ABOUT THIS EPISODE
Transcript: Why is the universe accelerating, and how does this relate to the more standard cosmological idea that since the big bang the expansion rate has been decelerating due to the action of gravity on all the matter of universe? For the answer to this we have to go back to Einstein in the 1920s. Einstein solved the equations of General Relativity and realized that the solutions naturally indicated expansion or contraction. When told that the universe was static, Einstein added a term to the solution of his equations called the cosmological constant to suppress the natural expansion. Thus the cosmological constant represents something that acts opposite to gravity. Gravity is an attractive force; the cosmological constant represents something that is repulsive. In the standard model of the universe with a cosmological constant the big bang is followed by a period of deceleration due to all the matter in the universe. And then at some epoch several billion years ago the deceleration changes into an acceleration, and the rate of expansion increases. We are currently witnessing a phase of acceleration in the universe and its evidence that the term in gravity is balanced by another term, the cosmological constant.
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OTHER EPISODES IN THIS PODCAST
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: 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 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 …
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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…
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