There’s nothing really stunning about this announcement – one of the simplest ways to explain the odd behavior of galactic rotation, the rapid expansion of the Universe and sundry other oddities is to modify gravitation so that it behaves differently at different length scales. Occam’s Razor smiles benignly on such endeavors.

So this report today seems to be just another attempt to do just that:

“Last August, an astronomer at the University of Arizona at Tucson and his colleagues reported that a collision between two huge clusters of galaxies 3 billion light-years away, known as the Bullet Cluster, had caused clouds of dark matter to separate from normal matter. Many scientists said the observations were proof of dark matter’s existence and a serious blow for alternative explanations aiming to do away with dark matter with modified theories of gravity. 

Now John Moffat, an astronomer at the University of Waterloo in Canada, and Joel Brownstein, his graduate student, say those announcements were premature. 

In a study detailed in the Nov. 21 issue of the Monthly Notices of the Royal Astronomical Society, the pair says their Modified Gravity (MOG) theory can explain the Bullet Cluster observation. MOG differs from other modified gravity theories in its details, but is similar in that it predict that the force of gravity changes with distance.

‘MOG gravity is stronger if you go out from the center of the galaxy than it is in Newtonian gravity,’ Moffat explained. ‘The stronger gravity mimics what dark matter does. With dark matter, you take Einstein and Newtonian gravity and you shovel in more dark matter. If there’s more matter, you get more gravity. Whereas for me, I say dark matter doesn’t exist. It’s the gravity that’s changed.'”

The problem has been that in most of these modifications to gravity, there is usually a change in the way gravity functions at the microscopic level as well. So far there’s been no observation which would indicate that the microscopic effects are there. Perhaps this modification will verify. Doing so would be a much simpler solution than invoking “dark matter”, but the simplest explanation has to actually work for it to accepted…

Read the rest here: SPACE.com — Scientists Say Dark Matter Doesn’t Exist