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1. Aristotle, the Greek philosopher whose ideas influenced the whole of the western world for over two thousand years, proposed this arrangement circa 350 BCE.

2. Galileo is the Italian philosopher and scientist (1564-1642) who is also famous for dropping balls of different weights from the Tower of Pisa. (Thus again proving that Aristotle was wrong. Aristotle had stated that heavy objects fall faster than light ones.)

3. Galileo was lucky that nothing worse was ordered for him. A few decades before, in February 1600, an Italian philosopher-monk named Giordano Bruno was burned at the stake by the Catholic Church for saying that the Earth moved around the sun. (Bruno also thought, as Epicurus did, that the universe must contain other planets that orbited distant stars.)

4. About three-quarters of observed galaxies are spiral, with arms containing enormous quantities of dust (the birthplace and material of new stars). Spiral galaxies (and possibly all others) appear to contain an unknown dark matter (whose possible presence explains why stars in galaxies rotate faster than can be accounted for by the observable matter within their galaxies).
Current theories hold that dark matter constitutes about thirty percent of the total matter within the universe. Observations made using the Hubble telescope suggest that much of the dark matter associated with galaxies may be due to the presence of ancient white dwarfs (the burnt-out remnants of normal stars). Dark matter has been detected and mapped by observing its gravitational-lensing effects upon the shapes of some 200,000 distant galaxies; it appears to be distributed in a honey-comb-like manner throughout the universe.

5. See “The Evolution of Galaxy Clusters,” by J. Patrick Henry, Ulrich G. Briel and Hans Bohringer in Scientific American, December 1998, 52-57.

6. Andromeda, a spiral galaxy just 2.2 million light-years away, is expected to collide with our galaxy in approximately two billion years time.

7. Our sun is less than half this age.

8. Newton (1642-1727) was the first to scientifically investigate why white light, when passed through a glass prism, splits into a rainbow-like band of colours (called a spectrum). His writings nicely demonstrate how much can be deduced from careful observation of a seemingly minor phenomenon. (This text can be read in a sidebar (“Newton on Light and Colors”) under “Newton, Sir Isaac” in the Encarta Reference Library 2002 (Microsoft Corporation).

9. Spectra often show patterns of dark bands. These bands are caused by the absence (or presence) of chemical elements, either in the emitting source or along the path that the light has taken. This property is used by instruments called spectrometers to detect and measure the presence of minute traces of chemicals, and has applications in forensic, industrial, and research laboratories, as well as astronomical observatories.

10. A shift toward the red end of the spectrum means that the wavelength of light has increased (i.e., has been stretched out) as its source moves away from us. We are all familiar with this as we hear its effects with sound waves. Sound from a police car siren or from the horn of a train, for example, is heard at a higher pitch as the source moves toward us (because this forward movement compresses the sound waves and they arrive at our ears more closely spaced together); as the source passes by and moves away from us, the pitch rapidly drops to a lower frequency. Wave frequency change due to relative motion is called the Doppler effect.

11. Edwin Hubble (1889-1951) showed this in 1929 by graphing galactic red shift against their distance from the Milky Way. (The Hubble Space Telescope was so named to honour the discoverer of this very significant observation.)

12. See Fred Hoyle, The Nature of the Universe (Oxford: Basil Blackwell, 1950).

13. Gases cool when they expand and heat up when compressed (as is readily noted when using a hand pump to inflate a bicycle tire). Refrigerators exploit this property, using a pump to compress a gas outside the refrigerator (usually in tubes on the back, where excess heat dissipates into the environment) and allowing the gas to expand, and therefore cool, inside (usually in tubes surrounding the freezer box).

14. Since light from the most distant galaxies we can observe takes over thirteen billion years to reach us, the Big Bang must have occurred before then.

15. Matter and energy are different aspects of the same thing (as E = mc2 informs us), and one can be turned into the other. (The symbols E, m, and c, stand for energy, mass, and the speed of light, respectively. Since c is so very large, and is multiplied by itself in this equation, a tiny piece of matter is equivalent to a very large amount of energy. Thus, it takes a very large amount of energy to produce a speck of matter.)

16. This radiation has since been accurately measured (by instruments on the COBE, or Cosmic Background Explorer, spacecraft) to be energy at three degrees above absolute zero. Calculations of the temperature changes which residual radiation would undergo over time following the Big Bang predict precisely this temperature.
Another COBE experiment mapped the universe’s very early energy distribution, and found small ripples that could have been the variations that led to the formation of galaxies and galactic clusters. (If the originating Big Bang radiation was perfectly uniformly distributed, the specks of matter that formed from it [via E = mc2, or rather, m = E/c2] would also have been perfectly uniformly distributed, and gravitational pulls on each speck would have balanced on every side. In such a case, there would have been no gravitationally caused condensation, and therefore no stars, galaxies, planets, life, or us.)
Recent measurements of the polarization of cosmic background radiation provides additional evidence of the veracity of the Big Bang theory.

17. Quasars are enormously bright objects located toward the edge of our universe, and look similar to stars (hence their name—“quasi-stella”). Quasars existed only within the first few billion years or so of our universe’s formation. They depended upon the presence of supermassive black holes (gigantic agglomerations of matter about one hundred million times more massive than our sun). Each quasar emitted massive amounts of energy (the light we are seeing now, billions of years later—typically about three times more radiation than is currently emitted by the sum total of all of the stars in our galaxy). Electromagnetic radiations from quasars were produced by electrically charged matter (i.e., gases, stars, star clusters and even galaxies) spinning around the black hole before being swallowed. (Once inside a black hole’s boundary—the “event horizon”—nothing can escape, not even light; hence the name, black hole.)

18. One intriguing argument against the idea that the universe could have existed forever, as required by the Steady State theory, is that we have not been overrun by visiting aliens, either directly or by way of von Neumann probes. (These are devices that technologically competent life forms will be able to construct that explore planetary systems and use what they find to replicate themselves many-fold, before moving on again.) Of course, this argument fails if we are the only intelligent beings in the universe.
For more about self-replicating machines, see John von Neumann (A. W. Burks, ed.), Theory of Self-Reproducing Automata (Urbana: University of Illinois Press, 1966).

19. See Donald Goldsmith, The Runaway Universe: The Race to Find the Future of the Cosmos (Perseus Publishing, 2000).

20. Also known as “dark energy”—named (as is dark matter) because it cannot be seen.
Space is not a void as most assume; it is filled with a form of energy called dark or vacuum energy. This energy exerts a very weak negative gravitational force that builds in magnitude as the intervening space increases. Its weak nature explains why its repulsive force needs trans-universe distances to have any affect. Vacuum energy may owe its existence to a dynamical quantum field (similar to an electro-magnetic field) called “quintessence,” or it may be an inert property of empty space (accounted for by the cosmological constant), a possibility first proposed by Einstein.
Dark energy accounts for about 65% of the universe’s mass. Normal matter, of which we and everything we see are made, amounts to only 4%. Dark matter (see earlier) accounts for the rest.

21. Inflation theory suggests that the energy contained within the universe’s gravitational field exactly equals in amount, but opposes in type, the energy contained within all other constituents of the universe (photons and particles, etc.). Thus, since they balance out, the universe could have been created from nothing. This poses questions such as: “what existed to cause nothing to become something?” and, “are nothing and something one and the same thing, and if so, just what does that mean?”

22. Theoretically, many inflation-causing bubbles could occur, each growing to contain a universe. Each universe would be discrete and unique, and each could perhaps be controlled by physical laws different from those that control events in our universe.
Current thoughts about the beginning of our universe (and the possibility that it could be only one of many) are presented by Martin Rees in “Exploring Our Universe and Others,” in the December 1999 issue of Scientific American, 78-83. (This article also provides a pictorial summary of the evolution of our universe from its beginning to its possible ending.)
See also Theories of Everything: The Quest for Ultimate Explanation by John D. Barrow (New York: Oxford University Press. 1990). This thought-provoking book explores the significance of the initial conditions, laws, constants, and other critical factors, in the development of our understanding of what makes the universe behave the way we observe it behaving. Barrow makes a somewhat difficult subject enjoyable to readers as he describes the thinking of philosophers, mathematicians and scientists, from the early days of science to the quantum theories of the present.

23. Our “gigantic” universe is mostly space. It has been calculated that, if all the space separating galaxies, stars, electrons from nuclei in atoms, etc., were removed, then the whole of the universe’s matter would occupy a volume less than that enclosed by a sphere whose radius equalled the distance between our sun and Mars.

24. This assumption may be incorrect. Recent measurements of the absorption spectra shown by light that passed less than a billion years after the Big Bang through gas clouds containing metallic atoms, suggest that the electronic charge at that time differed slightly from today’s value. This does not mean that the laws of physics have changed, but it does warn us to be careful about the assumptions we make: values thought to be constant, may not actually be so.

25. 10-37 is shorthand for 1 divided by 1037, a very tiny fraction of anything.

26. In other words about one thousandth of a second, a relatively short period of time for what transpired. This “inflationary” period immediately followed the energy insertion we call the Big Bang. (The whole episode might be compared to the rapid inflation of an automobile air-bag that follows the detonation of its initiating charge.)

27. This inflationary behaviour explains the homogeneity of the cosmos by showing that it could have resulted from the universe’s initial uniformity being preserved by the rapidity of its expansion.
An excellent description of inflation is given in Michael White and John Gribbin’s book, Stephen Hawking: A Life in Science (London: Penguin Books, 1992).

28. This is because, to produce the amount of matter we observe in our universe today, the initial radiation energy density—and thus its temperature—must have been so high that any matter forming would have been immediately broken apart by radiation bombardment.

29. Neutrons, protons, and other particles of matter, would have formed from little packets of energy much earlier, but they would have been immediately broken apart by collisions with highly energetic radiation quanta.

30. Smoot and Davidson summarize existing theories about events during various time periods, particularly the initial seconds following the Big Bang, in two colourful plates (between pages 182-183) of their book. See George Smoot and Keay Davidson, Wrinkles in Time: The Imprint of Creation (Little, Brown and Company (U.K.) Ltd., 1993).

31. The extremely high early temperatures forced hydrogen nuclei to fuse together and form helium. This early fusion stopped after expansion sufficiently lowered the temperature, and the universe was left with the 23-24% helium content we now find throughout space. (Although fusion continues in the centre of stars, next to none of the helium produced by this means escapes into space.)

32. There are many millions of black holes in our galaxy alone. They range in size from small, just a few times larger than our sun, to supermassive. Supermassive black holes can contain millions or billions of times more matter than our sun.
The Chandra X-ray satellite telescope has determined (by analyzing radiations from objects twelve billion light-years distant from the Earth) that twelve billion years ago the universe teemed with billions of active supermassive black holes sucking up gas, stars, and debris. This same telescope has recently confirmed that our galaxy, the Milky Way, rotates around a supermassive black hole (this one some two and a half million times more massive than our sun). A different detection method (red-shift spectrography) has found more than thirty supermassive black holes in our neighbourhood, including one in Andromeda. Many (if not all) galaxies rotate around supermassive black holes, most of which have engulfed much of the matter in their vicinity and thus become dormant.

33. See “The First Stars in the Universe,” by Richard B. Larson and Volker Bromm, Scientific American, December 2001, 64-71, for an alternative, computer-generated, account of early star formation.

34. Published in 1905, Einstein’s E = mc2 equation explains the origin of the large amounts of energy our sun and the stars release, although the particular sequence of events occurring in a star’s core was not deduced until theoretical work was conducted leading to the atomic bomb in the 1940’s.

35. The power of an atomic bomb comes from atomic fission (splitting apart), whereas the vastly greater power of a hydrogen bomb comes from atomic fusion (joining together).
It is relatively simple to make atomic bombs using radioactive isotopes of uranium, because they are constantly splitting apart (with each split releasing energy, other emissions, and neutrons, which then bang into and split other atoms—producing the so-called chain reaction). All that’s required is to drive together pieces of uranium (the more radioactive, “enriched” isotope U-235, is used). (The difficulty stems from finding a way to force the lumps together sufficiently quickly that many atoms split before the resultant energy release pushes everything too far apart [which stops the chain reaction]. This problem was solved by detonating a containing shell of conventional explosives.)
It is slightly more difficult to force enough hydrogen atoms together to make a hydrogen bomb. Physicists succeeded by exploding an atomic bomb and using the extremely high pressure this developed to compress surrounding tritium (an isotope of hydrogen that contains two, rather than one, neutrons in its nucleus). Squeezed tightly enough together, tritium atoms fuse to form slightly lighter atoms of helium; the small amount of extraneous matter is expelled in the form of large amounts of energy.

36. The announcement that “cold fusion” was possible created much excitement a few years ago. Many thought, for a while, that everyone could one day have a little fusion reactor in their home, turning hydrogen gas into an unlimited amount of cheap energy. (Energy generated this way would be cheap because the hydrogen gas used as fuel can be produced by electrolytically splitting water—which requires significantly less energy than that released when hydrogen is fused to form helium.)
Unfortunately, the experimental results could not be repeated: nuclear fusion cannot be achieved in the way proposed. (This cost-benefit does not apply to hydrogen fuel cells. The amount of electrical energy required to produce the fuel hydrogen exceeds that released when it is later combined with oxygen in fuel cells. Automobile companies are gearing up to use fuel cells in transportation because fuel cell emissions are pollution-free [and because of government legislation], not because hydrogen provides low-cost energy.)

37. Hydrogen was more plentiful earlier in the universe’s life, and stars were generally bigger than they are today. Larger stars burn faster and have a shorter life.

38. It was earlier proposed that hypernova, about a hundred times larger than the average supernova, could occur and be the source of extremely intense gamma-ray bursts (GRBs) of energy that have been detected, but GRBs are now thought to signal the birth of black holes.

39. The remnants of a supernova recorded by Chinese astronomers as occurring July 4, 1054 CE, can still be seen in the Crab Nebula. When first observed, it remained bright enough to be visible during the day for more than three weeks. (Since the Crab Nebula is 6,300 light-years away, the supernova actually exploded 6,300 years before it was first observed on Earth.)
On February 24th, 1987, astronomers observed a star, known to have been about twenty times more massive than our sun, exploding as a supernova. The emissions from its remains are being carefully monitored to learn more about the processes involved.

40. The visible universe is calculated to be approximately 13.7 billion years old.

41. There are so many stars in the universe that modern telescopes would be able to detect supernovae occurring every minute, if they were aimed in the right direction.

42. Most stars pair up to form binary (or larger) systems and orbit each other around a common centre of gravity. Single stars, like our sun, are the exception, rather than the rule. Binary systems would produce complex effects on orbiting planets, and this might affect the number of planets supporting life forms.

43. Part of Orion’s sword, the Great Orion Nebula (about 1500 light-years distant from us) contains a star-forming region. About 700 young stars lie within the centre of this nebula, and some 150 of these are surrounded by rings of gas and dust particles that herald the future formation of planetary systems (see section five of this chapter [[1]]).

44. Asteroids are pieces of matter that have been left over from this process. Most of our sun’s asteroids move in an elliptical orbit (the asteroid belt) between the orbits of Mars and Jupiter. Significantly more of the early dust from which our planetary system originated still orbits the sun as chunks of dust and ice outside Pluto (the Oort Belt). These lumps can be displaced from their orbits by passing stars, and some have taken up elliptical orbits around the sun, occasionally becoming visible as comets.

45. However, some planets have been observed directly by telescopes (see http://www.eso.org/outreach/press-rel/pr-1998/pr-18-98.html).

46. Two planets (with a strong likelihood of there being a third occupying a life-favourable position) have been found to orbit the star 55 Cancri, by this method.

47. Light-bending was predicted by Einstein’s General Theory of Relativity (published in 1916). When a solar eclipse occurred in 1919, a team of astronomers used the opportunity to check the theory’s accuracy. As the moon blocked the sun’s radiance, they were able to photograph light coming from stars located behind the sun. Since the sun itself lay on a straight line drawn between these stars and the Earth, this could only happen if the light from these stars bent, as predicted, as it travelled close to the sun.

48. Some of the light from the star HD 209458 is periodically blocked by a planet that orbits it.

49. The thousands of gaps in Saturn’s rings are likely to have been created by satellites of various sizes. Saturn has about twenty confirmed moons, an additional dozen or so possible ones, plus millions of smaller chunks formed from frozen gas and water.

50. The planet that orbits Boötis has been investigated in this manner.

51. The same process (i.e., radioactive decay of elements such as plutonium) is used to provide heat (subsequently converted into electrical energy) in satellites sent to inspect planets that are too remote from the sun to allow effective use of solar panels.
It is conjectured that radioactive elements in the Earth’s core created an atomic reactor that still operates, keeping the core molten even though heat is continually being lost through the Earth’s mantle. See Brad Lemley, “Nuclear Planet,” Discover, August 2002, 36-42. For information on naturally occurring nuclear reactors, see http://nuclearplanet.com/.

52. Calculations involving the rate of radioactive decay, as well as the amount and kind of decay products, give scientists one method of dating the Earth’s beginning. For instance, analysis of the decay products of uranium isotopes found locked within zircon crystals from the Jack Hills section of north-western Australia, shows that these particular crystals are between 4.3 and 4.4 billion years old.

53. Just a little cooler than the temperature at the sun’s surface. (The temperature of the sun’s core is very much hotter—about 16,000,000C.)

54. See “The Sound of One Rock Falling,” Discover, February 2002, 18.

55. A “purpose” of sorts can also be determined within open systems by examining the “feedback” received from their significant supersystem. Outputs that are accepted imply that the supersystem “wants” more of the same, thus providing a “purpose” or reason to continue their production. Outputs that are rejected by the supersystem cannot be exchanged for needed supplies so production must eventually cease. Thus, production of acceptable outputs (i.e., fulfilling the “purpose” of meeting the supersystem’s requirements) is a necessity for continued existence. (However, we should note that large supersystems, such as our biosphere, can tolerate lengthy periods of non-productivity [and even negative contributions] from a portion of their subsystems, just as organizations can from a few of their employees. This buffering capacity can disguise the true state of affairs and “false purposes” may be followed for long periods of time before becoming apparent.)
See “General Systems Theory,” a postscript to Chapter Seven for further elaboration of these concepts.

56. This is not as surprising as it may at first seem, because, if superstring theory is correct, absolutely everything in existence is built from miniscule, vibrating, energy fields.

57. In fact, if any religion placed God in this position and was content to have Him play no part in our affairs, then such a religion would survive any form of investigation or attack. (But then, such a God wouldn’t meet our current psychological needs at all.)

58. And surely any Designing God must have therefore also desired all to unfold exactly as it does. In such a case, it could be considered rather impertinent of us to ask Him to intervene to satisfy our own fleeting desires.

59. If the universe is simply part of something that has always existed, then the reason it exists needs no explanation—the continued existence of something needs no more accounting for than the continued existence of nothing. Only changes of state need explaining (for example, where something exists which did not exist before).

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