What is the Universe Like?What is the Universe Like?

Chapter 31Chapter 31

The universe is everything…all The universe is everything…all matter and all energymatter and all energy

The universe is expanding. The The universe is expanding. The evidence is the “evidence is the “red-shiftred-shift” of the light ” of the light from most galaxiesfrom most galaxies red-shift:red-shift: a shift toward the red end of a shift toward the red end of

the spectrum in the observed spectral the spectrum in the observed spectral lines of stars or galaxies. Known as the lines of stars or galaxies. Known as the “Doppler Effect.”“Doppler Effect.”

If the universe is expanding now, this If the universe is expanding now, this implies that it was once smaller.implies that it was once smaller.

If we imagine what the universe was If we imagine what the universe was like about 15 billion years ago, like about 15 billion years ago, everything would have been in one everything would have been in one spot.spot.

So, about 15 billion years ago, the So, about 15 billion years ago, the universe began expanding. This is universe began expanding. This is called “called “the big bangthe big bang”” big-bang theory:big-bang theory: a scientific theory that a scientific theory that

states that the universe began 10 to 20 states that the universe began 10 to 20 billion years ago in an enormous explosion.billion years ago in an enormous explosion.

If the big-bang theory is correct, we If the big-bang theory is correct, we should see evidence of the explosion should see evidence of the explosion about 15 billion light-years away. This about 15 billion light-years away. This evidence was discovered in 1965. It is evidence was discovered in 1965. It is called “called “cosmic background radiation.cosmic background radiation.””  

There are three possibilities of how the There are three possibilities of how the universe might end:universe might end: The universe might expand foreverThe universe might expand forever The expansion of the universe might slow The expansion of the universe might slow

down and the universe will stay one sizedown and the universe will stay one size The universe might begin shrinking, The universe might begin shrinking,

eventually collapsing into a “big-crunch.”eventually collapsing into a “big-crunch.”