The dark-matter concordance cosmological model fails
The currently (2010) widely accepted/believed description of the birth
and evolution of the universe and of its contents is "Lambda Cold Dark
Matter Concordance Cosmological Model" (LCDM CCM)
(see
here ). Often LCDM CCM experts state that the current scientific
epoch is that of
precision
cosmology, because the many parameters that define this
model have been measured extremely precisely and because this
model excellently accounts for the large-scale structure, as
is evident for example in the distribution of galaxies and
galaxy-clusters and the microwave back-ground temperature
variations.
Within the
CCM
exotic dark matter needs to be postulated in order to account for
the large rotational velocities of stars about their galaxies and for
additional mass in galaxy clusters, if the observations are
interpreted from the point of view of Newtonian dynamics. The dark
matter particles are not part of the Standard Model of Particle
Physics, which is otherwise extremely successful in describing all
observed matter phenomena. Within the CCM, (exotic) dark matter forms
the first gravitationally bound structures which merge until today
forming ever larger and more massive dark-matter halos.
Baryonic (i.e. normal) matter falls into these halos forming stars and
the visible universe. Within the CCM galaxies form through heavy
merging activity, such that lesser (un-merged) sub-halos remain as
satellites about the larger more massive halos. As a result of the
heavy merging activity, galaxies turn out to be dominated by a central
bulge (essentially an elliptical galaxy) and disk galaxies are small
and thick. Galaxies like the Milky Way galaxy ought to have thousands
of satellites. Among the old, well-known major and presently not well
solved challenges for the CCM on galaxy scales are for example the
observed small number of satellite galaxies around major galaxies
(e.g. the Milky Way has only about 30 satellites), although many
standard cosmologists would claim that the missing satellite problem
has been solved. And, the observed existence of very extended but
thin rotating disk galaxies, of which at least 30% do not have a
bulge, cannot be understood. Tom Shanks summarises some of the more
fundamental problems with the CCM
here .
My own research was very much confined to the early version of the
LCDM CCM (mid-1990's) when I began performing numerical experiments on
the satellite galaxies of the Milky Way. I was quite happy with the
CCM, as everyone else, and did not bother with the fundamental issues
raised by some. With time, however, it became apparent that the LCDM
CCM accounts poorly for the properties of the satellite galaxies and
their distribution about the Milky Way. Warm dark matter models fared
no better.
By considering other major galaxies I began to realise that actually I
do not know any single galaxy whatsoever which looks like an object
that may be described successfully within the framework of the
dark-matter CCM (for example in terms of a galaxy's distribution of
dark matter within it, or in terms of the thinness and extent of the
visible matter in galaxies, or even in terms of the
star-formation behaviour of galaxies ).
Perhaps the tide began turning significantly in 1999 when I for the
first time heard an excellent talk at Harvard University by Stacy
McGaugh on his research on rotationally supported galaxies (see
Prof. Dr. Stacy McGaugh for much information on this
issue). Stacy explained in a most convincing manner that an
alternative description via modified gravity (or "extended
gravitational theory") actually leads to a far superior understanding
of galactic properties than the CCM. See
McGaugh's MOND
pages for an introduction to MOND.
Since then it has become rather clear that the CCM (with cold or warm
dark matter with at most very weak coupling to baryonic matter) is
ruled out as a viable description of the universe. The research paper
published in
2010,
Local Group tests of dark-matter concordance cosmology: Towards a new
paradigm for structure formation, leads to this conclusion. In
this research paper five problems for the CCM are found, in addition
to the well-documented previously known problems that had mostly not
been resolved. Each of the five problems poses a challenge for CCM,
and together they exclude it with very high confidence indeed. The
Disk-of-Satellite issue is but one of
the problems.
Currently (July 2010), it is not evident at all how the properties of
dark matter can be adapted such that the resulting distribution of
visible matter around and in galaxies can be made consistent with the
observations. A very strong coupling between the baryons and dark
matter particles would need to be postulated, but this involves
introducing a "fifth" force which is only relevant for the
dark-matter-baryon interaction and is none of the known three forces
with known mediating boson-particles (electromagnetic, weak and
strong), which make the Standard Model of Particle Physics so
successful.
Thus, in order to keep a cosmology with exotic dark matter and dark
energy we would need to postulate a cosmological model which
relies on
1) the existence of dark
matter,
2) the existence of dark energy,
3) an unknown "dark/fifth force" coupling dark matter and baryons and perhaps
4) an additional unknown "dark coupling" acting only between dark energy and dark matter.
This may be seen as post-adjustment epicycle modelling and these
additions of new unknown purely speculative dark components of the
universe may be conceived as not being very motivating, especially so
since a much more elegant solution is already on the horizon in the
form of modified or extended gravity. This may require a modification
of Einstein's field equations, but this is not unnatural given that
the currently used field equations are of the simplest form anyway and
do allow modifications. Some (hot, i.e. relativistic) dark matter
particles may be around even if gravity is modified (see the seminal
contributions
by Angus,
Famaey & Diaferio, 2010, MNRAS). Indeed, there is a natural
required
extension of the Standard Model of
Particle Physics which involves the existence of sterile neutrinos to
account for the observational fact that the active neutrinos have a
mass (which they do not in the pure Standard Model of Particle
Physics).
On a philosophical note, it is not at all surprising that astronomers
are indeed finding problems in our description of how space-time
couples to matter under circumstances when the curvature is very small
(weak-field limit). After all, we still do not know, at a fundamental
level, how matter couples to space-time and if it is even physically
sensible to consider space-time as disjoint from matter as is
currently the case (Einstein's field equation for example allows
cosmological solutions for universes without any matter content). Is
space-time a physical concept independent of matter, or is it an
emergent property from matter? In this view space-time without matter
would be a physically non-sensical concept.
The years 2008-2010 may stand out
in the historical context,
as the transition period when break-through results affirmed the
above interpretation of the current lack of understanding of
cosmology. Noteworthy is the reported failure to detect dark matter
particles by the on-going experiments. The following research
papers may be counted as key events in this historic process:
Disney, Romano, Garcia-Appadoo, West, Dalcanton & Cortese:
Galaxies
appear simpler than expected (2008, Nature). Within the CCM,
a dark-matter halo with a given mass would contain baryonic galaxies
with a large range of properties (as specified by a large range of
allowed specific angular momenta, baryon fractions, ages,
dark-matter specific angular momenta etc.). This paper demonstrates
that real galaxies follow a simple scaling relation and that the
large variation of galaxies is not observed. It is completely
unknown how the properties of the dark-matter particles would need
to be adapted to explain this result within a dark-matter
cosmological model. The dark-matter particles would have to be
nearly exactly coupled to the baryons to achieve this.
Gentile, Famaey, Zhao & Paolo:
Universality of galactic surface densities within one dark halo
scale-length (2009, Nature). It is shown that the surface density
of luminous (normal) matter within the putative (mathematically
formal) dark-matter halo scale radius is invariant among
galaxies. This result demonstrates a physical coupling between baryons
and dark matter particles which is not contained in the CCM, and would
only be fixed within the dark-matter hypothesis if a fifth (dark)
force is invented. However, the baryon surface density invariance is
automatically contained in the alternative-gravity theory (notably
Mordehai Milgrom's MOND).
Peebles & Nusser:
Nearby
galaxies as pointers to a better theory of cosmic evolution
(2010, Nature). With this review the authors show that the
distribution of matter in the Local Volume of galaxies is
next-to-incompatible with the expectations from the CCM. Basically,
there are too massive isolated galaxies just beyond the edge of the
filaments.
Kroupa, Famaey, de Boer, Dabringhausen, Pawlowski, Boily, Jerjen,
Forbes, Hensler & Metz :
Local
Group tests of dark-matter Concordance Cosmology: Towards a new
paradigm for structure formation (2010, A & A). This research
paper demonstrates that the Local Group of galaxies is not
explainable within the context of the CCM, but that it is very
naturally accountable within a modified gravitational framework
(without dark matter on galaxy scales).
XENON100 collaboration:
First Dark Matter Results
from the XENON100 Experiment (2010, arXiv:1005.0380). The
XENON100 experiment in Italy fails to detect WIMP scattering events
and excludes a favoured cross section with 90%
significance. Furthermore, the reported detection of two WIMP events
by the cryogenic dark matter search
(CDMS) experiment in the USA
is falsified, consistent with the reported CDMS result that theirs
is a statistically not significant detection.
Sawangwit & Shanks:
Beam
profile sensitivity of the WMAP CMB power spectrum (2010,
MNRAS). See also
Sawangwit
& Shanks and the
RAS press release.
The authors demonstrate that there is a serious systematic issue with the
resolution of the WMAP instrument used to construct the WMAP, which is
a key anchor for the high-precision LCDM CCM description of the
universe. They demonstrate that the currently permissible
re-interpretation of the WMAP data even allow a pure-baryonic (no-dark
matter) cosmological model, and that the evidence for dark energy via
the Sachs-Wolfe Effect may be absent. That is, WMAP may not be
providing any evidence for dark energy.
Interestingly, in a 2009 research
paper, Pierre-Marie Robitaille finds that a careful review
of the COBE instrument reveals numerous problems in these experiments:
inadequate antenna characterization and testing, improper treatment of
systematic errors, and failure to correctly measure the external
calibrator. In addition, he suggests that it appears that the CMB
anisotropies represent imaging artifacts generated when the COBE team
inappropriately removed a systematic quadrupole signal from underlying
random maps.
Given the above problems with the CCM, and in particular the surfaced
issues with the COBE and WMAP data analysis, it is not permissible any
longer to refer to the CCM as anything close to being of high
precision nor as a confirmed theoretical construct. Rather, we are
currently in the process of experiencing a major re-shaping of our
world view but are not yet in the situation of having a successful
theory of space-time and matter and the coupling between the two. A
historical parallel is immediately evident in that about 100 years ago
physicists (e.g. Planck, Einstein, de Broglie, Bohr) were just
beginning to realise that the quantum world and the world at very high
velocities was very different from the classical physics
experienced on a daily basis, but neither the Theory of General
Relativity nor Quantum Mechanics had been developed yet to the level
known about three decade later. It was becoming clear that dynamics
on large and small scales was definitely non-Newtonian.
Progress and Sociology
Scientific progress in understanding our world lies at the very
foundation of our technological civilization. It is an established
fact that without the theoretical research on completely new
approaches to problems achieved about 100 years ago in Europe we would
not today have mobile phones nor GPS navigation nor the energy sources
so badly needed to power our societies. Here the key strides forward
were the development of quantum mechanics and of the special theory of
relativity at a time when practical aspects of these theoretical
break-throughs were not even on the horizon. Thus, break-throughs that
were achieved at a cost to society of only the salary of a few
theoreticians, today amount to industry worth many billions of Dollars
or Euros, and probably significantly more given the dependency of the
entire planet-wide civilization on information and high-tech
industries.
How is such progress achieved, and how can it be
supported to the best efficiency, given that society nourishes further
progress through providing a fraction of its tax revenues?
The above issues on cosmology are an excellent modern case in point:
Given that many major problems with the CCM both at the fundamental
level and at the level of galactic astrophysics have been known since
at least five years if not longer, why is it that a large fraction of
the community keeps stressing the excellent agreement between the CCM
and observations? A recent research study may perhaps be relevant for
this issue: Daniele Fanelli:
Do Pressures to Publish Increase Scientists' Bias? An Empirical
Support from US States Data (2010).
The above discourse has already alluded to the notion that true
progress on the issues at hand will only be attainable once the vacuum
and the coupling of matter to space-time are understood. It is indeed
sad to observe from afar that in the US grant-supported research on
galactic astrophysics within a modified gravitational framework is all
but non-existent. It is, on the other hand, impressive to see research
on galactic astrophysics within a modified gravitational framework
thriving in Israel with the brilliant theoretical contributions by
among others, Milgrom, Beckenstein, Horwitz. In Europe an increasing
amount of research is being done in this direction too, and notably in
France through the epochal work among others of Combes, Blanchet and
Famaey, in Italy by the work of Diaferio, Capozziello, Ciotti, Nipoti
and Scarpa, not to mention the ground-breaking research on MOND and
extensions of it by Zhao and students in Scotland and Sanders in the
Netherlands. For example, a historical conference was held at the end
of June 2010 in Strasbourg (MGADS)
with the aim of assembling the community developing alternative or
extended gravitational theories in the astrophysical and cosmological
context, while a previous conference on an alternative view of
satellite galaxies had been held in Bad Honnef in Germany in May 2009
(
TDGBonn), where the modified-gravity community was well
represented. Furthermore, at the Lorentz Center in Leiden, a
conference
on
New Directions in Modern Cosmology is taking place at the end of
September 2010.
This suggests that a scientific system, as is established in the US,
which nearly exclusively relies on peer-review for funding to the
extent that the salaries of the scientists significantly depend on
successful grant-proposals, is doomed to fail in terms of supporting
truly innovative approaches to current problems. In the US it
matters too much what the others think, how others judge a
researcher's standing, ideas and output. In contrast, research in
France and Italy, while under-funded, stands out as not being heavily
dependent on grant money, and indeed the researchers are much freer to
follow intuitive notions and thus innovative paths to old
problems. Concerning the fundamental problems in galactic astrophysics
at least, and possibly other research fields as well, Europe (mostly
through France) thus appears to be leading significantly ahead of the
US.
But, even in Europe there are many instances that researchers had to
distance themselves from MOND-type research as result of a
well-founded angst of either not getting the next job or not
getting some grant. These are stories worth reporting, as they are
very relevant for expenditure of tax-payers money for achieving
current scientific progress. Perhaps the most famous story is about
Albert Einstein himself, who was not hirable in the academic system
for years until he essentially completely revolutionised our world
view, both on the quantum and the cosmological scales.
The current scientific system, as based on a peer-reviewed
research-proposal process, contains the potential of failure in that
much activity can be kept funded while not leading to major
break-throughs at the fundamental level. In Germany for example, the
very major fraction of the university resources that are funded by the
common hand are given into the possession of a few professors for
their entire academic life-span and their own disposal, while the
large majority of researchers do not carry any significant weight and
do not have a good chance to improve their situation. The current way
of using tax-payers money for funding research thus poses, at worst, a
possible challenge, and at best merely a hindrance, to continued
development of technological societies.
Prof. Dr. Pavel Kroupa (University of Bonn;
http://www.astro.uni-bonn.de/~pavel/ )
Pavel Kroupa and Mordehai Milgrom
at MGADS, Strasbourg, 29.06.2010.
