What Are Scientific Theories? Chapter 3

THEORY A collection of statements that when taken together attempt to explain a broad class of related phenomena

Theory vs. Hypothesis -Hypotheses are untested explanations. -Theories are the result of many hypotheses being tested.

Theory vs. Hypothesis -Hypotheses tend to be single statements. -Theories are more complex, multiple statements.

Theory vs. Hypothesis -Hypotheses explain one observation. -Theories explain nature and movements of all materials.

Theory vs. Hypothesis -Hypotheses are based on observations. -Theories attempt to explain the unobservable.

Do Living and Nonliving Things Differ Because of an Unseen Vital Force?

Does the Vital Force Exist? Needham put gravy in a bottle Needham put gravy in a bottle Heated the gravy in a fire Heated the gravy in a fire Assumed that heating would kill anything in the gravy Assumed that heating would kill anything in the gravy Corked the bottle to keep anything out Corked the bottle to keep anything out Living things arose, therefore spontaneous generation must have occurred Living things arose, therefore spontaneous generation must have occurred

Does the Vital Force Exist? Spontaneous Generation Theory Spontaneous Generation Theory Living things are generated spontaneously from nonliving materials when an unseen life- giving, vital force enters the nonliving material Living things are generated spontaneously from nonliving materials when an unseen life- giving, vital force enters the nonliving material Different kinds of nonliving materials give rise to different kinds of living things Different kinds of nonliving materials give rise to different kinds of living things Spontaneous generation has occurred in the past and still occurs today Spontaneous generation has occurred in the past and still occurs today

Was There a Flaw in Needham’s Experiment? Spallanzani looked for a flaw Spallanzani looked for a flaw Thought heating and corking were not done properly Thought heating and corking were not done properly Spallanzani did his own experiment Spallanzani did his own experiment Corked some bottles with no heat (control group) Corked some bottles with no heat (control group) Heated some bottles for a few minutes Heated some bottles for a few minutes Heated some bottles for an hour Heated some bottles for an hour Nothing grew in the last set of bottles Nothing grew in the last set of bottles

Was There a Flaw in Needham’s Experiment? Biogenesis Theory Biogenesis Theory New life arises only from prior life New life arises only from prior life The kind of new life that arises depends on the kind of life that preceded it—that is, there is a continuity of life forms from one generation to the next. The kind of new life that arises depends on the kind of life that preceded it—that is, there is a continuity of life forms from one generation to the next.

Does “Fierce” Heat Weaken the Vital Force? Bottles exposed to fierce heat could still generate life Bottles exposed to fierce heat could still generate life

Does the Vital Force Need “Elastic” Air? Needham kept adding to his original conclusion to keep it consistent with observed results Needham kept adding to his original conclusion to keep it consistent with observed results BIAS!!!!!! BIAS!!!!!!

How Are Theories Tested? Planning tests with specific predictions Comparing those predictions with specific results

How Are Theories Tested? More difficult than testing hypotheses More difficult than testing hypotheses Theories often explain the unobservable Theories often explain the unobservable Supporters of the theory might change their theory to make tests unconvincing Supporters of the theory might change their theory to make tests unconvincing Cause cannot always be manipulated as a variable so additional argument (theoretical rationale) must be used Cause cannot always be manipulated as a variable so additional argument (theoretical rationale) must be used

How Do People Make Scientific Discoveries? Scientific inquiry is NOT only explained through observation Scientific inquiry is NOT only explained through observation Create concepts and conceptual systems Create concepts and conceptual systems Concept cannot be understood alone Concept cannot be understood alone Must be within context of other concepts Must be within context of other concepts Many people believe in concepts no longer accepted by the scientific community Many people believe in concepts no longer accepted by the scientific community Have to fight intuitive explanations Have to fight intuitive explanations

What Happens to Tested Theories? Rejected theories help us understand the nature of scientific inquiry Rejected theories help us understand the nature of scientific inquiry Well-accepted theories allow us to explain puzzling observations without referring to supernatural reasons Well-accepted theories allow us to explain puzzling observations without referring to supernatural reasons Theories give structure to established knowledge Theories give structure to established knowledge Lead to new well-accepted theories Lead to new well-accepted theories