Here’s what you’ll learn when you read this story:

• Scientists have long been puzzled by why matter dominated antimatter in the early universe, when both should have been created equally and annihilated each other.
• A new study suggests that a mirror universe may have formed alongside ours in the Big Bang, preserving laws of physics that appear to be violated locally.
• The authors found that the same matter-antimatter imbalance likely occurred in both universes during cosmic inflation.

The standard model of particle physics has done wonders for humanity’s never-ending quest to understand the universe and our place within it, but it still leaves some pretty big, glaring questions unanswered. And one of those big questions is arguably the most important of them all: Why is there something rather than nothing?

The conundrum at the heart of this question is matter-antimatter (or baryon) asymmetry, which states that in the early Universe, matter and antimatter should’ve been created in equal amounts. Because these particles annihilate each other and convert their mass to pure energy, the universe should have no matter in it. But of course, you, I, and everything we can sense around us all suggest that’s definitely not what happened.

One way to explain this imbalance is simple—just violate the known rules. These rules are known as charge conjugation (C), parity transformation (P), and time reversal (T), or CPT, and they govern how the universe behaves at all locations and at all times.

Well, at almost all times. The idea is that maybe, at some point in the chaos of the early Universe, a CPT violation could have cause dasymmetry in mesons between matter and antimatter, potentially producing one extra matter particle in every billion.

Now, a new study published in the The European Physical Journal C argues that local violations of CPT might have been possible in the early Universe because we’re not actually looking at the entire picture. In other words, the Big Bang may have created a mirror universe alongside our own—one with opposite spatial orientations and reversed time coordinates, where time effectively runs backwards relative to ours. Together, the two universes preserve CPT symmetry as a whole, but within each individual universe, those supposedly immutable laws appear to be locally violated.

“The combined CPT symmetry is widely regarded as exact, and its violation would necessarily indicate physics beyond the Standard Model (SM) of particle physics,” the authors wrote. “We propose that the Big Bang generated […] a pair of universes with opposite orientations, and that CPT symmetry may have been locally violated during the earliest stages of cosmic evolution.”

The authors argue that this local symmetry breaking would have created enough imbalance in the early Universe’s inflaton field to produce the matter-antimatter asymmetry we observe today. (The inflation field is the hypothetical scalar quantum field thought to have driven the universe’s expansion faster than the speed of light during the first moments after the Big Bang). When the authors plugged the numbers into these fields, they found the expected asymmetry in both universes at roughly one part per billion—enough to kick-start a universe dominated by matter (or antimatter).

“A mass difference between the inflaton and its corresponding anti-inflaton field can lead to unequal particle–antiparticle production rates during reheating,” the authors wrote. “The paired-universe model preserves the geometric integrity of spacetime symmetries while providing a natural setting in which CPT symmetry may be globally conserved but locally broken.”

Is there any way to prove this dual-universe theory? Well, the authors suggest that primordial gravitational waves (generated by this inflationary period) or neutrino asymmetries could carry a fingerprint of these CPT asymmetries from the early universe. The theory could also have implications for how we understand other, longstanding cosmological mysteries, such as dark matter and dark energy.