When Gravity Theories Fail to Explain Observed Spin Rate Of Galaxies

The apparent variable strength of the force of gravity apparent in observations of differential rotational velocities of galaxies is a drive in creating the hypothesis that unknown or dark matter exists in the universe and in galaxies. Many galaxies have been observed to rotate at speeds fast enough that they ought to be flung apart because there isn’t enough mass and gravity to hold them together. Dark matter has been hypothesized as a hidden source of extra gravity sufficient to hold those galaxies intact.

Obviously the flattening out of space-time away from the densest mass toward the galactic enter in accord with Einstein’s general theory might account for velocity differences of mass in different regions of a galaxy. Space time itself may not be smoothly distorted by gravity-there may be washboard like folds of crenellated packings of space acting as speed bumps to create ‘friction’ to the mass passing in three or nine dimensions of space and one of time.

Theories of gravity are challenged today to reconcile with and observational differences of expected behavior.

Additional theories exist such as Milgrom’s MOND and Moffat’s MOG offering theories that correct Newton’s equation that the force of gravity drops off at the square root of the distance.

http://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

www.astro.umd.edu/~ssm/mond

MOND theory (modified Newtonian dynamics) expects that gravitational force drops off inversely proportional to the distance and that there is a two-stage break for gravitational force selection at Newton’s or at MOND equation rates; if the speed of rotation is above a certain threshold gravitational rate ‘planes’ and has Newton’s value while if below that speed it has MOND’s value.

Obviously it would be helpful to understand what gravity actually is in addition to knowing how to make an equation to describe its apparent force in the Universe. String theory and extra dimensions may provide extra theoretical descriptions of how and why gravity acts as it does. Compact dimensions being wound up like the mainspring of a clock may unwind in the expansion of the universe or addition of space to our three large, known space dimensions. Really, there is quite an opportunity for cosmologists to advance a plethora of new and unsupported theories that might tie in to the observed astrophysics of Universe1, and that isn’t such a bad thing.