section 4: the big bang theory

Stars, Galaxies, and the Universe Section 4

Section 4: The Big Bang Theory

Preview

• Key Ideas

• Hubble’s Observations

• A Theory Emerges

• Big Bang Theory

• Universal Expansion

• A Universe of Surprises

• Maps In Action


Hubble’s Observations

• cosmology the study of the origin, properties, processes, and evolution of the universe

• Cosmologists and astronomers can use the light given off by an entire galaxy to create the spectrum for that galaxy.

• Edwin Hubble used galactic spectra to uncover new information about our universe.


Hubble’s Observations, continued

Measuring Red Shifts

• Hubble found that the spectra of galaxies, except for the few closest to Earth, were shifted toward the red end of the spectrum.

• Hubble determined the speed at which the galaxies were moving away from Earth.

• Hubble found that the most distant galaxies showed the greatest red shift and thus were moving away from Earth the fastest.


Hubble’s Observations, continued

The Expanding Universe

• Using Hubble’s observations, astronomers have been able to determine that the universe is expanding.

• The expanding universe can be thought of as a raisin cake rising in the oven. If you were able to sit on one raisin, you would see all the other raisins moving away from you.

• Similarly, galaxies in the universe are moving farther away from each other due to the expansion of the universe.


A Theory Emerges

• Although cosmologists have proposed several different theories to explain the expansion of the universe, the current and most widely accepted 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 3 to 15 billion years ago exploded and began expanding in all directions

• By the mid-20th century, almost all astronomers and cosmologists accepted the big bang theory.


A Theory Emerges, continued

Cosmic Background Radiation

• cosmic background radiation radiation uniformly detected from every direction in space; considered a remnant of the big bang

• Astronomers believe that cosmic background radiation formed shortly after the big bang.

• The background radiation has cooled after the big bang, and is now about 270 °C below zero.



Ripples in Space

• Maps of cosmic background radiation over the whole sky look very smooth. But on satellite maps that show where temperatures differ from the average background temperature, “ripples” become apparent.

• These ripples are irregularities caused by small fluctuations in the distribution of matter in the early universe.

• The ripples are thought to indicate the first stages in the formation of the universe’s first galaxies.



Timeline of the Big Bang


Big Bang Theory

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Universal Expansion

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A Universe of Surprises

Dark Matter

• Analysis of the ripples in the cosmic background radiation suggests that the matter that humans, the planets, the stars and the matter between the stars makes up only 4% of the universe.

• About 23% of the universe is made up of a type of matter that does not give off light but that has gravity. This type of matter is called dark matter.


A Universe of Surprises, continued

Dark Energy

• Most of the universe is made up of an unknown material called dark energy.

• Scientists think that dark energy acts as a force that opposes gravity. Many scientists think that some form of undetectable dark energy is pushing galaxies apart.

• Because of dark energy, the universe is not only expanding, but the rate of expansion also seems to be accelerating.

section 4: the big bang theory

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