1. The UniverseSection 3 Section 3: Origin of the Universe Preview Key Ideas Bellringer What Is the Universe? What Happened at the Beginning? Predicting the Future of the Universe

2. The UniverseSection 3 Key Ideas 〉 What makes up the universe? 〉 How did the universe begin? 〉 How do scientists make predictions about the future of the universe?

3. The UniverseSection 3 Bellringer Based on what you have learned, as well as previous knowledge, answer the following questions. 1. Why do you think scientists refer to observing distant objects in the universe as “looking back in time”? 2. Explain why scientists study the same types of electromagnetic waves, such as visible light, microwaves, and X rays, to understand the universe as they do for understanding stars or planets.

4. The UniverseSection 3 Bellringer, continued 3. While the universe is always expanding, the gravity of the universe’s mass is also pulling it inward. What are some possible outcomes as a result of these two competing forces?

5. The UniverseSection 3 What Is the Universe? 〉 What makes up the universe ? 〉 The universe consists of all space, matter, and energy that exists—now, in the past, or in the future. universe: the sum of all space, matter, and energy that exist, that have existed in the past, and that will exist in the future

6. The UniverseSection 3 What Is the Universe? continued Everything is part of the universe. We see the universe now as it was in the past. –It takes time for light to travel in space. –The farther away an object is, the older the light that we receive from that object. Most of the universe is empty space. –Space is a vacuum with no air and no air pressure.

7. The UniverseSection 3 What Happened at the Beginning? 〉 How did the universe begin ? 〉 By studying ancient light and looking at other evidence, scientists have been able to theorize that the universe formed during a cataclysmic event known as the big bang.

8. The UniverseSection 3 What Happened at the Beginning? continued The universe is expanding. –Observations of spectral lines from other galaxies indicated that they were moving away from us. –Red shift is an apparent shift toward longer wavelengths of light caused when a luminous object moves away from the observer. –This red shift can be explained by the Doppler effect. Doppler effect: an observed change in the frequency of a wave when the source or observer is moving

9. The UniverseSection 3 Visual Concept: Red Shift

10. The UniverseSection 3 What Happened at the Beginning? continued Expansion implies that the universe was once smaller. –Long ago, the entire universe might have been contained in an extremely small space. –All of the matter in the universe appears to expand rapidly outward, like a gigantic explosion.

11. The UniverseSection 3 Visual Concept: Universal Expansion

12. The UniverseSection 3 What Happened at the Beginning? continued Did the universe start with a big bang? –Scientists have proposed several different theories to explain the expansion of the universe. –The most complete and widely accepted theory is the big bang theory. big bang theory: the theory that all matter and energy in the universe was compressed into an extremely small volume that 13 to 15 billion years ago exploded and began expanding in all directions

13. The UniverseSection 3 Visual Concept: Big Bang Theory

14. The UniverseSection 3 What Happened at the Beginning? continued Cosmic background radiation supports the big bang theory. –Cosmic background radiation is a steady but very dim signal from all over the sky in the form of radiation at microwave wavelengths. –Many scientists believe that the microwaves are dim remnants of the radiation produced during the big bang.

15. The UniverseSection 3 What Happened at the Beginning? continued Radiation dominated the early universe. –According to the big bang theory, expansion cooled the universe enough for matter such as protons, neutrons, and electrons to form. The big bang theory is constantly being tested. –Like all theories, the big bang theory is constantly tested against each new discovery about the universe. –The big bang theory may be refined, revised, or replaced as new information is discovered.

16. The UniverseSection 3 Predicting the Future of the Universe 〉 How do scientists make predictions about the future of the universe ? 〉 Scientists use their increasing knowledge of the universe to hypothesize what might happen to the universe in the future.

17. The UniverseSection 3 Predicting the Future of the Universe, continued The future of the universe is uncertain. –The universe is expanding, but the combined gravity of all the mass in the universe is also pulling the universe inward. –The competition between these forces leaves three possibilities: 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.

18. The UniverseSection 3 Predicting the Future of the Universe, continued The future of the universe depends on mass. –If there is not enough mass, the gravitational pull will be too small to stop the expansion. –If the universe keeps expanding, it may expand at a steady rate or speed up and expand faster. –If there is just the right amount of mass, the expansion will continually slow down, but will never stop completely. –If there is too much mass, gravity will eventually overcome expansion and the universe will contract.

19. The UniverseSection 3 Future of the Universe

20. The UniverseSection 3 Predicting the Future of the Universe, continued New technology helps scientists test theories. –Powerful telescopes and other sensitive equipment help scientists study the universe. –Scientists make observations to test theories and develop new explanations.

21. The UniverseSection 3 Predicting the Future of the Universe, continued There is debate about dark matter. –There is more matter in the universe than what is visible. –Scientists call this dark matter. –Dark matter may be planets, black holes, or brown dwarfs (starlike objects that lack enough mass to begin fusion).

22. The UniverseSection 3 Predicting the Future of the Universe, continued Scientists use mathematics to build better models. –Theories can be expressed in mathematical form. –Mathematical models can be used to help test theories that are not easily observed. –Albert Einstein developed the general theory of relativity, which he expressed in mathematical form. –This mathematical model has been tested and supported by observation.

23. The UniverseSection 3 Visual Concept: Structure of the Universe