The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion; the universe does not expand "into" anything and does not require space to exist "outside" it. To any observer in the universe, it appears that all but the nearest galaxies (which are bound by gravity) recede at speeds that are proportional to their distance from the observer, on average. While objects cannot move faster than light, this limitation only applies with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.
Cosmic expansion is a key feature of Big Bang cosmology. It can be modeled mathematically with the Friedmann–Lemaître–Robertson–Walker metric, where it corresponds to an increase in the scale of the spatial part of the universe's spacetime metric (which governs the size and geometry of spacetime). Within this framework, stationary objects separate over time because space is expanding. However, this is not a generally covariant description but rather only a choice of coordinates. Contrary to common misconception, it is equally valid to adopt a description in which space does not expand and objects simply move apart under the influence of their mutual gravity. Although cosmic expansion is often framed as a consequence of general relativity, it is also predicted by Newtonian gravity.
According to inflation theory, during the inflationary epoch about 10−32 of a second after the Big Bang, the universe suddenly expanded, and its volume increased by a factor of at least 1078 (an expansion of distance by a factor of at least 1026 in each of the three dimensions). This would be equivalent to expanding an object 1 nanometer (10−9 m, about half the width of a molecule of DNA) in length to one approximately 10.6 light years (about 1017 m or 62 trillion miles) long. Cosmic expansion subsequently decelerated down to much slower rates, until at around 9.
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Explores the foundations of the Big Bang Theory, including thermal equilibrium, radiation-dominated stage, and the prediction of the Cosmic Microwave Background (CMB).
Explores the impact of COVID-19 on astronomy and the European Southern Observatory, delves into the Friedmann equations, and discusses the concept of dark energy.
Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of gravity. Gravitational collapse is a fundamental mechanism for structure formation in the universe. Over time an initial, relatively smooth distribution of matter will collapse to form pockets of higher density, typically creating a hierarchy of condensed structures such as clusters of galaxies, stellar groups, stars and planets.
In stellar physics, the Jeans instability causes the collapse of interstellar gas clouds and subsequent star formation, named after James Jeans. It occurs when the internal gas pressure is not strong enough to prevent gravitational collapse of a region filled with matter. For stability, the cloud must be in hydrostatic equilibrium, which in case of a spherical cloud translates to where is the enclosed mass, is the pressure, is the density of the gas (at radius ), is the gravitational constant, and is the radius.
The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion; the universe does not expand "into" anything and does not require space to exist "outside" it. To any observer in the universe, it appears that all but the nearest galaxies (which are bound by gravity) recede at speeds that are proportional to their distance from the observer, on average.
This course is the basic introduction to modern cosmology. It introduces students to the main concepts and formalism of cosmology, the observational status of Hot Big Bang theory
and discusses major
Cosmology is the study of the structure and evolution of the universe as a whole. This course describes the principal themes of cosmology, as seen
from the point of view of observations.
Introduce the students to general relativity and its classical tests.
Be captivated by the exotic objects that populate the Radio Sky and gain a solid understanding of their physics and the fundamental techniques we use to observe them.
Ce cours décrit les principaux concepts physiques utilisés en astrophysique. Il est proposé à l'EPFL aux étudiants de 2eme année de Bachelor en physique.
This course covers the principles and practices of radio astronomical observations, in particular with modern interferometers. Topics range from radio telescope technology to the measurement equation
We present a comprehensive discussion on lattice techniques for the simulation of scalar and gauge field dynamics in an expanding universe. After reviewing the continuum formulation of scalar and gaug
By using the first-principles approach, we derive a system of three quantum kinetic equations governing the production and evolution of charged scalar particles by an electric field in an expanding un
This thesis is concerned with gauge theories, their complicated vacuum and resulting effects. After an introduction to the subject, it is divided into four parts.Firstly, we treat the problem of chi