Atoms and Stars
IST 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
o Email if much work will be late
•
•
•
•
Review of readings
Updating the course
Emphasizing main points one more time
Review for Final
12/08/08
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2
Upcoming …
• Tonight, December 8 (last regular class)
o Review of Readings
o Review for Final Exam
o 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
o Nothing that night but the Final Exam
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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.
12/08/08
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4
Your Current Status
• Grades I have for you:
o Online Grade Report, link off the course web
site (see first slide)
o Enter first name, last name, password the get
report
• Grade you are headed for:
o Grade What-If on course web site
• Ask for help with these if you are having
problems
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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
12/08/08
Atoms and Stars, Class 14
6
ths
16
on the Final (Q1)
• Doing the math for converting 16ths
(inches, ounces) to decimal (inches, pounds)
o 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.
o So the result of the division will be there, but
you will have to know what you are looking
for.
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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.
12/08/08
Atoms and Stars, Class 14
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Experiment 7 (Specific Gravity)
• Specific Gravity
o Ratio of weight of a given volume of a
substance (e.g. wood, iron) divided by weight
of same volume of water
o A property of the substance
• Conclusions:
o Volume of displaced water = volume of object
(Archimedes)
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Experiment 7
• Conclusions from experiments:
o Volume of displaced water = volume of object
(Archimedes)
o Specific Gravity greater than 1: object sinks in
water
o Specific Gravity less than 1: object floats in
water
o For an object that floats in water, weight of
displaced water = object’s weight (Archimedes)
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Experiment 7
• Conclusions from experiments:
o For an object that floats in water, fraction
underwater = Specific Gravity
o For an object that sinks in water, weight of
object in water + weight of displaced water =
object’s weight in air
o If Specific Gravity of object less that the
Specific Gravity of a liquid, object floats in that
liquid (iron floats in mercury)
12/08/08
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Re-emphasizing Main Points
• Two pillars of science
o Experiment: makes science reliable
• Scientists led astray by logic (Aristotle) and belief
(church and geocentrism, Inquisition)
• Experiments base science on direct experience
o 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
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Re-emphasizing Main Points
• I have the experiments in this course to:
o Give you direct experience
o Illustrate experiments described in class
o Illustrate social nature of science within the lab
groups
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Readings: Global Warming
From last week
Readings: Global Warming (Q12)
• Light comes in to earth from sun
o Some absorbed on surface, warming earth and
reradiating heat (infrared) radiation
o Rest reflected, exits to space
o 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
o By 2100, projections = 2.5ºF to 11.5ºF (avg 7ºF)
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Atoms and Stars, Class 14
15
Atmosphere,
Climate and
Change by
Thomas
Graedel and
Paul
Crutzen,
Scientific
American
Library,
1997.
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Atoms and Stars, Class 14
16
New York Times, “Computers Add Sophistication, but Don’t Resolve Climate Debate,” Science Times Pg D3 8/31/04
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Atoms and Stars, Class 14
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Global Warming (cont’d)
• Largest effect in
Antarctic
o Snow reflects the
most, sea water the
least
o Arctic ice
disappearing
o Polar bears in danger
o Eskimos suing US
12/08/08
The New Yorker, cover, 12/12/05
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Global Warming (cont’d)
• What to do? Options:
o 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
o Cosmetic actions. Cite uncertainty, call for
more research
• Will never have 100% certainty
• Options:
o “Invisible hand” of market
• Trade CO2 permits
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Global Warming (cont’d)
• Options (cont’d):
o Limit CO2 production
• Increase energy efficiency, use waste energy, switch
to low-carbon fuels (natural gas) away from coal
and petroleum
o Remove CO2 once it is generated
• Sequestration – pressurized underground or under
deep ocean
o Geoengineering
• Stop sunlight from coming to Earth, e.g. by seeding
SO2 to form clouds or putting BIG mirrors in orbit
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Global Warming (cont’d)
• (DB) Recent poll says US thinks scientists
are confused about Global Warming. NOT!
o Deliberate confusion caused by industry groups
opposed to controls – citing 2 or 3 out of 2,500
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Readings: Icecaps and Hurricanes
Evidence for Global Warming:
• Thawing icecaps
• Coral bleaching
• Hurricanes
• Melting glaciers
• Desertification
• Rising sea levels
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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
12/08/08
Atoms and Stars, Class 14
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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
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DB: That’s not all…
• Many worldwide resource issues – “the
human footprint”
o 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.
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Readings
Readings: Knowledge or
Certainty
Jacob Bronowksi
• Absolute certainty is impossible in science
o 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
o Statistical uncertainty in measurements - Gauss
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Knowledge or Certainty
• 1795
• Science is discussion and argument
preceding knowledge
• Also Uncertainty Principal 1927 Werner
Heisenberg – cannot locate particle exactly
o Irreducible uncertainty or fuzzy focus
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Knowledge or Certainty
• No practical
effect at
macroscopic 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
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What is Science?
Moti Nissani, What Is Science?
• Difficult or impossible to give a dictionarytype definition for science
• (DB) Working scientists rarely think about
the history or philosophy of science
• Start with philosophy of Thales – free
inquiry
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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)
o But contradiction by experiment does not
always mean rejection of hypothesis – can lead
to reexamination of experiment or modification
of hypothesis
o Scientists “on the trail” have personal concerns
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What Is Science? (cont’d)
o Scientists “on the trail” have personal concerns
• Argument and community lead to progress
o Semmelweiss and deaths in maternity ward
•
•
•
•
•
•
12/08/08
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
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32
What Is Science? (cont’d)
• Theories unify many hypotheses and
experiments
o 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
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33
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
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35
Relativity
• Reminder about what this is about
o Computer simulation
• Often very difficult to tell whether or not
our measurements are in a moving
coordinate system
o 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
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Special Relativity
• For fast-moving objects
o
o
o
o
Max speed = c (speed of light)
Objects foreshortened
Time slows down
But the traveling person says the same about
you!
o Space and time  space-time
o E = mc2
 light has mass, is bent by gravity
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General Relativity
• For very heavy objects
o Space and time warp, cause gravity
o 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
o Says light bends twice as much as Special
Relativity says, observed 1918
12/08/08
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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)
12/08/08
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Quantum Mechanics
Two different types of things
• Particle (“thing,” “object”)
o Examples: baseball, soup can, projectile, star
o One location (or center)
o Newton’s three laws govern motion
• Wave
o Examples: waves in water, sound waves, radio
waves
o Spread out, exists in many places
o “Wave Equations” governed motion (not
Newton)
• Jump to slide 48
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Two different types of things
Particle
Wave
Position:
Definite – one
position (center)
Spread out, no one
place
Try to catch it –
result is:
Collision with
another:
Existence:
Get all or none
Only get part, if
that
Pass through each
other
In something – the
“medium” (before
Maxwell)
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Ricochet,
bounce, shatter
All by itself
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Demonstrations
• PhET (Physics Education Technology)
http://www.colorado.edu/physics/phet/web-pages/simulations-base.html
o Particles: Gas Properties – they bounce
o Waves: Sound >> Interference by Reflection
• Interference: light  peak, dark  trough
o 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”
o http://www.colorado.edu/physics/2000/schroedinger/two-slit2.html
o Confine a wave – it spreads out
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Particles collide…
Particles of gas mix together, collide
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44
but waves pass through each other
Sound wave and its reflection
(type – sound - is unimportant here)
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Waves “interfering”
Confine a wave and it spreads out
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46
Waves
• Wavelength –
distance between
peaks (or troughs)
• Fixed speed
• Until 20th century,
Wave / Particle –
we thought
everything was one
or the other
12/08/08
Wavelength
Atoms and Stars, Class 14
47
Wave-Particle Duality
• In 20th century, with rise of Quantum
Mechanics, we understood that everything
was both.
o For a wave, x (position) and v (velocity)
connected
• Momentum p = m × v (m = mass, amount of matter)
o Led to “Uncertainty Principle”
• Irreducible uncertainty in our knowledge
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Atoms and Stars, Class 14
48
Uncertainty Principle
• 1795 Carl Friedrich Gauss (college student)
• Also Uncertainty Principal 1927 Werner
Heisenberg – cannot locate particle exactly
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Atoms and Stars, Class 14
49
Quantum Mechanics
• At molecular level and smaller, waves and
particles merge – everything is both
o Wave – spread out, cannot contain it
o Particle – have it or don’t
o Q.M.: wave gives chance of “catching” particle
• Cannot be made certain
• Uncertainty Principle
o Carries over to regular world, makes clockwork
universe impossible over age of universe
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Atoms and Stars, Class 14
50
Quantum Mechanics (cont’d)
• Accounts for properties of ordinary
materials
o
o
o
o
o
Theoretical: keeps matter from collapsing
Color
Solid (strength), elastic, gaseous
Solid state electronics – semiconductors
Forces – due to exchanges of particles
• No Newtonian “action at a distance”
• E.g. electrical force carried by photons – particles of
light
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Atoms and Stars, Class 14
51
Conflict!
• Heavy (G.R.) and small (Q.M.) –
mathematical conflict. Example: Black Hole
o Competing theories of gravity – “embarrassing”
• G.R.: gravity caused by masses warping space-time
• Q.M. – gravity due to exchange of “gravitons” (not
found yet)
o “String Theory” might unite these two
12/08/08
• “Theory of Everything” – accelerating expansion(!)
• Matter and energy composed of elemental vibrating
strings and membranes
• Eleven dimensions, seven curled up too small to
experience directly – may have indirect experience
• Theory still developing, no unique experimental
evidence yet Atoms and Stars, Class 14
52
Issues:
• “Anthropic Principle” – physical rules seem
to favor life
o Room for God inside science?
o But “Inflationary Universe” may explain this
• Dark Matter
o Galaxies spinning fast, not enough mass to hold
them together so they should be flying apart but
this is not observed
o Must be Dark Matter at center of galaxies
12/08/08
Atoms and Stars, Class 14
53
Issues (cont’d):
• Dark Energy
o Big Bang should be
slowing down
o But outer half of universe
is accelerating!
o Current hypothesis is that
dark energy at outside
fringe is attracting the inner parts.
Source: NASA
• Between these two, we see only 5%. The
universe is still surprising us!
12/08/08
Atoms and Stars, Class 14
54
The end of the ride
• Strong dose of the value of science here
• One more time, about science:
o Two pillars – repeatable experiment (what makes it
reliable) and explanatory theory (what makes it valuable)
• Developed 1400 – 1800 AD: Copernicus to Dalton
o Developing hypotheses and theories is creative
o Has a boundary but expands aggressively
 not a complete basis for living
o
o
o
o
12/08/08
Now drives technology
We all use it
Conflicts with some, but not all, religious beliefs
People of all ethnicities have been able to contribute
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Review for Final