Tuesday, week 8

• Arney on The Force of Truth

• Zita on Uncertainty– Measurements– Pictures– Quantum mechanics

• Discussion

• Looking ahead

Tuesday, week 8

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/Lab-MolarVolume/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_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)

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?