It is difficult to falsify the hypothesis of dark matter, because, as with Ptolemy's epicycles, true believers can always add additional arbitrary fe… - John Moffat

Giving up Einstein's theory of gravity is simply unacceptable to many in the community. It may take a new generation of physicists to view the evidence with unclouded eyes.

Almost 30 percent of the total matter-energy budget is said to be composed of so-called cold dark matter and almost 70 percent of "dark energy," leaving only about 4 percent as visible matter in the form of the atoms that make up the stars, planets, interstellar dust, and ourselves. Such is the degree of discrepancy between theory and observations today.

To physicists such as myself, the huge amount of invisible dark matter needed to make Einstein's theory fit the astrophysical data is reason enough for exploring modified gravity theories.