arney on the force of truth zita on uncertainty –measurements –pictures –quantum mechanics...
Post on 20-Dec-2015
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TRANSCRIPT
• Arney on The Force of Truth
• Zita on Uncertainty– Measurements– Pictures– Quantum mechanics
• Discussion
• Looking ahead
Tuesday, week 8
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)
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_science/physics/atom_particle/electron.html
http://www.iun.edu/~cpanhd/C101webnotes/modern-atomic-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)
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.