PHYS1704 Astronomy (The Scientific Method) + practice questions PDF

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Summary

Justin Donnelly. A summarization of the Celestial Mechanics section of the Astronomy half of the Astronomy and Environment Module. Discusses philosophies of science and the development of the scientific method....

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The Scientific Method From the Greek, we have… Astrology “telling of the stars” (astron “star” + logia “speaking / reasoning”)

Astronomy “arranging of the stars” (astron “star” + nomos “arranging”)

Astrophysics “natural science of the stars” (astron “star” + physics “natural science”)

Astrology and astronomy were identical until ~15th century. Astrophysics is the application of physical law to astronomical observations in an effort to understand how the Universe works. Usually, astronomy is more associated with the observational aspects, and astrophysics more associated with theoretical aspects. All modern scientists that study the heavens are some mixture of astronomer and astrophysicist.

Useful Latin Terms (A-Z) a priori Latin (“from what comes before” – based on hypothesis or theory rather than experiment). B.Sc. abbr. Latin Baccalaureatus Scientiae (“Bachelor of Science”). cf.

abbr. Latin confer (“bring together” and hence “compare”).

e.g.

abbr. Latin. exempli gratia (“for example”).

etc.

abbr. Latin et cetera ("and the others", "and other things", "and the rest").

ibid., abbr. Latin ibidem means “the same” or “in the same place”. You would use ibid. to refer to the same author and work (e.g., book, html page, or journal article) as the one immediately preceding, rather than stating the entire reference again. i.e.

abbr. Latin. id est (“that is”).

i.a.

abbr. Latin inter alia (“among other things”).

N.B. abbr. Latin nota bene ("note well"). Ph.D.

abbr. Latin Philosophiæ Doctor ("Teacher of Philosophy").

Q.E.D. abbr. Latin quod erat demonstrandum (“that which was to be demonstrated”). The abbreviation is written at the end of a mathematical proof or philosophical argument, to signify that the last statement deduced was the one to be demonstrated, so the proof is complete.

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Student Notes - Astronomy - The Scientific Method (2017 01 26)

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Useful Definitions in the Philosophy of Science 

The Ancient Greeks Deduction

Using a general theory to make a specific prediction that can be tested. Also known as a syllogism.

Induction

Deriving a general theory from specific observations.

Socratic Dialogue A technique in which, rather than giving the student answers, a teacher presents the student with questions, with the result that the student comes to the desired knowledge by answering the questions. Sophistry

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A sophism is an illogical argument which sounds convincing on the surface, used to win a debate. (In Ancient Greece, the Sophists were teachers of rhetoric.)

Modern Philosophy Ockham’s Razor

If two theories explain the same phenomenon equally well, choose the simpler one.

Empiricism

The belief that all knowledge is derived from experience rather than theory – for example, the experience of the senses.

Determinism

The idea that given the initial set up of the Universe, the fate of everything in it is determined by the (predictable) laws of physics. (Also known as a “clockwork Universe”.)

Falsification Theory

A good theory should suggest a way in which the theory can be disproven (or falsified) by a new observation.

The “verification principle”

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Any proposition which is not subject to empirical verification is meaningless. Also known as “logical positivism”.

Scientific Terms Hypothesis

An educated guess, explaining the results of an experiment or observation. A hypothesis can be wildly speculative but must be testable.

Law

A hypothesis that has been repeatedly tested and has not been contradicted.

Theory

A theory is a synthesis of a large body of information that including hypotheses about the natural world which are well-tested by repeatable experiments. No theory can be proven to be true, but data can prove a theory to be false.

Types of Philosophy Epistemology

Questions about knowledge.

Metaphysics

Time, Space, God, Cause and Reality.

Ethics

Good and bad.

Aesthetics

Art and Beauty.

Political Philosophy

Epistemology and metaphysics are most applicable to thinking about science.

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Student Notes - Astronomy - The Scientific Method (2017 01 26)

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1) The Ancient Greeks The Ancient Greeks invented philosophy. They were the first to look for answers that we call “scientific” rather than “religious”. We will look at four of the main Classical Greek philosophers:

 Pythagoras lectured from behind a curtain to keep his message pure. A vegetarian, he believed in reincarnation and declared that eating beans was sinful.  He thought the answer was mathematics. His big breakthrough: mathematical truths had to be proved rather than just accepted.  One of his students discovered irrational numbers (numbers like  and 2 which cannot be expressed as a fraction). Pythagoras’ basis for understanding the Universe was rational numbers. To his shame, he had the student drowned.  This would not have happened with Socratic dialogue (see below).

 Socrates was a small, scruffy man with a pug nose.  He didn’t like verbal persuasion (“Sophistry”).  Encouraged students to question everything. The uncertainty that this irritating “Socratic dialogue” created gave him nickname – “the Gadfly”.  He said “know thyself.”

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Student Notes - Astronomy - The Scientific Method (2017 01 26)

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Plato’s Cave Analogy 1. The Cave Plato described a scenario in which what people take to be real would in fact be an illusion. Imagine a cave inhabited by prisoners who have been chained immobile since childhood: their arms, legs and heads are also fixed and they are compelled to gaze at a wall in front of them. Behind the prisoners is an enormous fire, and between the fire and the prisoners is a raised walkway, along which puppets of various animals, plants and other things are moved. The puppets cast shadows on the wall, and the prisoners watch these shadows. There are also echoes off the wall from the noise produced from the walkway. Plato asserted that the prisoners would take the shadows to be real things and the echoes to be real sounds, not just reflections of reality, since they are all they had ever seen. They would praise as clever whoever could best guess which shadow would come next, and think that person understood the nature of the world. The whole of their society would be based on the shadows on the wall. 2. Escape from the Cave Suppose that a prisoner is freed. If someone were to show him the things that had cast the shadows, he would not recognize them and could not name them; he would believe the shadows on the wall to be more real than what he sees. Suppose further, that the man were compelled to look at the fire: he would be struck blind and try to turn his gaze back toward the shadows. What if someone forcibly dragged such a man upward, out of the cave: wouldn't the man be angry at the one doing this to him? And if dragged all the way out into the sunlight, wouldn't he be distressed? After some time on the surface, however, the freed prisoner would acclimate. He would see more and more things around him, until he could look upon the sun. 3. Return to the cave Consider the condition of this man. Wouldn't he remember his first home, what passed for wisdom there, and his fellow prisoners, and consider himself happy and them pitiable? And wouldn't he disdain whatever honours, praises, and prizes were awarded there to the ones who guessed best which shadows followed which? Moreover, were he to return there, wouldn't he be rather bad at their game, no longer being accustomed to the darkness? Wouldn't the prisoners say of him that he went up and came back with his eyes corrupted, and that it's not even worth trying to go up? And if the man attempts to release them, wouldn’t they resist him? Plato’s Ideal Forms 

Plato was a “two-world” man: 1) the obvious everyday world we can see, 2) another world of perfect “forms”. Forms are like perfect templates. A chair in the real world is an inferior copy of the pure form of “chairness” – the ideal chair. Not everyone agreed with this.

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Student Notes - Astronomy - The Scientific Method (2017 01 26)

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 Aristotle wrote 400 books on nearly everything, from molluscs to immortal souls.  He tutored Alexander the Great.  Western philosophers are grateful to him because he invented inductive and deductive logic.

INDUCTION

DEDUCTION

Deriving a general theory from a number of observations. Informally, we sometimes call this a "bottom up" approach. For example: “All observed frogs can swim. Therefore, All frogs can swim.”

Using a general theory to make a specific prediction that can be tested. Deductive reasoning works from the more general to the more specific. Sometimes this is called a "top-down" approach. For example, a type of deductive logic called a syllogism, consists of two premises followed by a conclusion: “All frogs can swim. [premise 1] This is a frog, [premise 2] Therefore it can swim.” [conclusion]



In deduction, we might begin with thinking up a theory about our topic of interest. We then narrow that down into more specific hypotheses that we can test. This ultimately leads us to be able to test the hypotheses with specific data  a confirmation (or not) of our original theories.



The power of deduction is that it can be used to make predictions. (The frog will be able to swim and you won’t have to throw it in the water to find out!)

INDUCTION Observation  Pattern  Hypothesis  Theory

DEDUCTION Theory  Hypothesis  Observation  Confirmation These two methods of reasoning have a very different "feel" to them when you're conducting research. Inductive reasoning, by its very nature, is more open-ended and exploratory, especially at the beginning. Deductive reasoning is narrower in nature and is concerned with testing or confirming things you already think you know. Most social research involves both inductive and deductive reasoning processes at one time or another.

Platonic Dreamers vs. Aristotelian Realists Some people see philosophy as still divided into two camps: 1. Platonic tendencies – seeking hidden and ultimate mystical truths through the use of reason. 2. Aristotelian tendencies – methodical, cautious, rely on what the five senses tell us. These are a bit like “theoretical science” vs. “experimental science”.

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Student Notes - Astronomy - The Scientific Method (2017 01 26)

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2) Enlightenment Thinkers René Descartes (1596  1650) and Radical Doubt 

Modern philosophy is thought to have begun with Descartes, a French mathematician who refused to accept orthodox philosophical answers.



He sought to establish knowledge on a guaranteed basis, beyond doubt. By applying radical doubt, he found he could destroy his belief in all things!

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“My senses lie to me. They tell me that straight sticks in water appear bent. There is no conclusive way to prove that all my experiences aren’t just dreams or hallucinations.” Even his abstract thoughts might be wrong or illusory. An invisible demon might be hypnotising him into thinking he was awake and doing things when he wasn’t.

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His big breakthrough was to realise that he could be certain that at least his thoughts existed. Cogito Ergo Sum (“I think, therefore I am.”) Doubting is a kind of thinking, so trying to doubt that you’re thinking doesn’t work.

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Descartes thought that God would guarantee that abstract rational thinking (like mathematics) would be clear, but this still means that our sensory experiences could be flawed.

John Locke (1632  1704) and Empiricism 

The founder of Empiricism : the idea that fundamental human knowledge must come from the senses. Tabula Rasa: the human mind is a “blank slate” at birth and can only be filled with knowledge of the world through the senses.

David Hume (1711 76) and Empirical Scepticism 

A Scottish atheist, he was scathing about traditional “proofs” of the existence of God.

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An empiricist, but also sceptical about the powers of human reason.

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Pointed out a major weakness in induction: “If all the swans you have personally observed have been white, then it is scientifically very probable that so are all the swans in the world – until you visit Australia and see a black one. Then what happens?”

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Hume showed that induction is not as certain as logic. All science is temporary. Theories can only be disproved!

Ockham’s Razor 

If two theories explain the same phenomenon equally well, choose the simpler one.

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“Everything should be made as simple as possible, but not simpler.” – Einstein.

The Clockwork (Deterministic) Universe th



In the 17 Century Isaac Newton formulated his laws of motion and gravitation which gave rise to the concept of a mechanistic "clockwork" universe in which everything proceeded deterministically. Everything that happened was no more than the inevitable consequence of all it followed, including human behaviour. God and the soul were redundant.



The clockwork universe was challenged in the 20 century on a number of fronts. Results from quantum physics like the Heisenberg Uncertainty Principle showed that, far from following principles of cause and effect, reality at its fundamental level is inherently random or, more accurately, probabilistic.

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Student Notes - Astronomy - The Scientific Method (2017 01 26)

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3) The 20th Century

The Verification Principle 

Also known as the “Vienna Circle”, the Logical Positivists were social and physical scientists rather than philosophers. They thought that all philosophy was metaphysical nonsense.



They devised the verification principle: any proposition that cannot be tested empirically is nonsense.

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The verification principle collapsed fairly quickly, partly because a lot of modern science is conceptual and untestable in a simple “look and see” way. Nobody has ever seen a quark.

Karl Popper (1902  1994) and Falsification Theory 

Like David Hume before him, Karl Popper suggested scientific theories must always be provisional. True scientists will always suggest ways in which their theories could be falsified by a new, contradictory observation.

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Falsification Theory is a useful gate-keeping test, which distinguishes real science from pseudo-science.

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Max Planck (18581947) exhausted himself for years trying to refute his own revolutionary insight into matter and radiation which started quantum physics because it didn’t agree with the (considered sacrosanct) Second Law of Thermodynamics.

Thomas Kuhn (b. 1922) and Paradigm Shifts 

Thomas Kuhn said that one particular theory (paradigm ) is always taken for granted as the right way to examine the world. In Kuhn’s view, science progresses through sudden revolutionary changes. A paradigm shift is a radical change in thinking from an accepted point of view to a new one. This happens when new scientific discoveries produce too many anomalies in the current paradigm.

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Cosmological paradigms have been: Aristotelian, Ptolemaic, Copernican and Newtonian and are currently Einsteinian.

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Student Notes - Astronomy - The Scientific Method (2017 01 26)

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4) The Scientific Method 

The scientific method is a never-ending cycle of hypothesis, prediction, data gathering, and verification. It is especially important to understand the meaning of the word “theory” as it is used in science compared to its everyday meaning.

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A scientific hypothesis is an educated guess, explaining the results of an experiment or observation. A hypothesis can be wildly speculative but must be testable.

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A scientific law is a hypothesis that has been repeatedly tested and not been contradicted.



A scientific theory is a synthesis of a large body of information that encompasses hypotheses about the natural world which are well-tested by repeatable experiments. No theory can be proven to be true, but data can prove a theory to be false.



In science a model is not usually called a theory until its ideas are shown to fit observed data successfully. In every-day language, however, the word “theory” is often used to refer to ideas that are much more fanciful and less secure.

Criteria for a Good Scientific Model 1. The model fits the data. 2. The model makes predictions that can be tested. If the predictions are wrong, the model is disproved. 3. The model should be as simple as possible. The principle that the best explanation is the one that requires the fewest unverifiable assumptions is called Ockam’s razor.

The Scientific method 1. Make an observation. 2. Ask a question about the observation. 3. Hypothesise an explanation. 4. Make a prediction from the hypothesis (deduction) and conduct an experiment to test the prediction. 5. If the experiment matches the prediction, accept the hypothesis. Otherwise, reject it and come up with a new hypothesis. 6. All steps of this procedure as subject to peer review.

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Student Notes - Astronomy - The Scientific Method (2017 01 26)

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An example of the scientific method that led to the discovery of cosmic rays (radiation from space): 1. Make an observation. th For example, in the late 19 century, devices for measuring electric charge (electroscopes) were seen to lose the charge stored in them over time. 2. Ask a question about the observation. “What’s causing the charge to be lost?” 3. Hypothesise a proposed explanation. Natural radiation is known to create charge – if radiation is creating an opposite charge in the electroscopes, this could be cancelling out the charge already on them. 4. Deduction – make a prediction from the hypothesis. Natural radiation comes from the earth. If we move the electroscopes further from the earth, the charge should disappear more slowly. 5. Conduct an experiment to test the prediction. In 1910 a German Jesuit priest, Fr. Wülf, ascended the 330 m Eiffel tower with an electroscope and found that the discharge of the electroscope increased with height. 6. If the experiment matches the prediction, accept the hypothesis. Otherwise, reject it and come up with a new hypothesis. The hypothesis (that the radiation came from the earth) was rejected and a new hypothesis (that the radiation was coming from space) was created. As the altitude increased, there was less atmosphere above the detector to protect it from the cosmic rays, so the rate of discharge increased. This hypothesis was tested and eventually found to be true. This was how cosmic rays were discovered.

What’s causing the charge to disappear?

1st Hypothesis: natural radiation from the Earth is cancelling the charge. (2nd hypothesis: the discharging radiation is coming not from Earth but f...