Scientists have been searching for “dark matter” – an unknown and invisible substance thought to make up the vast majority of matter in the universe – for nearly a century. The reason for this persistence is that dark matter is needed to account for the fact that galaxies don’t seem to obey the fundamental laws of physics. However, dark matter searches have remained unsuccessful.

But there are other approaches to make sense of why galaxies behave so strangely. Our new study, published in the Journal of Cosmology and Astroparticle Physics, shows that, by tweaking the laws of gravity on the enormous scales of galaxies, we may not actually need dark matter after all.

The Swiss astronomer Fritz Zwicky discovered in the 1930s that velocities in galaxy clusters were too high to account for how much matter we could see. A similar phenomenon was described by several groups of astronomers, such as Vera Rubin and Kent Ford, when they studied the motion of stars at the far edges of the Andromeda Galaxy.

The Big Bang didn’t just result in our familiar universe, according to a mind-bending new theory — it also generated a second “anti-universe” that extended backwards in time, like a mirror image of our own.

A new story in Physics World explores the new theory, which was proposed by a trio of Canadian physicists who say that it could explain the existence of dark matter.

The new theory, which is laid out in a recent paper in the journal Physical Review of Letters, aims to preserve a rule of physics called CPT symmetry. In the anti-universe before the Big Bang, it suggests, time ran backwards and the cosmos were made of antimatter instead of matter.