Transcript Z on Uncertainty

Tuesday, week 8
• Arney on The Force of Truth
• Zita on Uncertainty
– Measurements
– Pictures
– Quantum mechanics
• Discussion
• Looking ahead
Break time
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)
Measurements
http://dbhs.wvusd.k12.ca.us/webdocs/GasLaw/LabMolarVolume/Mg-and-ruler.JPG
Uncertainties in Measurements
Accuracy? (dx=2mm) Precision? (x=1mm?)
Reproducibility?
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”
Picture problems
http://www.sbi-online.org/sbi_home/case_of_the_month/2005_january_sbi_case_of_the_month
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
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)
Pictures of WMDs?
http://www.globalsecurity.org/wmd/library/news/iraq/2003/iraq-030205-powell-un-17300pf.htm
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.”
Maps and models
… as representations of reality…
What is reality?
Reality can surprise you.
Predictions can be wrong.
Pictures of particles?
http://www.windows.ucar.edu/tour/link=/physical_scie
nce/physics/atom_particle/electron.html
http://www.iun.edu/~cpanhd/C101webnotes/modernatomic-theory/images/orbitals.jpg
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)
Quantum mechanical uncertainty
What is the chance that an
electron with energy E2 will
be found in orbit r1?
Quantum mechanical uncertainty
Beyond theory-laden facts: Observations can
change measurement outcomes.
Old paradigm: Who decides position is a good
thing to measure?
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
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)
Looking ahead
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.
Research Progress reports
• Get specific
• What is the strongest evidence AGAINST?
• What is the strongest evidence FOR?
• What have you learned?