Universe Could Be Half Antimatter

Scientists explored how much antimatter might form through processes called baryogenesis (the theoretical creation of the observed imbalance between matter and antimatter in the early universe). They also discussed how these "antimatter objects" might look and how we could spot them.

The study used theoretical models of baryogenesis, looking at different ways that fundamental symmetries (like C and CP violation—processes that describe how particles behave when certain properties are reversed) could be broken.

The team found that a specific process, the Affleck-Dine mechanism, could create compact objects or dense clouds made of both antimatter and regular matter. These objects could share equally in the universe's total mass density.

The research suggests these antimatter objects could even account for up to 100 percent of dark matter (a mysterious substance that doesn't emit or reflect light but is thought to make up a large part of the universe's mass).

The nearest "antigalaxy" is thought to be at least 10 million parsecs (Mpc, about 32.6 million light-years) away.

"The universe would look as a huge piece of swiss cheese with high B bubbles instead of holes and homogeneous background with constant baryonic density," the authors said, describing a scenario where antimatter and matter exist as distinct regions.

If these anti-objects behave like stars, their thermal glow would be about L ≈ 10^39 ergs per second (a measure of energy output) for objects the size of our Sun. Even with so much antimatter, the researchers note that expected annihilation products (when matter and antimatter meet and destroy each other) would be tiny – not exceeding about one quadrillionth (10^-15) of the Cosmic Microwave Background (CMB, faint background radiation from the Big Bang).

The study points out that some theories of antimatter creation face challenges, like the "domain wall problem" (a theoretical issue that could prevent the universe from forming as observed). Also, previous models sometimes predicted too many density fluctuations.

The current estimates are simplified and require more detailed future calculations. Scientists will continue searching for cosmic antinuclei, extra antiprotons, positrons, and gamma rays from annihilation, which all offer a chance for discovery.