Tweak Gravity: What If There Is No Dark Matter?

INVISIBLE OR NONEXISTENT? A composite image of the galaxy cluster Abell 520 shows the inferred presence of matter, primarily dark matter, in blue. X-ray: NASA/CXC/UVic./A.Mahdavi et al.; Optical/Lensing: CFHT/UVic./A.Mahdavi et al.

From Scientific American:

Modifications to the theory of gravity could account for observational discrepancies, but not without introducing other complications.

Theorists and observational astronomers are hot on the trail of dark matter, the invisible material thought to account for puzzling mass disparities in large-scale astronomical structures. For instance, galaxies and galactic clusters behave as if they were far more massive than would be expected if they comprised only atoms and molecules, spinning faster than their observable mass would explain. What is more, the very presence of assemblages such as our Milky Way Galaxy speaks to the influence of more mass than we can see. If the mass of the universe were confined to atoms, the clumping of matter that allowed galaxies to take shape would never have transpired.

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