Atoms and Stars IST 2420

Atoms and StarsIST 2420 Class 14, December 8 Fall 2008 Instructor: David Bowen Course web site: www.is.wayne.edu/drbowen/aasf08

Agenda • Assignments, passbacks, initial signin sheet • Class information • Email if much work will be late • Review of readings • Updating the course • Emphasizing main points one more time • Review for Final Atoms and Stars, Class 14

Upcoming … Tonight, December 8 (last regular class) Review of Readings Review for Final Exam Due: all work to count in regular grade Work turned in after this class will count towards a Change of Grade after the regular grades come out Final Exam: next Monday, December 15 Nothing that night but the Final Exam Atoms and Stars, Class 14 3

Course Grades • If you are turning a bunch of work in at the end, I may not get it graded in time for the regular grades (see the Syllabus). • If this is you (turning it in late), what grade do you want for the regular grade? D, F, W, I • Email me to let me know – otherwise it’s my decision. Atoms and Stars, Class 14

Your Current Status • Grades I have for you: • Online Grade Report, link off the course web site (see first slide) • Enter first name, last name, password the get report • Grade you are headed for: • Grade What-If on course web site • Ask for help with these if you are having problems Atoms and Stars, Class 14

Opportunities for Q & A • Tonight during the Review Session • Day of the Final, Monday December 15, 5 – 6 PM (normal office hours) in the regular classroom (122 Cohn) • Call, email, set up an appointment • IM to WSU web guy Atoms and Stars, Class 14

16ths on the Final (Q1) • Doing the math for converting 16ths (inches, ounces) to decimal (inches, pounds) • If this type of problem is on the Final, there will also be a table of all divisions by 16, with a few non-16ths extras thrown in • 1/16 = .0625, 2/16 = .1250, 3/16 = .1875, 3/7 = .4286, 4/16 = .2500, etc. • So the result of the division will be there, but you will have to know what you are looking for. Atoms and Stars, Class 14

Makeup for Final Exam • Let me know by email that you want a makeup, within 24 hours after the Final (University regulation) • Date / Time, building and room to be settled by email. Atoms and Stars, Class 14

Experiment 7 (Specific Gravity) • Specific Gravity • Ratio of weight of a given volume of a substance (e.g. wood, iron) divided by weight of same volume of water • A property of the substance • Conclusions: • Volume of displaced water = volume of object (Archimedes) Atoms and Stars, Class 14

Experiment 7 • Conclusions from experiments: • Volume of displaced water = volume of object (Archimedes) • Specific Gravity greater than 1: object sinks in water • Specific Gravity less than 1: object floats in water • For an object that floats in water, weight of displaced water = object’s weight (Archimedes) Atoms and Stars, Class 14

Experiment 7 • Conclusions from experiments: • For an object that floats in water, fraction underwater = Specific Gravity • For an object that sinks in water, weight of object in water + weight of displaced water = object’s weight in air • If Specific Gravity of object less that the Specific Gravity of a liquid, object floats in that liquid (iron floats in mercury) Atoms and Stars, Class 14

Re-emphasizing Main Points • Two pillars of science • Experiment: makes science reliable • Scientists led astray by logic (Aristotle) and belief (church and geocentrism, Inquisition) • Experiments base science on direct experience • Theory: makes science valuable • Once you have a reliable theory, it tells you the answer in advance, can use it as technology • Two quotes from Copi, Reader Pg 8 Atoms and Stars, Class 14

Re-emphasizing Main Points • I have the experiments in this course to: • Give you direct experience • Illustrate experiments described in class • Illustrate social nature of science within the lab groups Atoms and Stars, Class 14

Readings: Global Warming From last week

Readings: Global Warming (Q12) • Light comes in to earth from sun • Some absorbed on surface, warming earth and reradiating heat (infrared) radiation • Rest reflected, exits to space • Greenhouse gases in upper atmosphere trap reradiated infrared radiation, some returned and further heats earth • Amount of warming now about 1ºF but projected to rise rapidly • By 2100, projections = 2.5ºF to 11.5ºF (avg 7ºF) Atoms and Stars, Class 14

Atmosphere, Climate and Change by Thomas Graedel and Paul Crutzen, Scientific American Library, 1997. Atoms and Stars, Class 14

New York Times, “Computers Add Sophistication, but Don’t Resolve Climate Debate,” Science Times Pg D3 8/31/04 Atoms and Stars, Class 14

Global Warming (cont’d) • Largest effect in Antarctic • Snow reflects the most, sea water the least • Arctic ice disappearing • Polar bears in danger • Eskimos suing US The New Yorker, cover, 12/12/05 Atoms and Stars, Class 14

Global Warming (cont’d) • What to do? Options: • Nothing. Live with it. (Physical and ecosystem consequences not known) • Humans can adapt quickly, natural world cannot – evolution is slow, but humans are free of evolution • Cosmetic actions. Cite uncertainty, call for more research • Will never have 100% certainty • Options: • “Invisible hand” of market • Trade CO2 permits Atoms and Stars, Class 14

Global Warming (cont’d) • Options (cont’d): • Limit CO2 production • Increase energy efficiency, use waste energy, switch to low-carbon fuels (natural gas) away from coal and petroleum • Remove CO2 once it is generated • Sequestration – pressurized underground or under deep ocean • Geoengineering • Stop sunlight from coming to Earth, e.g. by seeding SO2 to form clouds or putting BIG mirrors in orbit Atoms and Stars, Class 14

Global Warming (cont’d) • (DB) Recent poll says US thinks scientists are confused about Global Warming. NOT! • Deliberate confusion caused by industry groups opposed to controls – citing 2 or 3 out of 2,500 Atoms and Stars, Class 14

Readings: Icecaps and Hurricanes Evidence for Global Warming: • Thawing icecaps • Coral bleaching • Hurricanes • Melting glaciers • Desertification • Rising sea levels Atoms and Stars, Class 14

DB: That’s not all… • Intergovernmental Panel on Climate Change (IPCC) report 2007 • IPCC: joint organization of climate scientists and government leaders • We can now see the results directly, instead of using computer models • Some areas may see initial benefit, but if there is no end, all areas will suffer Atoms and Stars, Class 14

DB: That’s not all… • Insurance industry raising premiums to account for expected higher damages • Power and auto industries expect regulation, want it soon so they know what to plan for • Report released today on U.S. “National Security and the Threat of Climate Change” • Board of senior (retired) military • Reduced natural resources, so threats to stability • Increased needs for humanitarian aid • New sea lanes to be protected as ice melts Atoms and Stars, Class 14

DB: That’s not all… • Many worldwide resource issues – “the human footprint” • Population (6 billion  9 billion), water (drinking, irrigation, industrial), food, farmland, living in unsafe places, petroleum, trash, development • Managing the human footprint will be a major, continuing issue • I am not predicting disaster – I think we (you) will manage this, but not easy. Atoms and Stars, Class 14

Readings

Readings: Knowledge or Certainty Jacob Bronowksi • Absolute certainty is impossible in science • Looking at an object with infrared, then visible, then x-rays should yield greater detail. Infrared is very blurry, visible is pretty good, but x-rays are too high energy to be focused. Perfect detail of “God’s-eye” view is impossible • Statistical uncertainty in measurements - Gauss Atoms and Stars, Class 14

Knowledge or Certainty • 1795 • Science is discussion and argument preceding knowledge • Also Uncertainty Principal 1927 Werner Heisenberg – cannot locate particle exactly • Irreducible uncertainty or fuzzy focus Atoms and Stars, Class 14

Knowledge or Certainty • No practicaleffect atmacroscopic level, but a philosophical problem with The Mechanical Universe and with “The God’s eye view” • But certainty leads to tragedy – Nazis • (DB) Certainty and power combined Atoms and Stars, Class 14

What is Science? Moti Nissani, What Is Science? • Difficult or impossible to give a dictionary-type definition for science • (DB) Working scientists rarely think about the history or philosophy of science • Start with philosophy of Thales – free inquiry Atoms and Stars, Class 14

What Is Science? (cont’d) • Then hypothesis and experiment (Torricelli) • Falsifiability – reason and logic have not been not sufficient to discover the truth in science (DB: belief, either) • But contradiction by experiment does not always mean rejection of hypothesis – can lead to reexamination of experiment or modification of hypothesis • Scientists “on the trail” have personal concerns Atoms and Stars, Class 14

What Is Science? (cont’d) • Scientists “on the trail” have personal concerns • Argument and community lead to progress • Semmelweiss and deaths in maternity ward • Neighboring ward far safer • Did priest’s visit scare patients? • Washing hands – doctors did dissections beforehand • This fixed the problem • Profession slow to accept this change • Even scientists can be closed-minded, resist change Atoms and Stars, Class 14

What Is Science? (cont’d) • Theories unify many hypotheses and experiments • Price is often inaccessibility to non-scientists • Scientists usually not concerned with these issues or with philosophical uncertainty • Science many not be perfect, but it can still be very good • Many use technology but not the scientific foundation Atoms and Stars, Class 14

Physical Science Current Status

Physical Science: Current Status • Newton’s Laws, Maxwell’s Equations and similar classical theories (before ~ 1900) describe world we know and see • For things the size of molecules and smaller, need Quantum Mechanics • Very fast, need Special Relativity • Very heavy, need General Relativity • All three have weird things going on Atoms and Stars, Class 14

Relativity • Reminder about what this is about • Computer simulation • Often very difficult to tell whether or not our measurements are in a moving coordinate system • Earth spins on axis, moves around Sun, Sun moves around Galaxy, is Galaxy moving? • Theory of Relativity says we can only tell relative motion, not absolute Atoms and Stars, Class 14

Special Relativity • For fast-moving objects • Max speed = c (speed of light) • Objects foreshortened • Time slows down • But the traveling person says the same about you! • Space and time  space-time • E = mc2  light has mass, is bent by gravity Atoms and Stars, Class 14

General Relativity • For very heavy objects • Space and time warp, cause gravity • Perihelion (closest approach to sun) of Mercury’s ellipse not fixed as in Newton’s Laws, but advances 43 seconds of arc per century (observed), other effects in addition • Says light bends twice as much as Special Relativity says, observed 1918 Atoms and Stars, Class 14

General Relativity (cont’d) • “Einstein Halo” – light from far galaxy bent by near galaxy • Variation on gravitational lens • 12 found so far • Picture: New York Times, 12/6/05, Pg D4 (Science) Atoms and Stars, Class 14

Quantum Mechanics

Two different types of things Particle (“thing,” “object”) Examples: baseball, soup can, projectile, star One location (or center) Newton’s three laws govern motion Wave Examples: waves in water, sound waves, radio waves Spread out, exists in many places “Wave Equations” governed motion (not Newton) Jump to slide 48 Atoms and Stars, Class 14 41

Two different types of things Atoms and Stars, Class 14 42

Demonstrations PhET (Physics Education Technology)http://www.colorado.edu/physics/phet/web-pages/simulations-base.html Particles: Gas Properties – they bounce Waves: Sound >> Interference by Reflection Interference: light  peak, dark  trough http://www.colorado.edu/physics/2000/schroedinger/big_interference.html – some areas gray (unlit) Light: early 1800s, Thomas Young proved light is a wave – “double slit experiment” http://www.colorado.edu/physics/2000/schroedinger/two-slit2.html Confine a wave – it spreads out Atoms and Stars, Class 14 43

Particles collide… Particles of gas mix together, collide Atoms and Stars, Class 14 44

but waves pass through each other Sound wave and its reflection(type – sound - is unimportant here) Atoms and Stars, Class 14 45

Waves “interfering” Confine a wave and it spreads out Atoms and Stars, Class 14 46

Waves Wavelength – distance between peaks (or troughs) Fixed speed Until 20th century, Wave / Particle – we thought everything was one or the other Wavelength Atoms and Stars, Class 14 47

Wave-Particle Duality In 20th century, with rise of Quantum Mechanics, we understood that everything was both. For a wave, x (position) and v (velocity) connected Momentum p = m × v (m = mass, amount of matter) Led to “Uncertainty Principle” Irreducible uncertainty in our knowledge Atoms and Stars, Class 14 48

Uncertainty Principle 1795 Carl Friedrich Gauss (college student) Also Uncertainty Principal 1927 Werner Heisenberg – cannot locate particle exactly Atoms and Stars, Class 14 49

Quantum Mechanics • At molecular level and smaller, waves and particles merge – everything is both • Wave – spread out, cannot contain it • Particle – have it or don’t • Q.M.: wave gives chance of “catching” particle • Cannot be made certain • Uncertainty Principle • Carries over to regular world, makes clockwork universe impossible over age of universe Atoms and Stars, Class 14

Atoms and Stars IST 2420