Tuesday, week 8

1
Tuesday, week 8

• Arney on The Force of Truth
• Zita on Uncertainty
• Measurements
• Pictures
• Quantum mechanics
• Discussion
• Looking ahead

2
Break time
3
Zita on Uncertainty

• Measurements
• Pictures
• Quantum mechanics
• We may never hit the truth target. So what is
  the point of worrying about whether our beliefs
  are true?
• (Lynch, True to Life, p.27)

4
Measurements

• http//dbhs.wvusd.k12.ca.us/webdocs/GasLaw/Lab-Mol
  arVolume/Mg-and-ruler.JPG

5
Uncertainties in Measurements
Accuracy? (dx2mm) Precision? (?x1mm?) Reproduci
bility? Who decided this was a good
question? Correlation vs. cause? What does it
mean? (Why) does it matter? Month of birth is
important for adult stature
6
Picture problems

• http//www.sbi-online.org/sbi_home/case_of_the_mon
  th/2005_january_sbi_case_of_the_month

7
Uncertainties in Mammograms
Shadowing by/in dense tissue False positives,
false negatives Structure ? function? Motivations
radiologists vs HMOs Follow-up ultrasound,
surgical biopsy Diagnosis malignant phyllodes
tumor
8
Is too much faith put in pictures?
The picture promises certainty, and it cannot
deliver on that promise. However Mammograms do
not have to be infallible to save lives reduces
the risk of dying from breast cancer by about 10
amounts to thousands of lives saved every
year (Gladwell, p.7/8)
9
Pictures of WMDs?

• http//www.globalsecurity.org/wmd/library/news/ira
  q/2003/iraq-030205-powell-un-17300pf.htm

10
Uncertainties in WMD photos
Resolution, interpretation Structure ?
function? Who decided this was a telling photo?
Which is the fire truck? Motivations? Leaving
Saddam Hussein in possession of weapons of mass
destruction for a few more months or years is not
an option, not in a post-September 11 world.
11
Maps and models
as representations of reality What is
reality? Reality can surprise you. Predictions
can be wrong.
12
Pictures of particles?

• http//www.windows.ucar.edu/tour/link/physical_sc
  ience/physics/atom_particle/electron.html

http//www.iun.edu/cpanhd/C101webnotes/modern-ato
mic-theory/images/orbitals.jpg
13
Uncertainties in positions
There is a finite probability that once in a
very great while, your car will spontaneously
ooze through the brick wall of your garage and be
found the next morning on the street (Sagan,
Ch.17, Marriage of Skepticism Wonder,
Demon-Haunted World, 304)
14
Quantum mechanical uncertainty
What is the chance that an electron with energy
E2 will be found in orbit r1?
15
Quantum mechanical uncertainty
Beyond theory-laden facts Observations can
change measurement outcomes. Old paradigm Who
decides position is a good thing to measure?
16
How can QM be true, given all this uncertainty?

• Statistical predictions are highly uncertain for
  a few particles, and very accurate precise for
  systems of many particles
• modern electronics (e.g. semiconductors)
• diagnostics (scanning tunnelling microscope,
  SEM, atomic force microscope)
• lasers
• quantum computing

17
How to make decisions, in the face of uncertainty?

• The idea that the value of pursuing the truth
  rests on the possibility of certainty is a
  myth.
• (Lynch, 27)

18
Looking ahead
19
EVERYONE remember to

• Give feedback to your study group members on
  their Research Progress reports THIS WEEK
• Take the online Plagiarism quiz from week 6 if
  you have not already done so THIS WEEK
• Correction Common knowledge means whatever
  your peers can be sure to know without looking it
  up. CITE SOURCE for everything else.

20
Research Progress reports

• Get specific
• What is the strongest evidence AGAINST?
• What is the strongest evidence FOR?
• What have you learned?