Cosmic tango between the very small and the very large

While Einstein’s theory of general relativity can explain a wide variety of fascinating astrophysical and cosmological phenomena, some aspects of the larger-scale properties of the universe remain a mystery. A new study using loop quantum cosmology, a theory that uses quantum mechanics to extend gravitational physics beyond Einstein’s theory of general relativity, explains two main mysteries. While differences in theories occur at the smallest scales, much smaller than even a proton, they do have consequences at the largest accessible scales in the universe. The study, which appears online July 29 in the journal. Physical Review LettersIt also provides new predictions about the universe that future satellite missions could test.

Although an image away from the universe appears quite uniform, it has a large-scale structure, for example, because galaxies and dark matter are not evenly distributed throughout the universe. The origin of this structure dates back to the small inhomogeneities observed in the Cosmic Microwave Background (CMB), radiation that was emitted when the universe was 380,000 years old and that we can still see today. But the CMB itself has three puzzling features that are considered anomalies because they are difficult to explain using known physics.

“While viewing one of these anomalies may not be as statistically remarkable, seeing two or more together suggests that we live in an exceptional universe,” said Donghui Jeong, associate professor of astronomy and astrophysics at Penn State and author of the article. “A recent study in the journal Nature Astronomy proposed an explanation for one of these anomalies that raised so many additional concerns that they signaled a ‘possible crisis in cosmology’. However, using quantum loop cosmology, we have resolved two of these anomalies in naturally, avoiding that potential crisis. “

Research in the past three decades has vastly improved our understanding of the early universe, including how inhomogeneities occurred in the CMB in the first place. These inhomogeneities are the result of the inevitable quantum fluctuations in the early universe. During a highly accelerated phase of expansion in the early days, known as inflation, these minuscule primordial fluctuations stretched under the influence of gravity and sowed the inhomogeneities observed in the CMB.

“To understand how primordial seeds arose, we need a closer look at the early universe, where Einstein’s theory of general relativity falls apart,” said Abhay Ashtekar, professor of physics at Evan Pugh, chair of the Chair of Physics at the Eberly family and director of the Penn State Institute for Gravitation and the Cosmos. “The standard inflation paradigm based on general relativity treats space-time as a smooth continuum. Consider a shirt that looks like a two-dimensional surface, but on closer inspection you can see that it is woven by densely packed one-dimensional threads. In this of this In this way, the fabric of space-time is actually woven by quantum threads. By taking these threads into account, loop quantum cosmology allows us to go beyond the continuum described by general relativity where Einstein’s physics breaks, for example, beyond the Big Bang. “

Previous research by researchers on the early universe replaced the idea of ​​a Big Bang singularity, where the universe came out of nowhere, with the Big Bounce, where the current expanding universe grew out of a super-compressed mass that was created when the universe contracted its previous phase They discovered that all large-scale structures in the universe explained by general relativity are equally explained by inflation after this Big Bounce using loop quantum cosmology equations.

In the new study, the researchers determined that inflation under loop quantum cosmology also solves two of the main anomalies that appear under general relativity.

“The primordial fluctuations we’re talking about occur on an incredibly small Planck scale,” said Brajesh Gupt, a postdoctoral fellow at Penn State at the time of the research and currently at the Texas Advanced Computing Center at the University of Texas at Austin. “A Planck length is about 20 orders of magnitude smaller than the radius of a proton. But inflation corrections on this unimaginably small scale simultaneously explain two of the anomalies on the largest scales in the universe, in a cosmic tango of very small and very large. “

The researchers also produced new predictions about a fundamental cosmological parameter and primordial gravitational waves that could be tested during future satellite missions, including LiteBird and Cosmic Origins Explorer, which will continue to improve our understanding of the early universe.