Science is figuring stuff out and not fooling yourself Richard Feynman Copyright 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 person looking at an unmarried person A Yes B No C Cannot be determined Copyright 2009 Pearson Education Inc The Monty Hall Effect There 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 The game is simple There are three doors that are closed Two of them have a can of soup behind them and the other has a new car You try to 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 the soup 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 not chosen 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 change your choice The question is do you change doors if you want to have the best 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 Fallacy In the case of OJ Simpson the prosecution argued that there was huge amout of circumstantial evidence showing Simpson had committed the murder of his wife Nicole He had a long history of abusing her and as they said A slap is a prelude to homicide The defense attorney Alan Dershowitz responded with the following argument 4 million women are battered annually in the US by boyfriends and husbands but in 1992 1432 were killed by their partners This means that 1 in 2500 killed by their 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 sister This is a simple one You meet the parents of your girlfriend You know they have another child but you don t know if they are a girl or boy What is the chance that the other child is a girl A 33 1 in 3 B 50 50 50 C 67 2 in 3 Copyright 2009 Pearson Education Inc The other sister This is a simple one too You meet some cousins man and wife and you start talking to them They tell you they have 2 children and one of them is a girl What is the chance 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 Florida You meet some cousins man and wife and you start talking to them They tell you they have 2 children and one of them is a girl with the weird name Florida What is the chance that 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 birthdays How many students do you need in a room before the chance that two have the same birthday is 50 A 10 B 25 C 50 D 100 E 365 Copyright 2009 Pearson Education Inc What have we learned We have a very poor idea of statistical outcomes in certain situations and even a lousier idea of random processes Be careful when you deal with statistics Don t believe someone who says Well the chances are so small that it can t happen Copyright 2009 Pearson Education Inc Chapter 14 Our Galaxy Copyright 2009 Pearson Education Inc 14 1 The Milky Way Revealed Our 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 gas clouds obscure our view because they absorb visible light This is the interstellar medium that makes new star systems Copyright 2009 Pearson Education Inc All Sky View Copyright 2009 Pearson Education Inc We see our galaxy edge on Primary features disk bulge halo globular clusters Copyright 2009 Pearson Education Inc If we could view the Milky Way from above the disk 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 a little up and down motion Copyright 2009 Pearson Education Inc Orbits of stars in the bulge and halo have random orientations Copyright 2009 Pearson Education Inc Copyright 2009 Pearson Education Inc Thought Question Why 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 toward the disk C Halo stars knock them back into the disk Copyright 2009 Pearson Education Inc Thought Question Why 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 toward the disk C Halo stars knock them back into the disk Copyright 2009 Pearson Education Inc Sun s orbital motion radius and velocity tells us mass within Sun s orbit 1 0 1011MSun Copyright 2009 Pearson Education Inc Orbital Velocity Law r v Mr G 2 The orbital speed v and radius r of an object on a circular orbit around the galaxy tell us the mass Mr within that orbit Copyright 2009 Pearson Education Inc What have we learned What does our galaxy look like Our galaxy consists of a disk of stars and gas with a bulge of stars at the center of the disk surrounded by a large spherical halo How do stars orbit in our galaxy Stars in the disk orbit in circles going in the same direction with a little up and down motion Orbits of halo and bulge stars have random orientations Copyright 2009 Pearson Education Inc 14 2 Galactic Recycling Our 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 our galaxy Copyright 2009 Pearson Education Inc Star gas star cycle Recycles gas from old stars into new star systems Copyright 2009 Pearson Education Inc High mass stars have strong stellar winds that blow bubbles of hot gas Copyright 2009 Pearson Education Inc Lower mass stars return gas to interstellar space through stellar winds and planetary nebulae Copyright 2009 Pearson Education Inc X rays from hot gas in supernova remnants reveal newly made heavy elements Copyright 2009 Pearson Education Inc A supernova remnant cools and begins to emit visible light as it expands New elements …
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