The Music of the Big Bang: The Cosmic Microwave Background and the New Cosmology (Astronomers' Universe)
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The cosmic microwave background radiation is the afterglow of the big bang: a tenuous signal, more than 13 billion years old, which carries the answers to many of the questions about the nature of our Universe. It was serendipitously discovered in 1964, and thoroughly investigated in the last four decades by a large number of experiments. Two Nobel Prizes in Physics have already been awarded for research on the cosmic background radiation: one in 1978 to Arno Penzias and Robert Wilson, who first discovered it, the other in 2006, to George Smoot and John Mather, for the results of the COBE satellite. Most cosmological information is encoded in the cosmic background radiation by acoustic oscillations in the dense plasma that filled the primordial Universe: a "music" of the big bang, which cosmologists have long been trying to reconstruct and analyze, in order to distinguish different cosmological models, much like one can distinguish different musical instruments by their timbre and overtones. Only lately, has this amazing cosmic sound been unveiled by such experiments as BOOMERANG and MAXIMA and, more recently, by the WMAP satellite. This led to a giant leap in our understanding of the Universe, but the investigation is not over yet. The book focuses on how the exploration of the cosmic background radiation has shaped our picture of the Universe, leading even the non-specialized readers towards the frontier of cosmological research, helping them to understand, using a simple language and captivating metaphors, the mechanisms behind the Universe in which we live.
Primordial seeds. We also know that most of the matter in the Universe is of a completely different kind from the matter we are made of, and that we probably have to take into account an even stranger kind of energy. But even if we can take some pride in having made enormous progress in our understanding of the Universe, we cannot pretend to know all the answers. Every new finding generates further questions. Chapter 6 deals with some of the unanswered problems of modern cosmology.
Associated with an overdensity as a small depression in spacetime. Photons which were caught in the depression at the moment of decoupling had to spend more energy to climb out of the well, compared to photons which were already outside. This energy loss by photons translated into a frequency decrease (or a wavelength increase). Then, photons leaving a perturbed region were redshifted—this effect is called gravitational redshift, and is different in nature from the redshift induced by the.
Nearest neighbours, which initially were at a distance of 1 cm, now are 2 cm away. The next closest neighbours, however, have changed their distance from 2 cm to 4 cm, and so on. In other words, if we constantly extend the rubber band and assume the point of view of any one knot, it will look as if all the other knots are moving away, the more distant with higher velocities. Every knot might then be considered at the center of a recession motion, which of course is only apparent. In the Universe,.
The framework. At microscopic scales, instead, the importance of the other three interactions is enormous and gravity is totally irrelevant. At these scales we enter the world of quantum mechanics, and general relativity is a superfluous tool. In practice, for most physical problems we can use either quantum mechanics or general relativity to get a good description of reality. The two theories effectively live in different domains, and usually do not steal each other’s scene. Cosmologists often.
Than the critical value. We should not think that the critical density need be huge. Actually, it is roughly 10−29 grams per cubic centimeter, that is, about a hundred billion billion billion times smaller than the density of water (which is 1 gram per cubic centimeter). In order to imagine such a small value, we could visualize six hydrogen atoms in a cubic box one meter each side, or a gram of matter in a volume a hundred times larger than Earth. For comparison, in the air we breathe, and that.