> that has been falsified more than once
What has been falsified more than once?
What has been falsified more than once?
Our math says the universe comes up short on mass by over 3/4ths? Must be invisible matter we can't see or interact with see, the models still good!
Over simplification in the extreme, but also a far cry from the rock solid foundations it claims to be.
https://medium.com/starts-with-a-bang/five-reasons-we-think-...
"Five Reasons We Think Dark Matter Exists: No other idea explains even two of these."
"1.) Galaxy Clusters"
"2.) Galactic Rotation Curves"
"3.) The Cosmic Microwave Background"
"4.) The Bullet Cluster"
"5.) Large-Scale Structure Formation"
From these 5, only dark matter matches all. Whereas MOND theories match only one, the "item number 2" and only as an attempt to after-the-fact-explanation of what's anyway observed, not as any prediction of anything new.
As I've quoted in my another message here:
"the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later. This is not a case of tweaking the model to fit the data; this is a case of the best kind of science you hope for: where you make predictions, make the observations, and what you see validates and confirms the predictions you had made."
Moreover, there's nothing "large" of the possible space that is now excluded. The possible space includes everything that "behaves like matter". What's (still just "probably") eliminated is just what were for us, humans, in this particular moment of our history very convenient to happen: that the energies needed are exactly such that WIMPs that were conveniently postulated to be such can be generated by the device which design and maintenance costs less than 2% of the total cost of the F-35 fighter planes (the money invested and planned to be invested in F-35 is 75 times bigger than the international investment in LHC). It would have been luck if it had happened, but the possibilities are much bigger and include such which are going to remain physically unreachable to be produced by our technologies.
That we, humans, can't produce some particles doesn't disprove that dark matter exists when we have precise observations that can only be explained by dark matter and effectively by nothing else.
Dark matter can be placed arbitrarily so it can match pretty much anything. I remember recently there was a galaxy with negligible deviation of the GR-predicted rotation curve and that was taken as evidence for dark matter too (even though MOND was still the better fit for that case).
"Dark Matter" started out ok but has become a "god of the gaps" argument, I expect eventually MOND or similar solutions will be developed for all those issues.
Also, I gather that while MOND does seem not predict these observations exactly, it is not fully developed yet and often the presence of some "normal" cold gas (undetectable via light) could make it fit. Also, to get dark matter to fit the observations requires post-hoc assumptions and parameter adjustments. Eg:
"The amplitude of the third peak observed by WMAP merely falsifies the simple ansatz I used to make the prediction, not MOND itself. Indeed, I pointed out in the original papers that the ansatz must fail at some level, so I am hardly surprised that it does. All this means is that there are degrees of freedom (like a scalar field) that can oscillate separately from baryons in whatever the relavistic parent theory of MOND might turn out to be. The real test was for ΛCDM: the third peak had to be higher than predicted by pure baryonic damping. ΛCDM survives this test. It "wins ugly" in that, in order to obtain a fit, we have had to nearly double the baryon density over what it was so confidently known to be before it wasn't. That, and the no-CDM prediction for the second peak is still bang on. Amazing coincidence, that." http://astroweb.case.edu/ssm/mond/
>"the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later."
I'm afraid I have never seen this although I have looked into this topic (as a layperson). Can you give an example of this? It would make the dark matter idea much more convincing.
Quite the opposite, and that statement is obviously uninformed. The science behind dark matter is very precise and exact. That's why the alternative theories can't come even near: once the same rigor which was applied to test dark matter is applied to the alternatives, the alternative theories simply break.
> I'm afraid I have never seen this ... Can you give an example of this?
I've given you the link to the complete articles and also highlighted the major points. Try to read and understand them fully, then search for more. For example, even on the MOND page that you linked you can read:
"2013: ΛCDM provides an excellent fit to the improved CMB data just as MOND provides an excellent fit to improved rotation curve data. As before, one's interpretation depends entriely upon which you find more impressive."
Note: "rotation curve" from that quote is the "item 2" from my posts before. So, no, still the match of the single "item 2" is definitely not "more impressive." The "CMB" mentioned on your page is the "item 3" from all 5 which are explainable by ΛCDM (and specifically, ΛCDM is the model part of which the "dark matter" is: https://lambda.gsfc.nasa.gov/education/graphic_history/univ_... see there 4 and 5).
Edit: response to your later response below:
> The claimed predictions from the 1970s and 1980s are not mentioned on that page.
They are mentioned even on the very page that you linked to: that page, among other points, followed the history of the tests and effectively concludes that, yes, finally, in 2013 ΛCDM wins the "item 3". Read carefully. Learn what ΛCDM is. MOND can still only claim "item 2." Which actual "authority" can show anything else? Also, behind "darkmattercrisis" blog are just a few guys with very fringe positions.
From what I have seen they can get precise post-dictions but not precise pre-dictions because there are so many free parameters (basically you can put dark matter wherever you need it).
>"I've given you the link to the complete articles and also highlighted the major points. Try to read and understand them fully, then search for more."
The claimed predictions from the 1970s and 1980s are not mentioned on that page.
Also, that "startswithabang" guy is more like a catholic inquisitor than a scientist. I wouldn't consider him a reliable source because this behavior indicates he lacks the required capacity for curiosity, he can only repeat what authority figures say:
"The blogger (@StartsWithABang) contacted @scilogscom on January 24 by replying to a 15-day old tweet that announced our blog’s move to the new domain. He tweeted “Bummed that @scilogscom is in the business of promoting contrarian scientist viewpoints.”, and asks the SciLogs.com community manager (@notscientific) “[Why] are you allowing @scilogscom to promote contrarian voices that undermine public understanding of [science]?”, adding “You have taken on “Dark Matter Crisis” blog, whose mission is to undermine all of physical cosmology & promote MOND.”
The two agreed to discuss the issue via email, with the blogger adding that he was “personally worried that you are promoting clicks & false controversy over quality science content”, and states that he is “very, VERY disappointed about this move that @scilogscom has made”.
By now the SciLogs.com community manager has explained to us what happened after these tweets. He and the publishing director responsible for SciLogs.com unfortunately assumed that the blogger’s criticism was justified. They decided to close our blog without conferring with others or asking us for a statement. After we complained about the discontinuation, they performed an internal investigation, which involved reaching out to astrophysicists and other people, and have realized that discontinuing our blog was a big mistake. We attribute SciLogs.com’s poor judgement to two factors: neither the community manager nor the publishing director has an (astro)physical background, it was the first time that SciLogs.com had experienced an attack against one of its blogs." https://darkmattercrisis.wordpress.com/2013/03/08/the-dark-m...
Anyway, I can tell you know even less about this topic than me so let's leave it at that.
They are mentioned, they just aren't elaborated: you have to do your own homework if you apparently "understand" the subject enough to claim your own opinion. A begin of that homework, however, as I've already written, you even have on the initial page that you chose to post, specifically:
"2013: ΛCDM provides an excellent fit to the improved CMB data"
As I've said, that's the "item 3" from the 5 item list, and it's ultimately confirmed by ESA's Planck satellite results in 2013. That is a strong confirmation.
Note: more details and the timeline are on the very page you've initially posted. Ad hominems don't change the facts.
No, they were not mentioned. If they were, you would be quoting it.
>'"2013: ΛCDM provides an excellent fit to the improved CMB data"
As I've said, that's the "item 3" from the 5 item list, and it's ultimately confirmed by ESA's Planck satellite results in 2013. That is a strong confirmation.'
You have to read the entire quote. This "fit" was a post-diction, not a pre-diction: "in order to obtain a fit, we have had to nearly double the baryon density over what it was so confidently known to be before it wasn't."
Post-dictions can be interesting as part of model development but are unable to confirm a model. The new, (possibly adjusted) model then need to be checked against new data.
https://lambda.gsfc.nasa.gov/education/graphic_history/baryo...
"There is general good agreement between the recent CMB and D/H+BBN determinations shown in the figure."
I don't see the "double" anywhere there. And the values could be traced to all the sources mentioned there.
Here in a recent comment he addresses the "galaxy cluster" issue: https://tritonstation.wordpress.com/2018/11/21/hypothesis-te...
He is currently active at this blog: https://tritonstation.wordpress.com/
It looks like this doubling happened in ~2000 so it wouldnt show up in your chart.
Since 2000 many new satellite measurements were done and the values improved. As I've quoted your page Planck in 2013 ultimately made the most precise CMB measurements that most conclusively fit the "dark matter" model and provably don't fit the "MOND" model. And for that proof there were no "factor 2" corrections, as you also confirm, at least since 2000. The way you wanted to believe, and how you quoted some other parts of the same document, was that that had to be done for that 2013 proof, and it obviously haven't had. BTW the nature of the measurements, especially those made decades ago, is such that when we started with some value and then later measured something only 2 times smaller or bigger (but then all repeated measurements remain closer to one another), it's still OK. It's not the absolute values that prove this or that, it's the measured shapes that match or not the very complex calculations. And that's what happened in 2013 with Planck: what was measured for more than a decade with other satellites, and finally most precisely with Planck, shows the shape that in practice can't match the MOND predictions but nicely matches what the "dark matter" model predicts.
The point is that "suddenly" people started measuring a higher baryon density to make it fit what was required for lambda-CDM model to fit the CMB measurements. Ie, the lambda-CDM model did not pre-dict the spectrum beforehand, they had to tune it to match the data.
And see how the squares and triangles start moving upwards once the blue circles appear: http://www.astro.umd.edu/~ssm/mond/BBNLCDMMOND.jpg
Remember the oil drop experiment mentioned by Feynman in his cargo cult science talk? That is what this looks like to Mcgaugh: http://calteches.library.caltech.edu/51/2/CargoCult.htm
I have to say, it is very frustrating to discuss this since you seem to misunderstand every simple point being made, and before that has been corrected you have gone on to miss another point that needs to be addressed. We are not discussing this at a very deep level... Perhaps English is not your native language, but I am just letting you know. I hope no offense is taken.
W...what? Do you really believe that different scientific organizations in different countries around the world financed and sent different satellites into space but misrepresented the actually measured values only to "fit" some old theoretical predictions?
Really?
Then there's really no point discussing anything about science with you.
Yes.
> so it can match pretty much anything
At the time you do the initial placement. But that's not the only relevant time.
You can scatter any type of DM on a spacelike hypersurface any way you want, but then you have to figure out the successor (and predecessor) spacelike hypersurface, and there you have to bite a bullet: you can constrain the DM or throw away the well-posedness of the initial-value problem.
Your constraints are dominated by the hyperbolic-elliptic PDEs. The hyperbolic portion lets you lay down initial values for your dark matter on a spacelike slice. You then need an equation of motion for your DM, as you do for your visible matter, so that you can evolve the contents of that initial spacelike slice in time. The elliptical portion are the Hamiltonian and momentum constraints.
Without satisfying these constraints you tend to lose uniqueness, which destroys the predictive power of your model.
If you're spraying down a dust of non-interacting DM particles within some spacelike region, as you evolve from your initial configuration you end up with each particle growing into an everywhere-timelike worldtube. (Non-(self-)interaction is just to make this really clear without the distractions of decays or daughter products from scatterings. Each dark matter particle has its own worldtube extending arbitrarily far in to the future or past.)
The simplest Cold Dark Matter models have a conventional nonrelativistic and relativistic dynamics determined by two parameters: particle rest-mass and interaction cross-section. In our simple non-interacting cold DM dust case the interaction is purely gravitational, so we're left with every particle having an identical rest mass.
Now, lay down the visible matter in a galaxy (or cluster!). You can lay down the dark matter dust arbitrarily to form a halo which could support a realistic galaxy rotation curve on your initial surface. You are right that you can put it practically anywhere, and are not restricted to uniform density. However, when you evolve in time, you inevitably find that you are stuck with a narrow range of mass densities at various points in the galaxy (or cluster!), but still have freedom to set down differing particle number density, higher numbers at lower particle mass. If your particles are too light, the gravitational coupling with the visible matter is too slight; worse, the gravitational coupling between the DM particles is too slight too, and your galaxy quickly disassembles. If your particles are too heavy, instead you get dynamic heating of hydrogen gas, and you get far too much star formation and metal enrichment.
You can go the other way too: first put down a test particle DM halo and then add hydrogen gas, or a modern galaxy, or whatever else, and see how the system evolves. It is a feature of the standard galaxy astrophysics that DM and visible matter do not have to be near each other at all times. (This gets important when you consider galaxy clusters rather than just galaxies; laying out CDM is hard work, as I've been describing, but you can't just drop in MOND. It's also testable at solar-system scales; we can look for post-Newton dynamics in the Jupiter system, or in the inner solar system, and test whether it's compatible with General Relativity (with a fine dark matter dust of up to a few Phobos-masses inside Neptune's orbit) or whether it's compatible with a different post-Newtonian dynamics, like MOND, where the galaxy's MOND corrections will generate a quadrupole anomaly stronger around the outer planets and their moons than around the inner planets).
More complicated particle CDM theories are still stuck with the general rules of the simple model above: the stress-energy in the large has to hang around in the right places for long periods of time; the stress-energy can't just pop in and out of existence at a point (it needs to be thermal, so its worldtubes cannot even be nearly lightlike, let alone timelike); and it has to have a reasonable number density). Crucially, non-gravitational coupling to the Standard Model imposes further restrictions on the initial surface, it does not relax them.
More complicated particle CDM is usually motivated by problems in particle physics, models for for which galaxy (and cluster!) astrophysics can provide observational evidence. Some WIMP models are good tests for SUSY models, so one experimental search might test two models grown from very different underlying theories. One does not have to believe the "WIMP miracle" conjecture when one can outright test it observationally and in a laboratory setting.
> MOND
By construction you can't put MOND just anywhere on your initial values surface; it is a phenomenon arising from visible matter. You can't put down MOND first and then add matching matter and see what happens. (Well, there are relativistic theories which start by taking MOND and then proceed to take General Relativity by introducing one or more fields until they get a good match with MOND. Some of those approaches might let you put down a "MOND field" first and add matter that -- Famaey and McGauch have a good, if aging, overview in Chapter 7 of https://arxiv.org/abs/1112.3960 -- but at some point you might ask if you can start with an already-relativistic theory like General Relativity and recover MOND from that instead. MOND does appear to work for galaxies, after all, even if it needs modification for much larger and much smaller structures.)
Or you're getting closer to finding out what the real parameters are?
If you eliminate all possibilities and have to make up some new parameters, sure, that feels like you're not doing science and might as well be a creationist. But what you describe, narrowing down the space of possible explanations from infinitely many to only a few, is the dream of every theoretical physicist.
By that metric, epicycles were rock-solid.