There has been another attempt to explain away the radial acceleration relation as being fine in ΛCDM. That’s good; I’m glad people are finally starting to address this issue. But lets be clear: this is a beginning, not a solution. Indeed, it seems more like a rush to create truth by assertion than an honest scientific investigation. I would be more impressed if these papers were (i) refereed rather than rushed onto the arXiv, and (ii) honestly addressed the requirements I laid out.
This latest paper complains about IC 2574 not falling on the radial acceleration relation. This is the galaxy that I just pointed out (about the same time they must have been posting the preprint) does adhere to the relation. So, I guess post-factual reality has come to science.
Rather than consider the assertions piecemeal, lets take a step back. We have established that galaxies obey a single effective force law. Federico Lelli has shown that this applies to pressure supported elliptical galaxies as well as rotating disks.
Lets start with what Newton said about the solar system: “Everything happens… as if the force between two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.” Knowing how this story turns out, consider the following.
Suppose someone came to you and told you Newton was wrong. The solar system doesn’t operate on an inverse square law, it operates on an inverse cube law. It just looks like an inverse square law because there is dark matter arranged just so as to make this so. No matter whether we look at the motion of the planets around the sun, or moons around their planets, or any of the assorted miscellaneous asteroids and cometary debris. Everything happens as if there is an inverse square law, when really it is an inverse cube law plus dark matter arranged just so.
Would you believe this assertion?
I hope not. It is a gross violation of the rule of parsimony. Occam would spin in his grave.
Yet this is exactly what we’re doing with dark matter halos. There is one observed, effective force law in galaxies. The dark matter has to be arranged just so as to make this so.
Convenient that it is invisible.
Maybe dark matter will prove to be correct, but there is ample reason to worry. I worry that we have not yet detected it. We are well past the point that we should have. The supersymmetric sector in which WIMP dark matter is hypothesized to live flunked the “golden test” of the Bs meson decay, and looks more and more like a brilliant idea nature declined to implement. And I wonder why the radial acceleration relation hasn’t been predicted before if it is such a “natural” outcome of galaxy formation simulations. Are we doing fair science here? Or just trying to shove the cat back in the bag?
I really don’t know what the final answer will look like. But I’ve talked to a lot of scientists who seem pretty darn sure. If you are sure you know the final answer, then you are violating some basic principles of the scientific method: the principle of parsimony, the principle of doubt, and the principle of objectivity. Mind your confirmation bias!
That’ll do for now. What wonders await among tomorrow’s arXiv postings?
Triton Station 
Your careful work and public outreach through this blog is much appreciated.
As you said, LCDM did not predict the RAR, and post-hoc fitting is not predicting. It would be valuable to show that LCDM could also fit an inverse RAR -a dummy relation going in the opposite direction- in the same “natural” way as claimed in this arxiv paper and in others.
LikeLike
We sort of did this all the way back in 1998, ApJ, 508, 132, where we showed that you could swap the photometry and rotation curves of NGC 2403 and UGC 128 [galaxies with the same asymptotic Vflat, but different rotation curve shapes V(R)] and get a perfectly reasonable fit with dark matter but not with MOND (i.e., you could fool one but not the other). I’ve also shown that non-RAR predictions can be obtained from LCDM (e.g., in arxiv:1404.7525). There are lots of simulations out there, many of which do other things (like transforming cusps into cores). So there is no consensus among simulators that the EAGLE and APOSTLE simulations are correct. To really do what you’re suggesting, I think the proper experiment would be to publish fake data that did the wrong thing then watch the simulators match it. This would be unethical, if all too apropos to this era of fake news.
LikeLike
Unethical, but certainly entertaining! and thanks for the links.
Speaking of entertainment, starting at 09:29 In this talk (https://vimeo.com/5490979), David Deutsch has many radical things to say about bad scientific theories and the way to deal with criticism of low quality (of course he himself has an agenda and argues for his pet theory):
“You can’t blame a theory’s opponents for not developing it. For not getting it.”
“The proponents of Everett’s theory focused on defending it against criticism of rather poor quality.”
“Defending a theory against its predecessors is inherently backwards looking.”
“What is the point of having better tires on your car if you’re not going to use them for going somewhere”
About the last one, it looks as though this is exactly what you’ve done with the RAR – moving somewhere that could not have been foreseen by other theories.
LikeLike
Trying to look forward! That is the problem with contending with these various claims. It takes real time and effort to demonstrate whether or not they are spurious. This is innately backwards looking.
LikeLike