1. Objectives Distinguish the different models of the universe.
Section 30.3
Cosmology
Objectives
Distinguish the different models of the universe.
Compare and contrast how expansion is relative to each of the models.
Explain the importance of the Hubble constant.

2. Section 30.3
Cosmology
The Big Bang theory was formulated by comparing evidence and models to describe the beginning of the universe.
Review Vocabulary
radiation: the process of emitting radiant energy in the form of waves or particles
Speed of Light = 180,000 miles / second
Light year: The distance that light can travel in one Earth year = 5.86 trillion miles

3. Section 30.3
Cosmology
Big Bang Model
The study of the universe—its nature, origin, and evolution—is called cosmology.
The theory that the universe began as a point and has been expanding since is the Big Bang theory.
Movie Clip 1

4. The Big Bang Theory
The universe began as a single cosmic explosion about 14 billion years ago.

5. Big Bang Model Outward expansion
Section 30.3
Cosmology
Big Bang Model
Outward expansion
In the Big Bang model, the momentum of the outward expansion of the universe is opposed by the inward force of gravity acting on the matter of the universe to slow that expansion.

6. After the Big Bang Gravity pulls matter into small clumps
Clumps become huge clouds of dust and gas
Clouds become solar systems and galaxies

7. Cosmic Background Radiation
Section 30.3
Cosmology
Cosmic Background Radiation
Discovery
In 1965, scientists discovered a persistent background noise in their radio antenna. This noise was caused by weak radiation, called the cosmic background radiation, that appeared to come from all directions of space and corresponded to an emitting object having a temperature of about K (–270C).

9. Major Piece of Evidence #1: Background Radiation
Energy left over from the Big Bang is evenly spread throughout the universe.
This background radiation is observable!

10. Cosmic Background Radiation
Section 30.3
Cosmology
Cosmic Background Radiation
Mapping the radiation
Earth’s atmosphere blocks much of the cosmic background radiation, so it is best observed from high-altitude balloons or satellites. An orbiting observatory called the Wilkinson Microwave Anisotropy Probe (WMAP), launched by NASA in 2001, mapped the radiation in greater detail.

11. Cosmic Background Radiation
Section 30.3
Cosmology
Cosmic Background Radiation
Mapping the radiation
The peak of the radiation measured by WMAP has a wavelength of approximately 1 mm; thus, it is microwave radiation in the radio portion of the electromagnetic spectrum.

12. Cosmic Background Radiation
Section 30.3
Cosmology
Cosmic Background Radiation
Discovery
The temperature was very close to the temperature predicted by the Big Bang theory, and the radiation was interpreted to be from the beginning of the Big Bang.

13. Major Piece of Evidence #2: Temperature
The temperature in deep space is around 3° K.
Leftover heat from Big Bang keeps space just above absolute zero

14. Major Piece of Evidence #3: Expanding Universe
Every object in the universe is moving away from the center.
Think of waves spreading out from where you drop a pebble into a pond.
Except - The universe does not have a “center”

15. Expanding Universe
Objects near the very edge of the universe are the oldest
The most distant known objects in the universe are over 12 billion light years from the Earth

16. Cosmic Background Radiation
Section 30.3
Cosmology
Cosmic Background Radiation
Acceleration of the expansion
According to every standard model, the expansion of the universe is slowing down due to gravity. However, there was a surprising discovery that the expansion of the universe is now accelerating. Astronomers have labeled this acceleration dark energy.

17. Big Bang Model Outward expansion
Section 30.3
Cosmology
Big Bang Model
Outward expansion
When the rate of expansion of the universe is known, it is possible to calculate the time since the expansion started and determine the age of the universe.

18. Big Bang Model Outward expansion
Section 30.3
Cosmology
Big Bang Model
Outward expansion
Based on the best value for H that has been calculated from Hubble Space Telescope data and the data on the cosmic background radiation, the age of the universe can be pinpointed to 13.7 billion years.

19. Hubble's orbit outside the distortion of Earth's atmosphere allows it to take extremely sharp images with almost no background light. Hubble's Deep Field have been some of the most detailed visible-light images ever, allowing a deep view into space and time. Many Hubble observations have led to breakthroughs in astrophysics, such as accurately determining the rate of expansion of the universe.

20. Big Bang Model Possible outcomes
Section 30.3
Cosmology
Big Bang Model
Possible outcomes
Based on the Big Bang theory, there are three possible outcomes for the universe.
The universe could be an open universe and continues to expand forever.
Open universe
Movie Clip 2

21. Open Universe: The End
The universe will continue to expand. All stars will die as the last of their energy is released. Eventually, all matter will be reduced to single atoms moving away from each other. There will be nothing left.
The end.

22. Closed Universe: Collapse
Gravitational attraction between objects will cause the expansion of the universe to slow and, eventually, come to a halt. Gravity will then begin to pull everything back to the center of the universe.
Kind of like a rebounding bungee cord.

23. Closed Universe: Déjà vu
Eventually, all matter and energy will again condense into a single point, possibly no larger than a dime. Another Big Bang will occur and the formation of the universe will begin all over again.
May occur every billion years.

24. Big Bang Model Possible outcomes
Section 30.3
Cosmology
Big Bang Model
Possible outcomes
The universe could be a closed universe where the expansion stops and all of the mass is pulled back to the original point of origin, or it could be a flat universe where the expansion becomes so slow that it seems to stop.
Closed universe
Flat universe

25. Big Bang Model Critical density
Section 30.3
Cosmology
Big Bang Model
Critical density
All three outcomes are based on the premise that the rate of expansion has slowed since the beginning of the universe, but the density of the universe is what is unknown.

26. Big Bang Model Critical density
Section 30.3
Cosmology
Big Bang Model
Critical density
At the critical density, there is a balance, so that the expansion will come to a halt in an infinite amount of time. The critical density, about 6 × 10–27 kg/m3, means that, on average, there are only two hydrogen atoms for every cubic meter of space.

27. Contents of the Universe
Section 30.3
Cosmology
Contents of the Universe
Dark matter and energy
Cosmologists estimate that the universe is composed of dark matter (21 percent), dark energy (75 percent), and luminous matter.
What is unknown today is the nature of the dark matter and dark energy.

28. Contents of the Universe
Section 30.3
Cosmology
Contents of the Universe
Dark matter and energy
Dark matter is thought to consist of subatomic particles, but of the known particles, none display the right properties to explain or fully define dark matter.
Although scientists recognize the effects of dark energy, they still do not know what it is.