Physics 270 Experimental Physics

The Scientific Method

Science as a Collection of FactsFact 1Fact 2Fact 3

One possible definition: activities aimed at understanding the natural worldScientists 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 ExperimentsEmpirical formulasModelsLaws / TheoryLets do some experiments!

Develop multiple approaches since you arent sure which one will work.

GoalStart

Painting by Rene Magritte

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

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 structureReductionism versus Wholism

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 explanationstarts 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 patternsstarts with observationsobserved patternsdevelopment of modeltestable predictionscompetition of modelstheoryDeduction versus Induction

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 Pasteurs 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 questionAppeal to emotionArgument from authoritySweeping GeneralizationIrrelevant ConclusionDenying the antecedent

Fallacies

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