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a23_21_Expansion - The Expansion and Age of the Universe...

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The Expansion and Age of the Universe
Recall that in 1924, Edwin Hubble finds Cepheids in M31showing that the Andromedanebulais really a galaxyThe photographic plate of Messier 31 on which Hubble discovered the firstCepheid variable star in a spiral nebula. The objects marked "N" are novae. Atfirst Hubble marked the object in the upper right corner as a nova, but he soonrealized it was a variable and marked it"VAR!"?
Then in 1930 Hubble discovers his expansion lawVexp= H x D
But with the discovery of the expansion of theuniverse, several big questions soon arose.1. How big is the universe? Is it infinite?2. What will happen in the future? Will the universe just keepexpanding forever?3. How did the expansion start?4. Where did all this matter itself come from?5. How old is the universe?6. What is it expanding into?
Olbers Paradox:Why is the sky dark?If an infinite number of stars fill the Universe,should not the night sky be infinitely bright ?Heinrich Wilhelm Matthaus Olbers (1758-1840)Is the Universe Infinite?-- an age old question --
Occasional references appears in humanity's quest toexplain the dark abyss, structure and size of the Universe.Following the trial of Galileo, Johannes Kepler opposed the popularlyaccepted superstitious belief -- spread and actively maintained by TheChurch throughout the Seventeenth Century – namely, the belief in auniform and infinitely large universe where"eternal stars maintaintheir vigil on the Earth as the center of God's creation".A brave Kepler argued that as the night sky appears black, theUniverse could not be filled with eternal stars, nor could it be infinite insize .If the Universe were filled with eternal stars, then no matter thedirection, " Kepler argued, "the field of view should be solidlyblanketed with stars, as bright as the surface of the Sun.There would be no gaps through which to see the vault beyond. "
Did the Universe really start in a Big Bang?
A distaste for a universe that was expanding led a trio ofastronomers and physicists to propose a completelydifferent model.This model, proposed by T. Gold, H. Bondi, andF. Hoyle,was called theSteady Statemodel and stated that theuniverse always looks the same and is of infinite age. Asthe universe thins out due to the Hubble flow of expansion,matter is created out of nothing.This requires continuous creation of matter but surprisinglyvery little to make the theory work with observations.Fred Hoylemockingly called the expansion model of theuniversethe Big Bangmodel.And thats how it got that name.
Another fierce critic wasFritz Zwicky, a Bulgarian-bornastronomer, infamous among astronomers for hiseccentricity and recalcitrance.Working at Caltech, Zwicky questioned whether Hubblesdata really showed that distant galaxies were moving at all.
In the halls of the Physics building at Caltech, Zwicky used to start a conversation tostudents, whose name he did not know with the words: "Who the devil are you?"

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Term
Fall
Professor
staff
Tags
Big Bang, Cosmic microwave background radiation

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