Copyright © 2009 Pearson Education, Inc.Science is figuring stuff out and notScience is figuring stuff out and notfooling yourselffooling yourselfRichardFeynmanCopyright © 2009 Pearson Education, Inc.So let’s fool ourselves…• Jack is looking at Anne, but Anne is looking at George.Jack is married, but George is not. Is a married personlooking at an unmarried person?• A) Yes. <==• B) No.• C) Cannot be determined.Copyright © 2009 Pearson Education, Inc.The Monty Hall EffectThere used to be a popular game show called “Let’s Make A Deal”hosted by Monte Hall. Based on that show, here is a question. Thegame is simple. There are three doors that are closed. Two of themhave a can of soup behind them and the other has a new car. You tryto guess the door which has the car (unless you really like soup!).Monty Hall, the host, of course knows where the car is and where thesoup is.So here goes. You are asked to chose a door. But before it is opened,Monty Hall says “Wait. Let me open up a door you have notchosen.” He opens up another door and there is soup. He now says“Now that you know where one soup can is, do you want to changeyour choice?”The question is - do you change doors if you want to have thebest chance of winning the car.?• A. You don’t change. You keep the original door• B. You change to the unopened door. <==[Copyright © 2009 Pearson Education, Inc.The Prosecutor’s FallacyIn the case of OJ Simpson, the prosecution argued that there was huge amout ofcircumstantial evidence showing Simpson had committed the murder of hiswife Nicole. He had a long history of abusing her, and as they said “A slap is aprelude to homicide.” The defense attorney, Alan Dershowitz responded withthe following argument:4 million women are battered annually in the US by boyfriends and husbands, butin 1992 1432 were killed by their partners. This means that 1 in 2500 killed bytheir husbands. Therefore, few men who abuse their wives go on to kill them.True? Yes. Convincing? Yes.But wrong.Why?Copyright © 2009 Pearson Education, Inc.The other sisterThis is a simple one. You meet the parents of your girlfriend.You know they have another child but you don’t know ifthey are a girl or boy. What is the chance that the otherchild is a girl?A. 33% (1 in 3)B. 50% ( 50/50) <==C. 67% (2 in 3)Copyright © 2009 Pearson Education, Inc.The other sisterThis is a simple one too. You meet some cousins (man andwife) and you start talking to them. They tell you theyhave 2 children and one of them is a girl. What is thechance that the other child is a daughter?A. 33% (1 in 3) <==B. 50% (50/50)C. 67% (2 in 3)Copyright © 2009 Pearson Education, Inc.The Sister Named FloridaYou meet some cousins (man and wife) and you start talking tothem. They tell you they have 2 children and one of themis a girl with the weird name Florida. What is the chancethat the other child is a daughter?A. 33%B. 50% (50/50), same as the previous question <==C. 67%Copyright © 2009 Pearson Education, Inc.Common birthdaysHow many students do you need in a room beforethe chance that two have the same birthday is50%?A. 10B. 25 <==C. 50D. 100E. 365Copyright © 2009 Pearson Education, Inc.What have we learned?We have a very poor idea of statisticaloutcomes in certain situations, and even alousier idea of random processes. Be carefulwhen you deal with statistics. Don’t believesomeone who says “Well, the chances areso small that it can’t happen.”Copyright © 2009 Pearson Education, Inc.Chapter 14Our GalaxyCopyright © 2009 Pearson Education, Inc.14.1 The Milky Way RevealedOur goals for learning:• What does our galaxy look like?• How do stars orbit in our galaxy?Copyright © 2009 Pearson Education, Inc.What does our galaxy look like?Copyright © 2009 Pearson Education, Inc.The Milky Way galaxy appears in our sky as a faint band of light.Copyright © 2009 Pearson Education, Inc.Dusty gasclouds obscureour viewbecause theyabsorb visiblelight.This is theinterstellarmedium thatmakes newstar systems.Copyright © 2009 Pearson Education, Inc.All-Sky ViewCopyright © 2009 Pearson Education, Inc.We see our galaxy edge-on.Primary features: disk, bulge, halo, globular clustersCopyright © 2009 Pearson Education, Inc.If we could view the Milky Way from above thedisk, we would see its spiral arms.Copyright © 2009 Pearson Education, Inc.How do stars orbit in our galaxy?Copyright © 2009 Pearson Education, Inc.Stars in the disk all orbit in the same direction with alittle up-and-down motion.Copyright © 2009 Pearson Education, Inc.Orbits of starsin the bulgeand halo haverandomorientations.Copyright © 2009 Pearson Education, Inc.Copyright © 2009 Pearson Education, Inc.Thought QuestionWhy do orbits of bulge stars bob up and down?A. They’re stuck to the interstellar medium.B. The gravity of disk stars pulls them towardthe disk.C. Halo stars knock them back into the disk.Copyright © 2009 Pearson Education, Inc.Thought QuestionWhy do orbits of bulge stars bob up and down?A. They’re stuck to the interstellar medium.B. The gravity of disk stars pulls themtoward the disk.C. Halo stars knock them back into the disk.Copyright © 2009 Pearson Education, Inc.Sun’s orbitalmotion (radiusand velocity) tellsus mass withinSun’s orbit: 1.0 ! 1011MSunCopyright © 2009 Pearson Education, Inc.Orbital Velocity Law• The orbital speed (v) and radius (r) of an object on acircular orbit around the galaxy tell us the mass (Mr)within that orbit.! Mr=r " v2GCopyright © 2009 Pearson Education, Inc.What have we learned?• What does our galaxy look like?— Our galaxy consists of a disk of stars andgas, with a bulge of stars at the center of thedisk, surrounded by a large spherical halo.• How do stars orbit in our galaxy?— Stars in the disk orbit in circles going in thesame direction with a little up-and-downmotion.— Orbits of halo and bulge stars have randomorientations.Copyright © 2009 Pearson Education, Inc.14.2 Galactic RecyclingOur goals for learning:• How is gas recycled in our galaxy?• Where do stars tend to form in our galaxy?Copyright © 2009 Pearson Education, Inc.How is gas recycled in ourgalaxy?Copyright © 2009 Pearson Education, Inc.Star–gas–starcycleRecycles gasfrom old starsinto new starsystemsCopyright © 2009 Pearson Education, Inc.High-mass starshave strongstellar windsthat blowbubbles of hotgas.Copyright © 2009 Pearson Education, Inc.Lower-mass stars return gas to interstellar
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