Notes

Reading Check- What had to happen to the early universe before matter could form?
The universe had to expand so it's temperature would cool.

Looking Closer- When did the first stars in the universe form?
About 400 million years ago.

Reading Check- What force could prevent the universe from expanding forever?
Forces from the Big Bang are pushing matter in the universe apart, but gravity is also pulling matter in the universe together.

Critical Thinking- Why does the amount of matter in the universe affect what its future will be?
If there isn't enough mass, gravity will be too weak to stop the expansion. So the Universe would keep expanding. If there is too much mass, gravity will eventually overcome the expansion... The right amount of mass the Universe's expansion will slow down, but will never fully stop.

Reading Check- Why can't scientists predict exactly what will happen in the future of the universe? Because they aren't sure about how much matter is in the Universe, so they are trying to figure that out first.

Reading Check- Why do scientists think there is a great deal of invisible matter in the Universe?
Because the gravitational force between galaxies are too large to be made by the observed amount of matter in the Universe. So there has to be some "Missing Matter."

Looking Closer- What causes light to bend as it moves past the sun? The sun's mass curves space near the sun, which causes light from stars to bend while moving past the sun.