here is an argument from the observed structure of the universe that appears to decisively falsify MOND and TeVeS in favor of General Relativity and dark matter.
the last graph in the next link plots the per spectrum of matter (how it clusters) versus INVERSE distance. GR with no dark matter and MOND (snd TeVeS) with no dark matter are convincingly falsified while GE plus dark matter agrees nicely with the data.
Why the Universe needs Dark Matter (and not MOND) in one graph – Starts With A Bang
for those who want the scholarly preprint of the argument:
http://arxiv.org/pdf/1112.1320v1.pdf
so IMO MOND is dead.
The article presents a very convincing argument. For a long time I had been hoping that MOND-like alterations to gravity would make dark matter...just go away.
The ghost-like properties of DM just seem so contrived. The DM concept just doesn't "feel" natural.
When faced with the choice between... 1. gravity is a little wrong and needs to be tweaked or 2. there is 5 times more stuff that you have no way of seeing pulling everything everywhere that passes though itself and ordinary matter interacting more or less only gravitationally and we don't know what it's made of or how it was made or where it comes from.
Occam's razor says choose item 1. (when faced with equally competing theories that match observation, choose the simplest.) Unfortunately choice 1 no longer matches observation. Choice 2. still really really sucks.
Ask me what I know and I won't say very much. Ask me what I think and you'll get an earful.
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All the world's a hammer and I'm the only nail.
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chas53 (07-24-2014),not_Fritz_Argelander (07-24-2014)
I can understand your pain but I cannot share it. It really is a matter of esthetics and Occam's razor actually cuts both ways. So in the spirit of simply sharing differences I'll reply to your points in detail below.
The neutrino is no more ghost like in its properties than DM. In fact the earliest candidate for DM was neutrinos. It didn't work out though. But the history of the discovery of the neutrino gives courage that postulating a new kind of matter to be found in order to preserve laws of physics that are in some sense "beautiful" often pays off. Bohr wanted to give up conservation of energy to explain weak interaction decays. Pauli rightly asserted that conservation of energy was too beautiful to give up and postulated a missing hard to detect particle to save conservation of energy from Bohr.
There are a couple of things here. First MOND is a really ugly tweaking. The equations for MOND look really forced and artificial. Here is a discussion that I vehemently disagree with:When faced with the choice between... 1. gravity is a little wrong and needs to be tweaked or 2. there is 5 times more stuff that you have no way of seeing pulling everything everywhere that passes though itself and ordinary matter interacting more or less only gravitationally and we don't know what it's made of or how it was made or where it comes from.
The MOND pages
IMO MOND is just a fudge without any conceptual motivation. Notice how the meaning of the modification of Newtonian dynamics is ambiguous: it can be interpreted either as a modification of the simplified Newton's second law (F=ma no longer holds) OR Poisson's equation for the Newtonian gravitational field is modified to be a particularly ugly equation.
The Newtonian Poisson equation is beautiful. The MOND Poisson equation is repellently ugly. Dirac said:
Your statement that dark matter alternative amounts to "there is 5 times more stuff that you have no way of seeing pulling everything everywhere that passes though itself and ordinary matter interacting more or less only gravitationally and we don't know what it's made of or how it was made or where it comes from" is unfair on several counts. The leading candidates interact both via gravitation and the weak interaction. It should also undergo "dark matter anti dark matter annihilation" so we should be seeing excess gamma rays from galactic halos (like those seen by Fermi). Plus supersymmetry provides a natural zoo of dark matter particles. Axions are another. Massive additional flavors of neutrino are another possibility. These additional forms of matter are all more natural than throwing away Poisson's equation.It seems that if one is working from the point of view of getting beauty in one's equations, and if one has really a sound insight, one is on a sure line of progress. If there is not complete agreement between the results of one's work and experiment, one should not allow oneself to be too discouraged, because the discrepancy may well be due to minor features that are not properly taken into account and that will get cleared up with further development of the theory.
I disagree about Ockham's razor. Choice 1 is profoundly more complicated and introduces a fudge factor into the Poisson equation. My gut tells me that HAS to be wrong. Also note that the anti dark matter folks complain that no one has seen dark matter in a lab. Well, to be fair, the MOND folks have not tested their modified Poisson equation in a lab EITHER. In fact it can be regarded as beyond our technology to test. So MOND is less testable than Dark Matter.Occam's razor says choose item 1. (when faced with equally competing theories that match observation, choose the simplest.) Unfortunately choice 1 no longer matches observation. Choice 2. still really really sucks.
Ockham is neutral. MOND is just gosh awful ugly and less testable (in a laboratory) than Dark Matter.
PS I have a Poisson equation afterthought......
One of the beautiful things about physics is that there are parallel mathematical structures in the different fields. Consider Poisson's equation which in its normal non MOND form can be found here:
Poisson's equation - Wikipedia, the free encyclopedia
Note that the same cute little equation describes gravitational and electrostatic fields. Poisson's equation also models static temperature distributions and a whole wealth of problem areas.
Poisson's equation (and the related Gauss's Law) has many consequences that are well attested and beautiful. The net zero interior acceleration due to a uniform spherical shell of mass or charge is a consequence. The effective shielding of conductors is another.
It seems very artificial to modify Poisson's equation specially for gravitation and not for other fields.