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What the universe looked like in the 14th century.
The Ptolemaic system

Geocentrism is the belief that the sun, the planets and all the stars revolve around the Earth. It used to be the standard model of the universe from ancient times until the 16th-17th centuries, when new evidence (especially after the invention of the telescope) convinced most "natural philosophers" (i.e. scientists) that the Earth revolved around the sun instead.

Religious institutions took longer to be convinced, with some of them still endorsing geocentrism centuries after it became laughably discredited. And, believe it or not, a few cranks still hold on to it today. You can thank the Old Testament for the lingering belief in this one. It has at least four verses claiming that the earth "cannot be moved," and one stating that the sun goes around the earth. It should not be confused with egocentrism, which is the belief that the sun, the stars, the other planets and the Earth all revolve around oneself.


[edit] History

Ptolemy's universe with added cherubs.

Geocentrism was the standard model throughout the Western world during antiquity, the Middle Ages and the Renaissance.

Aristarchus of Samos was the first person to challenge the geocentric model, suggesting a heliocentric universe in the third century BCE but he had little following. Ptolemy's theory of the solar system placed all celestial bodies orbiting around the Earth, with epicycles introduced to compensate for the retrograde motion of planets such as Mars.

The ancient Greeks noted that if the Earth did move around the sun, the stars should appear to shift their positions from one part of the year to the next, a phenomenon they failed to observe. Alternatively the stars would have to be so ridiculously far away that the shift in position was too small to be seen by the naked eye, which would make for a ludicrously large empty space between the most distant planet, Saturn, and the "fixed stars". Measurements dependent on naked-eye instruments could detect a parallax of something like one arc-minute, which meant that the distance to the "fixed stars" had to be at least 700 times larger than the distance to Saturn if the Earth moved around the sun.[1]:201 The ancient Greeks dismissed this possibility as absurd, but of course, today we know that the stars are in fact much farther away than that.

Some late medieval scholars, notably Nicholas of Cusa and Nicolas Oresme, brought up the possibility that the Earth might move, but Copernicus was the one who really revived heliocentrism in 1514, drawing on Aristarchus.[2] Galileo Galilei promoted the Copernican theory, provoking hostility from the Church who denounced it as heresy. Probably due to this controversy, Copernicus's book was still listed on the Index (the list of books banned by the Catholic Church) between 1616 and 1758.

[edit] Victory of heliocentrism

It was a mixture of different reasons that led to the final victory of heliocentrism (symbolized by the Catholic Church's capitulation in 1758). In 1551, the astronomer Erasmus Reinhold published the Prutenic Tables[wp], astronomical tables, computed by the Copernican model, which were an improvement on tables based on Ptolemaic astronomy. In 1588, Tycho Brahe published his compromise system, Geo-Heliocentrism[wp], which some took as a desperate move to save geocentrism. (Another compromise which is rarely mentioned today is to have the Earth make a daily rotation, but remain fixed at the center, with no annual orbit of the Sun.) Galileo's telescopic observations (announced beginning in his 1610 Starry Messenger[wp]) revealed a heavens different from the traditional conceptions: the phases of Venus, mountains on the Moon, satellites of Jupiter and spots on the Sun. The heavens could never again be regarded as totally different from Earth. Johannes Kepler improved on the Copernican theory and provided better predictions of planetary movements than the Ptolemaic system could. Newton's 1687 Principia[wp] put the mechanics of the Solar System on a secure mathematical and physical basis: gravity and momentum were the same everywhere. By 1729, it was an anticlimax when James Bradley discovered stellar aberration[wp], measuring the orbital speed of the Earth in orbit.[3][1]

[edit] For the Bible tells us so

Page from a Luther Bible which someone has helpfully scrawled on.

Geocentric is suggested in several Biblical passages, depending on how these passages are interpreted. In order of appearance, the verses are:

  • Joshua 10:12-13: On the day the LORD gave the Amorites over to Israel, Joshua said to the LORD in the presence of Israel: "O sun, stand still over Gibeon, O moon, over the Valley of Aijalon." So the sun stood still, and the moon stopped, till the nation avenged itself on its enemies, as it is written in the Book of Jashar. The sun stopped in the middle of the sky and delayed going down about a full day.
  • 1 Chronicles 16:30: Fear before him, all the earth: the world also shall be stable, that it be not moved.
  • Psalm 19:6: It [the sun] rises at one end of the heavens and makes its circuit to the other; nothing is hidden from its heat.
  • Psalm 93:1: The LORD reigneth, he is clothed with majesty; the LORD is clothed with strength, wherewith he hath girded himself: the world also is established, that it cannot be moved.
  • Psalm 96:10: Say among the heathen that the LORD reigneth: the world also shall be established that it shall not be moved: he shall judge the people righteously.
  • Psalm 104:5: (Bless the LORD . . .) Who laid the foundations of the earth, that it should not be removed for ever.
  • Ecclesiastes 1:5: The sun also ariseth, and the sun goeth down, and hasteth to his place where he arose.

It is difficult to explain these as obvious metaphors, when for a couple of thousand years, up until the beginnings of modern science, no one commented on their being metaphors. Everyone believed that the Sun went around a stationary Earth, and thought that that was what the Bible was saying.

[edit] What the Bible does not tell us

The Bible has little interest in the planets. And no one suggests that the Tychonian model of the Solar System is supported by the Bible. However, it is also not true that the Bible supports any model of the movements of the planets; not, in particular, the Ptolemaic system. In fact, as Galileo pointed out, if one carefully examines the story of Joshua, it is inconsistent with the motion of the Sun in that model.[4] One must go beyond the Bible for any model of the movements of the heavens.

[edit] Modern geocentrism

In the modern world, small subsets of Biblical literalists and other scientifically illiterate cranks promote some form of geocentric worldview, although the details of their explanations vary.

Geocentric models claim the earth does not move at all, which means that the entire universe revolves around the earth daily. (This would mean that the stars and galaxies revolve around the Earth once every 24 hours, despite modern astronomy demonstrating that they are many light-years away and would therefore have to race round faster than light.[5]) A person can take a relativistic view, that "all motion is relative", and claim one cannot tell the difference between the earth being in motion and it being fixed. This has the drawback that it rescues the Bible's statements from being false by saying that they are meaningless. This is generally felt not any better.

The Tychonian system. How could anyone living today mistake this for a sensible compromise?

Twenty-first century believers in a fixed earth may distance themselves from the Ptolemaic system of epicycles. Some call their model "geocentricity" in an attempt to make that clear. They may prefer a "compromise" position first suggested by Tycho Brahe: the sun revolves around the Earth, but the planets revolve around the sun. The Bible says nothing about the motions of the planets (and the stars), so any description of the movements of the heavenly bodies can fit the Bible, as long as the Earth is fixed and the sun is in a closed path around the Earth. Robert Sungenis, founder of Catholic Apologetics International, is an example of an influential modern geocentrist.

In addition to the minority of stubborn fundamentalists who insist on a geocentric model for dogmatic reasons, there are also a substantial number of undereducated people who hold a kind of passive geocentrism for ignorance, believing (if they even think about it at all) that the sun must orbit the Earth daily because that is what we appear to see. (As to what the stars are doing, who notices or cares what they are doing? In a light-polluted city night, what's the last time you saw a star?) According to recent polls in the United States, Great Britain and Germany, between 16% and 19% of people actually believe the sun goes round the earth.[6]

In early 2016, the rapper B.o.B. made news when he tweeted his geocentrist view to his millions of twitter followers. The incident brought this eccentric view into the spotlight, and motivated Neil DeGrasse Tyson to engage in a twitter and rap battle with him[7]. Astrophysicist Lawrence Krauss wrote in Slate such views can be useful — even if grotesque — when they can be used to check our assumptions. He proposes three easy ways where everyone can test geocentrism.[8]

[edit] Debunking geocentrism

Modern geocentrists cite 19th century experiments which tried to measure the movement of the Earth, and got a zero answer. Such were the Michelson-Morley experiment[wp] and the use of a water-filled telescope by George Biddell Airy[wp], two experiments meant to evidence aether, a hypothetical medium in which light would propagate. Alas both failed, as light seems to be content with no medium at all. Hopefully, the special theory of relativity perfectly accounts for these results in a heliocentric model. The modern rejection of geocentrism can be fairly described by (borrowing a phrase from Dobzhansky), "Nothing in astronomy makes sense except in the light of heliocentrism", leaving the geocentrists with casting doubt on particulars in isolation.

If, however, one decides to play the game that the geocentrists want, one ought to be aware that they have answers for many of the obvious arguments against geocentrism. Whether or not their answers are sufficient, one should be aware that in pursuing these lines, one is playing on the geocentrists' home field, where they are likely more familiar with the arguments. (If one is as familiar as they are, after all, guidance from is not needed.)

[edit] Geocentrists' replies to arguments against their position

What the universe looked like in the 15th century.

Geocentrists have some common replies to common arguments against their position:

  • They will argue, correctly, that pictures from outer space showing the Earth in motion can be explained by the relative motion from the camera, not absolute motion of Earth.
  • They will argue that phenomena that reveal the motion of the Earth, such as the Foucault pendulum[wp] and the Coriolis effect[wp], are accounted for by appealing to something like Mach's principle[wp], by which any consequence of rotation of the Earth is the same as would occur with the movement of the "fixed stars" around a fixed Earth.
  • Phenomena such as the phases of Venus and Mercury and the apparent retrograde motion[wp] of Mars (and of the more distant planets) present no problem to modern geocentrism, for it typically adopts Tycho's model (in which those planets orbit the Sun).
  • Any geometric configuration of the Solar System, and thus any kinematic description of its motions, and any dynamic equations which have the Sun as the center, can equally (if not conveniently) be described with a coordinate system with the Earth as the zero point, for example in suitably chosen Lagrangian[wp] coordinates. (This is done within classical Newtonian mechanics.) Yes, this requires that there be postulated an extraordinary force, which has no known evidence, one which critics would call "ad hoc". For geocentrists, that is worth it. (It has the benefit, for the geocentrists, that few people can follow the mathematics at this point, and those who can are beyond hope of taking geocentrism seriously, anyway.)
  • Objects as far away as Neptune (whose orbit has a radius of 4 light-hours) would have to move faster than the speed of light to circle the Earth in 24 hours. In response, geocentrists will appeal to the Theory of General Relativity, which permits objects to take on any speed under special circumstances.[9]
  • We read about how a major earthquake changes the rotation of the Earth, which proves that the Earth really has a rotation. The geocentrists point out, however, that that is only a calculated estimate, and that we do not have the technology to measure the small differences that are involved.[citation needed] Even if this correlation with earthquakes should become measurable, as long as the cause of earthquakes are not well enough known to predict earthquakes, one cannot rule out that a change in the rotation of the heavens is the cause of earthquakes, or that there is a common cause for both.

[edit] Daily rotation of the Earth

See the main article on this topic: Rotation of the Earth
And now something a bit nearer to the truth.

One important counterargument to geocentrism is that the rotation of the Earth isn't completely smooth: there is a slight deviation (the Chandler wobble[wp]). The planet's rotation speeds up and slows down slightly and the point of its axis changes a little.[10]

Heliocentrists can explain this easily: the Earth moves. And as physical conditions change, the motions of the Earth change.

Geocentrists have to imagine that the stars and galaxies all wobble in (what appears to us) synchronicity while Earth stays still. Since these stars and galaxies are millions of light years[11] apart, however, their wobbles must all occur in the same pattern, but at different times according to their distance from Earth so that the light from these different objects reaches us at exactly the same time making it look simultaneous (for example, the apparent wobble of a star 10 light years away would actually be our observation of its wobble 10 years ago, in synchronicity with a coordinated wobble of another star somewhere across the universe 5 light-years in another direction, but that second star only wobbled 5 years ago).

Such a universe model seriously strains credibility.

[edit] Position of the Earth at the center of the universe

In the 14th century, Jean Buridan considered the motion of the Earth, but decided against it. But he did propose an argument against the center of the universe being the center of the Earth (that, after all, is the literal meaning of "geocentrism"). He observed that the Earth is not symmetrical, that land predominates in one hemisphere (his own) and water in the antipodes. Then, when there is erosion of land into the water, there is a shift in the location of the center of gravity of Earth, which, if the center of gravity of the Earth was the center of the universe, would require a motion of the Earth to compensate for the change.[3]:165[12]

[edit] Denial of the Copernican principle

The geocentric documentary, The Principle, also brings up the later development from heliocentrism, that the Earth is not special, in any way, from anywhere else in the universe. This is more of a guiding principle than something which can be evidenced. Instances of it include:

  • The elimination of the Aristotelian distinction between the sub-lunar sphere of: ordinary matter, earth, water, air and fire; from the lunar sphere (and beyond) of celestial aether. This, we hope, has been established finally and without doubt by interplanetary rockets, as if there were any doubt since Newton. If one wants to deny that astronauts walked on the Moon, does one also deny the reality of exploration of Mars and all sorts of Solar System objects? Interplanetary rockets, made of terrestrial matter, behave like heavenly bodies when they enter the realm of the heavens. Meteorites (and photons and cosmic rays) behave like terrestrial matter when they land on Earth.
  • What is there which makes the Earth different from Mars? Mars is in motion, why not Earth?
  • The invariance of physical laws with respect to location. This is a consequence of Noether's theorem[wp] applied to conservation of momentum.

[edit] See also


[edit] External links

[edit] Footnotes

  1. 1.0 1.1 Thomas S. Kuhn (1957). The Copernican Revolution: Planetary Astronomy in the Development of Western Thought. Cambridge, MA: Harvard Unitversity Press. 
  2. Aristarchus of Samos
  3. 3.0 3.1 John Freely (2012). Before Galileo: The Birth of Modern Science in Medieval Europe. New York: Overlook Duckworth. ISBN 9781590206072. 
  4. Letter to Benedetto Castelli, 1613 December 21, in Maurice A. Finocchiaro (1989). The Galileo Affair: A Documentary History. University of California Press. pp. 49-55. ISBN 978-0-520-066662-5. 
  5. Actually, the problem of faster-than-light travel occurs at the position of the planet Neptune, which has a mean distance of about 4 light-hours, as can be measured by the radio delay of space probes, and thus a path length, circumference = 4×2π > 24 light-hours to traverse in a day.
  6. New Poll Gauges Americans' General Knowledge Levelsmodern medievalism: Geocentrism
  7. Watch Neil deGrasse Tyson Drop the Mic in His B.o.B Rap Battle
  8. How a Celebrity’s Silly Belief in Flat Earth Can Be Useful by Lawrence Krauss
  9. An Introduction to the Theory of Relativity, W. G. V. Rosser, London, Butterworths, 1964, p. 460
  10. What is the Chandler wobble?
  11. Well, of course, the geocentrists can claim, contrary to all the evidence, that stars are really only little mysterious points of light only a few light years away. (Remember, "nothing in astronomy makes sense except in the light of heliocentrism".) The argument still works, we're saying that stars are making this strangely coordinated dance, instantly changing so that their light will appear on Earth in synchrony. Even if the separation is a matter of as little as days, it is still demanding thousands of ad hoc changes which just happen to look like it is really the Earth which is changing its motions.
  12. Jean Buridan (1964). "Jean Buridan on the Diurnal Rotation of the Earth". Medieval Philosophy: Selected readings from Augustine to Buridan. New York: Modern Library. pp. 542-547.  [1]
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