MOND, FUGE and Dark Matter Light

In What FUGE does not explain, I make the outrageous claim that dark matter does not exist (at least not in the FUGE model).  This is based on the fact that, in the FUGE model, the mass-energy of the universe at this time is equivalent to 8.77×10⁵²kg.

 

However, it should be noted that the amount ordinary matter in the universe is calculated, per the standard cosmological model, to be 1.46×10⁵³kg, which is higher than I arrive at.  This is because of the assumption of inflation, and the assumption of dark matter and dark energy.  The 1.5×10⁵³kg figure is based on an assumption of total energy density of 9.9×10^-27kg/m³, applied to a universe that is 46.5 billion light years in radius and multiplied by 4.8% (the proportion of ordinary matter in the standard cosmological model).  If we apply that critical density to a FUGE universe, with a radius of 13.77 billion light years, without reducing it, the figure becomes 9.17×10⁵²kg.  Note that my calculated critical density, for 13.77 billion light years, is 9.448×10^-27kg/m³, hence the 8.77×10⁵²kg figure above.

 

The complexity of this, and the outrageousness of my claim, caused me to search for any evidence that dark matter does not exist.  I found that there are indeed people who believe, for other reasons, that dark matter may not be real.  One such person is Pavel Kroupa, a professor of astrophysics at the University of Bonn and the Astronomical Institute of Charles University in Prague.  He claims that his observations falsify dark matter as a hypothesis and favours MOND, or modified Newtonian Dynamics.

 

MOND relies on an acceleration constant, a₀, which the theory’s creator (Mordehai Milgrom) worked out was about 1.2×10^-10m/s².  Basically, the theory posits that gravity works one way in high acceleration scenarios and another way in low acceleration scenarios (where a is much lower than a₀).  Unfortunately, Milgrom worked out the value via a form of numeromancy, taking the data and working out what value of a₀ would make this theory fit.

 

However, it is interesting to note that if we set a₀=c.H₀/2π, where H₀ is the inverse of the age of the universe (1/13.77 billion years = 2.301×10^-18s), we arrive at a₀=1.098×10^-10m/s².  The physical meaning of this would need to be established and note that, if it is a true relationship, then it would imply that a₀ would be a parameter that decreases with the age of the universe.  If so, then it should be possible to see hints of that in the universe today.

 

Another problem with MOND, as detailed by Milgrom himself at Scholarpedia (a location where, I discovered later, the relationship 2πa₀≈c.H₀ was identified), is that:

 

For galaxy clusters, MOND reduces greatly the observed mass discrepancy: from a factor of ∼10, required by standard dynamics, to a factor of about 2. But, this systematically remnant discrepancy is yet to be accounted for. It could be due to, e.g., the presence of some small fraction of the yet undetected, “missing baryons”, which are known to exist (unlike the bulk of the putative “dark matter”, which cannot be made of baryons).

 

Note commentary in What the FUGE model does not explain.

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And yes, I am suggesting that perhaps there *might* be some dark matter, just not as much of it as previously thought.  Call it “dark matter light”.

Note that within the MOND world, there remains a category referred to as "missing baryons" to cover a mass discrepancy, but that is not considered (by Milgrom) to be "dark matter".  However, since "dark matter" is a catch-all term to describe the phenomenon, not necessary matter per se, my pathetic little joke still works.

I should also be noted that Pavel Kroupa seems to be saying there is no dark matter whatsoever, but it's unclear whether this means there is no mass discrepancy.  I have sought clarity on that question.