Overview of Contemporary Astronomy

The Forth Evening

http://edu-observatory.org/olli/Astronomy/Week4.html

Quoting from Alan Lightman's, "A Modern Day Yankee In A Connecticut Court and other essays on Science". Conversations with Papa Joe The Forth Evening Read: Conversations_with_Papa_Joe_IV.pdf Listen: Conversations_with_Papa_Joe_IV.mp3 Key Words and Phrases: Equation can describe the behavior of time, space, matter and energy. Newton's laws, thermodynamics Quantum Mechanics -- Summary of Important Ideas in Quantum Physics http://faculty.wcas.northwestern.edu/~infocom/Ideas/qn_summary.pdf Simplicity, intuition, guesses. Dirac Emma Noether GR Predicted BH Gravitational Time Dilation Space and time are malleable Tests of GR (Solar Eclipses 1919, 1922) Documentar Sirius, Hunter, Constellations

EQUATIONS Perhaps the most powerful aspect of physics, and indeed perhaps the most amazing thing about the cosmos as a whole, is the universality of physical laws and theories. A few scant equations small enough to fit on your favorite T-shirt can explain a variety of phenomena from one edge of the universe to the other, and from the earliest moments of the Big Bang to the unfathomable future.

SPECIAL RELATIVITY Five Papers That Shook the World https://physicsworld.com/a/five-papers-that-shook-the-world/ ON THE ELECTRODYNAMICS OF MOVING BODIES By A. Einstein http://www.fourmilab.ch/etexts/einstein/specrel/specrel.pdf

GENERAL RELATIVITY Wikipedia - General relativity https://en.wikipedia.org/wiki/General_relativity General relativity (GR), also known as the general theory of relativity (GTR), is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of partial differential equations. Documentary: Life of Albert Einstein (90 min) Start at 1:22:45 https://www.youtube.com/watch?v=R_yk45m4E3M <== https://www.youtube.com/watch?v=ASzECGtSpqQ <== Beautiful, Simple and Profound -- Final Development and Testing GR http://edu-observatory.org/olli/GR/Week1.html Beautiful, Simple and Profound -- Classical Tests of Relativity http://edu-observatory.org/olli/GR/Week2.html Beautiful, Simple and Profound -- Modern Tests of Relativity http://edu-observatory.org/olli/GR/Week3.html Beautiful, Simple and Profound -- Detection of Gravitational Waves http://edu-observatory.org/olli/GR/Week4.html Black Holes -- Prediction, Properties, and Structure http://edu-observatory.org/olli/BH/Week1.html Black Holes -- Formation, Evolution, and Hawking Radiation http://edu-observatory.org/olli/BH/Week2.html Black Holes -- Observational Evidence http://edu-observatory.org/olli/BH/Week3.html Black Holes -- Open Questions http://edu-observatory.org/olli/BH/Week4.html Einstein's description of gravity just got much harder to beat https://phys.org/news/2020-10-einstein-description-gravity-harder.html Einstein's theory of general relativity-the idea that gravity is matter warping spacetime-has withstood over 100 years of scrutiny and testing, including the newest test from the Event Horizon Telescope collaboration, published today in the latest issue of Physical Review Letters. According to the findings, Einstein's theory just got 500 times harder to beat. Despite its successes, Einstein's robust theory remains mathematically irreconcilable with quantum mechanics, the scientific understanding of the subatomic world. Testing general relativity is important because the ultimate theory of the universe must encompass both gravity and quantum mechanics.

QUANTUM MECHANICS Summary of Important Ideas in Quantum Physics https://faculty.wcas.northwestern.edu/~infocom/Ideas/qn_summary.pdf Heisenberg's uncertainty principle http://en.wikipedia.org/wiki/Heisenberg%27s_uncertainty_principle http://www.youtube.com/watch?v=a8FTr2qMutA (4+ min) Heisenberg's uncertainty principle tells us that it is impossible to simultaneously measure the position and momentum of a particle with arbitrary precision. In our everyday lives we virtually never come up against this limit, hence why it seems peculiar. In this experiment a laser is shone through a narrow slit onto a screen. As the slit is made narrower, the spot on the screen also becomes narrower. But at a certain point, the spot starts becoming wider. This is because the photons of light have been so localized at the slit that their horizontal momentum must become less well defined in order to satisfy Heisenberg's uncertainty principle. Quantum vacuum fluctuation (or Quantum Fluctuation for short) http://en.wikipedia.org/wiki/Quantum_fluctuation Quoting from the above Wikipedia page: "In quantum physics, a quantum vacuum fluctuation (or quantum fluctuation or vacuum fluctuation) is the temporary change in the amount of energy in a point in space, arising from Werner Heisenberg's uncertainty principle. "According to one formulation of the principle, energy and time can be related by the relation "That means that conservation of energy can appear to be violated, but only for small times. This allows the creation of particle-antiparticle pairs of virtual particles. The effects of these particles are measurable, for example, in the effective charge of the electron, different from its "naked" charge. "In the modern view, energy is always conserved, but the eigenstates of the Hamiltonian (energy observable) are not the same as (i.e., the Hamiltonian doesn't commute with) the particle number operators. "Quantum fluctuations may have been very important in the origin of the structure of the universe: according to the model of inflation the ones that existed when inflation began were amplified and formed the seed of all current observed structure." Quoting from A USENET Posting by Steve Carlip (UC Davis): "CMB fluctuations give evidence for (though not proof of) inflation. "So far, I haven't said anything about where the initial density variations of the pre-recombination plasma came from. There are many possibilities. We know, at least, that they must be there -- even if we try to start with a perfectly smooth, unvarying plasma, the Heisenberg uncertainty principle tells us that there must be a minimum level of quantum fluctuations. "Inflationary" models propose that the very early Universe -- before the time of primordial nucleosynthesis -- underwent a very rapid expansion. Such an expansion would smooth out/dilute any earlier inhomogeneities, leaving only the quantum fluctuations, which would be "stretched" in size by the rapidly expanding space. "Such models predict a special pattern of fluctuations. In particular, although any particular fluctuation is random, the average number at any particular scale is predictable. This pattern on initial variations, in turn, should show up in the details of the CMB variations. So far, observations match the predictions of inflation very well. Most people in the field don't consider this conclusive -- one can imagine other ways of getting a similar pattern of initial perturbations -- but it is suggestive." Inflation (cosmology) http://en.wikipedia.org/wiki/Inflation_(cosmology) In physical cosmology, cosmic inflation, cosmological inflation, or just inflation is the extremely rapid exponential expansion of the early universe by a factor of at least 10^78 in volume, driven by a negative-pressure vacuum energy density. The inflationary epoch comprises the first part of the electroweak epoch following the grand unification epoch. It lasted from 10^-36 seconds after the Big Bang to sometime between 10^-33 and 10^-32 seconds. Following the inflationary period, the universe continued to expand, but at a slower rate. The term "inflation" is also used to refer to the hypothesis that inflation occurred, to the theory of inflation, or to the inflationary epoch. The inflationary hypothesis was originally proposed in 1980 by American physicist Alan Guth, who named it "inflation". It was also proposed by Katsuhiko Sato in 1981. As a direct consequence of this expansion, all of the observable universe originated in a small causally connected region. Inflation answers the classic conundrum of the Big Bang cosmology: why does the universe appear flat, homogeneous, and isotropic in accordance with the cosmological principle when one would expect, on the basis of the physics of the Big Bang, a highly curved, heterogeneous universe? Inflation also explains the origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the universe (see galaxy formation and evolution and structure formation). Why did Alan Guth say "the universe may be the ultimate free lunch"? https://www.quora.com/Why-did-Alan-Guth-say-the-universe-may-be-the-ultimate-free-lunch?share=1 Alan Guth is the first and main father of inflationary cosmology, see e.g. Alan Guth and inflation. His comment about the "universe as the ultimate free lunch" is an explanation of a striking feature of inflationary cosmology. During cosmic inflation, the Universe is created basically from nothing. The energy conservation law and the mass conservation law are explicitly violated in cosmology as modernized by Einstein's general theory of relativity and Guth's (and Linde's) cosmic inflation makes this violation maximum. During inflation, the volume of the Universe - e.g. the volume of a tetrahedron between four (newborn or future) galaxies - increases exponentially with cosmic time. Nevertheless, the density of mass or energy in that tetrahedron is basically constant during inflation. So the total mass/energy increases exponentially, just like the volume! At some moment, the inflationary epoch ends and the energy produced in the Universe "out of nothing" is converted to particles that give rise to the seeds of galaxies as we know them today. There is a proverb that there's never any free lunch. Everything costs something, everything is a trade-off, and so on. Alan Guth pointed out that the model of the expansion of the very early Universe that he discovered is the greatest counterexample to that proverb and wisdom - because there actually is a completely free lunch. The Universe, essentially all the matter in it, was created (almost) out of nothing.

BOOK RECOMMENDATIONSThe Stars: A New Way to See Themby H. A. Rey https://www.amazon.com/Stars-New-Way-See-Them/dp/0544763440 This book contains the most lucid explanation of the sidereal day I have ever read. If you are looking for a book that explains the big bang theory and modern astronomical theories, this is not your book. If you are want to look up at the sky and recognize stars like old friends, then this is your book. Along the way, you will learn enough about the relative motions of the earth, sun, planets and stars to understand why different parts of the sky are visible at different times of the year, and from various places on earth.365 Starry Nights; An introduction to Astronomy for every night of the yearby Chet Raymo https://www.amazon.com/365-Starry-Nights-Introduction-Astronomy/dp/0671766066 365 Starry Nights is a unique and fascinating introduction to astronomy designed to give you a complete, clear picture of the sky every night of the year. Divided into 365 concise, illustrated essays, it focuses on the aesthetic as well as the scientific aspects of stargazing. It offers the most up-to-date information available, with hundreds of charts, drawings, and maps-that take you beyond the visible canopy of stars and constellations into the unseen realm of nebulae and galaxies. This simple yet substantial text is full of critical information and helpful hints on how to observe the stars; describe their position; calculate their age, brightness, and distance; and much more. Whether you observe the sky with a telescope or the naked eye, 365 Starry Nights makes the infinite intimate and brings the heavens within your grasp. Keep this invaluable, informative guide close at hand, and you'll find that the sky is the limit 365 nights a year.The Equations: Icons of Knowledgeby Sander Bais https://www.amazon.com/Equations-Icons-Knowledge-Sander-Bais/dp/0674019679 An intriguing little book...founded on a quarrel with what the author calls the 'fashionable dogma' of not including equations in science books intended for general readers. 'The veto is like asking somebody to explain art without showing pictures,' Bais argues. And he's right. His book is worth a look for anyone feeling brave enough to journey into the language of physical science on its own ground: the terra firma of mathematics. --Anthony Doerr (Boston Globe 2006-01-15) The author writes clearly and incisively about the physical ideas...Most books of this genre take it as axiomatic that they must avoid equations. Bais embraces them, building his book around the equations of physics and using them as the vehicle for describing the counter-intuitive world of relativity theory, quantum mechanics, and string theory. --David M. Bressoud (Mathematical Association of America) Let me say at once that I learnt a great deal from the author's broad-brush approach...The physics is very readable, with connections between different parts of the subject made well. And because the book is so short, the reader has a real chance to see "the big picture"...There is no doubt that The Equations is a bold and original book. And, in my view, imagination of this kind will be needed in the future if maths and science education is to avoid sliding gradually into lightweight stuff about what Newton ate for breakfast. --David Acheson (Times Higher Education Supplement 2006-03-10)

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