Earth Science 25.3 The Universe 25.3 Part B The Expanding Universe

Earth Science 25.3 The Universe The Expanding Universe: Recall the Doppler Effect from our previous chapter. Remember that when a source is moving away, it’s light appears redder than it actually is because it’s wavelengths appear lengthened. Objects approaching have their light waves shifted toward the blue or shorter wavelengths. Therefore, the Doppler Effect reveals whether a star is moving away from Earth or toward the Earth.

Earth Science 25.3 The Universe The Expanding Universe: The amount of light shift allows us to calculate the rate of movement by the object in relation to the Earth. Large Doppler shifts indicate higher speeds, smaller shifts indicate lower speeds.

Earth Science 25.3 The Universe Red Shifts: One of the most important discoveries of modern astronomy was made in 1929 by Edwin Hubble. Observations completed years before revealed that most galaxies have Doppler shifts toward the red end of the spectrum. This red shift occurs because light waves are “stretched”, which shows that Earth and the source are moving away from each other.

Earth Science 25.3 The Universe Red Shifts: Hubble set out to explain this red shift. Hubble realized that dimmer galaxies were probably farther away than brighter galaxies. He tried to determine whether a relationship existed between the distances to galaxies and their red shifts. Hubble used estimated distances based on relative brightness and Doppler red shifts to discover that galaxies that exhibit the greatest red shifts are the most distant.

Earth Science 25.3 The Universe Hubble’s Law: A consequence of the universal red shift is that it predicts that most galaxies; except for a few nearby, are moving away from us. Recall that the amount of Doppler shift depends on the speed at which the object is moving away. Because the more distant galaxies had greater red shifts, Hubble concluded that they must be moving away from us at greater speeds.

Earth Science 25.3 The Universe Hubble’s Law: This idea is currently known as Hubble’s Law. Hubble’s law states Galaxies are retreating from us at a speed that is proportional to their distance. Hubble was surprised at this discovery because it implied that the more distant galaxies are moving away from us many times faster than those galaxies near us. This means that the red shifts of distant galaxies demonstrate that the universe is expanding around us.

Earth Science 25.3 The Universe Hubble’s Law: To help visualize the nature of this expanding universe, imagine a loaf of raisin bread that has been set out to rise for a few hours. As the dough doubles in size, so does the distance between all the raisins. However, the raisins that were originally farther apart travelled a greater distance in the same time span than those located closer together. Raisin Dough Analogy

Earth Science 25.3 The Universe Hubble’s Law: We therefore conclude that in an expanding universe, as in the raisin dough analogy, those objects located farther apart move away from each other at a more rapid rate. Another feature of the expanding universe can be demonstrated by this analogy. No matter which raisin you select, it will move away from all the other raisins. Raisin Dough Analogy

Earth Science 25.3 The Universe Hubble’s Law: Likewise, no matter where one is located in the universe, every other galaxy (except those located in the same cluster) will be moving away from you. Hubble had indeed advanced our knowledge of the universe with this theory. Because of his great contributions to astronomy, the Hubble Space telescope is named in his honor. Raisin Dough Analogy

Earth Science 25.3 The Universe The Big Bang Theory: How did the universe begin? Any theory about the origin of the universe must account for Hubble’s Law; the fact that all distant galaxies are moving away from us. Although all galaxies appear to be moving away from Earth, it seems unlikely that our planet is the center of the universe. Raisin Dough Analogy

Earth Science 25.3 The Universe The Big Bang Theory: A more probable explanation exists. Imagine a balloon with paper punch dots glued to it’s surface. When the balloon is inflated, each dot spreads apart from every other dot. Similarly, if the universe is expanding, every galaxy would be moving away from every other galaxy. This concept of the expanding universe led to the widely excepted big bang theory.

Earth Science 25.3 The Universe The Big Bang Theory: According to the Big Bang Theory, the universe began as a violent explosion from which the universe continues to expand, evolve and cool. The Big Bang Theory states that at one time, the entire universe was confined to a dense, hot, super-massive ball. Than, about 13.7 billion years ago, a violent explosion occurred, hurling this matter in all directions. The Big Bang marks the beginning of the universe; all matter and space were created in this instant.

Earth Science 25.3 The Universe The Big Bang Theory: Recall that protons, neutrons, and electrons are some of the subatomic particles that make up all matter. Scientists think that these particles formed within a few seconds from the energy of the big bang. Scientists can model conditions in the early universe, using machines called particle accelerators. These devices smash subatomic particles together at high speeds.

Earth Science 25.3 The Universe These collisions of subatomic particles produce other particles that may exist for only a few billionths of a second. But these experiments give scientists a brief glimpse of matter in the early universe. After several hundred thousand years, the universe became cool enough for atoms to form. Gases in the universe continue to cool and condense. These gases eventually formed the stars and galaxies.

Earth Science 25.3 The Universe Supporting Evidence: Scientists have gathered substantial evidence that supports the big bang theory. For example, the red shift of galaxies we have discussed already indicates that the universe is still expanding. Scientists discovered a type of radiation called cosmic microwave background radiation. This energy was detected as faint radio signals coming from every direction of space. Scientists think that this radiation was produced during the big bang.

Earth Science 25.3 The Universe The Big Crunch: If the universe began with the big bang, how will it end? One view is that the universe will last forever. In this scenario, the stars will slowly burn out, being replaced by an invisible form of matter and black holes that will ravel outward through an endless , dark, cold universe.

Earth Science 25.3 The Universe The Big Crunch: The other possibility is that the outward flight of galaxies will slow and eventually stop. Gravitational construction would follow, causing the galaxies to collapse into the high-density, high-energy mass from which the universe began. This scenario, the big bang operating in reverse, is called ”the big crunch”.

Earth Science 25.3 The Universe Material called “dark matter” could affect the rate at which the universe expands. Dark matter is matter that can not be directly observed because it does not give off radiation. Galaxies contain most of the visible mass in the universe, but there is evidence that what we see makes up less than 1/10th of the universe’s mass. Measurements of galactic rotation indicates that dark matter accounts for the rest of the universe’s mass.

Earth Science 25.3 The Universe Whether the universe will expand forever or collapse upon itself depends on it’s average density. If the average density of the universe is more than it’s critical density; about one atom for every cubic meter, the gravitational field is enough to stop the outward expansion and cause the universe to contract. But, if the density of the universe is less than the critical value, it will expand forever.

Earth Science 25.3 The Universe Current estimates place the density of the universe below the critical density, which predicts an ever expanding, open universe. However, the universe is expanding faster now than it was in the past. This may be due to a theoretical new force that astronomers have named “dark energy”. The view currently favored by scientists is that we live in an expanding universe with no ending point.