Physics 270 – Experimental Physics

“The Scientific Method”

Science as a Collection of Facts

Fact 1 Fact 2 Fact 3 …

One possible definition: activities aimed at understanding the natural world

Scientists have shared values and perspectives that characterize a scientific approach to understanding nature: a demand for naturalistic explanations supported by empirical evidence that are testable against the natural world.

Other shared elements include observations, rational argument, inference, skepticism, peer review and reproducibility of work.

Observations of phenomena Experiments Empirical formulas Models Laws / Theory

Let’s do some experiments!

Simplify the phenomenaby creating a model system

on which calculationscan be carried out to

study the phenomena.

Develop multiple approaches since you aren’t sure which one will work.

GoalStart

Painting by Rene Magritte

In science results are presented using precise(though technical) arguments,

…with…testable consequencesfalsifiabilityreproducibility

Experimental VerificationAnd Reproducibility

“Truth” in scienceDescriptions of some aspect of nature in terms of a model. Any view of the natural world that a scientist devises is just a model loaded with assumptions and approximations of that world.

Models, in general, have limited applicability.

As data and technology improve, models are replacedby others which explain a larger range of phenomena.

ReductionReduce a complicated problem into its constituents and aims to understand that complex problem through the study of its components

Wholisma phenomena must be viewed as a

whole in order to understand its structure

Reductionism versus Reductionism versus WholismWholism

Reductionist Example: The Structure of Proteins

Proteins consist of amino acids.These are assembled into ribosomes.The order of assembly is determined by RNA after it is copied from DNA.DNA consists of 4 units called nucleotides.

The structure of proteins is very complicated, but here the problem has been reduced to the assemblage of simpler building blocks.

Holistic Example: An ant hill

Complex physical, chemical, and biological structure built and sustained by millions of ants.

Cannot be understood by braking the ants into tiny parts.

Its essence is in the complexity of the whole.

Deduction – logical development of the consequences of an explanation

starts with theoretical model ⇒ testable prediction ⇒ observations under specific

conditions⇒ confirmation or rejection of

the prediction and/or the model

• Enrico Fermi proposed the existence of the neutrino in 1930 because the observed decay products from beta decay seemed to violate mass and energy conservation.

• In 1956, Cowen and co-workers detected its existence.

Induction – generalization of observed patterns

starts with observations⇒observed patterns⇒development of model⇒testable predictions⇒competition of models⇒theory

Deduction versus Deduction versus InductionInduction

• John Snow in 1854 observed that patients who had contracted cholera had been drinking water from a particular pump in London.

• He suspected that the cholera was spread by contaminated water.

• Led to Louis Pasteur’s formulation of germ theory in 1857.

• Bacteria and viruses were later confirmed by direct observation, establishing their connection to disease.

http://espanol.video.yahoo.com/watch/327162/2140779

Circular Reasoning – Begging the question

Appeal to emotion Argument from authority Sweeping Generalization Irrelevant Conclusion Denying the antecedent

FallaciesFallacies

For a given measureable parameter, there exists a true value of that parameter for a set of circumstances at a given time.

We do not know what it is, nor do we have any independent means of knowing it.

Precision versus Accuracy

Probabilistic versus Deterministic Models