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Expanding Universe Doppler effect Einstein’s Equation ( Hubble’s law Models of the Universe Doppler Effect – ReD ShIfTs • Doppler effect is the result of sound increasing or decreasing in pitch as an object moves towards or away form you. (APPLIES TO ANY WAVES) • If a light-emitting object is moving away from a person, each wave of light leaves the object from a point slightly farther away from the person than the previous wave did. Therefore, the distance between waves, or wavelength, that the person sees is longer than it would be if the object were motionless. • In visible light, the longest wavelength belongs to red light, and shortest to the violet light • most often used by astronomers to measure the velocity of galaxies. Vesto Slipher • First to encounter redshifting galaxies • Discovered a new cosmic riddle for astronomers of his time. • In 1916, he observed about fifty nearby galaxies in Lowell Observatory in Arizona, spreading his light out using a prism, and recorded the results onto film • Almost every object he observed had its light stretched to redder colors, indicating essentially everything in the universe was moving away from earth. Hi, I’m Vesto Edwin Hubble • • • • • discovered the existent of other distant galaxies In 1929, while working at the Carnegie Observatories in Pasadena, California, he measured the red shifts of a number of distant galaxies and their relative distances When he plotted the numbers, he discovered, that the red shift of distant galaxies increased as a linear function of their distance = universe expands Also discovered that the galaxies were receding from us at a velocity proportional to their distance. The more distant the galaxy, the greater its red shift, and therefore the higher the velocity; this relationship was known as Hubble’s law. Hubble’s Law • is a statement of a direct link between the distance to a galaxy and its recessional velocity as determined by the red shift. It states that the velocity (v) of a galaxy moving away from Earth is proportional to the galaxy's distance (d) from Earth. As distance increases, velocity also increases. The constant value that relates velocity and distance is called Hubble's constant and is usually written as H0. Or mathematically like this: • H0 is the proportionality between recession velocity and distance of a galaxy = the universes’ rate of expansion • H0 identified in 1929, but its numeric value is still uncertain. • Astronomers know that it falls between 50 and 80 kilometers per second-megaparsec. A megaparsec is a unit of length equal to 1 million parsecs. A parsec is 30.86 trillion km (19.18 trillion mi). • These units are used to make redshift calculations easier. • Could be represented as 1.5 × 10-15 to 3.1 × 10-15 1/s or • How do you find the the velocity of moving galaxies? Astronomers know the speed of which the galaxies are moving by their color. As I stated when something moves toward you very, very fast, it looks a little bit bluer, and when it moves away it looks redder. So astronomers can measure speeds by how red a galaxy looks. • How do you find the distance of the moving galaxy? You tell me because I already told you the answer. So what’s my point… • Hubble’s law could determine the age of our universe, about 12-15 billion years old because Ho offers the needed information. • When we know the definite value of the Hubble constant, the future of the universe could be determined. • Hubble’s law has an apparent linearity our universe is uniformly expanding no matter which galaxy we are in, all of the other galaxies are moving away from us earth is not the center of the universe and everything else is receding from us. • Suggests that the galaxies are not moving away through space, they are moving away with space. And again……. Loser who said the Universe was finite Heinrich Olbers • In the early 1800s, German astronomer, argued that our universe were finite. • He said, “If the universe was finite and contained starts throughout, then if you looked in any particular direction, you line of sight would eventually fall on the surface of a star. Although the apparent size of a star in the sky becomes smaller as the distance to the star increases, the brightness of the smaller surface remains a constant.” • Therefore, if the universe was infinite, then the whole surface of the night sky should be as bright as a star. However, as we know, the sky has dark areas, proving that it is finite. Confused with the IDEA? Isaac Newton • discovery of the law of gravity • realized that gravity is always attractive. • Every object in the sky attracts each other If the universe were finite, the attractive forces of all the objects in the universe should have caused the entire universe to collapse on itself. Albert Einstein • theory of gravity in the general theory of relativity • encountered same as Newton’s problem • His equations said the universe was either expanding or collapsing. Created the My name is Albert! cosmological constant : BAD! • “the greatest blunder of my life” But why didn’t the universe collapse like Newton and Einstein’s equation suggested ? •Because the universe had been expanding from the moment of its creation and it is in a constant state of change. Models of our universe • Closed (left) – [high mass] a universe that would eventually stop expanding and re-collapses on itself, possibly leading to another big bang. • Flat (center) – [critical mass] a universe which would also expand forever, but the expansion rate would slow to close zero after an infinite amount of time . • Open (right) – [low mass] a universe that will continue its expansion forever C L O S E D O P E n The fate of the universes