In search of the asymmetry of the universe
If the universe would be symmetrical, there would be neither you nor me nor anything else – except a lot of energy. Because then matter and antimatter, which must have existed at that time (symmetry presupposed) in identical quantity, would have annihilated each other shortly after the big bang. This did not happen. Matter retained the upper hand. So we know that the universe cannot be symmetrical. But why? The physics supplies us to it – still – keone clues. Astrophysicists have therefore been looking for visual traces for a long time, which might reveal something about the nature of the asymmetry and its first occurrence.
An exciting new approach uses so-called 4-point correlation functions – usually abbreviated as 4PCF in English. Don’t worry, this is mathematics, but the practical implementation is relatively simple. 4PCF have the advantage that they allow to find and nail down asymmetries. Practically, this is done as follows: You pick four galaxies each from the set of known galaxies, measure their distances r1, r2, and r3, and then put the quartet into different boxes for each combination of r1, r2, and r3. So you end up counting how many different galaxy tetrahedra there are with side lengths r1, r2, and r3. If the universe were symmetric, all different sized tetrahedra should be equally likely.
But they’re not, as astronomers at the University of Florida have found in a new paper. The UF scientists examined a million trillion galactic quadrupeds in the universe and discovered that at one point in time, the universe favored a particular set of shapes over their mirror images. This idea, known as a violation of parity symmetry, points to a tiny period in the history of our universe when the laws of physics were different than they are today, which had enormous implications for the evolution of the universe.
This finding, made with a high degree of statistical certainty, has two main consequences. First, this parity violation could have imprinted itself on future galaxies only during a period of extreme inflation in the earliest moments of the universe, confirming a central component of the Big Bang theory of the origin of the cosmos. The violation of parity would also help answer perhaps the most important question in cosmology: Why is there something and not nothing? That’s because parity violation is required to explain why there is more matter than antimatter – an essential prerequisite for galaxies, stars, planets and life to have formed in the way they did.
“I’ve always been interested in the big questions of the universe. What is the beginning of the universe? What are the rules by which it evolves? Why is there something and not nothing?” said Zachary Slepian, UF astronomy professor who led the new study. “This work addresses those big questions.” Slepian worked with UF postdoctoral researcher and first author of the study, Jiamin Hou, and Lawrence Berkeley National Laboratory physicist Robert Cahn to conduct the analysis.
Parity symmetry states that physical laws should not favor one particular shape over its mirror image. Scientists commonly use the term “handedness” to describe this feature, since our left and right hands are such mirror images that we are all familiar with. There is no way to rotate the left hand to look exactly like the right hand, which means they are always distinguishable from each other.
A violation of parity would mean that the universe has a preference for either left-handed or right-handed shapes. The technical aspects of the analysis currently make it difficult to say whether the universe prefers “right-handed” or “left-handed” shapes. But scientists saw clear evidence that the cosmos has a preference.