Thursday, April 8 th Agenda  Finish Section 18.1: The Universe  Origin of the universe, red shift, big bang theory  In-Class Assignments Section 18.1 review, pg. 594: #1-7 Study Guide, section 18.1  Homework “Telescope Interference” Worksheet  Movie: “The Fate of the Milky Way“ Quiz over section 18.1 next time

The Universe is Expanding  After spending many years studying light from distant galaxies, astronomer Edwin Hubble announced his conclusion that the universe is expanding.  The atoms contained in stars emit light in a specific pattern of spectral lines.  Then Hubble examined the light from stars in other galaxies, he found this pattern of lines was shifted toward the red end of the spectrum.

The Universe is Expanding  Red shift: a shift toward the red end of the spectrum in the observed spectral lines of stars or galaxies.  The red shift in light means that every galaxy is moving away from Earth and away from each other.  In other words, the universe is expanding.

The Universe was Once Smaller  Imagine time running backward.  If every galaxy normally moves away from every other galaxy, then as time goes backward, the galaxies appear to move closer together.  This suggests that long ago the whole universe was contained in an extremely small volume.

Big Bang Theory  Big bang theory: a scientific theory that states that the universe began 10 billion to 20 billion years ago in an enormous explosion.  According to this theory, NOTHING existed before the big bang.  The explosion released all of the matter and energy that still exists in the universe today.

Cosmic Background Radiation Supports the Big Bang Theory  In 1965, a steady but very dim signal from the sky in the form of radiation at microwave wavelengths was detected.  This radiation, called cosmic background radiation, had been predicted by the big bang theory.  Many scientists believe that this radiation is the dim remains of the energetic radiation produced during the big bang.

From the Big Bang to Atoms  According to the big bang theory, expansion cooled the universe enough for matter such as protons, neutrons, and electrons to form just a few seconds after the big bang.  After about a million years, the universe expanded and cooled enough for regular hydrogen atoms to form.  Hydrogen serves as the building block for stars to make other elements and the stage was set for the formation of stars, galaxies, and planets.

The Future of the Universe is Uncertain  The universe is still expanding, but it may not do so forever.  The combined gravity of all of the mass in the universe is pulling the universe inward, in the opposite direction of expansion.  Think of it like a tug-of-war.

The Future of the Universe is Uncertain  The competition between these two forces leaves 3 possible outcomes for the universe: 1.The universe will keep expanding forever. 2.The expansion of the universe will gradually slow down, and the universe will approach a limit in size. 3.The universe will stop expanding and start to fall back in on itself.

The Fate of the Universe Depends on Mass  If there is not enough mass in the universe, the gravitational force will be too weak to stop the expansion, so the universe will keep expanding forever.  If there is just the right amount of mass, the expansion will continually slow down but never stop completely.  If there is more mass than this, gravity will eventually win out over expansion and the universe will start to contract.

The Fate of the Universe Depends on Mass  Eventually, a contracting universe might collapse back to a point in a “big crunch”.  This could be the end of the universe, or it could produce another big bang, starting the cycle all over again.

In-Class Assignments  Section 18.1 review, pg. 594: #1-7  Study Guide, section 18.1

Homework  “Telescope Interference” Worksheet  Movie: “ The Fate of the Milky Way” “ Be ready for a quiz covering section 18.1 next time…