This paper and its proposed solution is less notable than its discussion of the problem with the standard model of cosmology, which is known as the "impossible early galaxy problem". In general, modified gravity theories lead to earlier structure development in cosmology, so this problem favors such theories relative to dark matter, although modified gravity isn't necessarily the only possible solution.
To understand the formation and evolution of galaxies at redshifts z < 10, one must invariably introduce specific models (e.g., for the star formation) in order to fully interpret the data. Unfortunately, this tends to render the analysis compliant to the theory and its assumptions, so consensus is still somewhat elusive.
Nonetheless, the surprisingly early appearance of massive galaxies challenges the standard model, and the halo mass function estimated from galaxy surveys at z > 4 appears to be inconsistent with the predictions of LCDM, giving rise to what has been termed "The Impossibly Early Galaxy Problem" by some workers in the field. A simple resolution to this question may not be forthcoming.
The situation with the halos themselves, however, is more straightforward and, in this paper, we use linear perturbation theory to derive the halo mass function over the redshift range z < 10 for the R_h=ct universe. We use this predicted halo distribution to demonstrate that both its dependence on mass and its very weak dependence on redshift are compatible with the data.
Manoj K. Yennapureddy, Fulvio Melia, "A Cosmological Solution to the Impossibly Early Galaxy Problem" (March 19, 2018).The difficulties with LCDM may eventually be overcome with refinements to the underlying theory of star formation and galaxy evolution within the halos. For now, however, we demonstrate that the unexpected early formation of structure may also simply be due to an incorrect choice of the cosmology, rather than to yet unknown astrophysical issues associated with the condensation of mass fluctuations and subsequent galaxy formation.
A related issue is that we don't know how black holes got so big so fast under existing cosmology models.
Metal enrichment in the intergalactic medium in the very early universe also challenges our models.
14 comments:
sabine hossenfelder pointed out a lot cold dark matter cosmology of this relies on computer simulation which may or may not be accurate.
how does MOND improve the situation? starting with an all baryon universe, gravity after critical acceleration ao drops off close to 1/r rather than 1/r2
are there any papers that explicitly show with "computer simulation" that with a baryon only universe, MOND does give rise to earlier structures?
"are there any papers that explicitly show with "computer simulation" that with a baryon only universe, MOND does give rise to earlier structures?"
Yes.
http://astroweb.case.edu/ssm/mond/LSSinMOND.html
thanks, what about MOND and black holes got so big so fast problem?
I think that one can roughly approximate MOND early cosmology as the same as LamdaCDM but faster. But, there is certainly less work done in MOND and I don't have time in the next few days to go looking.
Apparently there are Warm Dark Matter ‘top down’ cosmologies which can form structure early like this, so I would like to mix (i) a large scale WDM empiricism with (ii) a local MOND view for galactic scales. Not impossible with quantum inertia.
for your next blog topic this paper just came out
Search for a new X(16.7) boson and dark photons in the NA64 experiment at CERN
We report the first results on a direct search for a new 16.7 MeV boson (X) which could explain the anomalous excess of e+e- pairs observed in the excited Be-8 nucleus decays. Due to its coupling to electrons, the X could be produced in the bremsstrahlung reaction e- Z -> e- Z X by a 100 GeV e- beam incident on an active target in the NA64 experiment at the CERN SPS and observed through the subsequent decay into a e+e- pair. With 5.4\times 10^{10} electrons on target, no evidence for such decays was found, allowing to set first limits on the X-e^- coupling in the range 1.3\times 10^{-4}\lesssim \epsilon_e \lesssim 4.2\times 10^{-4} excluding part of the allowed parameter space. We also set new bounds on the mixing strength of photons with dark photons (A') from non-observation of the decay A'->e+e- of the bremsstrahlung A' with a mass \lesssim 23 MeV.
https://arxiv.org/abs/1803.07748
well there is still some parameter space left
No sure that a null result for a not very well motivated BSM particle search is very newsworthy.
perhaps not but i think its very cool research teams are attempting to validate this. if you read the paper they state there is still a parameter space left and that many research groups may explore this region in the coming years as well as dark photons
re: dark matter vs mond
there's also the issue of weak gravitational lensing - the amount of mass energy responsible to create weak gravitational lensing in galaxy clusters minus the visible baryonic mass results in a deficit, in which there is a need for 5 times more dark matter. this number matches the number obtained from CMB BAO. this results in the mainstream view nonbaryonic dark matter must exist, and these difficulties is a matter of refining both dark matter properties and computer simulations. MOND stacy mcgaugh et al is a minority view.
personally i wonder if geons the size of galaxy clusters could explain this. geons or glueballs or strangelets could explain "dark matter" without adding new particles to the SM
there's also the issue of weak gravitational lensing - the amount of mass energy responsible to create weak gravitational lensing in galaxy clusters minus the visible baryonic mass results in a deficit, in which there is a need for 5 times more dark matter. this number matches the number obtained from CMB BAO. this results in the mainstream view nonbaryonic dark matter must exist, and these difficulties is a matter of refining both dark matter properties and computer simulations. MOND stacy mcgaugh et al is a minority view.
While this is definitely a problem for MOND in sensu stricto it is not a serious problem for modified gravity theories generally. It just means that the MOND equation isn't quite right. Both MOG and Deur come up with equations the deal with this issue. I don't see it as any stronger an argument for dark matter than rotation curves are.
In Deur's model the key point is that the shape of the source of the field as well as the strength of the field matters, and in clusters you get the equivalent of "force tubes" that are seen in QCD from the same non-Abelian self-interaction of gluons in analogy to gravitons. I don't know how MOG does it at the technical level, but it does.
There is a scaling relation analogous to Tully-Fisher that works for clusters which also suggested a plausible gravity modification solution.
does Deur's model make any predictions that can be tested experimentally?
Heaps. Search Deur on this blog and read his papers. There are only about four or five papers or so. They aren't long and they aren't terribly technical. There is also a power point presentation linked in one of my prior posts that others have found useful to understanding the work.
He calls it not a violation of GR and SM, but it does contradict GR in some respects, some of which are common to all quantum gravity theories with gravitons (e.g. localizing gravitational energy and conserving mass-energy locally), and in particular, his self-interaction analysis produces results contrary to GR as conventionally applied in major textbooks. This said, apart from his analysis of self-interaction of gravitons, it is basically standard quantum gravity via a graviton which is very mainstream with some innovated approaches to making numerical approximations (starting from the static limit with scalar gravitons on the theory that tensor graviton contributions distinct from scalar gravitons are very modest in most circumstances).
His background in QCD also makes him more credible with respect to self-interacting bosons than lots of conventional GR investigators who go from GR to quantum gravity, instead of some other physics field.
One of the big predictions distinct to this theory is that the apparently amount of dark matter in elliptical galaxies is a function of how non-spherical they are, which holds up, and which would not be predicted by almost any other theory.
it'd be interested to hear what other QCD theorists think.
it sounds to me this graviton-graviton QCD theory is similar to the older theory of geons. entities trapped by their own gravitational self-energy.
geons or glueballs i suspect could explain the third peak in CMB
in the news galaxy NGC 1052-DF2
has no dark matter but apparently none of the effects of MOND either.
so the news says this "rules out" MOND. it is unknown how a galaxy without dark matter keeping newton einstein intact can form though
@neo I have a post up and an inquiry out to Stacy McGaugh
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