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The Big Bang Theory Age of the Earth, Solar System and Universe • Universe: 13.8 billion years • Solar System: 4.6 billion years old • Earth: 4.5 billion years old Evidence for the age of the universe • Life cycle of stars • Calculating the rate of expansion • Background microwave radiation Radioactive Decay • Radioactive Decay: The decay of radioactive elements into other elements • Mass and energy gets released in the form of radiation Radiometric Dating • Radiometric Dating: Uses the rate of decay of elements to date objects Evidence for the age of the Earth • Dating earth rocks, meteorites, lunar rocks Studying the Sky • Observation: star gazing, record keeping, telescopes The Laws of Physics • The laws of physics: scientists use the laws of physics on Earth and then apply that knowledge to the rest of the universe Technology Technology: • NASA • Space shuttle flights • Space telescopes • International space station • Robotic spacecraft missions • Probes • Orbiters Steady State Theory • Steady State Theory: 1917 • The universe is not expanding or contracting Expanding Universe Theory • Expanding Universe Theory: 1925 • The universe is continually moving outward The Big Bang Theory • The Big Bang Theory: 1927 • 13.8 billion years ago all the matter in the universe was very hot and dense • Since then, it has expanded and continues to expand **current theory** Evidence for the Big Bang 1. The abundance of light elements • The ratio of hydrogen and helium we see in the universe tells us how long ago the Big Bang happened 2. Background Microwave Radiation • There is microwave radiation everywhere in the universe left over from the Big Bang Evidence for the Big Bang 3. The evolution of stars • Scientists calculate the age of the universe by observing stars at different stages in their life cycle 4. Hubble’s Red Shift of light data • Distant galaxies are showing a red shift in light because they are moving away from our galaxy Theories about the Future of the Universe • The Big Rip Theory • The expansion of the universe is accelerating and someday it will be going so fast that matter will tear itself apart Theories about the Future of the Universe • The Big Crunch Theory • Someday the universe will reach its maximum and then matter will start collapsing back in on itself