Transcript Search for Life in the Universe

Search for Life in the Universe
Chapter 2
Science of Life in the Universe
(Part 3)
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Outline
• Nature of Modern Science
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Induction: Discovery Science
Deduction: Hypothesis-Driven Science
Falsification: Confidence Through Self-Attack
Ockham’s Razor: Minimum Complexity
Nonscience: Outside the Domain of Science
Pseudoscience: Dictating to Science by Nonscience
• Tools and Methods of the Search for Life
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Origin and Evolution of Life on Earth
Search for Life Beyond Earth
Future of Life on Earth
Golden Age of Astrobiology?
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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
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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
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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
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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
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Nonscience: Outside the Domain of
Science
• Nonscience: important in human thinking:
– Values: science says nothing about them
– Religion/belief: science says nothing about
them, unless religion/belief try to be science
– Art: science says nothing about artistic value
– 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
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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
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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?
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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
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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
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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?
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