Lecture_21 - What have we learned? Chapter 17 The Beginning...

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1 Chapter 17 Chapter 17 The Beginning of Time The Beginning of Time What have we learned? What have we learned? Galaxies are the building blocks of the universe The universe is expanding – distant galaxies are receding from the Milky Way with velocities proportional to distance (Hubble’s Law: V = H 0 x d ) Hubble’s constant (H 0 ) gives the age of the universe (for a constant expansion rate) as about 14 billion years On distance scales of 100 million light years, galaxies are clustered in long chains and sheets around empty voids On scales of billions of light years the universe appears more smooth Supermassive black holes ( quasars ) were formed in the early universe Galaxies and clusters of galaxies all contain DARK MATTER which determines the way mass collects together The expansion of the universe appears to be accelerating due to the presence of DARK ENERGY The total mass-energy content of the universe is – 4-5% normal matter; 23% dark matter; 72% dark energy WHAT THEORY EXPLAINS ALL THIS? Our Goals for Learning • What were conditions like in the early universe? • What is the history of the universe according to the Big Bang theory? The Big Bang The Big Bang The theory that best explains the observed facts is one in which the universe (space and time) had a BEGINNING! The universe must have been much denser and hotter early in time. Objects at redshift z = 1 (wavelength shift of lines is 100%) emitted their light when the universe was HALF its present size! RUN THE HUBBLE EXPANSION BACKWARDS RUN THE HUBBLE EXPANSION BACKWARDS
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2 Temperature scales with size of universe, which is measured by the redshift (z) of distant galaxies. Early universe must have been extremely hot and incredibly dense! Pure energy creation of matter. WHEN THE UNIVERSE WAS LESS THAN 1 SECOND OLD IT WAS HOTTER THAN THE HOTTEST STARS! 1s
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Lecture_21 - What have we learned? Chapter 17 The Beginning...

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