The Origin of the Universe Chapter 20.3 Notes

What is the Universe? The universe consists of all space, matter, and energy that exists—now, in the past, or in the future It is everything physical that exists in space and time It consists of mostly empty space

The Universe is Expanding In 1929, American astronomer Edwin Hubble announced that the universe is expanding He based his theory on spectral lines and noticed that they were almost always shifted towards the red end of the spectrum The red shift is explained by the Doppler effect The Doppler effect is a change in the observed frequency of a wave when an object or observer is moving The faster a light source moves away, the more the light stretches to longer wavelengths, and the more it shifts toward the red end of the spectrum

Red shift vs Blue shift When an object is approaching us, the shift is toward shorter wavelengths at the spectrum’s blue end and is called blue shift Hubble found that most galaxies have red shifts and galaxies that are farther away have even greater red shifts He explained the red shift is occurring because galaxies are moving away from each other and the universe is expanding

Expansion Implies the Universe was Smaller Although galaxies that are close to each other are attracted to each other by gravity, most galaxies are moving away from one another If time was running backward, like a movie being rewound, and all galaxies are moving away from one another, this must mean that all galaxies were once very close to each other This logic implies that the universe might have been contained in an extremely small space

The Big Bang Theory The big bang theory states that the universe began with a gigantic explosion 13 billion to 15 billion years ago Scientists estimate the universe is about 13.7 billion years old Nothing existed before the big bang—no time and no space Out of nothingness came the vast system of space, time, matter, and energy that now makes up the universe Cosmic background radiation is the dim remnants of radiation at microwave wavelengths that was produced during the big bang A very dim signal exists in the sky

Predicting the Future Universe The universe is still expanding, but it may not do so forever The combined gravity of all of the mass in the universe is also pulling the universe inward, in the opposite direction of expansion There are three possible outcomes for the universe: 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 on itself

The Future of the Universe Depends on Mass The future of the universe depends on the amount of matter in the universe If there is not enough mass, the gravitational force will be too weak to stop the expansion, so the universe will keep expanding forever If there is just the right amount of mass, the expansion will continue to slow down but will never stop completely If there is too much mass, the gravity will eventually overcome the expansion and the universe will start to contract A contracting universe could collapse to a single point in what is called the big crunch

Dark Matter & The Theory of Relativity There is more matter in the universe than what is visible— this is called dark matter Dark matter may consist of planets, black holes, or brown dwarfs What it really is and where it is located remains a mystery In 1916, Albert Einstein expanded on Newton’s theory of gravity by developing the general theory of relativity Mass curves space (think of your body curving a mattress) Larger galaxies distort space more than stars do