Extraterrestrial Philosophy. The Relevance of Philosophical Principles for an Astrophysicist

Transcription

1 Extraterrestrial Philosophy The Relevance of Philosophical Principles for an Astrophysicist 1

2 Core Questions What are some key philosophical principles that are generally associated with astrophysics? Are these principles relevant? In what way have they influenced studies? How will future studies be affected? 2

3 Structure of Talk Introduction to topic The Anthropic Principle The Copernican Principle The Cosmological Principle Philosophical Insight Case Study: Data Inference Bias in Science Relevance to Astrophysics Solutions Future Developments Case Study: Searches Case Study: Classification 3

4 Philosophy and Physics Once there was a dean at my university who was a scientist with high intelligence but low boiling point. One day at a faculty meeting, after I said something that displeased him, he replied, Peter, you have never made a contribution of interest to scientists.... You philosophers of science, he meant, have nothing to offer us scientists. - Peter Achinstein, The Book of Evidence 4

5 Importance of Philosophy Philosophical considerations shaped classical and contemporary physics - as we ve seen A physical theory that is philosophically problematic is not an ideal formulation The outcomes of philosophical thought can (and should?) be considered by physicists How can physicists use these? 5

6 Astrophysics Astrophysicist: an astronomer who investigates the physics of astronomical objects and events Galactic: referring to Earth s home galaxy, the Milky Way This is a diverse field, and yet a relatively narrow subsection of physics How does philosophy affect studies in this field? 6

7 The Anthropic Principle Observations are necessarily consistent with the existence of (human?) observers Raised by Brandon Carter (1974) to argue for selection effects due to humans as observers Symmetry: human observations agree with human existence - imperative Observation selection effects and the Self Sampling Assumption (Bostrom, 2002) 7

8 The Copernican Principle The Earth is not in a privileged position Describes the shift from an Earth-centric universe Symmetry: equality of observations from Earth vs. observations on the other side of the universe It does not mean that all of spacetime is like that of Earth, just that our situation is not unique (Cirkovic 2009) 8

9 The Cosmological Principle Space is universally homogeneous and isotropic Universal properties are the same for all observers Symmetry: space/physics near Earth vs. space/ physics on the other side of the universe Physicists can then assume that a representative fraction resembles the whole (Pan, 2010) Not spacetime! 9

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11 Philosophical Insight Observational bias: observations as fundamentally biased by the observers, and hence asymmetric Incompleteness: not everything in the universe is observed/observable Universality: a representative fraction of the universe is observed/observable How are these significant? 11

12 Case Study: Searches Galactic supernova remnants: selection effects leading to incomplete distribution, of faint SNRs (beyond sensitivity) and small SNRs (beyond resolution) - controversial -D relation This is an example of incompleteness due to the limits of instruments, making it difficult (and dangerous) to draw conclusions based on known 12

13 Case Study: Classification Galaxy Zoo I: volunteer identification of galaxies - there was a human-induced bias of identifying right-handed spirals, checked by mirror-imaging half the galaxies (Land, 2008) Supernovae: Optical data are what we perceive with our unaided inborn detectors - our eyes - and in our anthropic chauvinism, explaining the explosion seems most interesting. (Cardall, 2002) Both examples of observational bias 13

14 Case Study: Classification Galaxy Zoo I: volunteer identification of galaxies - there was a human-induced bias of identifying right-handed spirals, checked by mirror-imaging half the RIGHT galaxies (Land, 2008) LEFT (CLOCKWISE) Supernovae: Optical data are what we perceive with our unaided inborn detectors - our eyes - and in our anthropic chauvinism, explaining the explosion seems most interesting. (Cardall, 2002) Both examples of observational bias 13 (ANTI-CLOCKWISE)

15 Case Study: Classification Galaxy Zoo I: volunteer identification of galaxies - there was a human-induced bias of identifying right-handed spirals, checked by mirror-imaging half the RIGHT galaxies (Land, 2008) LEFT (CLOCKWISE) Supernovae: Optical data are what we perceive with our unaided inborn detectors - our eyes - and in our anthropic chauvinism, explaining the explosion seems most interesting. (Cardall, 2002) Both examples of observational bias 13 (ANTI-CLOCKWISE)

16 Case Study: Classification Galaxy Zoo I: volunteer identification of galaxies - there was a human-induced bias of identifying right-handed spirals, checked by mirror-imaging half the RIGHT galaxies (Land, 2008) LEFT (CLOCKWISE) Supernovae: Optical data are what we perceive with our unaided inborn detectors - our eyes - and in our anthropic chauvinism, explaining the explosion seems most interesting. (Cardall, 2002) Both examples of observational bias 13 (ANTI-CLOCKWISE)

17 Case Study: Data Inference Hubble s constant: Hubble s Malmquist bias, then de Vaucouleurs (Ho = 100) vs. Sandage (Ho = 50) debate - resolved (?) by HST Key Project (2001) Universality has been applied here - by assuming that subsets (galaxies, Cepheids, etc) can be used to infer a global variable - very subject to bias! 14

18 Bias in Astrophysics Key idea: it is important to be aware of the lack of symmetry between observations and reality! Biases affect approach and judgement on results The scientific method aims to minimise the effect of biases through analysis and review Royal Society: Nullius in verba - on no one s word 15

19 Tunnel Bias: Universal? Piattelli-Palmarini (1994) argues for the existence of a set of intrinsic biases deriving from possibly universal heuristics - he calls these tunnels What is the significance of a bias that affects everyone in potentially the same way? 16

20 Tunnel Bias: Universal? Piattelli-Palmarini (1994) argues for the existence of a set of intrinsic biases deriving from possibly universal heuristics - he calls these tunnels What is the significance of a bias that affects everyone in potentially the same way? 16

21 Relevance to Astrophysics Universality is limited in its application - likely to be hindered by observational/observer biases Incompleteness is basically impossible to avoid in astrophysics, but derives from observation bias Observational and observer biases are extremely important both philosophically and scientifically How close to reality can observations get? 17

22 Solutions (?) Searches: automated searches that encode specific processes and are systematic and repeatable, with logical definition of search parameters Classification: Bayesian classification (e.g. IRAS data via Autoclass, Ivezic 2000), and the use of a continuous spectrum to classify vs. discrete groups Data inference: Bayesian reasoning in considering probabilities (e.g. catastrophe bias, Cirkovic 2007) 18

23 Future Developments Current trends indicate an increasing awareness of the influence of anthropic bias on research Once identified, many biases can be avoided The most systematic way to implement searches is through the logical codification of processes Explicit consideration of bias may elucidate issues Bayesian reasoning is very effective at forcing this! 19

24 Image References

25 Thanks for listening! Questions? 21