Introduction to Astrophysics
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Frontiers in Astrophysics
Only in the last century did scientists really begin to understand the physics of the cosmos.
Putting eyes to telescopes and pencils to paper, 20th century observers and theorists were the first to grasp the vastness of space and glimpse the diversity of its contents. The points of light rotating overhead at night, those explorers discovered, are to the cosmos as a cover to a book. And the book turned out to be an elaborate mystery story full of peculiar characters and surprising plot twists, with the ending still unwritten.
Today’s scholars of the nighttime sky tell a story of a universe incomprehensibly huge. Once misjudged to be a fixed sphere of stars encircling the sun and planets, the cosmos is now a ballooning expanse of space populated by billions and billions of galaxies, each containing billions and billions of stars. The galaxies aggregate in intricate clusters, forming great walls that envelop vast voids. Light from the most distant galaxies reaches Earth only after a transit time of billions of years.
And day after day, the universe grows bigger. Galactic clusters recede from one another at rapid speeds as the space separating them expands. Permeating all the intervening space is a faint glow of cosmic radiation, the apparent remnant heat from a cataclysmic explosion – the Big Bang – that burst the universe into existence almost 14 billion years ago.
Today’s astronomical explorers seek answers to several deep questions about the nature of space, the astrophysical objects it contains, and the universe’s composition, history and future. Guiding this quest are the 20th century’s grandest theoretical accomplishments: quantum mechanics and Einstein’s theory of general relativity. Quantum theory specifies the ground rules for explaining matter’s basic particles and the forces acting between them, while general relativity governs the large-scale behavior of the cosmos, describing gravity, space and time.
Despite their great success in realms small and large, quantum theory and general relativity have left scientists in the dark about several fundemental issues. Read Article