ASTR 121 (O'Connell) Study Guide

1. INTRODUCTION: SCIENTIFIC DISCOVERY AND THE SCALE OF THE UNIVERSE

The European Southern Observatory Very Large Telescope, Chile.

A. WHAT IS SCIENCE?

Definition: systematic understanding of empirical natural phenomena.

"Empirical" = experienced or observed
Science is both a body of knowledge and a way of thinking.
Scientific values & methods are relatively new in human history; started ca. 1500.

• Logical; rational

• Clear, orderly; choose simplest alternative

• Cumulative development
  New interpretations are required to be consistent with all established facts.
  This is a challenging requirement!

• Science is based on an empirical criterion of truth: ideas are tested by objective experiment/observation in the real world.
  • Evaluation of evidence must be rigorous, objective, and public.

  • Any valid scientific proposition is falsifiable by empirical tests. I.e. it is well enough defined that you can specify in advance those outcomes that would show the idea to be wrong.

  • The results of tests must be repeatable.

  • Confidence in ideas grows with the number of independent tests or validations. "Independence" implies verification not only by different people but also by different lines of evidence or methods of inquiry.

The "Scientific Method" was not invented or prescribed wholesale by some individual or group. Rather, it emerged over a period of several centuries as the set of analytical techniques that proved most successful in the struggle to understand nature.
The usual formalized statement of "The Scientific Method" (e.g. Hypothesis ===> Prediction ===> Experiment ===> Interpretation ===> Repeat) is misleading.
Scientists frequently simply explore the characteristics of new phenomena, without any particular intent to distinguish between interpretations but with the hope that they might prove interesting or important.
A number of sciences, including astronomy, deal with phenomena that cannot be manipulated by humans. Experiments are impossible in these cases. These sciences must rely instead on passive observations. (For astronomy, the only exception is that we can, with difficulty, sample and experiment with the surfaces and atmospheres of some of the other bodies in the solar system.)

B. ALTERNATIVE MODES OF THOUGHT

• Idealism (e.g. Greek philosophy, Plato)
  Deductions about the physical world are made from abstract, a priori postulates; it is assumed that empirical evidence is corrupted.
  Fine for mathematics, badly flawed for real world.

• Revelation (religion)
  Explanations are sought by appeal to a spiritual realm beyond the natural world ("super"-natural).
  Prior to the development of science, physical phenomena were usually interpreted as the product of deliberate and purposeful manipulation by supernatural agencies, with motives largely beyond human understanding. Knowledge of these agencies was possible only through intentional revelation by them.
  By contrast, science deals only with the natural world. It seeks explanations of natural phenomena in terms of other natural phenomena.
  Supernatural explanations are not acceptable to scientists because there is no way to test them.
  Objective empirical tests are impossible for the supernatural world. Science cannot predict supernatural behavior or intervention in the natural world since the laws of nature don't apply.
  However, science could in principle detect supernatural intervention in the natural world a posteriori (after the fact). Frequent intervention would produce an arbitrary and largely unintelligible world. The fact that discontinuities in natural law have never been verified shows that direct intervention is rare at current levels of detection.

  Revelation produces a hierarchy of privilege. Access to the truth, and the corresponding power, is normally accorded only to a few (priests, prophets, gurus). Non-democratic.

• Authority
  Ideas are tested by appeal to the pronouncements of an individual or small group. These cannot be questioned or superseded.
  The most familiar, and dangerous, variety of authoritative "truth" is found in dictatorships. But authority is also the basis of the case law system ("precedent") in American jurisprudence.

  Despite the public impression, science is not based on authority. Instead, it operates by consensus. Any scientist is entitled to question and retest any idea at any time and attempt to convince others to change their minds. Science is democratic.
  Scientific "authorities" are respected not because of who they are but instead because of what they say. Their ideas are continuously subjected to new tests. The best idea prevails.
  Young scientists often aspire to overthrow "authorities" like Einstein; they almost always fail because their ideas are not as good.

• Pseudo-science
  Examples: astrology, extra-sensory perception (ESP), psychic forecasts, telekinesis, UFO abductions, cold fusion
  Pseudo-scientific investigations sometimes seem scientific, but they fail to meet the basic criteria listed above.
  The evidence is always inadequate
  It is not simply that there is no good scientific explanation for pseudo-scientific phenomena. In most cases, the phenomena themselves have not been demonstrated to exist.
  For instance, we know that penicillin kills certain types of dangerous bacteria. But no one has ever convincingly been shown to be able to read someone else's mind.

  At any time, there are thousands of well-documented phenomena that science does not properly understand. These are what active scientists devote their careers to studying. If credible evidence emerges for any of the marginal "pseudo" areas, they will then receive mainstream scientific attention.

  Hallmarks: uncritical acceptance of poorly documented phenomena; lack of experiments or inadequate experimental controls; inexperienced observers; non-repeatability; often self-deception; sometimes deliberate fraud. Almost always: lack of consistency with established principles or facts (e.g. foreseeing the future contradicts the theory of special relativity).
  Most pseudo-science is harmless, except for the sloppy thinking and miseducation it encourages. But some pseudo-science poses tangible threats to you & society. For example:
  Fraudulent or ineffective "alternative" health-care (such as homeopathy, in which the active therapeutic ingredients are diluted to the point where not a single molecule remains).
  False criminal prosecutions (murder, child abuse, etc.) based on erroneous psychotherapy (e.g. "suppressed" memories "recovered" by hypnosis).

C. SKEPTICISM

Scientists insist on the best possible evidence in support of new ideas. The adjective that best describes the scientific approach to evidence is "relentless". Accepted ideas, no matter how well established, are constantly tested against new evidence, sifted for quality. All preconceptions are subject to scrutiny. History shows that truth only emerges through this kind of skeptical "scrubbing" of ideas and evidence. The ideas that survive this process are very robust.
Competition over ideas, often intense, is a hallmark of science in practice. There are strong incentives for scientists to discover new phenomena or interpretations that countervail the accepted wisdom. That is how young people make careers in science.
However, scientific doubt isn't frivolous; it must be based on the quality of the empirical evidence. Good scientists are scrupulous in their treatment (positive or negative) of the evidence; their reputations suffer otherwise.
Skepticism is not an established element in many other modes of human thinking. Most people are uncomfortable with skepticism and instead see virtue in conviction, certainty, and strong beliefs. As Bertrand Russell remarked, this may be the "fundamental cause of trouble in the world today."

"He believed in the primacy of doubt, not as a blemish upon our ability to know but as the essence of knowing."
                      ---- J. Gleick, writing about physicist Richard Feynman.

D. SCIENCE vs. TECHNOLOGY

• Science: Attempt to understand universe, build conceptual framework.
  Adjectives used: "unapplied," "pure" or "basic"
  Examples: principles of gravitation, electromagnetism, biochemistry, astronomy

• Technology: Application of basic concepts to societal needs.
  Examples: structural engineering, electrical generators, weapons, pharmacology.
  All technology has a societal motivation, whether for good or ill, but the main motivation for "basic" science is simply curiosity and the desire to understand.

  
  

E. RESULTS OF SCIENCE

Basic result of science

Nature is understandable and operates according to a small set of universal principles, or "laws"

Some other key results

Laws are the same everywhere in the observed universe
All matter, including living systems, is organized hierarchically from a smaller set of subunits
The structure of molecules & atoms is determined by electromagnetic force
The Sun is a star
The Earth is a planet
Genetic information is transmitted by DNA molecules
Most communicable diseases are caused by microorganisms
The universe is very ancient, and its structure and contents have changed systematically with time

Precursors

Very few of the important results of science had recognizable precedents in earlier modes of thought (prior to 1500 AD).
The main exceptions are Greek physics and astronomy, e.g. the models of the solar system by Ptolemy, ca. 130 AD, or the atomic theory of Democritus, ca. 420 BC. The Greeks made great progress. However, they disdained empirical testing of scientific ideas, which circumscribed their ultimate accomplishments. See Study Guide 6.

How well determined are scientific results?

Some scientific results are known with effective certainty (e.g. Earth is a planet; only one Sun in the solar system).
But scientific ideas are mostly approximations to the truth. They systematically improve by discarding older, less successful interpretations. But they are usually not claimed to be absolute.
You can picture the progress of science as an inward spiral toward the truth.
A simple practical measure of the validity of scientific ideas: If our scientific understanding of nature was seriously flawed, then most of our technology would simply not work. The validity of ideas like Newton's laws of motion or Maxwell's description of electromagnetism is tested continuously in every assembly line, automobile, and DVD player in the world.

Influence on society:

As a new mode of thinking about the natural world, science succeeded brilliantly. It demonstrated that humans can solve many problems which at first seemed intractable: e.g. questions like "what causes bubonic plague?" or "what are the stars?"
Success in science has been a great source of optimism in human cultures. This was a major wellspring for the Enlightenment and the political philosophies that culminated in the founding of Western democracy.

Science provides a demonstrably reliable and powerful understanding of the physical & biological world. Over the past two centuries it has transformed human societies. It is now the basis of most of our technology, our wealth, and our collective and individual well-being. The impact of science on our society is discussed further in Study Guide 9.

The Moon and Venus at dusk

F. ASTRONOMY AS A SCIENCE

Relevance to society:

1. Astronomy investigates ultimate origins (an adjunct or alternative to religion)
   
2. Astronomy provides our basic global perspective of time & space, i.e. a cosmic context
   
3. Astronomy was fundamental to the development of scientific thinking and the formulation of the first generalized physical laws (Newton).
   
4. Study of the other planets and our cosmic environment is essential to assessing the long-term viability of Earth's biosphere.

History of societal influence:

• All societies: practical time- and calendar-keeping, navigation
• 5000 BC - 1609 AD: aware of solar system (planets, sun)
• 16th-17th centuries: astronomy leads in demolishment of medieval thinking
• 1609: newly-invented telescope reveals vast stellar system beyond planets
• Late 1600's: astronomy leads Newton to his laws of motion, which initiate the "scientific revolution" and modern technology
• 19th century: speculation about extraterrestrial life
• 20th century: recognition of galaxies ("island universes"); expanding, evolving universe; Big Bang; extraterrestrial cause of mass biological extinctions; extra-solar planets

G. ASTRONOMICAL DISTANCES AND AGES

Humans directly experience only a very small range of the ages, distances, masses, densities, velocities, and energy releases that prevail in the universe around us.
Unfortunately, this means that astronomical scales (not to mention atomic or molecular scales) are completely non-intuitive.
It is important for astronomers to develop a good cosmic perspective. But it is difficult for anyone to visualize the scales involved. Because the cosmic range is so enormous, scientists make regular use of scientific mathematical notation ("powers of ten"). For a review of this notation, see Supplement I (PDF file).

Example astronomical scale models

1. Example of the contrast between human perceptions and physical reality: the Earth's atmosphere. It seems enormous and all-encompassing, but it represents only a tiny fraction of the Earth's diameter; see this image.
   Can you propose a scale model for this?

2. A sample cosmic time scale:
   • The age of the Sun is 5 billion years. Use the letters in our textbook to represent this span of time. How many years per letter?
     We discussed this in the introductory lecture, and we determined that there would be 2500 years per letter if the entire textbook represented the age of the Sun. All of recorded human history would fit within the first three letters of the text!
     The Earth is only about 10% younger than the Sun, so our scale model graphically illustrates the vast span of time over which the surface, atmosphere, and biosphere of our planet have been shaped into their present form.

   • The "dripping faucet effect": the very long time scales that characterize planetary evolution mean that small but persistent changes can eventually have major consequences. We will see many examples of these (e.g. polar precession, continental drift).

3. A healthy, fruit-based cosmic distance scale model:
   • Use an orange to represent the Sun.
     In this model, the Earth to Sun distance (defined to be one "Astronomical Unit") is 25 ft.
     [Useful mnemonic: Earth diam : Sun diam : Astron Unit = 1:100:10,000]

   • What is the scale distance to the next nearest star (Alpha Centauri) in this model?
     An additional interesting piece of information that might help you think about this question is that the Sun is about 10 billion times brighter than the brightest stars as seen from Earth.

Seeds textbook: Ch 1 and the "Windows on Science Boxes 2.1-2.5" in Ch 2.
Study Guide 1
Optional reading: Alan Cromer: Uncommon Sense; Bertrand Russell: A History of Western Philosophy; Carl Sagan: The Demon Haunted World

Seeds textbook: Ch 1
Study Guide 2
Supplement I (PDF file) Skim and then refer to this later as needed.
Optional: Cosmic History: A Brief Narrative
Optional: browse the material on the structure & evolution of the universe in the Seeds textbook Ch 16 and 18

History of Science from Encyclopedia Britannica

Note: you must be logged on through UVa to access Britannica
Web Index for History & Philosophy of Science, Technology, & Medicine
Internet Encyclopedia of Philosophy
Field Guide to Critical Thinking (from Skeptical Inquirer Magazine)
Bad Astronomy (a site devoted to debunking astronomical misconceptions, fraud, and pseudoscience, run by UVa Astronomy grad Phil Plait)
Simanek's Pseudo Science & Related Links
More Discussion of UFO's & Pseudoscience (Study Guide 18)

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