O TYM ODCINKU
Transcript: Universe with matter in it will be continuously decelerating over time since the big bang. Cosmologists refer to this as the deceleration parameter, and it’s written as a little q with a subscript zero. In standard cosmologies q0 equals a half for a flat universe, less than a half for an open universe, and more than a half for a closed universe. The relationship is more complex in cosmologies with a cosmological constant. Measuring the deceleration depends on comparing the properties of distant objects like galaxies with nearby objects. This is difficult because of the problem of look-back time. When we look at distant objects we are looking at objects as they were and not as they are now, so when we compare objects that are distant or high redshift with nearby objects we are not comparing like with like. Unless astronomers can model and predict the rate of cosmic evolution of stellar systems like galaxies they can not do cosmological tests based on a comparison of distant objects with nearby objects. To this point it has been very difficult to conduct this type of cosmological test.
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WYSZUKAJ MINIONE ODCINKI
Wyszukaj minione odcinki 22. The Big Bang, Inflation, and General Cosmology.
INNE ODCINKI W TYM PODCASCIE
Transcript: In the big bang model it’s possible to calculate the abundance of light elements created by fusion reactions in the early phases of the expansion. This is called cosmic nucleosynthesis. The calculations depend on only one fundamental parameter of the universe which is the density of p…
Transcript: The best traditional test of cosmic nucleosynthesis and the predictions of the big bang model is the helium abundance in the universe. In the model of the big bang the predicted helium abundance is relatively insensitive to the cosmic density, so astronomers need a measurement accurate…
Transcript: What is the physical meaning of the cosmological constant? Astronomers do not know and physicists are puzzled too, but they’ve both come up with the idea of dark energy. In physics the vacuum is not totally empty. Particles and anti-particles can be created from the vacuum, and the g…
Transcript: The cosmic abundance of light elements is a primary piece of evidence in favor of the big bang model. Stars are fusion factories, and main sequence stars create helium from hydrogen by the fusion process in their cores. However, a careful accounting of stellar fusion over the history …
Transcript: The problem with using helium 3, helium 4, or lithium 7 for testing cosmic nucleosynthesis in the big bang model is that all three of these are created in stars, and lithium can be destroyed in stars. So it’s difficult to estimate which of the nuclear abundances are primordial, origina…
Zastrzeżenie: Podcast i grafika osadzone na tej stronie pochodzą z Dr. Christopher D. Impey, Professor, Astronomy, który jest własnością jego właściciela i nie jest powiązany ani wspierany przez Listen Notes, Inc.
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