“But then if you mathematically factor in the fact that
Verlinde’s prediction doesn’t have any free parameters,
whereas the dark matter prediction does, then you find
Verlinde’s model is actually performing slightly better.”
First test of rival to Einstein’s gravity kills off dark matter
11–20 of 87 posts
Re: First test of rival to Einstein’s gravity kills off dark matter
#12What would be the next test? Clusters or that dark matter dwarf galaxy causing ripples in our Milky Way?
Re: First test of rival to Einstein’s gravity kills off dark matter
#13You may find the top answer to this SE question helpful (asked 5 years ago, though): http://physics.stackexchange.com/questions/6561/are-modified... . Especially I think the following comment is spot on: "Galaxy rotation curves are not very good tests for GR itself, since there are so many parameters about mass distribution in a galaxy which are simply not nearly as precisely understood as GR itself"
That says MOND is a non-theory, so now I'm even more confused since this theory "builds on" MOND.
Re: First test of rival to Einstein’s gravity kills off dark matter
#14“But then if you mathematically factor in the fact that Verlinde’s prediction doesn’t have any free parameters, whereas the dark matter prediction does, then you find Verlinde’s model is actually performing slightly better.” What? How does this work?
principle of parsimony
Re: First test of rival to Einstein’s gravity kills off dark matter
#15“But then if you mathematically factor in the fact that Verlinde’s prediction doesn’t have any free parameters, whereas the dark matter prediction does, then you find Verlinde’s model is actually performing slightly better.” What? How does this work?
Say that you want to estimate what is the chance that observation 1 fits theory A just by accident (the lower this chance is the higher your confidence can be that theory A is "real").
If theory A has parameters you can adjust, it becomes easier for an observation to fit the theory just by accident (because you can adjust the free parameter).
This is a fairly flawed description, but it should be a good enough ELI5.
Re: First test of rival to Einstein’s gravity kills off dark matter
#16“But then if you mathematically factor in the fact that Verlinde’s prediction doesn’t have any free parameters, whereas the dark matter prediction does, then you find Verlinde’s model is actually performing slightly better.” What? How does this work?
From the discussion section of Verlinde's paper[1]:
> We have shown that the emergent laws of gravity, when one takes into account the volume law contribution to the entropy, start to deviate from the familiar gravitational laws precisely in those situations where the observations tell us they do. We have only made use of the natural constants of nature, and provided reasonably straightforward arguments and calculations to derive the scales and the behavior of the observed phenomena. [..]
> In our view this undercuts the common assumption that the laws of gravity should stay as they are, and hence it removes the rationale of the dark matter hypothesis. Once there is a conceptual reason for a new phase of the gravitational force, which is governed by different laws, and this is combined with a confirmation of its quantitative behavior, the weight of the evidence tips in the other direction.
Re: First test of rival to Einstein’s gravity kills off dark matter
#17> String theorist Lubos Motl savaged Verlinde’s ideas in a recent blog post: “I wouldn’t okay this wrong piece of work as an undergraduate term paper.”
I find this rudeness and pedantry in academia infuriating. There's no justification for this level of nastiness -- not in private, public, peer review, or science as a whole. Seeking out the unknown and creative explanations thereof is the hallmark of good science; check your ego at the door. I know nothing about him... but in my book, Lubos Motl can go pound sand.
Re: First test of rival to Einstein’s gravity kills off dark matter
#18Totally OT: I read "Einsteins graffitti" and could watch my own brain trying to make sense of the sentence. And fail.
Re: First test of rival to Einstein’s gravity kills off dark matter
#19Folks, the observation doesn't test Verlinde's idea, this tests a very general class of models, such as the well-known MOND scheme.
> Milgrom, however, supports the work. He also points out that according to his own 2013 analysis of gravitational lensing data in galaxies, MOND produces similarly impressive results as Verlinde’s gravitational model does in Brouwer’s study.
(Also: http://motls.blogspot.ca/2016/11/verlindes-de-sitter-mond-is... )
This data cannot distinguish between Verlinde and other explanations for MOND-like behavior. We've long known that MOND seems to fit a subset of all observational data better the dark matter, in particular the Tully–Fisher relation
https://en.wikipedia.org/wiki/Tully%E2%80%93Fisher_relation
However, for the rest of the data (e.g., the CMB, large-scale structure, the bullet cluster), MOND is generally considered to give a worse fit than dark matter, or to be silent (because it's not obvious how to extend MOND to a complete cosmological theory). That's why experts think the totality of evidence supports dark matter.
Nothing has changed.
Re: First test of rival to Einstein’s gravity kills off dark matter
#20> String theorist Lubos Motl savaged Verlinde’s ideas in a recent blog post: “I wouldn’t okay this wrong piece of work as an undergraduate term paper.” I find this rudeness and pedantry in academia infuriating. There's no justification for this level of nastiness -- not in private, public, peer review, or science as a whole. Seeking out the unknown and creative explanations thereof is the hallmark of good science; ch…
Lubos Motl hasn't been in academia for almost a decade. Almost everyone inside and outside it finds him obnoxious.