ASTRO 142 Chapter Notes - Chapter 11: Friedmann Equations, Scale Factor, Big Bang
Document Summary
Make sure you understand what can slow down the expansion of the universe and what might speed it up. As the universe expands, gravity pulls on the universe, and slows the expansion down over time. The most plausible explanation is that the light from the supernovae, which exploded billions of years ago, traveled a greater distance than theorists had predicted. Scale factor is the parameter that describes how the size of the universe is changing with respect to its size at a current time. It is the ratio of the proper distance between 2 objects at some time t to the proper distance between the 2 objects at some reference time t0. What are the three possible fates of the universe: if the energy per unit mass at infinity is negative, e < 0, then the sphere has net negative energy. Its expansion will halt at some point before it reaches infinite radius.
