Scientific Inquiry
SCI 105
Evaluating Theoretical Hypotheses
Facets of Models
A model is
Abstract: details are intentionally omitted
Similar but not the same: to the real world
object that it represents
Part of the imaginary world
Its fitness to the (part of) real world needs to be
evaluated
It can be used to answer questions related to the
phenomena
Does it look
(physically) like
our campus?
Representations of Models
It’s crucial that a model can be presented
clearly and accurately, since it is
imaginary! (But it may be a fact if it’s right.)
Ways to present a (theoretical) model
Plain language: flexible, but lengthy and often
ambiguous
Visual symbols and diagrams: concise and
illustrative, but might not be accurate
Formal symbols and formulae: accurate, but
may be hard to convey the hidden meanings
Theoretical Models: A Simple Illustration
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DL
0
35
37 38
42
T(oC)
Heat transfer
Q
Q = c * (T - T0)
Linear expansion
DL = cl * (T - T0)
Theoretical Hypotheses
A theoretical hypothesis is to ask
Does the model fit the real world
In the intended aspects
To the intended degree of accuracy
Possible outcomes
True: fits as claimed
False: doesn’t fit
All scientific claims are hypotheses
The difference is in the fitness
A Model for Model Evaluation
Fit or not
Real World
Model
Observation/
Experimentation
Reasoning/
Calculation
Agree/Disagree
Data
Prediction
The Components
Real world: described in common language
Model : described in scientific terms
Hypothesis: specify the aspects and degree of accuracy
Data: expected results
All specific info that may be directly relevant
Obtained thru a process of physical interactions
Prediction: output from the model
Doesn’t need to be said ahead of time
A Six-Step Program
Real World
Identify a problem
No
Model doesn’t fit
Model
Describe it w/ sci.
terms
Prediction
Data agrees
prediction?
Data
Obtained by
observation or exp
Yes
No
Model does fit
D & P w/o
fitness?
Yes
Inconclusive
The Double Helix Case
RW problem: the DNA structure
Model: two-chain helical structure w/
bases mixed-paired in the center
Prediction: X(or diamond)-shaped pattern
in x-ray diffraction; A-T and
C-G ratios are 1:1
Data: Francis’s “B Form”; Chargaff’s
results; data that lead to Pauling’s
theories; and Avery’s results
Announcements
H/W Assignment
Ex 2.7: p 51-2 in Giere’s text
Identify the four components
Try to fit the episode into the 6-step program
Write a sentence/paragraph for each of comp/step
Submit a printed copy by Mon, at beginning of class