Thursday, November 15, 2007

Attack of MOG

Here at Colorado, instead of simply requiring graduate students to attend colloquia as they do at BYU, we are required to take "seminar" classes for each of our first four semesters. These are designed to run like a journal club on steroids. A group of professors selects a topic and a paper for each class, then the students take turns presenting that paper to the class in a presentation/discussion format. It's a lot of work, but I have found it to be very rewarding.

This semester, I am in a seminar on the largest, gravitationally bound objects in the universe, galaxy clusters. Galaxy clusters are interesting for a number of reason, but probably the hottest reason to study them right now is cosmology. This has resulted in about half of the classes being devoted to cosmology. A few weeks ago we studied the now famous paper by Clowe et al. on the Bullet Cluster and the existence of dark matter. This paper produced the stunning image on the right that I imagine you have all seen. This was seen as very strong evidence for the existence of dark matter, as opposed to modified theories of gravity (e.g. modified Newtonian dynamics (MOND) and modified gravity (MOG)) that attempt to explain the evidence for dark matter by saying that the problem is with our theories of gravity rather than missing mass. The Bullet Cluster observation was seen as a nail in the coffin for those theories.

Some people, like Dr. John Moffat at the University of Waterloo (Canada), refuse to give up on MOG despite the evidence. There is a story about him on (found here). He has published a paper attempting to explain the bullet cluster observation using a modified version of general relativity (MOG) and he claims that MOG can explain it. For those of you who'd like to read it, you can find it here.

I respect his efforts and I think people should question the current cosmological models, but at some point you have to give up on disproven theories. MOG already suffers from the problem that you have to fine tune the parameters one way to get galaxy rotation curves to work and another way to get galaxy cluster observations to match. Besides that, MOG doesn't mesh with other cosmological evidence, like the flat universe from WMAP, without further changing the parameters. At some point, enough in enough and we all just need to declare MOG dead and get on with cosmology. I think that point was the picture above by Clowe et al.


  1. Coincidentally that is what I concluded with my research. I haven't seen anything yet (Full blown GR, MOG, or MOND) that could reproduce the flat rotation curves without creating problems, such as closed timelike curves and the like. I think that GR can give a correction and there is evidence to that but it won't make dark matter go away. We still have that "problem" to deal with.

  2. Nick, I completely agree with you. You should study the life of Fred Hoyle. He is the textbook example of one of the worlds brightest minds who spent their whole life studying theories that go against all evidence and sense, just because he refused to accept modern Cosmological theory and evidence.

    Look, theories aren't perfect, but at some point you have to confess some theories are so successful there must be some truth to them and others have been so unsuccessful, something is wrong.

    Now the question: what do you do with something like Supersymmetry that seems to solve all your problems,(Produces dark matter with right abundances, gives rise to a positive cosmological constant small like we see, fixes things in particle physics like hierarchy problems, etc...) but we haven't directly detected it yet?

    COME ON LHC!!!


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