Strictly speaking, this bulky subsection is not a necessary segment of the Planetary Remote Sensing Section since the latter pertains almost exclusively to our Solar System - an infinitesimal component of the Cosmos. Still, remote sensing is a mainstay of observational Astronomy, itself a closely allied field to Cosmology - the science that studies the origin, evolution, and behavior of the Universe as a whole. Both visual and instrumental observations made through telescopes use interpretive techniques similar to - but usually more complex and advanced - those which we have been employing to study the Earth and neighboring planets. And more and more astronomical observations are being made from space platforms that operate above the distorting atmosphere. Spectral measurements across the EM spectrum are the principal data sources supporting the various modern cosmological models. Astronomers are true members of the remote sensing community.

The illustration below demonstrates the power and versatility of multispectral measurements that continue to provide important, often critical information pertinent to astronomical, and by extrapolation, to the higher level that underlies cosmological thinking. Shown are composite images of the Milky Way galaxy acquired over different parts of the spectrum using satellite- mounted sensors. Because the labelling is likely be blurred on your screen, from the top these spectral regions are: Light from the excitation of atomic hydrogen; the same, for molecular hydrogen; infrared; near infrared; optical; x-ray radiation; gamma rays; a "reference" or "finder" image.

These panels were assembled at NASA Goddard Space Flight Center's Astrophysics Data Center using results from satellites developed there and elsewhere. To view higher resolution versions of each region and to learn how the data were obtained, click on their Web site at this address: http://adc.gsfc.nasa.gov/mw/milkyway.html

Cosmology is one of the writer's (NMS) hobbies and special interests - has been since his high school days and first acquaintance with the sciences. It was once a tentative choice as a career until it became obvious that my mathematical abilities were too limited to allow me to master the essential concepts of Physics to the degree needed to excel in Astronomy and Cosmology. But, I have over the years "devoured" a number of texts and popular accounts (starting with Isaac Azimov paperbacks) that deal with the three main areas of Physics - Quantum Mechanics, which deals with the very small; Newtonian Physics, which covers the physics of "everyday world" scales, and Relativity/Astrophysics, which examines the very large (scales at cosmological sizes), especially under relativistic conditions in which measurements are made on objects traveling at speeds near that of light. This has endowed me with enough elementary expertise to attempt this subsection, which is an condensed survey of current knowledge of the fundamentals of Cosmology presented in a generalized descriptive narration rather than a rigorous, mathematically-developed synopsis. I have sought - but not yet obtained - reviews by professional astro-scientists in hopes of validating and improving its content (your critique, if you are so qualified, would be much appreciated and changes made accordingly). But, for now, I accept full responsibility for the errors of commission and omission that inevitably have made their way into this write-up.

My starting point was to read (and re-read) The Big Bang, by Joseph Silk, 2nd Ed., 1989, W.H. Freeman Co., which I also outlined in toto. From this the first version was prepared. Then, a number of magnificent illustrations made through the Hubble Space Telescope were "discovered"" on their Home Page on the Internet, downloaded, and incorporated into the text, which was then expanded and rewritten. Next, in Fall of 1997, The Whole Shebang: A State-of-the-Universe(s), by Timothy Ferris, 1997, Simon & Schuster was found in a bookstore during a visit to the Washington, D.C. area. After full reading - it is a highly recommended account in layman's language - more revisions were made.

Yet another trip there led to finding a just published textbook Foundations of Modern Cosmology, by J. Hawley and K. Holcomb, 1998, Oxford Press, scoped as a survey at the Senior-Graduate School level, which I went through at a cautious pace although consistently fascinated. I judge it to be the one of the best science books of any kind I have ever perused. It treats Cosmology in the proper way, from the viewpoint of Einsteinian Special and General Relativity. (Special Relativity, which came first, deals with spacetime in terms of the electrodynamics of moving systems; General Relativity is a refinement that brings in the proper role of gravity.) Only then did I fully realize that the approach to Cosmology that is (still) used in this Tutorial is incomplete and oversimplified, although adequate and reasonably valid in its context, despite its not being presented in the appropriate framework of Relativity. Rather than rewriting the entire subsection in terms of relativistic Cosmology - which would have greatly enlarged its length - I have extracted some of the important ideas and information from their book and incorporated these by splicing into the text. But, if you have - or develop from this subsection - an abiding curiosity about Cosmology in its fullest scope and want to learn more using a treatise that contains rather straightforward and manageable mathematics, I strongly urge you to order the book (it is not likely to be found at the usual bookstores) and put aside the month or so that will be needed to investigate the "foundations" of Cosmology (about 10 pages a day is the limit I advise, since you need to digest and ponder its many significances).

I have deliberately avoided explanatory coverage in this subsection of some of the more avant garde aspects of Cosmology, such as: Theories of Everything (a unified model including all physical aspects of the Universe's origin); Spontaneous Self Creation; Quantum Cosmology; Hawking radiation (which draws upon quantum mechanics, thermodynamics, and relativity); Hyperdimensional (greater than 3 and up to at least 10 dimensions) Space; Multiple Universes; Supersymmetry; Superstrings; Magnetic Monopoles; Wormholes and Time Travel. Perhaps key answers will come from observations made by the Planck Explorer spacecraft to be launched in the early 21st Century. Meanwhile, a paperback that considers most of these ideas is Hyperspace by Michio Kaku, 1994, Anchor Books (Doubleday) treats many of the above topics in a clear exposition and is another recommended read. Still another superb review is The Cosmic Blueprint, by Paul Davies, Touchstone Books, 1992; two of his more philosophical tomes that attempt to reconcile the modern world of science with metaphysical questions (including the role of God in creation) are listed at the end of this subsection. Two other excellent reviews, both published by the Oxford Press, are The Left Hand of Creation by John Barrow and Joseph Silk, updated edition, 1993, and The Life of the Cosmos by Lee Smolin, 1997.

I can't resist the temptation to say a few words (actually several paragraphs) about the most basic ideas that underly Relativity. Relativity is an outgrowth of Einstein's thoughts, in the early 1900s, about motion and gravity in a non-Newtonian framework (Newton's physics - especially in the realm of mechanics - works well in the dynamics of three dimensional space and at velocities common to everyday experience). Special Relativity, first espoused in 1905, is derived from the premise that the speed of light is truly a constant - an absolute value - which determines how one must approach the measurements of the physical phenomena of the Universe. The principle from which many conclusions about the relative aspects of time and motion in the physical universe are formulated springs from this simple statement: "The speed of light is the same when measured from all moving (inertial) frames of reference, regardless of their (relative) speeds." In other words, the speed of light is invariant, and will always have its precise value of 299,792 km/sec (186,282 miles/sec) whether it is measured from a point on Earth moving at its celestial velocity or from a spaceship traveling at hypervelocities. A corollary drawn from this principle is that, for any two systems moving at different uniform velocities, all the laws of Mechanics (in Physics) operate in the same way in both systems, i.e., are not influenced or moderated by their relative speeds. However, Relativity is most relevant and applicable for phenomena in which very high speeds are involved as well as aspects of Physics involving the quantum state of matter and energy.

At the low speeds (compared to light) that we travel in Earth life, we have all experienced the effects of small differential speeds in our auto on an Interstate relative to a car traveling at slightly lower speeds in the next lane (we actually sense that we are going fast because our eyes are aware of features off the highway that are standing still). But, relative to each other, the feeling of motion differences is minimal. But, an observer (say, a pedestrian) off to the side notes both cars as going fast. However, our sense of relative motions is accentuated when we compare our forward motion with autos moving against our direction in opposing lanes.

Now, assume we occupy a spacecraft moving at extreme speeds (approaching the speed of light). If we somehow can measure that light as it moves outside the spacecraft, regardless of our speed the light is found to be moving at its fixed value of almost 300,000 km/sec. From our frame of reference onboard, the relative motion of ourselves within the spacecraft is that of standing still with respect to the spacecraft itself but moving quite fast with respect to external objects and observers. For the rapidly moving spacecraft passenger, clocks onboard seem to move more slowly relative to stationary ones located elsewhere (say, on Earth), so that time dilates (interval between seconds increases) (intense gravitational fields produce the same effects). Not only do we look as though we are slowing down but we are dimensionally shortening in the direction of motion. To a distant observer, our spacecraft will appear distorted owing to the differences in time when light left different parts of the rapidly advancing vehicle. In effect, for anyone moving at high relativistic speeds, time stretches out and space shrinks. If we were to return to Earth after 20 years of high speed travel, we will have aged only a short time compared with the 20 years that the observer left behind has added to his life from the beginning of our journey.

From such reasoning, Einstein concluded that the proper dimensionality needed to explain the unusual phenomena that result from relativistic motions is four rather than the traditional three (space: length, width, and depth or height). The fourth dimension, that of time, is considered independent of spatial dimensions in Newtonian mechanics. In Einstein's deductions, time and space are interchangeable. The Universe is fundamentally a 4-D state. The role of time becomes paramount in measuring the positions of objects in motion: time enters in because locations are changing even as time is consumed in traveling from source to observer.

One corollary drawn from this aspect of Special Relativity is that the huge dimensions of the Universe require that we always consider time in measuring distances. Thus, light reaching us today from a galaxy 10 billion light years away actually is recording that moment in the galaxy's past at 10 billion years ago. We see the galaxy as it was then, not as it really is now (it may in fact by now have greatly evolved and has lost and gained many stars). Likewise, its position then relative to us is not the same as now. This distribution of objects throughout space, which gives information as we observe them today that represents different times and locales in the past, embodies the concept of spacetime.

In one of his thought experiments, Einstein envisioned what would happen to a beam of light moving beyond the interior of a space vehicle accelerating at relativistic speeds. Applying Special Relativity concepts, to the onboard observer the light is transmitted along a straight line, since both the light source and the vehicle are traveling at the same speeds. But to an outside observer at rest, the light beam would appear to curve, inasmuch as the position of its photons is shifted progressively as it travels out from the high speeding vehicle. Thus, under the influence of gravity-acceleration, the light which must travel the shortest distance between two points (A, source; B, target) will be subject to A's having moved a finite distance during the transit time relative to the observer at B - thus the light traces a curved line, from which it follows that space itself is curved in the sense that light traveling across it follows a curved path that still represents the shortest distance between points. (Any segment of a longitudinal line on a sphere is curved but nevertheless remains the shortest distance between the points at each end of the segment.)

Another of Einstein's conclusions then was that mass and energy are a continuum, such that under certain conditions, energy can "condense" to mass and, conversely, that mass is convertible to energy (hence: E = mc², with c being the speed of light]). From this equation, one can deduce that as an object moves faster up to speeds approaching that of light its energy will begin to increase notably. Likewise, to an external observer, the mass itself will increase towards infinity (although as measured on board, the mass remains the same, i.e., is treated as a "rest mass"). This mass-energy equivalence ranks with the space-time equivalence at the top of the list of his achievements. It also forms the basis for schemes to recover huge amounts of energy from "tapping" into the nuclei of atoms; the energy released from the explosion of an atomic bomb derives from this relationship.

General Relativity, put forth by Einstein in 1916, was his effort to fit gravity into the space-time picture. Gravity, from our experience, is strongly dependent on mass. Einstein recognized that gravity is also dependent on motion and the geometry of space. He thus postulated still another equivalence: that of acceleration and gravity. The falling ball in the elevator example illustrates this. If the elevator is stopped and a ball is dropped, it will move straight down at the acceleration appropriate to Earth's gravity. If, instead, it is released in a fast dropping (thus accelerating) elevator, when the elevator's rate of speed change just balances that of standard gravity, the ball will "hang" suspended in the elevator rather than falling. (This is similar to the effect of inducing weightlessness for a short period when an airplane accelerates into a fast dive; this effect, evidenced by free floating, is also experienced by astronauts in the Space Shuttle when it orbits at angular velocities that balance [offset] Earth's gravity.)

Gravity, on the grand scale (stars and galaxies), can be conceived as a force that influences geometry, in other words, gravity bends or distorts the fabric of space-time. Matter/energy determines the curvature of space-time and is said to "warp" space (this can be visualized as follows: consider a fastened rubber sheet on which a grid pattern is drawn; a heavy object, such as a rock, if allowed to drop on the sheet, will create a depression and distort the grid around that indentation). Gravity then, in Einstein's view, is just the effect of masses inducing curvature in the four-dimensional extension of space. The "acid test" of the validity of General Relativity is the actual observation of light from distant stars being bent (slightly, but measurable) during a full solar eclipse, so that the stars just beyond the edge of the Sun appear to shift in position relative their usual position in the sky.

These, then, are some rudiments of Relativity, probably expressed here so superficially in this condensation that only a vague insight into its characteristics, properties, and influences will be implanted. Consult any of the references cited above for more details. Keep in mind also that much of relativity is unfamiliar in terms of everyday life experiences, so that it is hard to picture the consequences of physical processes taking place at high speeds. Compared with the Cosmos, gravity is weak on Earth and the motions we are subjected to are quite slow by comparison. For us, Newtonian Physics works well; for the Universe as a whole Einsteinian Physics and Quantum Mechanics are needed to gain a proper picture of its operations.

Here endeth the Preface. Go back now to the Cosmology subsection which has wide scope and much relevant information but is of necessity still so brief that only a broad-picture comprehension is likely to emerge if you, like most, lack the advanced knowledge and training so esoteric to cosmologists and astrophysicists. The "worlds" of quantum mechanics and relativity lie well beyond the experience of ordinary living and can only be adequately fathomed through mathematics. The realms of the extremely small and the extremely large are indeed bizarre. As a parting thought, keep in mind that Cosmology, like Astronomy and all Science, is still growing as it solves problems and uncovers principles that will inevitably modify the basic concepts already developed as working ideas. Thus, there are today competing models for Universe expansion, precepts for the early moments of "creation" are still being debated, and even the Big Bang itself is being questioned both in its details and, by a few, in its essential correctness. Cosmology remains an inexact science and is still a work in progress.

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