing is observed. Therefore dark matter cannot exist.
Has any astrophysicist who supports the dark matter hypothesis published a counter argument to this?
Edit: A published paper of Kroupa's that gives much more detail about his point is here:
How about therefore thing we've yet to observe if it exists fails to behave as we naively expect.
This is a grand claim from one piece of work and feels more like a straw man grab at further research funding rather than finding the heffalon at the LHC https://arxiv.org/abs/1303.7367
Or in other words Occam's razor says you have a stripey horse in northern Europe rather than a zebra.
As I understand it, the "behavior" of dark matter in Kroupa's analysis is the behavior that is claimed for it by dark matter proponents. So if dark matter doesn't behave the way dark matter proponents say it does, the burden would be on the dark matter proponents to modify their models to say how it does behave.
AFAIK none of these alternatives offer a serious explanation of gravitational lensing for instance (yet, I'm happy for someone to make a theoretical breakthrough that explains away the need for an unknown new particle, but that just opens more questions around CP violation and so on)
1: Michelson-Morley experiment: https://physics.stackexchange.com/a/472611
However, "dark matter" is an admittedly lose framework it could be due to 1 new type of particles, 10, or higher dimensional effects and new physics we don't understand yet. Saying "therefore it doesn't exist" is ignoring the mountain of decades old solid data showing gaps in our knowledge exist.
And as for dark energy... "The universal expansion is accelerating". Well done you now know as much as 99% of the physicists in the world on this strange unexplained problem.
In any case competing theories will need to converge towards new experimental evidence and therefore towards each other, and then names and starting principles will be unimportant.
If I'm straw manning you, it is unintentional. How would you propose dark matter be falsified?
Over the next 20 years or so we will likely cover a huge amount of the phase space of direct observation of dark matter like candidates assuming they weakly interact with the standard model.
If we observe it, great we now know a huge chunk more than ever before of the universe.
If we fail to observe it then we have to go away and explain the Dark Matter problem another way. Axions are my personal favourite here because I claim nature for her beauty is sometimes horrible. But this could (in the most scary scenario) potentially be non quantisable interactions between unknown aspects of the universe. At that point we need to further our understanding of potential graviton candidates to evolve our theories of spacetime.
DM isn't a solid prediction like an aether it's a statement of a big gap in our knowledge that has implications to asto and particle physics models.
The big problem is then CP violation (why more matter than not, real why are we here at all stuff). This can't be explained by the standard model and stuff we can see and touch as far as we know. So we assume that this huge amount of it that we can't explain must come from interactions with new particles somewhere in some way at some energy scale.
Physicists try to narrow down that phase space of where and how but a lot of this stuff makes the search for the higgs, look like cheating and watching where your parents hid the Easter eggs. There is scary little to directly go on so theoreticians have to get clever.
Edit: There is also little to say that extra-SM CP violation _must_ be from the same source as Dark Matter astro candidates. The combination of the 2 fields is much more a car of. "Hmm we both have a missing piece in our jigsaw that has 3 of the same sides and a 4th we've never seen. That's odd let's look together to try and find it." Modeling of the early universe to today relies on some unknown amount of CP violation occurring and we know we see it in particle physics which describes everything we see eat and touch. So why the amounts are so different (orders of magnitude different) keeps some scientists up at night.
Yet there is no proof that such simplifications or constrains are valid on the scale of a typical galaxy. Moreover, when people managed to use full equations of General Relativity, then it was possible to account the effects previously thought to require the dark matter hypothesis.
So until it is mathematically proven that the current simulations are valid approximations, I will remain very skeptical about the dark matter.
The best-well known effect is the "missing mass" in rotating galaxies. Well recently we found galaxies that look like they have no dark matter in them - i.e. they behave as you would expect from classical gravity/centripetal force arguments [1]. So while you can tweak General Relativity to match some of the effects in typical galaxies, you would then expect the results to hold in all galaxies. The "outliers" are easily explained by Dark Matter - they just don't have it for whatever reason.
The simulations of Universe formation, sure have their limitations, but look much worse without DM.
Galaxy clusters look like they have unexplained mass in them. Crucially, this isn't only from observing their rotational speeds (so like galaxy rotations) but also from looking at the strength of gravitational lensing they induce. This is as compared to fluid-dynamics-y calculations of gas temperature, pressure etc.
Bullet cluster is another interesting case [2]. It is the result of a collision of two galaxies. In such cases, you expect (a) the stars to "fly through" each other, as they are basically point masses and only interact gravitationally, but (b) the gasses and dust to collide. In this case, most of the mass is in fact gas and dust, so it should be distributed in the middle of the cluster (having just had an inelastic collision). But in fact observed mass is where the stars are, further out of what looks like center of mass.
[1] https://www.nature.com/articles/d41586-022-01410-x [2] https://en.wikipedia.org/wiki/Bullet_Cluster
But GR is complex enough to allow very different behavior depending on the initial conditions of galaxy formations. So it would not be surprising to see different scale of deviations from Newtonian mechanics depending on Galaxy history or age.
You are saying that without another theory to explain something, the current theory must be true because ... How does this logic work exactly?
In the middle ages, there wasn't a theory that explained headaches, so dismissing the idea that we should cut hole in people's skulls to let out the evil spirits is "stupid"?
Dismissing the idea that lighting is caused by Zeus being angry is "stupid" because there is no other theory yet?
We know that General Relativity is incomplete. It cannot describe the work at high energies or very small scales. It is useful as far as it goes but it is not a perfect match.
Quantum Mechanics does describe the world of the small and the hot, but we cannot apply it to the larger world. QD, too, is incomplete. We look for a new theory that can combine the features of both but it evades us, so far.
Dark Matter is a similar theory. It describes a world. It seems to describe this work better than other theories like MOND. Looking for actual dark matter will let us see if DM is a good enough theory or not. If another theory can be found that is a better match, we can switch to that. In the meantime, every time we continue to try to verify/disprove DM.
Change that "must" to a "may" and you have something that matches what was written in GP.
The impression a lot of people have about dark matter is I think similar -- dark matter / dark energy basically comes up as an explanation for why theory doesn't match what we observe. Thus a lot of people assume there is simply a more reasonable explanation, like a hidden variable we haven't considered, that would result in a theory that matches our observations. When I was in high school physics this was my assumption as well. I think if that were really the problem, though, someone would have solved it by now. That said, never underestimate an entire school of thought's inability to see things differently.
> (b) We need to scientifically understand why the dark-matter based model, being the most falsified physical theory in the history of humankind, continues to be religiously believed to be true by the vast majority of the modern, highly-educated scientists. This is a problem for the sociological and philosophical sciences and suggests a breakdown of the scientific method [18].
There are few hot takes I agree with more. I don't care if the opponents of DM/DE are proponents of MOND, or proponents of something else involving pixies and turtles. We should continue to investigate DM/DE, but not with the religious fervor that we do today.
It's not true that there are no other theories; here in Norway we believe that it's caused by Thor hammering away up there. Some say he's hammering away at dark matter...
> Dismissing the idea that lighting is caused by Zeus being angry is "stupid" because there is no other theory yet?
I think you could have picked far better examples.
Hopefully I'm not misrepresenting his views, I think the paper is DOI:10.1140/epjp/i2011-11032-x
> any curved Riemannian space must be a subspace of a larger flat host space
This is not even wrong. Yes, you can always embed a Riemannian manifold in a Euclidean space. In fact, there are infinitely many ways to do so. But this is extra structure that you can choose to impose, if you want to - it's not intrinsic.
You might as well say that every string must be a substring of a larger "host" string.
> the 4D Riemann-Christoffel curvature tensor is identically equal to a geometrical tensor associated with the complementary subspace of the host space
Impossibly vague. Yes, sometimes things are equal to other things. What tensor, and associated how?
> Einstein’s field equations are automatically geometrized, with the stress-energy tensor expressed in terms of the contracted complementary tensor
This is a tautology. The Einstein field equations relate the Ricci tensor to the metric and the stress energy tensor, and the Ricci tensor is a contraction of the Riemann curvature tensor. This remains true even if you rename the Riemann curvature tensor "the complementary tensor".
But the deeper problem is this: the entire point of general relativity is that physics does not, in fact, care what coordinates we use. And this is built into the mathematical structure of the theory - there can't be any such thing as the "the coordinate basis vector approach to tensor calculus", because tensors (properly speaking: tensor fields) are, by definition, coordinate-independent objects.
General Relativity largely describes how geometry is nature - what may seem obvious from a mathematical perspective isn’t always so from a physical one. The results of using basis vectors for derivations aren’t riddled with artifacts of any particular coordinate system, as it would become immediately clear when expressing Christoffel symbols, for example - they wouldn’t be equal with other approaches.
One of the other students who was getting her PhD specializing in GR said that using a vector approach gave her intuition about concepts she had previously considered incomprehensible.
There are many more that DM doesn't address, or only addressed by extending it with parameters to fine-tune the result, a process which can also be done with MOND. I hate to keep posting this, but it's a good thorough review of the evidence for/against both DM and MOND, and DM does not fair as well as you imply:
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
Couldn't it be that that these dents are balanced out by bulges between the masses, that would additionally "push" smaller masses (like solar systems) towards larger masses (like the centers of galaxies)?
In an experiment it would look like this: the rubber sheet seals the top of a container filled with water. Now if you push down at some point, the increasing water pressure will push up all around that point. If you now added a marble onto that bulge, it would roll down a steeper angle than it would in the normal experiment ... just like if there was extra mass ("dark matter").
https://backreaction.blogspot.com/2021/11/does-anti-gravity-...
> Because I had this idea that anti-gravitating matter could surround normal galaxies and push in on them. Which would create an additional force that looks much like dark matter. Normally the excess force we observe is believed to be caused by more positive mass inside and around the galaxies. But aren’t those situations very similar? More positive mass inside, or negative mass outside pushing in? And if you remember, the important thing about dark energy is that it has negative pressure. Certainly if you have negative energy you can also get negative pressure somehow.
> So using anti-gravitating matter to explain dark matter and dark energy sounds good at first sight. But at second sight neither of those ideas work. The idea that galaxies would be surrounded by anti-gravitating matter doesn’t work because such an arrangement would be dramatically unstable. Remember the anti-gravitating stuff wants to clump just like normal matter. It wouldn’t enclose galaxies of normal matter, it would just form its own galaxies. So getting anti-gravity to explain dark matter doesn’t work even for galaxies, and that’s leaving aside all the other evidence for dark matter.
She goes into a lot more detail in the video (the blog post is just a transcript), but hearing her describe the thought process is interesting because she spent a lot of time on this theory (I’m assuming after she got her phd), so you’re in good company for coming to this initial conclusion at least :)
Just like entangled particles that are lightyears apart, when you measure the angular momentum of one, you know the other's because of conservation laws and not because of some hidden object nudging the particle the right way either.
Spacetime bulging the other way ("anti-gravity") would simply be a feature of spacetime to conserve some other property. In my example that would be the water pressure that wants to stay constant.
Some commenter below mention that this is like a waterbed. I like that analogy. If you put a large marble on a waterbed, not only will it create a trough, it will also ever so slightly lift everything around it.
https://science.slashdot.org/story/20/11/22/1714220/to-expla...
In your analogy rubber sheet analogy, it's about stacking another rubber layer on top of current one.
It has no prediction powers , but it would explain things like why gravity is so weak and why we can't detect it.
ie the observations seem to show more mature structures than predicted, we're finding.
I've been wondering if some MoND / non-DM kind of theory may better explain these new JWST observations.
- I'm not anything close to an astrophysicist, so give me some rope :-)
Specifically this paper[0] is mentioned as predicting it
> Remarkably, the data roughly follow the green line, which is an L* galaxy magically put in place at the inconceivably high redshift of z=10. Galaxies seem to have gotten big impossibly early. This is why you see us astronomers flipping our lids at the JWST results. Can’t happen.
> Except that it can, and was predicted[0] to do so by Bob Sanders a quarter century ago: “Objects of galaxy mass are the first virialized objects to form (by z=10) and larger structure develops rapidly.”
A MoND-like theory that allows the strength of gravity / inertia to vary over time can explain that. Granted, that sounds farfetched, but then, so does DM. Of course, it's easy to spend money looking for DM, and hard to spend money looking for a better theory of gravity.
https://news.ycombinator.com/item?id=29488993
> the observations seem to show more mature structures than predicted
Thank you for closing the loop for me! (would you happen to have a source?)
Probably. Certainly non-MoND people have:
> so give me some rope
Ok, here's some rope <https://telescoper.wordpress.com/2022/08/10/recalibration-of...>
Telescoper is an anagram of Peter Coles. It's his blog. He's a well known physical cosmologist <https://en.wikipedia.org/wiki/Peter_Coles>.
Adams et al., authors of the preprint linked in that blog entry, are all well-known astronomers. Adams is a research associate and Observational Astronomer at <https://en.wikipedia.org/wiki/Jodrell_Bank_Observatory> specializing in high-redshift galaxies, and is in several large-telescope international collaborations (ESO, SKA, MIGHTEE, LADUMA).
The punchline: those seemingly super-far-away galaxies are getting much much closer as JWST's calibrations proceed according to plan.
This paper also adapts GR in such a way that it is consistent with galactic rotation rates, the anisotropies of the CMB, and cosmological expansion -- while showing that the simple operation of gravity is the cause of each of these phenomena.
Cyclic Gravity and Cosmology (CGC) predicts that there are discrete specific sizes allowable for macro-objects. The instability of Bennu and the fact that it behaves more like loosely held scree rather than a compact mass -- is an example of a mass that is not exactly at one of the discrete allowable sizes. Please also refer to the link I included wherein I uploaded a video simulation of the formation of a solar system using this type of force law. (This is in section 18 of the paper)
I would greatly appreciate any comments on this idea. Copies may be downloaded here:
I think many people would be happy (myself included) if there is theory that wouldn't require dark matter and dark energy. But at the moment there is none and to me (and many astrophysicsts) the universe with dark matter is the best description we've found so far of what we observe.
Kepler and Newton's models produce better predictions over a long period than Ptolemaic models, which is great. But it's a bit of delusion to think that necessarily means they are analogous to the cosmological mechanisms that produce orbital mechanics.
It's incredibly hard to know until we've either observed DM particles or made good alternative hypothesises which also fit the data.
Dark matter, on the other hand, is not a conceptual necessity but an empirical one. Whereas aether was something people clung to because they couldn't imagine a world without it, dark matter is something scientists have been forced into even though the world would be more conceptually elegant without it.
The reason we teach the Michaelson-Morley experiment in basic Physics classes is because it's a bedrock example of Science functioning correctly. The reason people believed in the ether theory is because in the wake of Maxwell's revolutionary work, there needed to be an explanation of how light propagated that could be reconciled with Newton's mechanics which had been laid out 200 years earlier. In hindsight, we credit Einstein with finding the way out, but in the late 1800's it was in no way obvious that it was going to work out that way.
I don't know which aspects you think dark matter shares with miasma. Dark matter fits all the data; miasma doesn't.
DM's failures are more numerous, and it has to be extended with new assumptions to account for other observations. MOND's predictions fair better as favourable evidence actually [1].
[1] From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
More to the point, since epicycles are just a Fourier decomposition, they're actually perfectly correct. The problem, though, is that they are a nightmare to compute with unless you have a modern computer.
Once Kepler decided to use an ellipse to model solar orbits; however, things were vastly easier to compute. At that point, the epicycle model got swiftly pushed aside.
The reason why LCDM gets called epicycles is that there is charitably one free parameter per galaxy (dm: bm ratio -- but actually more, because it's an arbitrary distribution)... So the fact that it has high explanatory power is unsurprising. And what's should be dismaying is the number of things it can't explain, given just how many free parameters you're allowed to have in a DM model.
Where we run into trouble is by assigning too much credence (or too little skepticism) for that which has not been proven yet. This can be counter-productive as it may stifle research into other areas (in this case gravity). When we take the "best current theory" and deride skeptics of it to the point that it discourages other areas of investigation, that's a bug, not a feature.
Our current understanding of gravity is woefully inadequate, as shown by our inability to reproducibly measure the gravitational constant as well as we should be able to with current technology. The flyby anomaly is another example where DM does not help. I hope that the current popularity of DM does not stifle research into gravity.
I mean do we really believe that we know everything about this? Somehow, we A) know we have large knowledge gaps, AND B) believe that we understand things we have unanswered questions about.
We have a LOT of confidence about dark matter and exactly zero direct evidence.
It seems much more likely to me (I am not a scientist) that we are wrong about things that we assume to be hard facts and those error(s) have artificially produced the need for dark matter in order for things to make sense.
I think this is what the OP is saying though: There are many ideas about what dark matter is or could be, but astrophysicists model the early universe using only baryonic matter, the results _are wrong_.
As a theory, it's quite simple: in its absence, the physics doesn't work. If you add matter that behaves in a particular way, simulations align to observation.
What is dark matter? shrug I don't think we can call any answer to that question a theory yet, we don't have any way to falsify it. We have many hypotheses, but those aren't theories.
That doesn’t make any particular theory correct. It is only proof that our current model is wrong.
Filling the gaps with math, and calling the math “dark matter” does not make dark matter correct; one or more of our existing models is wrong.
They actually don't, numerous extra parameters have to be added for DM to account for observations. DM was invented to fix one problem with observation, and 15 more have cropped up which don't fit.
I think they expect particles to be thrown out and result with slowdown but dark objects as massive as stars wouldn't be thrown at such a huge rate to observe slowdown, am I right?
I mean, what else could you bring to the discussion by only guessing what is being discussed?
The article just talks about particles and dismisses them.
I see nothing about DM composed of massive objects.
What exactly does your comment bring to the discussion?
Consider the heliocentric/geocentric argument some centuries passed. Contrary to pop-science portrayals this wasn't an issue of Man against Church. The heliocentric view initially had numerous flaws and invalid assumptions. But because scientists of the time genuinely believed in the geocentric universe, they obsessed on these flaws and trying to use those to discredit the view, instead of impartially considering the idea and seeing if it could be patched and whether it would ultimately make more sense.
The "right" answer, with negligible refinement, can often look much worse than the wrong answer which has had decades, if not centuries of mass refinement. And that can drive those with a "belief" to the contrary, to want to attack it. The analogs outside of science are as endless as those within it.
https://www.forbes.com/sites/briankoberlein/2017/02/15/quant...
https://arxiv.org/pdf/1908.01589.pdf
I'm not here to debate with physics cranks; further replies will not be read.
We do not know that dark matter exists
> * The current best theory of the structure formation and galaxy evolution involves dark matter and critically depend on it to reproduce observations.
The stories we like to tell require dark matter. Otherwise our stories are wrong
> * There is a broad variety of Dark matter models that are consistent with simulations.
We have a lot of stories using dark matter. We really like it
> * It is possible there is some theory that somehow explains everything without the need of dark matter, but it doesn't exist (now), and very likely it would work effectively like dark matter. Without such theory, claiming DM doesn't exist is simply stupid IMO.
Our stories are just stories but it is all we have
> * There are a few cases where you can find tensions with the existing DM based paradigm.
Our stories are not internally consistent.
> * A final point. Even Modified Newtonian Dynamics theories require DM, because without it you cannot form enough structure early in the universe (as dark matter start to collapse earlier) and is essential to reproduce the amount of structure we see in the cosmic microwave background.
We really like stories with dark matter
I love Astrophysics! Pure math with constraints. Do not confuse it with reality
The stories which persist are useful. Calling them theorems or theory helps us rei-fy stories into propositions which can be used to do science. Science is about modelling things, understanding things, and testing things. It is a valid proposition to argue DM is defined by stories which remain untestable, but the proposition there are better alternatives ignores that to construct stories without DM which are better will demand addressing the problems DM has to exist, to define the blank spaces in other, testable stories. You think Absolute zero exists? It's just a story. We haven't got there, we got close, we observe what happens, but this mythical zero point.. What good is it, if we can't get there? I love temperature, the whole thing depends on a fantasy...
Do not confuse your projection of "what is reality" with reality. I love HN, where people make asserts which don't mean what they think they mean!
Nothing in astrophysics is like that, is there?
Different people have different priors. For some dark matter is more unlikely.
We really like to tell stories where 2+2=4, etc.
We know 2+2=4. We do not know that dark matter exists.
Which is why we really like telling stories about it.
My point is, we tell stories about literally everything, so i don't know what point you are trying to make.
If your criticism applies equally to basic facts, it is a bad criticism.
Given we can't observe reality directly, since we ourselves see it though a model, We can adapt the above list to everything.
The question isn't "is it a story" the question is "is it useful for prediction"
Much of astrophysics has been.
> Without such theory, claiming DM doesn't exist is simply stupid IMO.
Expressing flaws in an idea does not require a better one in any way. The search continues.
Expecting others to give up their theories that work well for 99% of the problem, or even only work well for the 10% they care about, just because there's a problem with it DOES require something better AND a reason to switch.
For example, architects (technically stability engineers. Architects don't really design buildings except in the artistic sense) are still simulating Newtonian dynamics on plates that fly through empty space held up by nothing. You want them to change? No problem, but you'll have to make something better and point out why they'd want to use something better ... but, truthfully, it works pretty well.
It also reduces the religious aspect, demoting DM to simply a tool used in specific situations, "we don't have anything better at the moment."
We have radio telescopes that can see all the way down to a few tens of MHz. This is far colder than the CMB, and certainly much too cold for the intergalactic medium.
> Plasma Physics hold ions permeating the Universe as a premise & has physical experiments reproducable in the lab to back up their claims
Yes, plasmas exist. There are lots of them in space. This is completely uncontroversial.
> And can use classical EM equations explain how the stars & galaxies work
Absolutely not. Galaxies are firmly in the nonclassical regime.
PV = nRT
What if the P is very low & V is very big...like it is in space? What would the plasma in dark discharge radiate?
> Absolutely not. Galaxies are firmly in the nonclassical regime.
According to some models. Do these models have reproducible experimental evidence? If not, I don't see how you can credibly be so sure of yourself...
Sure, exotic & speculative math is way more fun than reconciling with physical reality. Without reproducible experimental evidence, the model is non-falsifiable (& non-provable).
In contrast, the Plasma model does have physically reproducible experiments that are able to create galactic phenomena in the lab. Live physical experimentation...not computer simulations using math that has never been verified by physical experiment.
For an ideal gas. Plasmas are extremely far from being ideal gases.
> According to some models. Do these models have reproducible experimental evidence?
Yes, general relativity is extremely well supported by the evidence.
PBS Spacetime covers this topic in several videos, a good one being [1]. Matt (the host, an astrophysicist), describes what MOND (and other alternative theories, like relativistic-MOND) needs to do but haven't done yet:
1. Give the right answer in more than one special case. MOND may describe a few situations accurately, but it does not describe all situations where we have evidence for dark matter. Only some.
2. Consistent with other known laws and theories that are experimentally verified. According to Matt and others, MOND is not consistent with existing laws such as conservation of energy or angular momentum.
3. Make testable predictions beyond what it was tuned for.
Am I missing out on some extraordinary development in MOND and/or MOND-like theories that occurred recently?
> The current cosmological model only works by postulating the existence of dark matter – a substance that has never been detected, but that is supposed to constitute approximately 25% of all the universe. But a simple test suggests that dark matter does not in fact exist. If it did, we would expect lighter galaxies orbiting heavier ones to be slowed down by dark matter particles, but we detect no such slow-down. A host of other observational tests support the conclusion: dark matter is not there.
If you're going to claim that dark matter doesn't exist, you need to have a way to explain all of the cases that are known to show that dark matter does exist. Cases like the Bullet Cluster, where a collision left all of the visisble matter in one region, and all of the gravitational matter in another. How can this possibly happen if there is no such thing as invisible gravitational matter? How can there be galaxies like AGC 114905 that don't have any dark matter, if there is no such thing as dark matter for galaxies to have or not?
DM falsehood does not depend on any other known thing being correct. It particularly does not depend on MOND being correct.
The honest fallback position is not "this other thing is better", it is, "We do not know. We had hoped we did, but were wrong." Then, start entertaining hypotheses that encompass all observations, without prejudice, not just favored ones.
Oh wait, that's the definition of dark matter.
The way I see things, the much more prevalent attitude is, "we have a good idea of what's going on, we just haven't been able to confirm our confident assessments with objective data". Very few, if any, prominent people in the field admit, "we don't have any idea what's going on, it is all baseless conjecture that might pan out if 75% of the universe is made of some invisible stuff that we haven't been able to detect in 4 decades despite our best efforts". I'd like to see a paradigm shift from, "we have a good understanding of how things work, now we just need to detect the invisible particles that make all of our formulas work" to "we have really have no idea what is happening, but here is some wild speculation that is the best we can come up with".
A lot of the "dark matter" debate reminds me of the Alzheimers/amyloid situation. Groupthink develops among the establishment in the field, based on very little (if any) objective proof, which ends up discouraging and marginalizing those who pursue other theories.
No, actually calling it missing mass is dark matter. MOND would be another explanation, and there's no reason to conclude it's unworkable.
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Re...
Which is why I'm asking about MOND, which I just explained in my comment is falsified from the start (violation of existing established physics).
Why instead of? Dark matter is, so far, the best model we have. Seems sensible to continue research in that direction.
>futile dark matter detection projects.
Why are they futile?
DM also fails numerous observations, like the one described in this article, external field effects, and more. It failed numerous previous observations as well until more parameters were added to DM theories to account for actual observations.
> 3. Make testable predictions beyond what it was tuned for.
This is backwards. DM has been tuned to match certain predictions, where MOND's predictions are free of parameters and yet fit observations. That's actually strong evidence in favour of MOND.
See my other comments here for a reference to a paper that reviews the evidence for/against both.
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331/htm
You know what else smells like phlogiston? Oxygen. There really is an invisible, odorless, tasteless gas responsible for combustion, plant growth, and breathing. 17th century chemists thought that it was released during combustion, absorbed by plants, and expelled by the lungs. Turns out it's absorbed during combustion, released by plants, and taken in by the lungs.
Phlogiston was a reasonable theory, well supported by the available evidence at the time. It was also wrong. Most theories are. But this could not have possibly been predicted a priori.
That of course doesn't say one way or another that such hypothetical particles can account for the amount of mass needed.
The exact problem is that sprinkling extra mystery mass everywhere produces results inconsistent with observation.
No theory fits perfectly, but that is what we expect in a world of imperfect knowledge.
So far modified gravity theories can’t explain everything. That and they would have to integrate with general relativity for which evidence is only getting stronger.
Is that hypothesis correct? (i.e. would we expect lighter galaxies orbiting heavier ones to slow down if dark matter exists)
If it is correct, and we don't observe that effect, would it not be a very strong argument refuting the existence of dark matter?
For folks mentioning this as a "crackpot" or "anti-dm" theory, is the strong claim that the hypothesis is incorrect?
Would someone who relied on Newtonian dynamics 100 years ago likewise be incorrect to do so because it failed to explain many aspects of planetary motion?
It is well known that the relevant wake friction calculation ("classical Chandrasekhar") is for a pointlike structureless body. Satellite galaxies and their parents are not this. Importantly satellites can lose matter and thus mass, so one has to correct for the evaporation and tidal loss (especially to the halo) of the satellite galaxy; and the host galaxy's potential grows adiabatically over the lifetime of the system.
If the density of the halo and other sparse matter increases closer to the host galaxy, inward migration of the satellite sees two effects driven by the collision into more particles: more satellite mass is torn off by tidal interactions and more halo particles surrounding the host are swept into the satellite's wake. All that matter stays well above the surface of the host galaxy rather than descending into some inner halo or deep into the host galaxy itself. This serves to "suspend" the sinking satellite, posing a challenge for the "they should sink" reasoning; it also reduces the amplitude of the wake, which moderates the drag on the satellite. The combined result is that the evolution of specific angular momentum may not be enough to clearly support Kroupa's claim in the fine article linked at the top.
There has been a lively dialogue in academic publications about the scale of these effects for some twenty-five years. Kroupa's article touches upon his own position in these, but not those of others (e.g. HS Zhao, Binney) who work and publish in the area (with all of the above citing one another from time to time).
I don't mind this at all, personally, as at worst Kroupa is omitting something an interested reader could hunt down her- or himself, and after all it was "only" published on a general interest site whose present front page (https://iai.tv/articles) has an article by Eric "electric universe" Lerner entitled "The Big Bang Didn't Happen".
The view you provided helps understand the counter argument of why competing factors (e.g. losing mass) result in more sophisticated outcomes than "we would expect lighter galaxies orbiting heavier ones to be slowed down by dark matter particle". I still don't know enough about the subject to understand if the original authors claim and expectation is still likely. But your context helps me understand other factors that are in play.
Especially DM proponents!
What I do have is a metric fuckton of experience with incentives and mechanism design in technical fields: and mainstream physicists have been talking like people who have bonuses linked to specific outcomes for decades.
The moving goalposts around falsifiability, the too-coincidental synergies between supersymmetric-style (and there for string world) stuff and missing mass (dark matter), the growing group of highly-qualified skeptics, the curt public dismissals everything from LQG to constructor stuff to MOND as beneath refutation, the popularizers who go on PBS and don’t even acknowledge a debate.
And the alternative explanation, that it takes so long to learn this stuff that your career is over if Dark Matter or String Theory turns out to be hokum? Yeah, that scans.
There are simple situations where physics can be reasonably distinguished from the noise. Think Newton watching an apple fall from a tree -- these are test harnesses with a debugger and careful control of the environment. There are also astrophysical situations where it's very hard to squeeze insight out of the chaos. Instead of looking at an apple to derive Newtonian gravity, imagine instead trying to figure gravity out by looking at a flock of birds. There are tricky things in the way of our understanding, like lift, turbulence, and biomechanics. We hope to understand the bad situations someday, but right now it's tough. Instead of the nice test harness, these situations are like debugging through cryptic, un-reproducible user complaints. What's their OS? Do they have the right drivers installed? Do they have all of their ports blocked for some reason?
In astrophysics, one nice system is the Universe at very large scales: echos of the big bang, the clustering of matter, and the formation of structure. We have great data these days about the large scales, and general relativity (GR) + dark matter (DM) is a very predictive model here. To our chagrin, the data always matches the theory. It takes 5 or 6 parameters, but the model has withstood huge improvements in data quality without really changing since the 90s. The other nice situation is the small scales like our own solar system: we can measure things extremely precisely at home, and again GR works remarkably well. There are a few other good situations involving objects like pulsars. Finally there are the hard situations: intermediate scales that involve the messy physics of star and galaxy formation. We don't really know how these processes work, but we can cobble together simple models with DM that sort of match the data.
Modified gravities in the literature always seem to act exactly like general relativity + dark matter in the clean, understandable situations, although it takes various contortions (screening) for these models to do this. Modified gravity models seem to only act differently in the bad arenas that are hard to understand, when there trickier issues like galaxy and star formation. That's deeply suspicious, and really weakens the value proposition of these alternatives. It's like introducing a software feature to fix something that never happens on the dev machine, based on mysterious user reports that you can only half decipher.
Five or six freely chosen parameters is a lot. You know the von Neumann quote. If those parameters have continued to fit vastly more precise measurements without changing for 30 years that’s starting to sound like failure to falsify.
And if so, ultimately you folks have posed the particle/high-energy folks a problem: we found a shitload of weakly/non-interacting mass, where’s my particle bruh?
To the layperson, exotic undetectable mass sounds like something that will turn out to be a good metaphor for something deeper, but that doesn’t mean a lot via the definition of layperson.
Even laypeople know the string folks are full of shit: Witten has a Fields and not a Nobel for a reason.
Poor Alzheimer's research was/is stunted for a few people at the top pushing the wrong path. We'll see if that's the case for DM vs MOND vs something else.
Money will always be distributed to the wrong areas, but as long as you believe the human race to exist far into the future, it will eventually work itself out.
But with this subject we're at least working with observable data ...
Clinging to a single dominant theory is religious orthodoxy, not science. The essence of science is, "we don't pretend to know what we don't". There is plenty we do, that doesn't depend on DM.
https://you.com/search?q=Weakly+Interacting+Massive+Particle...
But DM has always reminded me of aether (https://en.m.wikipedia.org/wiki/Aether_(classical_element)) - a magical element that we add to current understanding of physics to correct for errors caused by missing knowledge. DM sounds so magical that it feels like an unknown force akeen to gravitation.
But once again, I don't know anything about this, so, who cares.
Ether was introduced because, previously, all other wave motion was waving something. It was standard issue. Waves in the ocean? Must be waving something. Waves in air? Must be waving something. Positing that there was nothing there "waving" would be the new thing.
Second, introduction of a "thing," only to find out that it is real is quite common. Witness the neutrino -- originally just a placeholder to make the math work.
It's all the ways in which it doesn't act like matter which make it interesting.
And this wikipedia article, <https://phys.org/news/2022-07-dark-ditch-favor-theory-gravit...>, seems to give a more balanced appraisal.
At issue is, rather, whether observations consistent with DM as formulated should be privileged over others that are not. Current behavior of cosmologists is that inconvenient observations should not count, and need not be paid any attention.
That is why the authors bring up sociological explanations for cosmologists' behavior. It is not scrupulous science.
> for each gram of normal matter there are 25 grams of the exotic dark matter
20% is four times 5%, yet there is 25x difference in mass? How does that work?
Certain celestial bodies don't follow those rules according to what we know about both the rules and those bodies.
So there's something we don't know about there. Either the body or the rule is missing something. If it's the body, then there's a whole mess of matter that's just imperceptible to our current methods. It is "dark" to our observation.
My interpretation of "dark matter" isn't that it's literally "matter" that is invisible and we are trying to find a way to detect it and interact with it.
Rather it's just a shorthand term that explains our math. We detect gravity. The only thing that we know that makes gravity is matter. We detect more gravity for the amount of matter we see. Therefore we call what we cannot detect "dark matter". But that's it. We have no other semblance that it is somehow "matter". We might as well call it "Unknown Gravity Generator".
Is that right or am I off base?
If I'm right, then could it just be as simple that gravity Works Differently at galactic scales much the same way that everything works differently at quantum scales and relativistic (ie high velocity) scales? And as such, we don't really need to "find" dark matter, but rather we just need to find out exactly under what circumstances the equations change - much as Einstein did for relativity? And it's a super hard problem because while we can make things move at the speed of light in a lab, we can't really give something galactic mass in a lab, and observing galactic-masses in the real world on a human scale is very hard as any relevant measurements would require multiple lifetimes to observe (hypothetically)
If I'm wrong, in what other ways is dark matter "matter-y" that makes it a useful term? And do scientists believe there is a chance we could actually be able to "generate" it an experimental environment?
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Re...
Its characterizing bulk behaviour is that dark matter exerts a pressure on galaxies immersed in it, effectively squashing them inwards (or, if you like, preventing discoid galaxies from flying apart as they spin quickly).
Under <https://en.wikipedia.org/wiki/Dimensional_analysis>, pressure has dimension L^{-1}MT^{-2}, which is the same as energy-density.
Energy-density is encoded in the (symmetric, gauge-invariant, conserved, (0,2)) matter tensor of the Einstein Field Equations of General Relativity.
Among other things this preserves notions that matter/energy cannot be created or destroyed, only converted from one form to another.
It is the microscopic constitution of the bulk energy-density, and the details about how or if it can be converted into photons or some other radiation, or other types of matter, that is not known, although the bulk behaviour imposes numerous constraints.
As with all matter in General Relativity, dark matter is subject to the strong equivalence principle, just like laboratory Cavendish experiments, or binary or triple pulsar systems, or in galaxies' peculiar motions within galaxy clusters.
Finally, your "as simple that gravity Works Differently at galactic scales" is a rejection of the Strong Equivalence Principle, and also raises the question of the (unknown) microscopic details of how the inverse square law holds up so well everywhere except the edges of many known galaxies. Typical approaches involve a new long-range ("fifth") force that in bulk effectively applies a tension on the outer reaches of galaxies where MOND transitions from the familiar 1/r^2 inverse square law for gravity to the slower-decaying 1/r law. Tension has the dimensions of negative pressure, so essentially rather than outside-the-galaxy dark matter pushing the outer gas clouds and stars inwards, we have something inside the galaxy reaching out and pulling the same gas clouds and stars inwards. One is then left struggling to do anything other than to describe the microscopic behaviours of a field that sources this negative pressure, and making that field denser somewhere towards the middle of galaxies.
My point is, dark matter explains the observations by being very flexible. There can be any amount of dark matter to fit the observations.
*N. Namba, "Stellar movement in the galaxy explained by inertial induction", Phys. Essays 15, 156(2002)
In addition, I mentioned the essence of gravity and inertia in a 2014 paper, showing that the existing theory of gravity is incomplete. The full text of this paper is now available on GALE ACADEMIC ONE FILE. Please see attached.
https://go.gale.com/ps/i.do?p=AONE&u=googlescholar&id=GALE|A...
However, we have observations which break the rules. https://en.wikipedia.org/wiki/Galaxy_rotation_curve
The thing to me, why do we assume kepler's law applies to galaxies? It has only been proven in relation to the solar system. Perhaps it has been proven to work for the exoplanets in other systems?
Also what exactly is dark matter? Is it some exotic unproven god or is it just dust, hydrogen that just doesnt glow or light up?
What about our observations are just wrong? What if we haven't adjusted our observations for https://en.wikipedia.org/wiki/Local_Interstellar_Cloud and thusly we are slightly off because of some latent glow from the local cloud? Or perhaps even going further and being in some transition to the neighbour cloud is throwing observations off.
We dont have the answers for anything here.
This very clearly must hold true for any "we" which refuses to read past the first line of an encyclopedia article.
You can't "prove" that something doesn't exist. And dark matter is simply a big fat "????" inserted into our math to make our equations match what we see.
I think it's fair for them to state that dark matter doesn't exist, in the same way that I can fairly confidently state that "The christian god" does not exist.
Doesn't explain how we got here, or what actually needs to change to make our equations match our observations, but it's a reasonable stance to encourage folks to stop spending time on an unlikely solution (even if it so far produces the best model we have).
Any attempt to "disprove" dark matter that doesn't address the hard observational fact that gravitational mass and visible mass are separable is invalid.
You're just saying, very clearly: Our observational data does not match our mathematical models for gravity, and our alternative models don't account for this case (bullet cluster)
I'm not disagreeing with you, and I'm not proposing MOND or derivatives are a valid solution, I'm just saying that you're still just positing:
"we saw thing X that doesn't work with our current model, or with our modified model, so there must be some mysterious "dark" matter that we have to add to bring our math back to matching what we observe."
So far, though - no experiment to actually find or record it, or make valid guesses about how or why it's distributed from a theoretical view, rather than as "glue" to hold our model back together, has been found (at least that I'm aware of).
So I guess I am disagreeing - It's not "directly observed" in any sense other than "something is wrong here and we can't explain why".
If it is consistently producing the best model, why is it an unlikely solution?
What would be more likely than the model which produces the best match to what we observe?
Namely, most of the experiments we can find to experimentally test for dark matter fail.
Just because a model fits our current data doesn't make it correct (honestly - my strong stance is no model is correct, but some models are useful, and some more useful than others).
Epicycles were a fantastic explanation for the timing and movements of planets appearing in the sky - They were the best model we had for hundreds of years, but the model was also utterly incorrect.
It wasn't until an almost rock solid assumption (that earth was the center of everything) was assaulted by Copernicus that we developed much more robust models.
I find it fairly interesting that epicycles were also an attempt to explain a observational data that was very hard to fit into current models. There's a fairly straight parallel to dark matter here.
I find it very compelling that we have a foundational assumption in our current model that isn't true, and that's why we're offsetting everything with dark matter to make the math line back up with reality.
You could definitely prove that something doesn't exist in any meaningful quantity. Happens all the time: The experiments searching for new particles end up proving that if they do exist, they interact too weakly to be detectable. Similarly you could make observations which place an upper bound on the dark matter density, possibly low enough that it cannot explain the galaxy rotation curves etc. anymore.
that 3 is greater in value than the number 2, yet smaller in size than the number 1.
But more seriously - you're conflating a mathematical model with the reality we're observing. Our number systems (all the varieties of math) are subject to foundational contradictions and paradoxes, and proofs within them can be incredible tools - but they are not objective truths.
We assume that the universe we experience and model is the same as the universe far, FAR away - and that's a reasonable and logical assumption - but it's STILL an assumption.
The Chandrasekhar-friction-based objection to dark matter seems to assume that dark matter must be a kind of soup that is standing still, while only the galaxies (or whatever objects) wade through it.
Dark Matter advocates, if honest, should be trying to patch up their definition to account for all these observations. Studiously ignoring them is unscrupulous.
Is dark matter in the same boat as string theory was, from a grant money and research standpoint?
It's not. Point by point:
> I've always heard that string theory was an untestable theory
True in a certain light, but misleading. Any theory of quantum gravity is going to be untestable with current methods: the relevant energy scales are just too high. That doesn't mean they won't ever be testable. We might figure out a qualitatively better collider design, or find a way to get useful data from astronomical observations, or find some other clever way around the problem. Or we might not. Theorists would love to have more experimental evidence to work with - but wanting doesn't make it so.
A somewhat more legitimate concern is the size of the "string landscape": (perturbative) string theory permits many, many, many different possible values for different physical constants. It's likely, but not certain, that this is also true nonperturbatively. If so, then we can't use the measured values of those constants as evidence for or against string theory. This is unfortunate, but hardly unique: the standard model, after all, permits infinitely many such possibilities.
> and research on it soaked up a large amount of academic budgets and grant money
Not really. Most physics funding goes to applied research, most pure research funding is for experimental work, and the majority of theory funding is not for high energy theory. I don't know whether most high energy theory grants go to string theorists: it's possible.
> And was ultimately fruitless
Only insofar as all work on quantum gravity has been "fruitless".
I don't think there have been any expirements re: strings? So it advances philosophy, but not really science yet.
Does it load for others?
Can someone knowledgeable in physics set me straight on the plausibility of this theory?
I honestly do not know how they estimate stellar masses. I suspect they just look at density of stars and have perhaps established that stars are more or less distributed randomly, but I'm armchairing here. Maybe an expert can chime in.
edit: 33% is definitely wrong, but I don't know the actual number...
Either you have to patch your gravity theory or assume there’s a bunch of stuff which interacts gravitationally but barely or not at all with electromagnetism.
* Elliptical galaxies exist where the rotation curve almost exclusively measures radial motion of blobs of gas (radiating specific wavelengths, whose redshift we can compare with other parts of the same galaxy), and sometimes other bright objects with characteristic spectra, which move outwards and inwards on an elliptical orbit; these galaxies may not spin around an axis, and may not even have anything like an equator. The anomaly is that the difference in these rising-and-falling orbits' is not as large as expected -- the outer reaches are dimmer, less dusty, and less gassy than the denser inner reaches, so there is less ordinary mass out there, but this reduction in mass density is not reflected in the orbital speeds;
* In discoid galaxies (spirals, etc.), the spin-axis of the central black hole may point at any angle relative to an axis through the galaxy centre, perpendicular to the thin disc; the polar jets of black holes can even blast mostly into the thin disc, rather than mostly out of it; the polar jets are indicative of the spin-axis of the central black hole;
* Galaxies may have more than one central black hole, especially the larger ellipticals. These central black holes typically do not have their spin axes point in the same direction, and where the spin axes are remotely close to perpendicular the black holes might not all spin in the same direction;
* Some central black holes are gargantuan, some are petite (ours is small, especially compared to the number of stars in the Milky Way), and some are apparently absent, but the rotation-curve anomalies appear to be very similar nevertheless.
That said, active central black holes -- "Active Galactic Nuclei" (AGN), of which quasars are a species -- can blow tremendous amounts of matter out of the central regions of their host galaxies, and that can alter the orbital speeds of gas and dust clouds in those galaxies generally, and much more so the behaviours of X-ray-bright gas and dust they shoot outwards into extragalactic space. AGNs can switch from very bright to essentially off, and as far as we can tell the switch-off of AGNs does not cause the rotation curve anomalies to relax. (Our extremely quiet central black hole may have been an AGN perhaps as recently as millions of years ago. <https://en.wikipedia.org/wiki/Galactic_Center#Gamma-_and_X-r...>).
Frame dragging by the rotation of central black holes in AGNs may be seen in the corkscrewing of their jet emissions: Galaxy 3C 348 shows this clearly <https://duckduckgo.com/?q=3C+348+galaxy&iax=images&ia=images...> as does the more popular M87 <https://apod.nasa.gov/apod/ap011101.html>
These jets are very bright in some characteristic wavelengths (radio in 3C 348, X-Rays in M87), but they're much sparser than the starry regions of their respective galaxies. These two galaxies are large ellipticals, and their jets do not align with anything like a central rotational axis as in a spiral galaxy.
The screw displacement related to frame dragging happens in the near region to the source black holes. Anomalous gas-cloud rotation curves are found in the far region, at the outer edges of galaxies.
Otherwise, the article actually seems a surprisingly reasonable complaint about being hard to get funding for trying to develop better alternative models which explain observations better.
But let's be careful to not overgeneralize here. The author is working out of Bonn, Germany. I have no idea how German research gets funded or what their priorities are. More importantly, I have no idea for how that funding model compares with the funding model being used by other countries. All I can reasonably ascertain after reading this article is Germany isn't funding research to develop better alternative models. I have no knowledge for what other countries are funding.
Gravity is damn near perfect on the scale of the solar system. A huge number of zeros of precision, makes great prediction, etc. Even blackholes (which is quite the corner case) seems fine with the current theory of gravity until you get down into the small details and the search for a grand unification of quantum and relativity.
However as the scale of a galaxy things break down. So there's at least 2 possibilities. One that the theory of gravity is wrong at large scales, or there's something else involved, like dark matter.
Seems natural that scientist have a working assumption that the theory of gravity is right, but the problems with it are getting more attention. There's not just one competing theory for the next step for gravity.
(1) the observed differences in gravitational forces come from a gravitational field source, not modified equations themselves
(2) The field sources are a form of matter, thus obeying some "obvious" laws like mass conservation
(3) The new kind of matter is also attracted by gravity itself, which even allows for limited predictions of how its mass distribution behaves
And we can only say it's never been observed directly, because there is indeed enough indirect evidence pointing towards its existence.
This is easy to explain. For Einstein's theory of gravitation you have the experimental evidence of every experiment every done, and against you have one guy with a half-baked argument.
"They are suppressing my work!"
"They do not want you to read this!"
Etc.
IANAP (physicist) but using this index it's hard not to imagine another place in the multiverse where this dark energy/matter cosmological model receives a high score on this rubric.
I agree it's probably very difficult to tell really novel and paradigm-shifting theories from the ramblings of cranks.
I suppose the Dark Matter model scores highly in some items of the Crackpot Index but very low in "the government is trying to suppress this", "everything they told you is a lie", and also the scientists who proposed it understood the established science and didn't randomly disregard it. I think the "conspiracy" aspect is what sets a crackpot apart.
Again, it's possible that a person is a crackpot AND he/she is also right about a particular theory!
We call that the Crackpot Jackpot.
But that is manifestly untrue. If every experiment confirmed Einstein we would not even be talking about dark matter.
> one guy with a half-baked argument
But that "one guy" happens to be an expert in the field. And his argument sounds fully baked to me.
However, it's true that some other theories that claim to explain the dark matter observations are in conflict with GR, which is why those theories are received very skeptically.
That is true for the "hypothesis" part, it is not true for the "observations" part. The observations do contradict GR. To be precise, they are at odds with the predictions of GR on the assumption that the universe is made entirely of ordinary matter. So there are two possibilities: 1) GR is wrong, 2) the universe is not made entirely of ordinary matter, i.e. there is "something else", which we call "dark matter". The problem is, there is no evidence for the existence of dark matter other than the observations that are at odds with the predictions of GR, and so the possibility that GR could be wrong still needs to be taken seriously at this point.
You could also say that deviations in Uranus’s orbit contradict GR under the assumption that Neptune doesn’t exist. But Neptune does exist, so this isn’t really a statement about GR at all.
This paper also adapts GR in such a way that it is consistent with galactic rotation rates, the anisotropies of the CMB, and cosmological expansion -- while showing that the simple operation of gravity is the cause of each of these phenomena.
Cyclic Gravity and Cosmology (CGC) predicts that there are discrete specific sizes allowable for macro-objects. The instability of Bennu and the fact that it behaves more like loosely held scree rather than a compact mass -- is an example of a mass that is not exactly at one of the discrete allowable sizes. Please also refer to the link I included wherein I uploaded a video simulation of the formation of a solar system using this type of force law. (This is in section 18 of the paper)
I would greatly appreciate any comments on this idea. Copies may be downloaded here:
Dark Matter is a fudge factor used to account for quite good, but still incomplete physical modeling.
We don't understand why our numbers don't add up so we made up a number to explain it is "compelling" to you?
Dark matter has always reeked of "ether" to me. I looked into some of the alt science on this a long time ago. There is a compelling case that our model of gravity is wrong. Fortunately gravity is such a weak force that at small ie solar system scales it doesn't matter. Which is why we can launch satellites around the system. However the failure shows at large scale like galaxies.
It is an observable fact that dark matter is a distinct substance from baryonic matter. Modified gravity is thoroughly disproven by the many galaxies that have been discovered that have been separated from their dark matter[1], or seem to have never had any in the first place [2]. A galaxy can't be separated from, or be lacking in, something that doesn't exist.
Any attempt to dismiss dark matter entirely without addressing this highly conclusive evidence is not valid.
It's such a simple explanation which explains so many otherwise unexplained things that I feel we should have pretty strong priors that it's true.
It does make the prediction that there's a lot of detectable massive particles out there. That's not a prediction which is easy to test, but to say there are no predictions isn't right.
And it doesn't explain anything! We have this entirely new substance and we don't know what it is, what it's made of, where it came from, or why we only have circumstantial evidence for its presence.
To use an analogy from the world of finance, that sounds like building a Balance Sheet model that "plugs" Retained Earnings so that Assets and Liabilities always balance. Of course it fits the data, its very existence is to explain away the part of the model that doesn't fit the data
https://en.m.wikipedia.org/wiki/User:Herostratus/Finland_doe...
Also
https://www.cbsnews.com/news/birds-arent-real-origin-60-minu...
Article makes hyperbolic claims that "dark matter doesn't exist". This is junk, sorry. And that article makes me deeply distrust the otherwise-reasonable-seeming research.
The three biggest issues with the sciences today are:
1) grant money purse strings controlled by bureaucrats with a political agenda
2) the "peer review process" and lack of open source, real-time, collaborative research
3) scientists who become dogmatic about their field of expertise, even if all of their work is built on a flawed theory
All three are interrelated and a cancer in terms of humanity's progress.
I'm sure you'll find plenty of examples of #3 in this thread, too.