Cosmic tango between the very small and the very large
Theory of loop quantum cosmology describes how tiny primordial features account for anomalies at the largest scales of the universe

Date:
July 29, 2020
Source:
Penn State
Summary:
A new study using the theory of quantum loop cosmology accounts for
two major mysteries about the large-scale structure of our universe.



FULL STORY ========================================================================== While Einstein's theory of general relativity can explain a large
array of fascinating astrophysical and cosmological phenomena, some
aspects of the properties of the universe at the largest-scales 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 - - accounts for two major mysteries. While
the differences in the theories occur at the tiniest of scales -- much
smaller than even a proton -- they have consequences at the largest of accessible scales in the universe. The study, which appears online July
29 in the journal Physical Review Letters, also provides new predictions
about the universe that future satellite missions could test.


========================================================================== While a zoomed-out picture of the universe looks fairly uniform, it does
have a large-scale structure, for example because galaxies and dark matter
are not uniformly distributed throughout the universe. The origin of this structure has been traced back to the tiny inhomogeneities observed in
the Cosmic Microwave Background (CMB) -- radiation that was emitted when
the universe was 380 thousand years young 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 seeing one of these anomalies may not be that statistically
remarkable, seeing two or more together suggests we live in an exceptional universe," said Donghui Jeong, associate professor of astronomy and astrophysics at Penn State and an author of the paper. "A recent study
in the journalNature Astronomy proposed an explanation for one of
these anomalies that raised so many additional concerns, they flagged a 'possible crisis in cosmology.' Using quantum loop cosmology, however, we
have resolved two of these anomalies naturally, avoiding that potential crisis." Research over the last three decades has greatly improved our understanding of the early universe, including how the inhomogeneities
in the CMB were produced in the first place. These inhomogeneities are a
result of inevitable quantum fluctuations in the early universe. During
a highly accelerated phase of expansion at very early times -- known as inflation -- these primordial, miniscule fluctuations were stretched under gravity's influence and seeded the observed inhomogeneities 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 breaks
down," said Abhay Ashtekar, Evan Pugh Professor of Physics, holder
of the Eberly Family Chair in Physics, and director of the Penn State
Institute for Gravitation and the Cosmos. "The standard inflationary
paradigm based on general relativity treats space time as a smooth
continuum. Consider a shirt that appears like a two-dimensional surface,
but on closer inspection you can see that it is woven by densely packed one-dimensional threads. In this way, the fabric of space time is really
woven by quantum threads. In accounting for these threads, loop quantum cosmology allows us to go beyond the continuum described by general
relativity where Einstein's physics breaks down -- for example beyond
the Big Bang." The researchers' previous investigation into the early
universe replaced the idea of a Big Bang singularity, where the universe emerged from nothing, with the Big Bounce, where the current expanding
universe emerged from a super- compressed mass that was created when
the universe contracted in its preceding phase. They found that all of
the large-scale structures of the universe accounted for by general
relativity are equally explained by inflation after this Big Bounce
using equations of loop quantum cosmology.

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

"The primordial fluctuations we are talking about occur at the incredibly
small Planck scale," said Brajesh Gupt, a postdoctoral researcher at Penn
State at the time of the research and currently at the Texas Advanced
Computing Center of the University of Texas at Austin. "A Planck length
is about 20 orders of magnitude smaller than the radius of a proton. But corrections to inflation at this unimaginably small scale simultaneously explain two of the anomalies at the largest scales in the universe, in
a cosmic tango of the very small and the 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 improve our understanding of the early universe.

In addition to Jeong, Ashtekar, and Gupt, the research team includes V.

Sreenath at the National Institute of Technology Karnataka in Surathkal,
India.

This work was supported by the National Science Foundation, NASA, the
Penn State Eberly College of Science, and the Inter-University Center
for Astronomy and Astrophysics in Pune, India.


========================================================================== Story Source: Materials provided by Penn_State. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Abhay Ashtekar, Brajesh Gupt, Donghui Jeong,
V. Sreenath. Alleviating the
Tension in the Cosmic Microwave Background using Planck-Scale
Physics.

Physical Review Letters, 2020; 125 (5) DOI: 10.1103/
PhysRevLett.125.051302 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200729205012.htm

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