We live immersed in cycles of vastly different dimensions and scales. Not everything moves in cycles: some time successions show linear development, i.e. irreversible changes. Examples are the geological epochs, which do not repeat in cycles but show progression from stage to stage; and human cultural development from paleolithic to neolithic to bronze age to iron age, or from hunting/gathering to agriculture to industry. Another example of non-cycles is the cascade or relay, often seen in chains of successive causation, such as hormone cascades or historical/political events. Nevertheless cycles abound, from the daily repetitions of night and day through annual repetitions of seasons to sunspot cycles to magnetic field reversals to supercontinent assembly/disassembly; at the short-duration end we have our cycles of breathing, heart-beat, and brain alpha waves.
In the following brief account, we outline some cycles, arranged in descending order of time duration. For completeness in indicating time scales, we include some non-cyclic progressions as well.
| 1. The longest cycle is one which we are not sure exists. It exists only if our universe is “closed”, i.e. if it contains enough matter that it will eventually stop expanding and start to contract, finally to the same singularity with which it began 10 billion years ago; that is, it will have gone from the Big Bang to the Big Crunch. That in itself is not yet a cycle, only a progression. However, if the Big Crunch of our own universe is then followed by the formation of the next universe, possibly different in some of its properties; and if there is then a succession in time of these universes, each expanding and shrinking in turn, then we have a cycle going. Since we don’t even know if this is happening or will happen (we may not be the first universe in the series), it is impossible to assign a duration to this cycle; but let us take a leap and say: | 100 billion years. |
| 2. The star cycle is the evolution of stars from their formation to their end, as either white dwarfs, neutron stars, or black holes. For each star it is a progression and not a cycle, but taking the aggregate of stars, we see a repetition of events. The nature and duration of the progression for each star depends on its initial mass and temperature. Stars which have already ended were the big hot ones, that run through their life spans faster. Our Sun, being medium size, has a long time to go. Smaller stars will last even longer. As a rough range, let us give this a time duration of about | 10 million to 1 billion years. |
| 3. The supercontinent cycle on Earth. Through the motion of tectonic plates on the Earth surface, the supercontinent Pangea has periodically assembled itself, with only the world ocean around it In the next stage Pangea starts rifting and then the pieces drift apart, leading to the wide dispersal of several separate continents (as is the case now). In time the smaller oceans between the continents start closing again and Pangea is reassembled (the shapes and sizes may differ somewhat). This cycle has already repeated several times in the Earth’s history. Average duration of this cycle is | 500 million years. |
| 4. Cycle of the mass extinctions on Earth. These are less regular than the previously mentioned cycles. If we count 8 such extinction waves (Cambrian 505 million years ago (mya), Ordovician 438 my a. Devonian 360 mya, Permian 248 my a (by far the most severe, wiping out 96% of all species), Triassic 213 mya, Jurassic 144 mya, Cretaceous (dinosaurs) 65 mya, and present), the average period can be estimated as about | 50 million years. |
| It should be mentioned that some theorists found a period of 26 million years, and ascribe the mass extinctions to periodic meteorite showers resulting from the invasion of the inner solar system by comets from the great comet belt outside the orbit of the outermost planets, Neptune and Pluto. (The Oort cloud.) A theory has been advanced to explain these periodic comet showers as due to the close approach of the Sun’s twin star, postulated to be in a very long and thin elliptical orbit. This twin star, which no one has ever seen, has been named Nemesis. Most scientists, however, doubt this explanation, ascribing the mass extinctions to purely geological factors, such as rising sea levels, ice ages, or continents passing over the poles; or accidental isolated meteorite impacts. | |
| 5. Magnetic field reversal of the Earth’s magnetic field has been mapped from the orientation of tiny magnetite crystals in rocks of known age. On the seafloor on each side of the Mid-Atlantic Ridge, for example, can be seen strips of alternating magnetic directions. Since the Mid-Atlantic Ridge is a spreading centre, seafloor rocks get progressively older as their distance from the ridge increases. The Earth’s magnetic field reverses from time to time because of events in the outer core, which is composed of molten iron. The field is generated there by a “geo-dynamo” mechanism, but its configuration can flip because of changes in the internal “weather”. This is not quite predictable, but the time period is about | 1 million years. |
| 6. The ice ages alternating with warmer inter-glacial periods form another cycle. The mechanisms are still under study; but an ice age is probably initiated by a positive feedback loop, where some factor causes cooling, which forms more polar ice, which drops the sea levels and changes the ocean currents, so that there are more nutrients at the ocean surface; then there is more photosynthesis at the ocean surface and the land surface (which got bigger), therefore less carbon dioxide in the atmosphere, therefore less greenhouse effect, therefore lower temperatures…and so on. Eventually this vicious cycle is broken by an effect in which the weathering of rocks releases carbon dioxide and we warm up to the next inter-glacial period. Average period of this cycle might be about | 100,000 years. |
| 7. Precession of the Earth’s axis (a slight wobble), which changes the position of the Sun along the Zodiac at different seasons of the year. For example, before 2000 BC, the Sun was in Taurus at the Spring Equinox; in Greco-Roman times it was in Aries (where astrological charts still routinely place it); (there was a legend about “the slaying of the bull”); now it is just finishing a period of being in Pisces in March; and in 2200 AD it will be in Aquarius. (This is why new-age people talk about the coming of the Age of Aquarius, the Aquarian conspiracy, etc.). The full cycle (from Taurus back to Taurus) takes about 26,000 years, while movement from one sign of the Zodiac to the next takes l/12th of that time, about 2,100 years. | 26,000 years – 2,100 years |
| 8. Here we leave the realm of astronomy and geology for a while and turn to human history. Next is the cycle of civilizations, as described by Arnold Toynbee, and also recently by Dorothy Baker. Each civilization goes through stages; according to Toynbee these are: genesis, rise or growth, zenith, breakdown, disintegration; according to Baker (who as a dramatist uses the stages of classical Greek drama as her model), they are: exposition, progression, climax, and resolution. Each civilization (Baker uses 8 of them) goes through its own unique progression, but taken over all civilizations we observe a cyclic pattern. The periods differ in length, but the average duration of each civilization is about | 1,000 years |
| 9. Within individual civilizations there is the alternation of ideational, idealistic, and sensate culture as outlined by Pitirim Sorokin. He traced these in the Greco-Roman and in the modem Western civilization, but perhaps they exist in other civilizations also. In the ideational culture, people concentrate on the spiritual aspects of life and give religion the top priority, in art, music, literature, politics, and daily life. The early Middle Ages in Europe is an example. In the sensate culture, material aspects are uppermost in the pursuit of all concerns. We live in a sensate culture now, though perhaps it is beginning to fade. The idealistic culture is a mid-point between the ideational and the sensate, perhaps like the Italian Renaissance. While each phase of this cycle may last about 300 years, the total duration of the cycle is again about | 1,000 years. |
| 10. Turning now to international politics, we see the so-called “long cycle” of hegemonic power. In each turn of the cycle, there is a top (hegemonic) power (a part played by Portugal, Netherlands, Britain (twice), USA in succession), a challenger power (Spain, France, (twice), Germany, USSR), and a global war to begin and end each period. The challenging power does not necessarily become the next hegemonic power; e.g. Spain challenged Portugal, but Netherlands inherited the power; Germany challenged Britain, but the mantIe went to the USA; and now, USSR challenged USA, but the mantle may go to Japan – who knows? But sometimes, the challenger becomes the successor, and sometimes the hegemon keeps its power for another term, as Britain did. This cycle of world hegemony began only with the rise of the modem nation state (about 1517 AD), and so has run through 5 periods only. It has not always been with us, and if the world reorganizes, it may not persist in the future. It actually cannot continue unmodified, because of the “global war” feature, which now would not be survivable. The duration of one turn of this cycle is about | 100 years. |
| 11. Turning now to economics, we come to the Kondratieff cycle. The world economy goes through structural cycles set in motion by technology. The years 1780 to 1840 were characterized by the loom and the spinning jenny; in brief, the textile industry. The years 1840 to 1897 were dominated by steel and the steam engine; i.e. heavy machinery industry. The years 1897 to 1950 featured electricity, chemicals, and the automobile. The present time since 1950 may be described in terms of electronics, computers, space, and nuclear energy. Note that we are describing successive stages of the industrial revolution. To this day, newly industrializing countries begin with the textile industry, as the Pacific Rim NICs (newly industrialized countries) did, and then proceed to further stages, maybe skipping over the heavy machinery stage (which the USSR under Stalin still emphasized) to go straight to the third and fourth stage. The period of this cycle is about | 50 years. |
| 12. The economic boom-bust cycle is of indefinite length, and has changed since the Great Depression of the 1930s. One reason for the change was the application of Keynesian policies by governments (now in disrepute or at least disuse), which decreased the amplitude. Another reason has been the “permanent war economy” (Seymour Melman’s term) since World War II, which caused inflation and recession to coexist as “stagflation”. If the cycle is still there, we can estimate its period as about | 25 years. |
| 13. Here we are back in astronomy, with the sunspot cycle. Periodically, magnetic storms appear at the Sun’s surface which appear as dark spots, because they are cooler than the surroundings (ca. 6000 degrees K). These storms interact with the Earth’s ionosphere via the solar wind (a stream of electrons from the Sun in which we are immersed) and interfere with radio reception, as well as having other effects. The period is | 11 years, i.e. close to 10 years. |
| 14. We can be quite brief now with the more familiar cycles. The next is the cycle of seasons in the temperate zones: spring, summer, autumn, and winter. This is also the cycle of spring equinox. summer solstice, autumn equinox, and winter solstice. Many religious holidays are placed close to these dates: Easter and Passover in spring, the Witches’ Sabbath or “Walpurgis Nacht” in summer, harvest festivals or Thanksgiving in autumn, and Christmas or Hanukkah in winter. The interval of course is | 1 year. |
| 15. The cycle of the Moon, from full moon to waning to new moon to waxing back to full mOOIL This corresponds to the revolution of the Moon around the Earth. By coincidence (?), its length corresponds to the timing of the estrus cycle in human females. Many myths have been woven around this. (See the preceding essay “Moontides”.) The period is of course | 28 days, or almost I month. |
| 16. The alternation of day and night, light and dark, wakefulness and sleep, gives us a very basic rhythm by which to live. Disruptions cause difficulties, as in jet lag (travel across time zones) or shift work. We are tuned by the circadian rhythm in our bodies to the Earth’s rotation around its axis. We are deeply imprinted as Earth creatures. The time of this cycle is | 1 day. |
| 17. The tides on the oceans and seas, ruled by the Moon and the Sun, occur with regularity. The periods differ somewhat, but are close to | 12 hours. |
| 18. Our breath (a cycle of in and out) varies in duration with our degree of activity or excitement, but is about | 5 seconds. |
| 19. Our heart-beat (a cycle of contractions of the two ventricles and the two auricles in tum) is about 70 beats a minute, i.e. a period of about | 1 second. |
| 20. The alpha waves in our brain (the basic “scan” pattern with eyes closed) have a frequency of about 10 cycles per second, i.e. a period of | 0.1 seconds. |
If rhythm is the essence of music (even the pitch of a tone is a vibration frequency), we and our planet and our universe live immersed in music.