Alternative theory of gravity explains large structure formation -- without dark matter

The light from galaxies in the background has been warped and “arced” by the galaxy cluster Abell 1689 in the foreground, and perhaps with some help by either dark matter or a stronger type of gravity on this large scale. Image Source: NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI),G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA.