The Big Bang Theory

Warm Up:

• Use your textbook on page 532 to describe the Big Bang Theory.

• What are 2 pieces of evidence for the Big Bang Theory?

THE BIG BANG THEORY

States that the universe began as a single cosmic explosion about 15

billion years ago.

What Happened After the Big Bang?

• After about 1 million years the universe cooled and H atoms formed

• Gravity pulled atoms (and then larger masses) together to form stars, planets, galaxies, etc.

Evidence for the Big Bang

• The presence of Background Radiation (energy left over from the Big Bang)– Detected as microwaves

– Maintains temp. of universe at 2.7 K

• Galaxies spreading away from the center of the universe (Red Shift)

How can scientists tell that galaxies are moving away?

As stars move away their light waves are stretched

As stars move closer their light waves are compressed

Red light waves are longer

Blue light waves are shorter

Spectral lines from stars (and galaxies) that are moving away will be shifted to the right (red end) of the spectrum

Galaxies seem to be racing away from the center of the Universe.

• Every galaxy seems to be moving away from Earth.

• After examining the Red Shift that appears from distant galaxies astronomers conclude the universe is expanding at tremendous speeds.

Expanding Universe• If the universe is expanding, then

the objects near the very edge of the universe are the oldest objects in the universe.

• The most distant known objects in the universe are over 12 billion light years from the Earth

Let’s look at that first picture again

What Happens Next?

• While the universe is still expanding due to the original force of the Big Bang, gravity is also pulling all matter inward in the opposite direction

What Happens Next?

• Astronomers think 3 possibilities could occur:– The universe could expand forever– The expansion will slow down and

reach its limit– The expansion will stop and then the

universe will contract

Expansion and Contraction is the most favored idea

• Gravitational attraction will eventually slow the expansion

• Matter and energy will eventually be pulled back together into one spot

• Another “big bang” could occur

Um… I think we may have been here before.

• This restructuring may occur once every 80 to 100 billion years.

Quasar