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Introduction - PowerPoint PPT Presentation

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Introduction. 0. What is Science?. A belief: that the physical world is governed by a set of unchanging laws that we can discover through careful observation. Is this true? We don’t know. Does it explain all aspects of the universe? I doubt it.

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What is Science?

  • A belief: that the physical world is governed by a set of unchanging laws that we can discover through careful observation.

  • Is this true? We don’t know.

  • Does it explain all aspects of the universe? I doubt it.

  • But: it has been very successful in allowing us to predict and control many aspects of our world.

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Scientific Principles

  • objective: bias and error due to human nature must be eliminated. Need for skeptical criticism.

  • reproducible: any skilled person can duplicate an experiment and get the same results.

  • falsifiable: any scientific theory makes predictions that can be tested. If the predictions are not fulfilled, the theory must be modified or discarded.

  • natural: every event has a set of causes that are governed by the same unchanging laws. No arbitrary or whimsical intervention by outside forces like gods or spirits occurs. (does free will exist?)

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Science as an ongoing activity

  • Science is an ongoing enterprise. New theories are based on previous observations and theories.

  • Science is progressive: new theories improve upon old theories. Students are expected to challenge and dispute with their teachers, not accept the old theories without questioning.

  • It’s a group activity: results are shared by all and subjected to confirmation and extension by anyone who is interested. Part of the fun in science is disproving a long-held theory.

Quote from physicist Albert Michelson in 1894:

“The more important fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote....Future discoveries must be looked for in the sixth place of decimals."

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The Scientific Method

  • How to investigate phenomena in an objective and rational manner.

  • 1. Careful observation and description.

  • 2. Formulating hypotheses (educated guesses) that explain the phenomenon in light of previous knowledge.

  • 3. Making predictions about related events, based on the hypothesis.

  • 4. Testing the predictions through experiments.

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Cycle of Scientific Practice

  • 1. Observe details of some phenomenon, and read what others have observed.

  • 2. Based on previous theory, experience and creativity, develop hypothesis (educated guess) about how it works.

  • 3. Make testable and falsifiable predictions based on hypothesis.

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Cycle of Scientific Practice, part 2

  • 4. Develop experiments and other tests of the predictions. Must be able to disprove the hypothesis.

  • 5. Refine the hypothesis based on experimental results, with new experiments to test.

  • 6. Report the hypothesis and the results.

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In Practice

  • The steps don’t occur in simple order—it all happens together.

  • Objectivity: experiments need to be repeatable by others, and give unambiguous results.

  • Experiments need to isolate a single variable being tested, and they need controls: standard for comparison.

  • Need repetition: avoid sampling error (unrepresentative results that occur by chance).

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When Things Go Wrong

  • Experimenter bias: especially with hard-to-detect phenomena.

  • “Common sense”: not testing a hypothesis because you think it is obviously true or because you relied on someone else’s authority. (Aristotle wrote that men and women have different numbers of teeth and provided lengthy arguments about why this should be. However, it isn’t true)

  • Ignoring data that doesn’t fit the hypothesis

  • Systematic errors: results due to faulty instruments, contamination, etc.

  • Insufficient repetition: need for statistical tests.

  • Fraud

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Law, Theory , Hypothesis

  • Hypothesis: educated guess, capable of being tested; the initial idea about how something works.

  • “Theory” is better: a hypothesis that has been tested many times successfully. But still, a good theory can be modified or discarded if necessary.

  • “Laws” of science are 19th century idea. Scientists today don’t expect to find absolute truth.

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Is Science True?

  • For dealing with the natural world, it works very well. It’s a way of sorting ideas out, retaining the ones that work and discarding the ones that don’t.

  • Has limits: morality, consciousness, the soul, beauty.

  • That’s why we have other fields of knowledge.

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What is Science?

  • Two things:

    • 1. an organized body of knowledge about the physical world (both practical knowledge and theoretical)

    • 2. a method of discovering new knowledge: the scientific method

  • scientific method: skeptical inquiry, attempting to reach an objective view of phenomena

    • based on an overall theory, an ongoing enterprise created by many people present and past.

    • develop hypotheses based on theory and observation. Hypotheses must be falsifiable

    • test hypotheses using controlled experiments: test with and without a single change

    • reproducible results

    • leading to extension of theory.

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What is Life?

  • No one definition: a lot of “I know it when I see it” (Justice Potter Stewart), which is not a very objective definition.

  • NASA: life is a self-sustaining set of chemical reactions capable of reproducing similar copies of itself.

    • This leads to natural selection: offspring that are better at surviving and reproducing end up taking over in future generations.

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Life is an Ongoing Process

  • Individuals are born and then die, but an individual’s life comes from previous life. “Life” is an unbroken chain of living cells extending back 3 billion years ago to our original common ancestor.

  • On Earth, all life we know about has the same DNA, proteins, cells, metabolic processes, etc.

  • Other planets: Mars and Venus (upper atmosphere) could have Earth life derived from meteorite impacts on Earth (or vice versa).

    • possibly independent origins on Europa, Titan, Mars, elsewhere?

  • But are there other forms of life on Earth we don’t know about?

    • haven’t made themselves obvious—no living rocks, for example

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What is Life?

Life is applied chemistry. All living systems are based on the interactions of chemical compounds, the sharing of electrons between atoms.

1. Metabolism: capture energy and use it to maintain, grow, reproduce.

2. Homeostasis: maintain a constant internal state despite external changes.

membrane separates inside from outside, only allows specific molecules to pass through.

3. Detect and respond to environmental changes.

4. Reproduction: produce offspring similar to itself.

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Flow of Energy and Matter

  • Energy is a one-way flow: from the Sun, which produces high-quality energy as visible light, into plants, then through various other organisms, finally ending up as waste heat, unable to do any work.

  • Matter is recycled constantly: between organisms and the non-living environment.

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All life on Earth is similar

  • made of same molecules in similar structures: DNA used for instructions and heredity, proteins do the necessary work, cells are surrounded by lipid membranes

  • The most common elements in living things: Carbon, Hydrogen, Oxygen, Nitrogen (CHON) are uncommon in the Earth’s crust.

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Evolution by Natural Selection

  • Offspring resemble their parents because the offspring are built from their parents’ genes.

  • Random changes in the DNA (mutations) occur at a slow but steady rate. This produces a lot of variation within a species.

  • Some members of a species are more “fit”: better able to survive and reproduce than other members of the species.

  • The genes from the more fit individuals will slowly take over the species.

  • Thus, the genes within a species slowly change (or occasionally, change rapidly).

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  • Those that carry the successful mutations eventually take over the species.

  • Can produce major changes over time: dog breeds, for example, in only 10,000 years or less. Or antibiotic-resistant bacteria.

  • If 2 groups within a species never mate, they develop differences that make mating impossible: new species

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Diversity of Life

  • Lots of different ways to make a living

  • Several million different species

  • Species: a group of similar organisms that can reproduce with each other but not with others.

  • One species splits into two different species very easily:

    • Isolate two groups so they can’t mate with each other

    • Different random mutations quickly cause differences in sexual attractiveness and fertility

    • When brought back together, the two groups no longer want to mate with each other, or they can’t produce fertile offspring.

    • They are now two different species.

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Basic Division of Life

  • Prokaryotes: simple cells with no internal compartments: especially, no separate nucleus that contains the DNA.

  • Eukaryotes: more complex cells with internal compartments and membranes, with the DNA contained in the nucleus, a special membrane-bound compartment.

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Major Sub-divisions

  • Prokaryotes: Eubacteria (common bacteria found everywhere) and Archaebacteria (special forms found in extreme conditions such as hot, high salt, acidic.

  • Eukaryotes: Protists (single celled), Fungi (digest their food externally), Plants (produce food from sunlight), Animals (move under their own power for part of their lives).