| Opening Remarks: Setting the Scene.
In our very first meeting, I described the approach which I shall take to the subject, an approach which I summarised through various contrasted representations of astronomy. A wonderful first lesson can be learned from the introductory sequence in the movie Contact, a sequence in which we travel, on increasingly large scales, through the observable universe, only to see it all captured in the eye of a young girl, the movie's protagonist (and astronomer-to-be). There is, I believe, a great metaphorical truth here: although we are contained within the universe, and a product of it, we are yet capable of visualising all of that within us - capturing it in our mind's eye, as it were.
In a more light-hearted way, I exemplified our human response to our relationship to the rest of the universe by showing several cartoons featuring Calvin & Hobbes and Garfield the Cat. The humour of the cartoons lay in the extent to which the people in them (Calvin, and Garfield's owner Jon Arbuckle) were made to feel so utterly intimidated by the immensity of space and our insignificance in the cosmos.
This is an understandable human reaction, to feel so overwhelmed by the vastness of it all that we merely gape in stupefaction at the sky, and feel that any deep investigation is forever beyond our reach (or perhaps not worth bothering about, if there's something more interesting on television).
By way of contrast, I considered a poem by Walt Whitman, who wrote (in 1865-1867):
"When I heard the learn'd astronomer,
When the proofs, the figures, were ranged in columns before me,
When I was shown the charts and diagrams, to add, divide, and measure them,
When I sitting heard the astronomer where he lectured, with much applause in the lecture-room,
How soon unaccountable I became tired and sick,
Till rising and gliding out I wander'd off by myself,
In the mystical moist night-air, and from time to time,
Look'd up in perfect silence at the stars.
With these words, Whitman reminds us of the danger of falling into sterile academic pursuits, studies in which we push numbers and formulae around and forget about the beauty and deep significance of what we are studying. It is not uncommon, for instance, for an astronomer to come back from the telescope with a stack of electronically-recorded data tapes, and thereafter to sit for weeks or months in front of the computer terminal analysing the data. The danger is that one might completely lose sight of what is represented by the numbers: the beauty of the stars, the scope for intelligent life out there, the profound history and evolution of the universe itself. No, we must take care to treat astronomy as more than just an academic exercise in physics and mathematics.
My intention, then, is to avoid both these traps in giving you an astronomer's considered look at the subject. I will apply and expect from you the kind of rigourous thought required in such a scientific pursuit - after all, what happens `out there' is in accordance with the laws of physics - but I will endeavour to make certain that we never lose the sense of mystery and excitement with which I hope you approach this course. I will accomplish this in various ways, some of them light-hearted (such as my inclusion of humour and music) but never meant to trivialise.
By the way, we astronomers are sometimes asked if our rational study of the stars reduces our own sense of wonder. Do we pay a penalty for looking so deeply? It is a good question, but the answer is `No.' To understand why, consider an analogy to professional musicians: does their analyis of a Beethoven symphony reduce their enjoyment of performing or hearing the piece? If you are a professional writer, do your insights into language not add to rather than hinder your appreciation of a play by Shakespeare? And so too with astronomers. Understanding the structure of the stars does nothing to decrease our appreciation of the beauties of the night sky or, more comprehensively, our amazement that such things exist at all. A study of physics need not engender a sterility of mind or imagination!
Remarks on Mathematics.Many of you (indeed, probably most of you) are perfectly capable of handling the mathematics of a traditional astronomy course. At the very highest levels, such as in the Theory of General Relativity which describes the structure of the cosmos itself, the mathematics is truly intimidating. Much of astronomy requires something less than that, but in almost every area of study mathematics is still of central importance; for, as Galileo Galilei (1564-1642) wrote: "La mathematica e l'alfabeto nel quale Dio ha scritto l'universo. (Mathematics is the alphabet with which God has written the universe.) The justice of this remark lies in our recognition that astronomy is a science, and indeed as exact a science as we can make it. In this course, however, and nothwithstanding the preparedness of most of you, I will dispense with mathematics in essentially everything, except in some simple calculations in the optional laboratory exercises described in the course outline. As I announced in the lecture, however, the term tests and examinations may include some optional mathematical questions for those of you with the necessary background. There will always be a choice which permits you to avoid such questions. Why do I do this? Mostly it is because I want to be able to reach all of you, even students lacking any kind of science background. I have to use a language (English) which we all speak, rather than the mathematics known to only some, no matter how concisely and precisely it would allow me to deliver the message. But it is also because I believe very strongly that unless one can convey in words what is going on, one does not fully comprehend the subject oneself! (I am, for instance, disappointed to encounter the occasional upper-year Physics student who is a mathematical whiz and who can solve quite complex equations, but who has a rather limited feel for what is going on in a given situation and thus a limited understanding of the `real physics.') My challenge, then, is to find the words to help you understand what makes the universe tick; your challenge is to develop that understanding. Please, however, never forget that yours will be, in some respects, an incomplete picture: astronomers and astrophysicists work with the mathematical physics which describes the gravitational interactions which keep the planets and asteroids in their courses, the nuclear reactions within the stars, the large-scale structure of the universe, and so forth. Only in this way can they make precise quantitative remarks about the order, stability, and evolution of the cosmos.
The Great Discoveries.It has been said that this century has seen a great revolution in our scientific thinking in at least four distinct areas. These areas are: Q.M. (Quantum Mechanics) , the discovery of the laws of physics which govern the behaviour of matter on the very smallest scales (e.g. within the atom). In addition to successfully explaining the observations, always an important aspect, Quantum Mechanics represented the end of any simply deterministic notions of everyday physical systems. At and shortly after the time of Newton, for instance, it was believed that one could in principle foretell the position of every particle of matter in the universe if one had a complete knowledge of their present positions and states of motion. Using the known forces and laws of mechanics, one could imagine working out how every single particle would move, change paths under the gravitational or electrical influence of others, rebound when suffering a collision, and so forth. In this way, the fate of the universe (however unknowable in actual practice because of the vast numbers of particles) was, at some very deep level, completely foreordained - a disquieting thought to those who believed in the concept of free will. Quantum mechanics changed all that with the introduction of an inescapable indeterminacy in the states of position and motion of all matter - not merely an imprecision in our ability to measure these things, but a real fuzziness in what these quantities `really are.' This profoundly changed the way in which physical systems are described (although the question of how `free will' functions in the world of physical laws is still a very deep one). C.D. (Continental Drift), the geophysical discovery that the Earth is not an inert static ball of rock, but rather that it is active and evolving. Of course, it has been known since prehistory that the Earth is active to at least the extent that there are volcanoes and earthquakes, but the recognition that the very continents themselves are afloat came as a revolutionary breakthrough. We now know of, and indeed can measure, the inexorable motion of the continental plates, and we understand the uplifting of entire mountain ranges as being caused by the collisions of these plates. DNA (Deoxyribonucleic Acid) , the discovery of the molecular structure of the DNA molecules which constitute our chromosomes and which provides a very natural understanding of the way in which Darwinian evolution works. The twisted double helix of the DNA molecule explains the simple mechanism of replication: the double strand unravels, and each separate segment is re-completed with the molecular building blocks which fit uniquely into the niches left; consequently, two DNA strands appear which are identical to the original one. Evolution is explained at the molecular level because of occasional random but minor imperfections in the replication: organisms within which the DNA-based genes are expressed in beneficial attributes (better protective coloration, say) are more likely to survive than others are, and many generations later the fitter organism is the preponderant species. E.U. (the Expanding Universe) , the discovery of evidence which implies that the universe had a beginning in the measureable past, at a time when it was much denser than at present, and that it is continuing to evolve in a way which allows us, in principle at least, to determine its eventual fate. Of these four important discoveries, only the last is `purely astronomical', but it is interesting to note that we will need to consider all of them in this course. Quantum Mechanics explains, in large measure, the physics of the matter which makes up the planets and the stars; Continental Drift arises in our study of the Earth and other terrestrial planets; and the nature of Life Itself - must it, for example, always be DNA-based? - will be our topic when we address the question of the potential for Extraterrestrial Intelligences and our hopes of making contact with them. In a very real sense, then, this course will cover all of the great modern discoveries of science!
We Live At a Special Time.Mention of extraterrestrials prompts me to note that, at least astronomically, we are alive at a very special time. It is possible that during your lifetimes we will make contact with intelligent extraterrestial species, or at least find incontrovertible evidence of their existence. The technology to make this kind of discovery simply did not exist until after the Second World War, since any realistic hope of success probably depends upon the science of radio astronomy (for reasons we will explore later in the year). You may know already that serious searches for such evidence have already been mounted and are continuing. For a wonderful depiction of this ambitious endeavour, please go and see the recent movie `Contact,' which shows what might happen if and when contact really is made. I feel obliged to tell you that the script-writers have had to take some liberties, to make the story more compelling! (The astronomy is not all correct, but it is a fine example of how realistically science can be portrayed on the screen.) Please note that I do not mean to say, in commenting on the special times we live in, that the SETI searches will probably succeed; it may be very unlikely that we will ever make such a discovery, for reasons which I will describe later in the course. Some scientists are very optimistic, while others are quite pessimistic about our chances. What is clear, however, is that such a discovery would have profound and probably unpredictable consequences for the human race, socially and psychologically as well as scientifically.
Your Astronomical AwarenessIn the lecture, I asked the class a series of questions in an effort to make you consider a variety of things. One of my objectives was to have you think about how much (or how little!) you might actually know about the subject of astronomy as you enter this course, but there was also a more serious purpose. Look, for instance, at questions 13 and 15, below. Most people today would not know the answers, whereas an average person of a thousand years ago would have. The sad truth is that most modern people have little or no awareness of the night sky, mostly because we live in brightly-lit cities, work inside buildings rather than out in the open, and fill our lives with activities which give us little occasion or reason to look at the sky. What a pity! (By the way, each of the true-false questions asked here will be answered at the appropriate stage in the course. Eventually, as the notes are put into place, I will return to this page and provide you links which will guide you to the relevant discussion. On the other hand, don't make the mistake of assuming that these particular questions define what I see as the most important objectives of this course! They were merely put together for fun.) The Questions: 1 Consider an artificial satellite orbiting very high above the Earth - one which has been launched as part of the American space program, for instance. As the years pass, it will gradually but inevitably lose energy and spiral downwards until it hits the ground. (This is a common theme in Star Trek.) True or false? 2 If the sun were to become a black hole, the Earth and all the other planets in the Solar System would be sucked into it. True or false? 3 The moon goes through its phases (new, crescent, full, etc) because of the different amount of the Earth's shadow which falls on it from time to time. True or false? 4 An astronaut in the Space Shuttle feels weightless because he or she is beyond the Earth's gravity. True or false? 5 The sun moves across the sky during the day, passing in front of a fixed pattern of stars which only become visible after the sun goes down. During the night, the stars themselves do not move across the sky. True or false? 6 If you pull the plug in an ordinary sink full of water, or flush a toilet, it can easily be seen that it drains out while circulating (swirling) in one direction in the Northern Hemisphere. Water in the identical sink or toilet would swirl in the other direction in the Southern Hemisphere. True or false? 7 On any given date, the moon is visible in the night-time sky from at least some part of the Earth - if we can't see it from North America, for instance, people living in Australia almost certainly can. True or false? 8 It is a fact that the Earth's orbit is not quite a perfect circle. (That much is indeed true.) One direct consequence is that summer occurs and the hottest days of the year are in July because that is when the Earth is closest to the sun. True or false? 9 Building a space station in orbit around the Earth will be quite easy because all the materials (girders, metal plates, etc) will be completely weightless, so the astronauts will be able to push them around effortlessly. True or false? 10 From the Earth, we never see the back side of the moon. This is because the moon does not rotate or spin at all, so is always facing us. True or false? 11 If you were to get into a rocket ship which had enough fuel to accelerate until it was going as fast as the speed of light, you would turn into a beam of pure energy. True or false? 12 If the Earth were to gradually slow down its rotation (spin) and come to a complete stop, we would all go floating off into space. True or false? 13 On certain days, the moon is not visible just after sunset, but rises somewhat later in the night - say, at 2:00 A.M. But on any given night the moon is sure to be visible to us at least part of the time (provided there is no cloud cover, of course). True or false? 14 If there were no clouds overhead, the moon would be visible to us in the day-time sky right now (on a Monday mid-afternoon in early September) from Kingston. True or false? 15 In early September of this year, Jupiter is conspicuously visible from dusk to dawn as a bright point of light in the night sky. True or false? 16 From Australia, the moon appears to be upside-down relative to the way we see it. True or false? 17 The full moon is measureably larger when it is close to the horizon, smaller when it is overhead. True or false? 18 Until the time of Columbus, it was believed by almost all learned people that the world was flat. True or false? 19 Per gram, your body generates hundreds of thousands of times more energy through metabolic processes than the sun does through nuclear reactions. True or false? Previous chapter:Next chapter
0: Physics 015: The Course Notes, Fall 2004 1: Opening Remarks: Setting the Scene. 2: The Science of Astronomy: 3: The Importance of Scale: A First Conservation Law. 4: The Dominance of Gravity. 5: Looking Up: 6: The Seasons: 7: The Spin of the Earth: Another Conservation Law. 8: The Earth: Shape, Size, and State of Rotation. 9: The Moon: Shape, Size, Nature. 10: The Relative Distances and Sizes of the Sun and Moon: 11: Further Considerations: Planets and Stars. 12: The Moving Earth: 13: Stellar Parallax: The Astronomical Chicken 14: Greek Cosmology: 15: Stonehenge: 16: The Pyramids: 17: Copernicus Suggests a Heliocentric Cosmology: 18: Tycho Brahe, the Master Observer: 19: Kepler the Mystic. 20: Galileo Provides the Proof: 21: Light: Introductory Remarks. 22: Light as a Wave: 23: Light as Particles. 24: Full Spectrum of Light: 25: Interpreting the Emitted Light: 26: Kirchhoff's Laws and Stellar Spectra. 27: Understanding Kirchhoff's Laws. 28: The Doppler Effect: 29: Astronomical Telescopes: 30: The Great Observatories: 31: Making the Most of Optical Astronomy: 32: Adaptive Optics: Beating the Sky. 33: Radio Astronomy: 34: Observing at Other Wavelengths: 35: Isaac Newton's Physics: 36: Newtonian Gravity Explains It All: 37: Weight: 38: The Success of Newtonian Gravity: 39: The Ultimate Failure of Newtonian Gravity: 40: Tsunamis and Tides: 41: The Organization of the Solar System: 42: Solar System Formation: 43: The Age of the Solar System: 44: Planetary Structure: The Earth. 45: Solar System Leftovers: 46: The Vulnerability of the Earth: 47: Venus: 48: Mars: 49: The Search for Martian Life: 50: Physics 015 - Parallel Readings.
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(Friday, 25 September, 2020.)