The spinning of a massive body like a galaxy bends and warps space-time according to the rules of general relativity.
Credit: University of Warwick
The puzzling prevalence of matter over antimatter in the universe might be related to the bizarre space-time stretching caused by our galaxy's spin, a new study suggests.
Antimatter is a strange cousin to the stuff that makes up galaxies, stars and us. For every matter particle there is thought to exist an antimatter partner with the same mass but opposite charge. When matter and antimatter meet, they annihilate, converting their mass into energy in a powerful explosion.
Though the universe today is almost completely made of matter, scientists don't understand why. The Big Bang that created the cosmos 13.7 billion years ago should have produced equal parts matter and antimatter, which would have annihilated, leaving the universe barren of either. Luckily, it didn't (hence the Earth and the life it supports are here).
To what we owe our good fortune, physicists haven't much of an idea. But a new study that takes the spinning of our galaxy into account could point the way. [Wacky Physics: The Coolest Little Particles in Nature]
Physicist Mark Hadley of the University of Warwick in England calculated the effects of the Milky Way's spin on the space-time around it. According to the theory of general relativity, the speed and angular momentum of such a large spinning body twists the space and time around it in a process called frame-dragging.
Because of the mammoth mass of our galaxy, this twisting should have an impact on space-time that is more than a million times stronger than that of Earth's spin, Hadley found.
These changes to space and time — in particular a stretching of time called time dilation — could in turn affect how particles break down. Because of their different properties, matter and antimatter particles might react differently to the time dilation and decay at different rates because of it. [Video: Flying Space-time's Warps and Twists]
For some time, physicists have measured this asymmetry in decay rates between matter and antimatter, and called the phenomenon charge-parity violation (CP violation). But no one yet has a firm explanation for how the asymmetries came about.
"These [violations] have been measured but never explained," Hadley said in a statement. "This research suggests that the experimental results in our laboratories are a consequence of galactic rotation twisting our local space-time. If that is shown to be correct then nature would be fundamentally symmetric after all."
Hadley thinks that matter and antimatter aren't actually asymmetric at the root of things, but that their differing responses to the changes wrought by galactic rotation simply give this appearance. He says that if the overall big picture of all particles is taken into account, the variation of different levels of time stretching averages out and CP violation disappears.
"CP violation is seen as the key to explaining the matter asymmetry in the universe, but the measured CP violation is inadequate to explain the universe that we see today," Hadley wrote in a paper describing his findings published this month in the journal Europhysics Letters.
Instead of using CP violation to explain the prevalence of matter over antimatter in the universe, Hadley suggests that space-time warping may solve the mystery. Perhaps the spinning of massive structures formed early in the universe also stretched out time and space in a way that affected the overall distribution of matter and antimatter, he proposed.
To test his hypothesis, Hadley said researchers could investigate the findings of two experiments going on right now: the particle collisions produced inside the world's largest atom smasher, the Large Hadron Collider at CERN in Geneva, and the BaBar experiment at the SLAC particle physics laboratory at California's Stanford University, which studies CP violation in the decay of particles called B mesons.
"This radical prediction is testable with the data that has already been collected at CERN and BaBar by looking for results that are skewed in the direction that the galaxy rotates," Hadley said.
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