lecture6_cosmology

lecture6_cosmology - Announcements Lunch office hours in...

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Announcements • Lunch office hours in the dining hall immediately after todays class. • Quiz covering relativity posted for Thursday. • Your universe is expanding
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Your Universe • Hubble first observed the uniform expansion of the Universe. • Einstein’s equations can be solved into four different shapes/destinies for the Universe given the observed amount of expansion.
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Figure 16.15 Cosmological Constant added new possibilities for evolution of the Universe
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Shape and Destiny are Tied together Could be any of the 3 Depends on the speed of the expansion the amount of mass to slow the expansion and the Strength of cosmological constant.
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Expanding and Homogeneous
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Expanding and Homogeneous
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Expanding and Homogeneous
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Expanding and Homogeneous
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Expanding and Homogeneous
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Big Bang Wrong Concept
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Big Bang is not an explosion in Space! Worse Concept
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Big Bang • The Big Bang had no center. • It is not an explosion of stuff through space. • It is the creation of time and space. • Matter and energy were uniformly spread through the Universe from the very beginning. • Objects basically condense at their original location while the Universe expands.
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One example of something that expands but has no center or edge is the surface of a balloon.
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Expansion stretches photon wavelengths causing a cosmological redshift directly related to lookback time. Light “stretches” with the Universe.
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Universal expansion – Do you expand? • A – No • B – Yes
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Universal expansion – Do you expand? • No. • The size of an atom is dictated by the electromagnetic force between the electrons and the nucleus. • The spacing of atoms in your body is set by the same forces. • Atoms and molecules have not changed size since the first neutral atoms formed 380,000 years after the big bang.
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What is expanding? But the universe is trying!!! 70 km/s / Mpc is the same as 2.2x10 -18 m/s per meter. So if you are one meter from you neighbor, the Universe is trying to drag you apart at 2.2x10 -18 m/s. So in about 500 seconds (about 8 minutes) you would move the diameter of the nucleus of an atom! Or, in 50,000,000 seconds (1.5 years) you would move by the diameter of an atom. You are bound by electrochemical bonds which can easily hold you together against such a slow expansion. So you are not expanding with the Universe. What about the Earth, or orbits of the planets? What would happen it they did expand?
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What is expanding? Two effects: The Earth is trying to get smaller due to its own gravity but its atomic forces prevent this contraction so it maintains its present size. So global expansion just reduces pressure on the planet by a tiny tiny amount, but doesn’t cause us to continuously expand. Orbits of the planets? – Not really, but for a complicated reason that the
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lecture6_cosmology - Announcements Lunch office hours in...

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