UNIVERSE

‌The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang Theory is the prevailing cosmological description of the development of the Universe. The earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center.

Earliest Conceptions of the Universe

All scientific thinking on the nature of the universe can be traced to the distinctive geometric patterns formed by the stars in the night sky. Even prehistoric people must have noticed that, apart from a daily rotation (which is now understood to arise from the spin of Earth, the stars did not seem to move with respect to one another: the stars appear “fixed.” Early nomads found that knowledge of the constellations could guide their travels, and they developed stories to help them remember the relative positions of the stars in the night sky. These stories became the mythical tales that are part of most cultures.

When nomads turned to farming, an intimate knowledge of the constellations served a new function—an aid in timekeeping, in particular for keeping track of the  seasons. People had noticed very early that certain celestial objects did not remain stationary relative to the “fixed” stars; instead, during the course of a year, they moved forward and backward in a narrow strip of the sky that contained 12 constellations constituting the signs of the Zodiac. Seven such wanderers were known to the ancients: as the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn. Foremost among the wanderers was the Sun: day and night came with its rising and setting, and its motion through the zodiac signaled the season to plant  and the season to reap.  

 Next in importance was the Moon: its position correlated with the tides, and its shape changed intriguingly over the course of a month. The Sun and Moon had the power of gods; why not then the other wanderers? Thus probably arose the astrological belief that the positions of the planets (from the Greek word planetes, “wanderers”) in the zodiac could influence worldly events and even cause the rise and fall of kings. In homage to this belief, Babylonian priests devised the week of seven days, whose names even in various modern languages (for example, English, French, or Norwegian) can still easily be traced to their origins in the seven planet Gods.

Astronomical Theories of the Ancient Greeks

The apex in the description of planetary motions during classical antiquity was reached with the Greeks, who were of course superb geometers. Like their predecessors, Greek astronomers adopted the natural picture, from the point of view of an observer on Earth, that Earth lay motionless at the center of a rigidly rotating  celestial sphere (to which the stars were “fixed”), and that the complex to-and-fro wanderings of the planets in the zodiac were to be described against this unchanging backdrop. They developed an epicyclic model that would reproduce the observed planetary motions with quite astonishing accuracy.

The model invoked small circles on top of large circles, all rotating at individual uniform speeds, and it culminated about 140 CE with the work of Ptolemy, who introduced the ingenious artifact of displaced centers for the circles to improve the empirical  fit. Although the model was purely kinematic and did not attempt to address the dynamical reasons for why the motions were as they were, it laid the groundwork for the paradigm  that nature is not capricious but possesses a regularity and precision that can be discovered from experience and used to predict future events.

‌ The application of the methods of Euclidean geometry, to planetary astronomy, by the Greeks led to other schools of thought as well. Pythagoras, (c. 570–c. 490 BCE), for example, argued that the world could be understood on rational principles (“all things are numbers”); that it was made of four elements—earth, water,  air,  and fire; that Earth was a sphere; and that the Moon shone by reflected light.

In the 4th century BCE Heracleides Ponticus, a follower of Pythagoras, taught that the spherical Earth rotated freely in space and that Mercury and Venus revolved about the Sun. From the different lengths of shadows cast in Syene and Alexandria at noon on the first day of summer, Eratosthenes (c. 276–194 BCE) computed the radius of Earth to an accuracy within 20 percent of the modern value.

‌ Starting with the size of Earth’s shadow cast on the Moon during a lunar eclipse, Aristarchus of Samos (c. 310–230 BCE) calculated the linear size of the Moon relative to Earth. From its measured angular size, he then obtained the distance to the Moon. He also proposed a clever scheme to measure the size and distance of the Sun. Although flawed, the method did enable him to deduce that the Sun is much larger than Earth. This deduction led Aristarchus to speculate that Earth revolves about the Sun rather than the other way around.

Unfortunately, except for the conception  that Earth is a sphere (inferred from Earth’s shadow on the Moon always being circular during a lunar eclipse), these ideas failed to gain general acceptance. The precise reasons remain unclear, but the growing separation between the empirical and aesthetic branches of learning must have played a major role. The unparalleled numerical accuracy achieved by the theory of epicyclic motions for planetary motions lent great empirical validity to the Ptolemaic system.

Henceforth, such computational matters could be left to practical astronomers without the necessity of having to ascertain the physical reality of the model. Instead, absolute truth was to be sought through the Platonic  ideal of pure thought. Even the Pythagoreans fell into this trap; the depths to which they eventually sank may be judged from the story that they discovered and then tried to conceal the fact that the square root of 2 is an irrational number  (i.e., cannot be expressed as a ratio of two integers). source credits to  Encyclopedia Britannica

Everything in the Universe is Connected. You are the Universe. The World is our Identity

‌ THINGS YOU MAY NOT KNOW: The universe's first stars ignited some 180 million years after the BIG BANG,  the explosive moment 13.8 billion years ago that marks the Origins of the Universe as we know it. Gravity had sculpted the first galaxies into shape by the time the universe turned 400 million years old, or less than 3 percent of its current age.

THINGS YOU MAY WANT TO SAVE: Our very own Universe!  Not enough cloud space to save all of the Universes, but who knows what the future will bring?

ZENTRAVELER SAYS: Everything in the Universe is Connected‌.

From here to Infinity is a relatively short ride! The next leg takes eons and eons as you fly through the Barycentric Dynamical Time Zone! …and on and on and on.  Follow the Zentraveler Newsletter often for Travel, Health and Zen-like stories  and such. Where else can you get a THREE IN ONE NEWSLETTER FOR THE PRICE OF FREE.

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