feynmann said:
According to Einstein's gravity.
Moffat and plenty of other physicists, theoretical and experimental, are trying to remove fudge factors and "unknowables" from physics in an attempt to simplify it. Moffat's MOG theory is very interesting, and I highly recommend the book to anyone interested. He also goes through a relatively comprehensive analysis of 'competing' theories and explains the inconsistencies in them while proving MOG does not break down the same way.
As far as dark matter, Moffat's MOG theory adds an additional vector field to gravity theory (which may, or may not be conceptually equivalent to dark
energy or the Cosmological Constant). In doing so, the theory is able to predict the perihelion advance of Mercury all the way through the seemingly anomalous orbital speed of matter toward the outside of galaxies and super galactic structures. This eliminates the need for dark matter, which at this point produces a more elegant, predictive theory that contains no free variables.
Dark energy is not eliminated necessarily, although it arises as a base concept of the theory and is considered a part of gravity rather than a mysterious property of spacetime.
Also, toward the end of the book (most of it was written chronologically - so the theory evolves over its course), Moffat makes some interesting claims that remove singularities from black holes and even universe at t=0.
Very interesting book and his arguments for MOG are a good read.
ZapperZ said:
Aren't you confusing "dark matter" with "dark energy"?
They are really not the same thing, and in fact, work in the opposite direction to each other.
And everyone who responded so far seems to not care about the confusion. So what are you people responding to?
Dark matter is generally considered to exist in a halo around massive structures, such as galaxies and galactic clusters, or in other mathematically convenient regions in cases like the bullet cluster. When explaining the behavior toward the outer edges of those structures, it's dark matter, not energy that is usually invoked.
Dark energy is often considered the force responsible for the acceleration in the expansion of the universe. Moffat et al often refer to it as vacuum energy under the postulation that it is stronger in a vacuum.
Although after reading Reinventing Gravity, it might be possible to confuse the two anyway, since dark
energy is more-or-less included in the theory and dark
matter is made irrelevant because the theory accomplishes the same thing. Basically, dark energy as a part of gravity is kind of the reason we don't need dark matter under MOG, to simplify it (probably too much).
