What does Veeky Forums think of the recent update to the radial acceleration relation for spiral galaxies?
arxiv.org
Regardless of whether dark matter or MOND is correct, this result clearly indicates that there is a fundamental relation between the gravitational potential from the baryons and the predicted potential from galactic rotation curves. This implies that it is the BARYONS that dictate the potential of galaxies, not dark matter.
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I think it's been slightly oversold. We already know there is strong relation between baryonic matter and the dynamics of a galaxy, the Tully-Fisher relation that MOND is based on. That part isn't new, this new relation is possibly just an extension of that relationship. What really needs to be done (And what the authors should have done) is go to a large hydrodynamical cosmological simulation like Illustris or EAGLE and see if the same relationship holds. Before claiming CDM cannot possibly explain this why not actually see if it does. You may in fact find this relationship already exists in standard dark matter simulations.
>mfw this post
I wish people would talk to me like this irl.
Stacy's point is merely just the data. At the end of the day, all they did was assume Newton holds and used a M/L to trace the baryonic potential. so even if MOND or DM didn't exist, we would still find this relation in nature. that's why the theory wasn't fleshed out.
Stacy has made a lot of papers in the past showing how MOND works, but his point with this paper is just to show the data, nothing about theory. I know some people have begun trying to do hydro sims with MOND, but the problem is most people won't even consider it and think its a crackpot theory.
I forgot to mention that Milgrom has also made a response already
Additionally after actually reading the papers around this one I'm more convinced it's overblown. This work is an extension of what people call the mass discrepancy acceleration relation (MDAR), it's been known about for sometime. Furthermore people actually have looked in simulations (albeit dark matter only, no baryons actually simulated) and this relation is explicable within standard CDM. Sadly as far as I can see no one has used a full hydro simulation to do this.
It is very interesting that Leli is on BOTH of those papers
There's data, then there's the conclusion and then there's what you say to the press. If you're going to use the words "challenge to dark matter" you should justify it. If you just want to present the relation that would be fine, but they went further than that.
Nobody is doing hydro with MOND because MOND can't do structure formation much less galaxy formation. When I talk about hydro I mean for dark matter simulations. This relationship speaks to the relation between baryonic and dark matter components, you need to simulate both. Nobody takes MOND seriously because it isn't a cosmological model, it just doesn't describe 99% of cosmology and the bits it does aren't justified. MOND is a data fitting model, not a physical one.
That's because he has literally nothing better to do. The guy I work with tried to solve some issues with MOND and he showed them to Milgrom who dismissed them on the basis that a model must prosper as it was first presented. Milgrom now thinks the solution is dark matter and MOND.
It's not unusual. I'm writing a rebuttal to another paper now and have both major authors on my paper.
a quick search on ADS shows people are doing MOND simulations.
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you are a CDM simulator aren't you? how does it feel to be so blind to anything that doesn't fit into your paradigm?
>MOND is a data fitting model, not a physical one.
also, this is a classic right here.
what do you think CDM is? how can you honestly say that it is a physical model when
a) we haven't detected it yet
b) the biggest evidence for it resides in SIMULATIONS
CDM arose as a means of fitting data, that's it. it is now the entrenched paradigm in cosmology simulations, but simulations are hardly reality. you do realize that points in hydro simulations are on the order of globular clusters or higher right? as in we still can't even simulate galaxies realistically even remotely? not to mention that GAIA just found nearly double the stellar mass in our own galaxy with its first data release.
>MOND simulations.
None of those are hydro galaxy formation simulations. The first one is just N body, no hydro. The second is about mergers, they start their simulations with galaxies already formed. The third is structure formation, not galaxy formation.
>you are a CDM simulator aren't you? how does it feel to be so blind to anything that doesn't fit into your paradigm?
No, I don't work on simulations at all. Don't confuse honest criticism with bias. I would sell my soul to disprove the standard model of cosmology but that doesn't mean I won't be critical of any challenge.
I just picked three abstracts at random, didn't say they were hydro. the point is that you said no one is doing it, and they are.
you also explicitly said in your post
>Nobody is doing hydro with MOND because MOND can't do structure formation much less galaxy formation
and the third abstract, once again taken at random, is exactly about structure formation in MOND.
It is circular reasoning to say,
"No one is doing MOND hydro-sims because it can't do formation, and no one is working on getting a MOND cosmology because there is no MOND hydro-sims"
>how can you honestly say that it is a physical model when
I didn't.
>CDM arose as a means of fitting data
Dark matter unlike MOND can actually explain why it fits the data. Why do rotation curves flatten in MOND? Because the model was designed to do that, it doesn't say how. Why do rotation curves flatten in CDM? Because dark matter halos follow the universal density profile which is a tribal result of even the most basic N body simulations from the early 90's. Cold dark matter forms NFW profiles ubiquitously which says rotation curves are flatten.
CDM wen't beyond fitting data. It predicted that WMAP would observe the mass density being much greater than the baryon density, the CMB is sensitive to both independently. That was confirmed. LCDM then predicted the scale and amplitude of the baryon acoustic peak, the same sound waves from the CDM frozen into galaxy clustering before it the peak was even detected. It naturally predicts the bullet cluster that no other model has even yet explained fully.
>you do realize that points in hydro simulations are on the order of globular clusters or higher right? as in we still can't even simulate galaxies realistically even remotely?
Large hydro sims have that kind of resolution but galaxy zooms have stellar mass resolution, disk columns have planet mass resolution. This isn't a criticism of dark matter, that's technology. You check what you're studying has converged at the resolution you're using.
>not to mention that GAIA just found nearly double the stellar mass in our own galaxy with its first data release.
[citation needed]
I want to see you're citation but I know this is bullshit. GAIA doesn't measure stellar mass.
>the point is that you said no one is doing it
What I actually said: "Nobody is doing hydro with MOND because MOND can't do structure formation much less galaxy formation."
>is exactly about structure formation in MOND.
I didn't say no one was doing structure formation, I said MOND couldn't as in "doesn't match data".
>No one is doing MOND hydro-sims because it can't do formation, and no one is working on getting a MOND cosmology because there is no MOND hydro-sims
I never said that or anything to that effect. Please stop stawmaning. You don't need hydro to do cosmology, you need hydro to do galaxy formation.
>trivial*
>went*
>CDM went beyond fitting data.
So has MOND. it is currently being used in numerical simulations for galaxy formation and interactions as I've already posted, as well as predicting the first two peaks of the CMB power spectrum
adsabs.harvard.edu
>Why do rotation curves flatten in MOND? Because the model was designed to do that
CDM halos were literally invented to do the exact same thing. the rest came after decades of further research and modeling
>Dark matter unlike MOND can actually explain why it fits the data
Except what it actually says is that that gravity needs to be changed. Flat rotation curves are a result of a different law of gravity. that sounds like an explanation and a prediction to me.
>I want to see you're citation but I know this is bullshit. GAIA doesn't measure stellar mass.
no shit it doesn't measure mass. What it does is map stars and it has found millions of previously undiscovered stars. these have mass. its not that hard to go from finding stars to realizing its adding mass.
also, here is an a priori prediction on the velocity dispersions of the dwarf satellites of M31 using MOND.
adsabs.harvard.edu
its fine if you think MOND is wrong, but please don't just assume all it is is a crazy data fit. it makes predictions that can be tested with data and people are doing it all the time.
>So has MOND. it is currently being used in numerical simulations for galaxy formation and interactions as I've already posted, as well as predicting the first two peaks of the CMB power spectrum
Simulations aren't evidence as you rightly pointed out. No dark matter can match the amplitudes first two peaks, it's the third peak that breaks key degeneracies. Those models would not fit the Planck data we have today because of the divergence at the 3rd peak, it doesn't follow their formula. Note there's no actual MOND in that, it's just removing the dark matter from the standard calculation. They even use the same software.
>CDM halos were literally invented to do the exact same thing. the rest came after decades of further research and modeling
As I said, it went beyond a data fitting model. MOND to this day does not explain why you should choose one interpolating function over another.
>Except what it actually says is that that gravity needs to be changed.
I don't care what you think it says. Science doesn't work like that. If you think it works differently great, build a model and go test it. If it works better than LCDM with fewer parameters then it may do well.
>it has found millions of previously undiscovered stars
Just because they weren't detected doesn't mean they weren't anticipated with number counts and modeling. We do not assume in astronomy there are vast gaps in the universe where there is no survey data. You account for incompleteness as best you can. You were talking out your ass. Where did the factor of 2 come from? You made it up.
If that were true. the rotational speeds in the center would be faster because that's where most of the baryons are.The centers of galaxies are actually not moving much faster than we'd expect with newtonian physics without dark matter. The largest discrepancies are actually in the gas surrounding the galaxies where there is a lot less mass aka a lot fewer baryons. They are also spinning a lot faster than mass- based models since servery-type estimates of mass actually give lower results than solar ratio luminosity ones.
It is a data fitting function like it or not. It was a model designed to fit the observed baryonic Tully-Fisher relation. To say it's a data fitting model does not mean it's fit to every observation it comes up against, it just means it was originally a fit to data and has no physical mechanism behind it.
>It was a model designed to fit the observed baryonic Tully-Fisher relation
MOND was developed in the 80s.
McGaugh did not develop the BTFR until 2000
>t just means it was originally a fit to data and has no physical mechanism behind it.
Here is the derivation of the MOND law.
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Tell me, where does it say it was a fit to data? Yes, it was built as a consideration that there is not any dark matter, but is a purely physically motivated law, grounded in physics.
The author also gives multiple tests for this theory in this paper and the other ones in this series as a means of confirming or disproving it.
>McGaugh did not develop the BTFR until 2000
My mistake I meant the normal Tully-Fisher relation.
>Here is the derivation of the MOND law.
Read what you post. It's just an arbitrary modification to Newtonian physics.
>Tell me, where does it say it was a fit to data?
How do they determine mu(x)? How did they determine a0?
Correct, it is a modification to Newtonian, not a fit.
Those are parameters to be found via observation. Their values are irrelevant to the physics or the maths.
I feel like we are talking past each other a lot and I apologize for this.
>not a fit.
>Those are parameters to be found via observation.
The it's a fit.
>Their values are irrelevant to the physics or the maths.
And mu is a function not a parameter. Yes the form of a modification affects the physics.
>The it's a fit.
then you are saying Hubble's Law is a fit to data and not a fundamental law as well?
v = Hd
what is H? how did the author find H?
Hubble's law is an empirical law with a single parameter. Yes it was fit to the data.
It's not a data fitting model however because Hubble's law isn't a model, it's just an empirical relation which doesn't even hold at high redshift. If Hubble's law however was v = J(d) where J is some function to be determined by the data, that would be a data fitting model.
A smaller system of lesser complexity will never be able to simulate a larger system of greater complexity
Even quantum wizardry and beyond will fail to grasp reality in its fullness
The best you can all hope for is a small fraction of the fidelity of truth
Please don't lose hope though. I love seeing you all discuss these things.
That is not at all true.
Hubble's Law is a direct result of the field equations. It is NOT an empirical relation at all and was theorized to exist before Hubble did his observations by Lemaître. The reason it does not hold at high redshifts is because the Hubble constant changes with time and has some functional form based on the value of Lambda
>Hubble's Law is a direct result of the field equations.
Hubble's law can be derived from the EFEs but it is not the only solution.
>It is NOT an empirical relation at all and was theorized to exist before Hubble did his observations by Lemaître.
Hubble in any case likely wasn't aware of Lemaîtres work and certainly didn't agree with it when it was republished. Hubble's paper makes it clear it's just a linear trend line, empirical.
As we are no longer discussing dark matter or MOND I think we've reached a stalemate.
I agree. We've gone off topic. Thanks for the fun though user