Search for Life in the Universe

1. Search for Life in the Universe Chapter 2 Science of Life in the Universe (Part 2) AST 248, Spring 2007

2. Apologies: Quiz Scan-Form Snafu • Should be Stony Brook Optscan forms (general-purpose NCS answer sheet), not Scantron forms, as originally announced • You can return Scantron forms in good condition to the campus bookstore: • Credit only toward purchase of Optscans • Need receipt of the original Scantron purchase • Difficulties: ask to speak with Kim at the bookstore • Again, apologies for my mistake. AST 248, Spring 2007

3. Outline • Nature of Modern Science • Nonscience & Pseudoscience • Objectivity & Theory • Tools and Methods of the Search for Life AST 248, Spring 2007

4. Induction: Discovery Science • Empirical science: observation(s)  interpretation  explanation  questions  more observation(s) • E.g., water on Europa: Voyager observations  interpreted as moving icebergs  explanation of motion by underlying water  question whether there can be life in the underlying water  plan a space mission to Europa AST 248, Spring 2007

5. Deduction: Hypothesis-Driven Science • Theoretical science: model or theory  prediction(s)  experimental or observational test(s)  refutation or consistency  modification of the model  new questions  new model(s) or theory(ies) • E.g., theory that amino acids can form under natural conditions  Miller-Urey experiment  consistency  the range of natural conditions?  models for the formation of RNA and DNA AST 248, Spring 2007

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7. Falsification: Confidence Through Self-Attack • Test forever but never prove: • Refutation: “beautiful theory killed by an ugly fact” • Consistency: OK only until a more sensitive experiment comes along • Modification/generalization: even for the best theories • Popper (19021994): • Falsification: science progresses best by constantly seeking ways to refute, not to uphold • Foundations of science: theories that have withstood prolonged, multiple attacks AST 248, Spring 2007

8. Ockham’s Razor: Minimum Complexity • William of Ockham (12851349): • Minimum complexity: seek the most economical hypotheses/parameters that account for the data • Less chance of error due to noise • More data per parameter  more secure parameter • Chaitin (1947) & Kolmogorov (19031987): • Algorithmic information content (AIC) • Too many possible parameterizations: exhaustive search of the AIC is not possible • Successful approximation methods found, details depending on problem AST 248, Spring 2007

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10. Nonscience: Outside the Domain of Science • Nonscience: important in human thinking: • Values or Love: no place for science • Religion/belief: no place for science, trouble if they try to be science • Art: artistic value is not science • Creativity & Intuition: does guide scientists to interesting questions and hypotheses • Scientific rigor: the final word in science • Subjects of nonscience are usually easily separated from science AST 248, Spring 2007

11. Pseudoscience: Dictating to Science by Nonscience • Pseudoscience: claims that can be tested scientifically but are not • Religious science: constantly upholds hypotheses instead of trying to falsify them • Unidentified flying objects (UFOs): none of the “sightings” stand to careful scrutiny • Short-lived triumph: sooner or later pseudoscience collapses under the weight of scientific evidence AST 248, Spring 2007

12. Objectivity & Theory • Scientists are only human • Personal interest • Intuition → bias • Popular ideas → paradigm • Objectivity through testing • Theory = hypothesis or set of hypotheses • Paradigm subjected to continuous testing • Predictions can lead to conflict with observations • Theory rejected • Or: theory modified AST 248, Spring 2007

13. Understanding Gravity • Gravity is both observed fact and theory • Newton’s theory successful only up to a point • Predict Neptune • Fail to explain precession of parahelion of Mercury • Einstein’s general theory of relativity • Generalized Newton (correspondence principle) • Explained precession of parahelion of Mercury • Predicted deflection of starlight • Predicted gravitation radiation • Many alternatives proposed (e.g., Brans & Dicke) • Binary pulsar: tested to 3rd order + radiation AST 248, Spring 2007

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15. Origin and Evolution of Life on Earth • Darwin (18091882): • Theory of natural selection • Ample evidence • Modern Addendum: importance of catastrophes • Earth: a long fossil record of life • Radioactive dating: when did fossil organisms live? • Chemical analysis: what were the conditions on Earth at the time? • Visible characteristics: how are different organism, past and present, related? • DNA: how are living organisms related? AST 248, Spring 2007

16. Search for Life Beyond Earth • Solar system (have tools, will travel): • Observe with telescopes on Earth or in orbit around the earth • Send spacecrafts for closer looks • Extrasolar life (have tools, no travel): • Explosion of telescope technology since WW II, at all wavelengths, with no end in sight • Imaging with higher sensitivity and resolution • Spectroscopy chemical composition, surface temperature, and motion (e.g., rotation) • Search for extraterrestrial intelligence (SETI): using radio signals AST 248, Spring 2007

17. Future of Life on Earth • Evolution of the Sun and Earth • Timescale: billions of years • Freezing: how has the Earth avoided it? • Short-term climatology • Greenhouse effect • Global warming • Runaway greenhouse effect, e.g., Venus • Leaving Earth • Ability to travel in space • Ability to change the climate in another planet AST 248, Spring 2007

18. Golden Age of Astrobiology? • Life beyond Earth has always fascinated humanity • For long the subject of myth, religion, or pure speculation • We now have an explosion of new tools and methods • Will we observe extraterrestrial life in our lifetimes? AST 248, Spring 2007