This is a short summary of a paper I have just published in Astrophysics and Space Science (here). Galaxies and galaxy clusters have been seen to rotate so fast that the (inertial) centrifugal forces should tear them apart. Yet, they sit there obviously a stable collection of bound stars. Therefore, the small amount of matter we can see lit up in fusion (ie: stars) seems to hold them together. How?
Some have proposed that matter that we cannot see is responsible: dark matter. This sounds fair enough, but dark matter is needed only in the outer edges of galaxies, and no particles have been detected that could provide the very specific new physics, and the extended distribution (the halo), needed to account for the observed galactic rotations. Dark matter is also not a satisfying theory because it is not falsifiable. Given any galaxy you can add dark matter wherever you want to fit your predicted rotation curve to that observed.
Instead of increasing the gravitational mass in the galaxy to hold it in by force, one can also decrease the inertial mass of the stars in it to make them more easily bind. I have suggested a model called "Modified inertia due to a Hubble-scale Casimir effect" (MiHsC), or quantised inertia (QI) for short, that does this. In QI the inertial mass decreases in a specific new way for low accelerations. Stars at the edge of galaxies have low accelerations, so QI predicts they have less inertial mass, for the same gravitational mass. A lower inertial mass means the stars can be more easily bent into a bound orbit, even by the small amount of stellar mass we see in the galaxy. In the paper I have shown that QI predicts the rotation speeds of galaxies and galaxy clusters without needing any fitting parameters or dark matter. QI also predicts the change from the Newtonian behaviour in the galactic centre, to the anomalous rotation near the edge.
The main controversy with QI is that it violates the equivalence principle (very slightly), but as I have discussed in another paper (in the discussion of the paper here) this violation could not have been detected by the torsion balance experiments that have been used to test this principle so far.
The main controversy with QI is that it violates the equivalence principle (very slightly), but as I have discussed in another paper (in the discussion of the paper here) this violation could not have been detected by the torsion balance experiments that have been used to test this principle so far.
