3.4-The Nature of Science

The ultimate success of the Copernican revolution…

led scientists, philosophers, and theologians to reassess the various modes of thinking that played a role in the 2000-year process of discovering Earth’s place in the universe

Science

the word comes from the Latin scientia, meaning “knowledge,” but not all knowledge is science

Why is science difficult to define?

not all science works in the same way

ex: of why it is hard to define science

• Science is supposed to proceed according to some thing called the scientific method

• Consider that your flashlight suddenly stopped working, you might suspect that the flashlight batteries had died

• Type of tentative explanation, or hypothesis, is sometimes called an educated guess-in this case, it is “educated” because you already know that flashlights need batteries

• Your hypothesis allows you to make a simple prediction, if you replace or recharge the batteries, the flashlight should work. You can test this prediction by doing that. If the flashlight now works, you've confirmed your hypothesis.

• If it doesn't, you must revise or discard your hypothesis, perhaps in favour of some other one that you can also test

The scientific method can be…

a useful idealization, but real science rarely progresses in such an orderly way

How does scientific progress begin?

with someone going out and looking at nature in a general way, rather than conducting a careful set of experiments

• ex: Galileo wasn’t looking for anything in particular when he pointed his telescope at the sky and made his first startling discoveries

Scientists are human beings…

and their intuition and personal beliefs inevitably influence their work

• ex: Copernicus adopted the idea that Earth orbits the Sun not because he had a carefully tested it but because he believed it made more sense than the prevailing view of an Earth-centered universe

  • he erred in the specific because he still held Plato’s ancient belief that heavenly motion must be in perfect circles

One way to define scientific thinking is to…

list the criteria that scientists use when they judge competing models of nature

Hallmarks of science

1. Modern science seeks explanations for observed phenomena that rely solely on natural causes

2. Science progresses through the creation and testing of models of nature that explain the observations as simply as possible

3. A scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions did not agree with observations

Hallmarks of Science in the Copernican revolution

1. shows up in the way Tycho’s careful measurements of planetary motion motivated Kepler to come up with a better explanation for those motions

2. evident in the way several competing models were compared and tested, most notably those of Ptolemy, Copernicus, and Kepler

3. that each model could make precise predictions about the future motions of the Sun, Moon, Planets, and stars in our sky. Kepler’s model gained acceptance because it worked, while the competing models lost favor because their predictions failed to match the observations

The Criterion of simplicity in the second hallmark….

deserves additional explanation

• Copernicus’s original model did not match the data noticeably better than Ptolemy’s model. If scientists had judged this model solely on the accuracy of its predictions, they might have rejected it immediately

• however, many scientists found elements of the Copernican model appealing, such as its simple explanation for apparent retrograde motion. They therefore kept the model alive until Kepler found a way to make it work

If agreement with data were the sole criterion for judgement…

we could imagine a modern-day Ptolemy adding millions or billions of additional circles to the geocentric model in an effort to improve its agreement with observations

• we would still choose the Copernican view over the geocentric view because its predictions would be just as accurate but follow a much simpler model of nature

Occam’s Razor

• the idea that scientists should prefer the simpler of 2 models that agree equally well with observations, after the medieval scholar William of Occam

What does the 3rd hallmark of science force us to face?

the question of what counts as an “observation” against which a prediction can be tested

• ex: only a handful of scientists have personally made detailed tests of Einstein’s theory of relativity, and it’s their personal reports of the results that have convinced other scientists of the theory’s validity. However, there’s an importance difference between personal testimony about a scientific test and a UFO: the first can be verified by anyone, at least in principle, while the second can’t

Moreover, scientific studies of eyewitness testimony…

show it to be notoriously unreliable, because different eyewitnesses often disagree on what they saw even immediately after an event has occurred

• as time passes, memories of the event may change further. in some cases in which memory has been checked against reality, people have reported vivid memories of events that never happened at all

• virtually all of us have experienced this effect: disagreements with a friend about who did what and when. Since both people can’t be right in such cases, at least one person must have a memory that differs from reality

• we can’t accept eyewitness testimony by itself as sufficient evidence in science, no matter who reports it or how many people offer similar testimony

It’s important to realize that science…

is not the only valid way of seeking knowledge

• ex: shopping for a car, learning to play drums, or pondering the meaning of life

• in each case you might make observations, exercise logic, and test hypotheses. Yet these pursuits clearly are not science, because they are not directed at developing testable explanations for observed natural phenomena. as long as nonscientific searches for knowledge make no claims about how the natural world works, they don’t conflict with science

Jean Foucault

• provided the first direct proof of rotation in 1851

• built a large pendulum that he carefully started swinging

• any pendulum tends to swing always in the same plane, but Earth’s rotation made Foucault’s pendulum appear to twist slowly in a circle

Coriolis effect

• 2nd direct proof that Earth rotates, first described by French physicist Gaspard-Gustave Coriolis

• would not occur if Earth were not rotating, is responsible for things such as the swirling of hurricanes and the fact that missiles that travel great distances on Earth deviate from straight-line paths

James Bradley

• first direct proof that Earth orbits the sun

• imagine starlight is like rain, falling straight down

• if your are standing still, you should hold your umbrella straight over your head, but if you are walking through the rain, you should tilt your umbrella forward, because your motion makes the rain appear to be coming down at an angle

• discovered that observing light from stars requires that telescopes be tilted slightly in the direction of Earth’s motion-just like the umbrella

  • aberration of starlight

stellar parallax

also provides direct proof that earth orbits the sun, and it was first measured in 1838 by German astronomer Friedrich Bessel

Pseudoscience

• claims about the natural world that seem to be based on observational evidence but do not treat evidence in a truly scientific way

• false science

How to distinguish real science from pseudoscience?

check whether a particular claim exhibits all 3 hallmarks of science

We generally think of science as being…

objective, meaning that all people should in principle be bale to find the same scientific results. There is a difference between the overall objectivity of science and the objectivity of individual scientists

• science is practiced by humans, and individual scientists may bring their personal biases and beliefs to their scientific work

Bias can occasionally…

show up even in the thinking of the scientific community as a whole

• some valid ideas may not be considered by any scientist because they fall too far outside the general patterns of thought of the time

• Einstein’s theory of relativity provides an example. Many scientists in the decades before Einstein had gleaned hints of the theory but didn’t investigate them, at least in part because they seemed too outlandish

How do we attempt to acquire knowledge in science?

through logical reasoning. a logical argument begins with a set of premises and leads to one or more conclusions

2 basic types of logical arguments

deductive and inductive

Deductive argument

the conclusion follows automatically from the premises

• Ex: Premise: all planets orbit the sun in ellipses with the sun at one focus. Premise: Earth is a planet. Conclusion: Earth orbits the sun in an ellipse with the sun at one focus

• we use a deductive argument to deduce a specific prediction from a more general theory. if the specific prediction proves to be false, then something must be wrong with the premises from which it was deduced. if it proves true, then we’ve acquired a piece of evidence in support of the premises

Inductive argument

• Premise: Birds fly up but eventually come back down. Premise: people who jump up fall back down. Premise: Rocks thrown up come back down. Premise: Balls thrown up come back down. Conclusion: What goes up must come down

• begins with specific facts that are used to generalize to a broader conclusion

• each premise supports the conclusion, which may explain why the conclusion was thought to be true for thousands of years

• However, no amount of additional examples could ever prove the conclusion to be true, and we need only a single counterexample-such as a rocket leaving earth-to prove the conclusion to be false

Both arguments…

are important in science

• inductive arguments to build scientific theories, because we infer general principles from observations and experiments

• deductive arguments to make specific predictions from hypotheses and theories, which we can test

  • explains why theories can never be proved true beyond all doubt-they can only be shown to be consistent with ever-larger bodies of evidence

  • theories can be proved false, however, if they fail to account for observed or experimental facts

What is the beauty of science?

it encourages continued testing by many people

• even if personal biases affect some results, tests by others should eventually uncover the mistakes

• if a new idea is correct but falls outside the scientific communities general patterns of thought, sufficient testing and verification will eventually force scientists to reconsider those patterns

• science ultimately provides a means of bringing people to agreement, at least on topics that can be subjected to scientific study

Theory

when a powerful yet simple model makes predictions that survive repeated and varied testing, scientists elevate its status and call it a theory (speculation or a hypothesis)

• Ex: Issac Newton’s theory of gravity-uses simple physical principles to explain many observations and experiments

A scientific theory can never…

be proved true beyond all doubt, because future observations may disagree with its predictions. however, anything that qualifies as a scientific theory must be supported by a large, compelling body of evidence

A scientific theory is not like…

a hypothesis or any type of guess

• we are free to change a hypothesis at any time, because it had not yet been carefully tested

• the results of the many tests that a scientific theory has already passed can’t simply disappear, so if a theory ever fails a new test, a replacement theory must still explain the past results