A View of Nature, Universe Where are we going? Jai-chan Hwang Contents Preface 1. Modern Cosmology: Assumptions and Limits 1. Science and cosmology 2. Modern cosmology begun by assumptions 3. Theory of gravity as an assumption 4. History of modern cosmology 5. Observation and interpretation 6. Observational facts in cosmology 7. Geometry and topology of the Universe 8. History of the Universe 9. Discovering the assumptions 10. Multiverse metaphysics 11. Misunderstandings of physical cosmology 12. Metaphysical questions 13. Meaning, purpose and indifference of the Universe 14. Limits of space and time 2. Astrobiology: Close encounter with our future 1. Where are we going? 2. Life and the universe 3. What is life 4. Conditions for life on Earth 5. Origin and evolution of life on Earth 6. Search for life in the solar system 7. The great silence 8. Arrival of the space age 9. Space exploration 10. The close encounter 11. Course of the future technology 12. Close encounter with the future 13. The great illusion 14. The last man 15. Eternal Silence Recommended readings Name index 1 자연의 전망, 우주 우리는 어디로 가는가? 황재찬 목차 책 소개 1. 현대우주론: 가정과 한계 1. 과학과 우주론 2. 가정으로 시작된 현대우주론 3. 가정으로서 중력이론 4. 현대우주론의 역사 5. 관측과 해석 6. 우주론 관측사실 7. 우주의 곡률과 토폴로지 8. 우주의 역사 9. 가정의 발견 10. 다중우주 형이상학 11. 현대우주론의 오해 12. 형이상학적 질문들 13. 우주의 의미, 목적, 무심함 14. 시간과 공간의 유무한성 2. 우주생물학: 미래와의 조우 1. 우리는 어디로 가는가? 2. 우주와 생명 3. 생명이란 무엇인가 4. 지구생명의 존재조건 5. 지구생명의 기원과 진화 6. 태양계 탐색 7. 거대한 침묵 8. 인간의 우주진출 9. 성간 탐색 10. 외계와의 조우 11. 미래기술의 향방 12. 미래와의 조우 13. 거대한 미몽 14. 최후의 인간 15. 영원한 침묵 추천도서 인명색인 2 Preface “Astronomy compels the soul to look upward, and leads us from this world to another.” Plato, The Republic, Book VII, Translated by Benjamin Jowett 1. Modern Cosmology: Assumptions and Limits 1.1 Science and cosmology Universe constructed by imagination “The universe is real but you can’t see it. You have to imagine it.” Alexander Calder, Interview in Katherine Kuh, The Artist’s Voice: Talks with Seventeen Artists (1962) “The universe is wider than our views of it.” Henry David Thoreau, Walden (1854) “The universe stretches beyond our finite powers of understanding.” Alfred North Whitehead, Modes of Thought (1938) “Philosophy, in one of its functions, is the critic of cosmologies.” Alfred North Whitehead, Science and the Modern World (1926) Condition for science “The epistemic counterpart to artist Calder’s dictum would be something like: ‘The universe is real, but you can’t grasp it as an object, you have to think of it as a Kantian Idea.’” Roberto Torretti, private communication (2013) “In my opinion, that knowledge only which is of being and of the unseen can make the soul look upwards.” Plato, The Republic, Book VII, Translated by Benjamin Jowett “All science has one aim, namely, to find a theory of nature.” Ralph Waldo Emerson, Nature (1836) Nullius in Verba “Nullius in Verba” Motto of The Royal Society (1660-) “Science in reality is more related with the art of ignoring and selecting observations, and manipulating experiments, in accordance with a preconceived theory. Detailed observation is often a hindrance to scientific reasoning. Ignore apparent phenomena and grasp the essence. Thus, in science theory often comes before observation. The trick is to treat the subject as an isolated, simplified, idealized and abstract (preferably mathematized) model, and to test and materialize it by fitting data to a model using the method of analysis and statistical techniques. In this way, the individuality is lost.” JH, Modern Cosmology: Assumptions and Limits, KIAS Newsletter (2011); arXiv:1206.6297 3 Creations of human mind “Physical concepts are free creations of human mind, and are not, however it may seem, uniquely determined by the external world.” Albert Einstein and Leopold Infeld, The Evolution of Physics (1938) “The eternal mystery of the world is its comprehensibility. … The fact that it is comprehensible is a miracle.” “The most incomprehensible thing about the world is that it is comprehensible.” Albert Einstein, Physics and Reality, Journal of the Franklin Institute, 221, 349 (1936); reprinted in Ideas and Opinions (1960) “It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we say about Nature.” Niels Bohr, quoted in A. Petersen, The Philosophy of Niels Bohr, Bull. Atom. Sci., September 1963, p. 8. Model’s utility and limit Nature replaced by model in science “The sciences do not try to explain, they hardly even try to interpret, they mainly make models. By a model is meant a mathematical construct which, with the addition of certain verbal interpretations, describes observed phenomena. The justification of such a mathematical construct is solely and precisely that it is expected to work.” John von Neumann, Method in the Physical Sciences, in The Unity of Knowledge, ed. L. Leary (1955); reprinted in The Neumann compendium Edited by F. Brody and T. Vamos (1995) “A theory is just a model of the universe, or a restricted part of it, and a set of rules that relate quantities in the model to observations that we make. It exists only in our minds and does not have any other reality (whatever that might mean).” “A scientific theory is just a mathematical model we make to describe our observations that: it exists only in our minds. So it is meaningless to ask: which is real, ‘real’ or ‘imaginary’ time? It is simply a matter of which is the more useful description.” “Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory. As philosopher of science Karl Popper has emphasized, a good theory is characterized by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation.” Stephen Hawking, A brief history of time (1988) Fallacy of misplaced concreteness “[Model is a] scientific approximation of reality. [W]hen a researcher begins to be not a methodological, but an ontological materialist, … when he considers his models, useful in other contexts, as cosmic realities, then he has started on a path that, in the end, can lead only to scientific decadence.” Konrad Rudnicki, The Cosmologist’s Second (1982) 4 “Error of mistaking the abstract for the concrete.” “Fallacy of misplaced concreteness.” Alfred North Whitehead, Science and the Modern World (1926) “Since all models are wrong the scientist cannot obtain a "correct" one by excessive elaboration. On the contrary following William of Occam he should seek an economical description of natural phenomena. Just as the ability to devise simple but evocative models is the signature of the great scientist so overelaboration and overparameterization is often the mark of mediocrity.” George E. P. Box, Science and Statistics, Journal of the American Statistical Association, 71, 791 (1976) Cosmology “All science is cosmology, I believe.” Karl R. Popper, The world of Parmenides: essays on the Presocratic enlightenment (1998); The Logic of Scientific Discovery (1959) PREFACE TO THE FIRST ENGLISH EDITION 1.2 Modern cosmology begun by assumptions Beginning of modern cosmology “Einstein’s first cosmological paper is a purely theoretical exercise containing not a single astronomical constant.” Paul Feyerabend, Against Method (1993) “From the standpoint of astronomy, of course, I have erected but a lofty castle in the air. For me, though, it was a burning question whether the relativity concept can be followed through to the finish or whether it leads to contradictions. I am satisfied now that I was able to think the idea through to completion without encountering contradictions. Now I am no longer plagued with the problem, while previously it gave me no peace. Whether the model I formed for myself corresponds to reality is another question, about which we shall probably never gain information.” Einstein, Letter to Willem de Sitter, before 12 March 1917, in Einstein, A. and Stachel, J., Collected papers, Vol. 08 Correspondence, 1914-1918 (1998) Cosmological principle “The normal physical laws we determine in our space-time vicinity are applicable at all other space-time points.” George F. R. Ellis, Cosmology and verifiability, Quarterly J. of Royal Astronomical Society, 16, 245 (1975) “The history of astronomy is a history of receding horizons.” Edwin P. Hubble, Realm of the Nebulae (1936) “The problem [is that] there is only one universe to be observed, and we effectively can only observe it from one space-time point.” “Given this situation, we are unable to obtain a model of the Universe without some specifically cosmological assumptions which are completely unverifiable.” George F. R. Ellis, Cosmology and verifiability, Quarterly J. of Royal Astronomical Society, 16, 245 (1975) “I dislike making of our lack of knowledge a principle of knowing something.” 5 Karl Popper, Quoted in Helge Kragh, The most philosophically of all sciences Karl Popper and physical cosmology (2012) ““Principles” in cosmology have often connoted assumptions unsupported by evidence, but without which the subject can make no progress.” Martin Rees, Before the Beginning (1997) Importance of principle “The theorist’s method involves his using as his foundation general postulates or "principles" from which he can deduce conclusions. His work thus falls into two parts. He must first discover his principles and then draw the conclusions which follow from them.