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Natural Science


Natural Science The Logic of Scientific Arguments * A T. rex tooth can tell us a lot about what this animal ate. * Conclusion: Scientific ideas can be tested through ... – PowerPoint PPT presentation

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Title: Natural Science

Natural Science
  • The Logic of Scientific Arguments

  • Taken together, the expectations generated by a
    scientific idea and the actual observations
    relevant to those expectations form a scientific
    argument. This is like an argument in a court
    case a logical description of what we think and
    why we think it.

  • expectation In science, a potential outcome of a
    scientific test that is arrived at by logically
    reasoning about a particular scientific idea
    (i.e., what we would logically expect to observe
    if a given hypothesis or theory were true or
    false). The expectations generated by an idea are
    sometimes called its predictions. Observations
    that match the expectations generated by an idea
    are generally interpreted as supporting evidence.
    Mismatches are generally interpreted as
    contradictory evidence.

  • observe To note, record, or attend to a result,
    occurrence, or phenomenon. Though we typically
    think of observations as having been made "with
    our own eyes," in science, observations may be
    made directly (by seeing, feeling, hearing,
    tasting, or smelling) or indirectly using tools.

  • scientific argument A logical description of a
    scientific idea and the evidence for or against
    it. In everyday language, an argument usually
    means a verbal disagreement, but here we use
    another meaning of the term a reasoned case for
    or against a particular viewpoint. Scientific
    arguments generally have a few basic components
    What is the idea? If this idea were true, what
    would we expect to observe in a given situation?
    Is this expectation borne out? How does that
    reflect on the likelihood that the idea is
    accurate or inaccurate?

  • A scientific argument uses evidence to make a
    case for whether a scientific idea is accurate or
    inaccurate. For example, the idea that illness in
    new mothers can be caused by doctors' dirty hands
    creates the expectation that illness rates should
    go down when doctors are required to wash their
    hands before attending births.

  • evidence Test results and/or observations that
    may either help support or help refute a
    scientific idea. In general, raw data are
    considered evidence only once they have been
    interpreted in a way that reflects on the
    accuracy of a scientific idea.

  • When this test was actually performed in the
    1800s, the results matched the expectations,
    forming a strong scientific argument in support
    of the idea.

  • test In science, an observation or experiment
    that could provide evidence regarding the
    accuracy of a scientific idea. Testing involves
    figuring out what one would expect to observe if
    an idea were correct and comparing that
    expectation to what one actually observes.

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  • Though the elements of a scientific argument
    (scientific idea, expectations generated by the
    idea, and relevant observations) are always
    related in the same logical way, in terms of the
    process of science, those elements may be
    assembled in different orders.

  • Sometimes the idea comes first and then
    scientists go looking for the observations that
    bear on it.
  • Sometimes the observations are made first, and
    they suggest a particular idea.
  • Sometimes the idea and the observations are
    already out there, and someone comes along later
    and figures out that the two might be related to
    one another.

  • Testing ideas with evidence may seem like common
    sense but there are some subtleties to the

  • Ideas can be tested in many ways.
  • Some tests are relatively straightforward, but
    some require a lot of time, effort, and/or the
    development of specialized tools.

  • Evidence can reflect on ideas in many different

  • There are multiple lines of evidence and many
    criteria to consider in evaluating an idea.

  • All testing involves making some assumptions.

  • Despite these details, it's important to remember
    that hypotheses and theories continue or end
    depending on whether they are useful in
    explaining data, generating expectations,
    providing satisfying explanations, inspiring
    research questions, answering questions, and
    solving problems.
  • Science filters through many ideas and builds on
    those that work.

  • Summary
  • Scientific arguments are logical descriptions of
    a scientific idea and the evidence for or against

  • Sometimes a scientific idea comes before any
    evidence relevant to it, and other times the
    evidence helps inspire the idea.

  • Tactics for testing ideas

  • Experiments are one way to test some sorts of
    ideas, but science doesn't use experiment alone.
    There are many other ways to scientifically test

  • What are experiments? An experiment is a test
    that involves manipulating some factor in a
    system in order to see how that affects the
    outcome. Ideally, experiments also involve
    controlling as many other factors as possible in
    order to isolate the cause of the experimental

  • Experiments can be quite simple tests set up in a
  • But large-scale experiments can also be performed
    out in the real world for example, experiments
    in ecology involved adding fertilizers and straw
    to oil spills to see how they affected the amount
    of oil over time.

  • Whether experiments are large- or small-scale,
    performed in the lab or in the field, and require
    years or mere milliseconds to complete,
    experiments are distinguished from other sorts of
    tests by their reliance on the intentional
    manipulation of some factors and, ideally, the
    control of others.

  • Natural experiments

  • Some aspects of the natural world cant be easily
    changed be people, so they can't be studied with
    direct experiments.
  • We simply can't go back in time and introduce
    finches to three separate island groups to see
    how they evolve. We can't move the planets around
    to see how their orbits would be altered by a new
    configuration. And we can't cause volcanoes to
    erupt in order to investigate how they affect the
    ecosystems that surround them.

  • However, such ancient, distant, and large-scale
    phenomena can be studied with the methods
    described below, and in many cases, we can
    observe the results of natural experiments on
    these systems.

  • Natural experiments occur when the universe, in a
    sense, performs an experiment for us that is,
    the relevant experimental set-up already exists,
    and all we have to do is observe the results.

  • We can't experimentally change things like
    volcanoes, but we can carefully observe the
    outcomes of these natural experiments.

  • For many ideas in science, testing via experiment
    is impossible, inappropriate, or only part of the
    picture. In those cases, testing is often a
    matter of making the right observations.

  • For example, we can't actually experiment on
    distant stars in order to test ideas about which
    nuclear reactions occur within them, but we can
    test those ideas by building sensors that allow
    us to observe what forms of radiation the stars

  • We can't perform experiments to test ideas about
    what Tyranosaurus rex ate, but we can test those
    ideas by making detailed observations of their
    fossilized teeth and comparing those to the teeth
    of modern organisms that eat different foods.

  • A T. rex tooth can tell us a lot about what this
    animal ate.

  • Conclusion
  • Scientific ideas can be tested through both
    experiments and other sorts of studies. Both
    provide important sources of evidence.

  • Experimenting with the stars
  • How can scientists run experiments on stars?

  • Scientists can and do observe the results of
    natural experiments on these massive balls of
    gas. In a natural experiment, the universe, in a
    sense, performs an experiment for us.

  • Albert Einstein's theory of general relativity,
    proposed in 1915, describes relationships between
    space, time, mass, and gravity.

  • Arthur Eddington, and Albert Einstein, right.
    Eddington was one of the astronomers who thought
    of a test of Einstein's theory of relativity.

  • One of the expectations it generates is that the
    gravitational field caused by mass should seem to
    bend light. In other words, if the theory of
    general relativity were true, as light passes
    close to very massive objects, its path should
    appear to shift.

  • General relativity leads us to expect that mass
    curves space-time and that should affect the path
    of light.

  • This might seem like an expectation that would be
    easy to test with a straightforward experiment
    get some large objects and compare the path of
    light when the objects are placed close to the
    path versus when they are placed far from the

  • But, in order for us to observe the deflection of
    light, the objects in question must be about as
    heavy as our own sun more than 300,000 times
    the mass of the Earth and so cannot easily be
    moved around for our experiment.

  • We can do a natural experiment. Starlight travels
    to Earth over long distances. As our planet moves
    around the sun, the light of those stars reaches
    us by paths that sometimes pass near our massive

  • We should be able to compare the path of
    starlight passing close to the sun to the path of
    starlight that reaches us without passing close
    to the sun, allowing us to figure out if
    observations support or refute Einstein's theory.

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  • But this natural experiment also contains a
    problem. The sun is so bright that it's difficult
    to see starlight passing near it. We want to be
    able to observe the starlight (when it's passing
    close to the sun) during the day, which is the
    time that the starlight can't be seen.

  • We cant turn off the light of the sun during the
    middle of the day. However, astronomer Arthur
    Eddington knew that during a solar eclipse, the
    moon comes between the Earth and the sun,
    blocking out the light of the sun for a few

  • This would let us observe the results of our
    natural experiment the path of starlight
    passing close to the sun.
  • On March 19, 1919, astronomers were ready.

  • During an eclipse, scientists took photos of
    groups of stars positioned near the sun and
    compared them to similar photos taken at night
    when the light of those stars would not pass
    close to the sun.

  • The photos revealed that the sun's gravity did
    indeed change the path of nearby starlight and
    provided strong evidence in support of general

  • A negative of a photographic plate of the eclipse
    with dashed lines showing star positions.

  • This natural experiment helped by a solar eclipse
    was good evidence for the validity of Einstein's
    theory of general relativity.