Astro 10-Lecture 2: The nature of science and scientific models

1. Astro 10-Lecture 2:The nature of science and scientific models Dr. Eric Korpela korpela@ssl.berkeley.edu http://setiathome.ssl.berkeley.edu/~korpela/ (510) 643-6538

2. Quiz #1 1. T/F There are many galaxies in our solar system. 2. What is 10-2 times 102? 3. If the sun were the size of a basketball, Jupiter would be: a. The size of a grapefruit b. 14 inches away from the sun c. About an inch in diameter d. Invisible to the naked eye

3. Quick Review of Last Week

4. Quick Review of Last Week

5. Quick Review of Last Week • Tour of some objects in universe

7. What is Astronomy? Literally: aster = star + nomie=naming (Astrology was already taken) Astronomy, in modern terms, is observational scientific study of the universe and its contents. Astrophysics is the combination of astronomy with theoretical understanding of the processes taking place in astronomical objects.

8. A more basic question: What is science? Is science a collection of facts? No! Science is a process. It’s a means by which we try to understand how the world works. Example: Watch a football game. Try to figure out the rules without knowing them or having a rule book. Science is the process of trying to create a universal rule book.

9. A scientific world-view Science is based upon careful observation of the world around us and trial-and-error experiments. Science tries to be a consistent and coherent picture. • Repeatable by anyone • Rules don’t vary from one area of science to another • Rules don’t vary from one place to another • Rules don’t vary from one time to another Science builds on and refines everyday experience and intuition.

10. How does science work? A scientist makes an educated guess about a rule: a hypothesis. • A hypothesis needs to be quantitative. • It needs to make predictions about the behavior of the universe. • A hypothesis builds on existing knowledge of the universe The hypothesis is tested by experiment or observation. • If the hypothesis fails a test it must be discarded or modified. Example Hypothesis: All objects fall when dropped…. • Is this hypothesis true or false? A hypothesis that never fails despite repeated tests of its predictions is called a theory. (In science, ‘a theory’ is something that is a near certainty.)

11. How does science work? • Science isn’t about ‘truth.’ It’s about what has worked so far. • No hypothesis can be proven to be true. It can only be shown to be false. (A hypothesis must be falsifiable.) • A complete hypothesis must work at all places and times. • Only one bad prediction is required to falsify a hypothesis. • Example: Newton’s Theory of Universal Gravitation • superceded by Einstein’s Theory of General Relativity • still a useful approximation for most situations despite having been falsified.

12. How would a scientist find the answer the following questions? How long does it take to cook a turkey? Why does it take that long to cook a turkey? The difference between these questions is the difference between observational fact and science.

13. The Scientific Method 1. Start with a set of observational facts we would like to explain. Each day the sun rises in the east and sets in the west. 2. Propose one or more hypotheses (or models) to explain them: A. The sun circles the earth each day. B. A new sun is created each day in the east and destroyed in the west C. The earth rotates from west to east. 3. Devise predictions from your models. Model A. Motion of the sun should be independent from other celestial bodies Model B. The appearance of spots on the sun should differ from day to day. People to the east of us should see the sun being created. Model C. All astronomical bodies should rise in the east and set in the west.

14. The Scientific Method 4. Gather observations to test your predictions All astronomical bodies rise in the east and set in the west every day. Spots on the sun differ only slightly from day to day. People living elsewhere see the same thing we do. 5. Modify your hypotheses to fit the observation, if necessary: A. All astronomical bodies circle the earth each day. B. New sun, moon, stars and planets are created each day in the east and destroyed in the west. These bodies are nearly identical to the ones from the previous day. People living elsewhere have been brainwashed into not seeing this process occurring. C. The earth rotates from west to east. 6. Discard implausible hypotheses (such a B) • Occam’s Razor: All else being equal, the simplest explanation is most likely to be correct.

15. The Scientific Method

16. The Scientific Method 7. Share your observations, methods, hypotheses and predictions with other scientists. (Peer review) • Another scientist may know of observations that contradict your hypothesis • Other scientists may devise tests of your hypothesis • Other scientists may come up with competing hypotheses. 8. Go to step 3. • A hypothesis is never proven to be true.

17. What does this mean to me? When you are reading an article or book about a scientific discovery or theory, think about: • What is the hypothesis being considered? • How is the hypothesis being tested? • What evidence supports/contradicts the hypothesis? • Are the scientists involved being objective (open to alternative explanation) or biased?

18. Pseudoscience An attempt to pass off unscientific theories as science. Bullshit Detector • Is the “scientist” trying to sell you something? • Is the “science” based upon case studies and testimonials? • Is the “theory” falsifiable? • Has the “research” been peer reviewed? • Is there a physically viable explanation for the effect reported?

19. Things that are not science... Astrology - It makes predictions, but the theory/method isn’t changed when predictions fail Creation Science - It makes no testable predictions. Not falsifiable. Psychic precognition - theory/method isn’t changed when predictions fail. Religion - Not falsifiable. ’Not science’ does not mean ‘not true’ any more than ‘science’ means ‘truth.’

20. People are very good at seeing patterns Card Demonstration EVEN WHEN NO PATTERN EXISTS

21. Time of day

22. You are here 38° The night sky Before we can get a handle on the behavior of things in the sky, we need to get a handle on our place on the earth.

23. A reminder of what degrees are • Invented by the Babylonians who believed certain numbers had magical properties (3, 6, 12, 24, 60) • They divided a full circle into 360 degrees (because 360 is divisible by 3, 6, 12, 24, 60, etc) • Each degree is divided into 60 arcminutes • Each arcminute is divided into 60 arcseconds. • We also get our time measurements from them 60 minutes per hour, 60 seconds per minute, 24 hours per day.

24. How big is a degree?

25. The night sky Before we can get a handle on the behavior of things in the sky, we need to get a handle on our place on the earth.

26. Zenith 90º The night sky The boundaries of what we can see are defined by the Earth Horizon S N

27. North Celestial Pole You are here 38° Projections of lines on the earth Celestial Equator

28. Projections of lines on the Earth

29. The Celestial Sphere

30. The Celestial Sphere

31. The Celestial Sphere

32. Projections of lines on the Earth

33. NCP 90º The night sky Where these projected points or line appear on the sky depends upon your latitude 38º Celestial Equator 38º S N

34. At the north pole… (Latitude=90°) Where these projected points or line appear on the sky depends upon your latitude NCP 90º Celestial Equator 90º S N

35. Celestial Equator NCP SCP Concept Test Where in the sky would the celestial equator and NCP be if you were located at the equator (0° latitude). S N

36. The Celestial Sphere

37. The Celestial Sphere

38. The Celestial Sphere The earth rotates under the stationary celestial sphere. However, it is often more convenient to think of the celestial sphere rotating above a stationary earth.

39. The Celestial Sphere

40. The Celestial Sphere

41. Precession

42. Precession