Chapter 22 Flashcards
What were conditions like in the early universe?
The early universe was filled with radiation and elementary particles. It was so hot and dense that the energy of radiation could turn into particles of matter and antimatter, which then collided and turned back into radiation.
How did the early universe change with time?
The universe has progressed through a series of eras, each marked by unique physical conditions. We know little about the Planck era, when the four forces may have all behaved as one. Gravity became distinct at the start of the GUT era, and electromagnetism and the weak force became distinct at the end of the electroweak era. Matter particles annihilated all the antimatter particles by the end of the particle era. Fusion of protons and neutrons into helium ceased at the end of the era of nucleosynthesis. Hydrogen nuclei captured all the free electrons, forming hydrogen atoms, at the end of the era of nuclei. Galaxies began to form at the end of the era of atoms. The era of galaxies continues to this day.
How do observations of the cosmic microwave background support the Big Bang theory?
Telescopes that can detect microwaves allow us to observe the cosmic microwave background—radiation left over from the Big Bang. Its spectrum matches the characteristics expected of the radiation released at the end of the era of nuclei, confirming a key prediction of the Big Bang theory.
How do the abundances of elements support the Big Bang theory?
The Big Bang theory predicts the ratio of protons to neutrons during the era of nucleosynthesis, and from this predicts that the chemical composition of the universe should be about 75% hydrogen and 25% helium (by mass). The prediction matches observations of the cosmic abundances of elements, another spectacular confirmation of the Big Bang theory.
What key features of the universe are explained by inflation?
The hypothesis that the universe underwent a rapid and dramatic period of inflation successfully explains three key features of the universe that are otherwise mysterious: (1) the density enhancements that led to galaxy formation, (2) the smoothness of the cosmic microwave background, and (3) the “flat” geometry of the observable universe.
Did inflation really occur?
We can test the idea of inflation because it makes specific predictions about the patterns we should observe in the cosmic microwave background. Observations made with microwave telescopes so far match those predictions, lending credence to the idea that inflation (or something much like it) really occurred.
Why is the darkness of the night sky evidence for the Big Bang?
Olbers’ paradox tells us that if the universe were infinite, unchanging, and everywhere the same, the entire night sky would be as bright as the surface of the Sun, and it would not be dark at night. The Big Bang theory solves this paradox by telling us that the night sky is dark because the universe has a finite age, which means we can see only a finite number of stars in the sky.
