What Are Scientific Theories? Chapter 3. THEORY A collection of statements that when taken together attempt to explain a broad class of related phenomena.

What Are Scientific Theories?What Are Scientific Theories?

Chapter 3Chapter 3

THEORYTHEORYA collection of statements that A collection of statements that when taken together attempt to when taken together attempt to explain a broad class of related explain a broad class of related phenomenaphenomena

Theory vs. HypothesisTheory vs. Hypothesis

-Hypotheses are untested -Hypotheses are untested explanations.explanations.

-Theories are the result of many -Theories are the result of many hypotheses being tested.hypotheses being tested.

Theory vs. HypothesisTheory vs. Hypothesis

-Hypotheses tend to be single -Hypotheses tend to be single statements. statements.

-Theories are more complex, multiple -Theories are more complex, multiple statements.statements.

Theory vs. HypothesisTheory vs. Hypothesis

-Hypotheses explain one observation. -Hypotheses explain one observation.

-Theories explain nature and -Theories explain nature and movements of all materials.movements of all materials.

Theory vs. HypothesisTheory vs. Hypothesis

-Hypotheses are based on -Hypotheses are based on observations.observations.

-Theories attempt to explain the -Theories attempt to explain the unobservable.unobservable.

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

Force?Force?

Does the Vital Force Exist?Does the Vital Force Exist?

Needham put gravy in a bottleNeedham put gravy in a bottleHeated the gravy in a fireHeated the gravy in a fireAssumed that heating would kill anything Assumed that heating would kill anything

in the gravyin the gravyCorked the bottle to keep anything outCorked the bottle to keep anything outLiving things arose, therefore spontaneous Living things arose, therefore spontaneous

generation must have occurredgeneration must have occurred

Does the Vital Force Exist?Does the Vital Force Exist?

Spontaneous Generation TheorySpontaneous Generation TheoryLiving things are generated spontaneously Living things are generated spontaneously

from nonliving materials when an unseen life-from nonliving materials when an unseen life-giving, vital force enters the nonliving materialgiving, vital force enters the nonliving material

Different kinds of nonliving materials give rise Different kinds of nonliving materials give rise to different kinds of living thingsto different kinds of living things

Spontaneous generation has occurred in the Spontaneous generation has occurred in the past and still occurs todaypast and still occurs today

Was There a Flaw in Needham’s Was There a Flaw in Needham’s Experiment?Experiment?

Spallanzani looked for a flawSpallanzani looked for a flawThought heating and corking were not Thought heating and corking were not

done properlydone properlySpallanzani did his own experimentSpallanzani did his own experiment

Corked some bottles with no heat (control Corked some bottles with no heat (control group)group)

Heated some bottles for a few minutesHeated some bottles for a few minutesHeated some bottles for an hourHeated some bottles for an hour

Nothing grew in the last set of bottlesNothing grew in the last set of bottles

Was There a Flaw in Needham’s Was There a Flaw in Needham’s Experiment?Experiment?

Biogenesis TheoryBiogenesis TheoryNew life arises only from prior lifeNew life arises only from prior lifeThe kind of new life that arises depends on The kind of new life that arises depends on

the kind of life that preceded it—that is, there the kind of life that preceded it—that is, there is a continuity of life forms from one is a continuity of life forms from one generation to the next.generation to the next.

Does “Fierce” Heat Weaken the Does “Fierce” Heat Weaken the Vital Force?Vital Force?

Bottles exposed to fierce heat could still Bottles exposed to fierce heat could still generate lifegenerate life

Does the Vital Force Need “Elastic” Does the Vital Force Need “Elastic” Air?Air?

Needham kept adding to his original Needham kept adding to his original conclusion to keep it consistent with conclusion to keep it consistent with observed resultsobserved results

BIAS!!!!!!BIAS!!!!!!

How Are Theories Tested?How Are Theories Tested?

Planning tests with specific predictionsPlanning tests with specific predictions

Comparing those predictions with specific Comparing those predictions with specific resultsresults

How Are Theories Tested?How Are Theories Tested?

More difficult than testing hypothesesMore difficult than testing hypothesesTheories often explain the unobservableTheories often explain the unobservableSupporters of the theory might change their Supporters of the theory might change their

theory to make tests unconvincingtheory to make tests unconvincingCause cannot always be manipulated as a Cause cannot always be manipulated as a

variable so additional argument (variable so additional argument (theoretical theoretical rationalerationale) must be used) must be used

How Do People Make Scientific How Do People Make Scientific Discoveries?Discoveries?

Scientific inquiry is NOT only explained Scientific inquiry is NOT only explained through observationthrough observationCreate concepts and conceptual systemsCreate concepts and conceptual systems

Concept cannot be understood aloneConcept cannot be understood aloneMust be within context of other conceptsMust be within context of other concepts

Many people believe in concepts no longer Many people believe in concepts no longer accepted by the scientific communityaccepted by the scientific communityHave to fight intuitive explanationsHave to fight intuitive explanations

What Happens to Tested Theories?What Happens to Tested Theories?

Rejected theories help us understand the Rejected theories help us understand the nature of scientific inquirynature of scientific inquiry

Well-accepted theories allow us to explain Well-accepted theories allow us to explain puzzling observations without referring to puzzling observations without referring to supernatural reasonssupernatural reasons

Theories give structure to established Theories give structure to established knowledgeknowledge

Lead to new well-accepted theoriesLead to new well-accepted theories