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Worldviews: Part 2- Aristotelian to Newtonian Worldview


Chapter 9: The Structure of the Universe on the Aristotelian Worldview

Those holding the Aristotelian worldview (people before 1600’s) had a certain set of beliefs. Earth is the center of the universe, the moon followed, then the sun and planets, then the stars. Teleology and Essentialism were also big parts of the worldview. Teleology is the idea that scientific explanation is suitably done in terms of goals, purposes, or functions fulfilled. These teleological explanations are in contrast to mechanistic explanations.

Essentialism is the idea that all objects have essential natures that explain why they act as they do. The essential nature of most objects was thought to be teleological.

Chapter 10: The Preface to Ptolemy’s Almagest- the Earth as Spherical, Stationary, and the Center of the Universe

Ptolemy in his Almagest (150 AD) defended the idea that Earth is spherical (people believed this since the time of Plato ~ 400 BC), stationary, and the center of the universe. According to DeWitt, although these beliefs may appear hopelessly naive now, Ptolemy had strong reasons to believe as he did.

To support the Earth as a sphere, Ptolemy noted the differences in sunrise time in different areas of the Earth, and the change is uniform, in line with a sphere. Also ships and mountains appear to emerge out of the horizon.

The Earth is stationary because otherwise if you threw a ball into the air, it would fall away from you (commonsense physics). Also we do not notice reasonable signs of high speed, like winds or vibration. Also the Earth would eventually slow down, just as rocks and things do when not constantly acted upon. Lastly, no stellar parallax was viewed (I think this is almost decisive).

Earth being the center of the universe is supported mostly by gravity. No matter where you are on the sphere, things tend to go perpendicular to the surface- they seek the center of the Earth. Since objects naturally seek the center of the universe, the Earth must be the center of the universe.

Chapter 11: Astronomical Data- The Empirical Facts

Theories must be able to explain and predict the existing facts. So what is that existing empirical data?

  • The stars move on a repeating 24 hour pattern, and they stay in the same position relative to each other.
  • The sun moves in an arc from east to west, and the point where the sun rises moves north and south. The sun also changes position relative to the stars.
  • The moon goes through phases, and also changes position relative to the stars.
  • The planets are “wanderers” and also move relative to the stars in various ways.

Chapter 12: Astronomical Data- The Philosophical/Conceptual Facts

Some philosophical beliefs came into play in preserving the Aristotelian view. Heavenly bodies were believed to move perfect circles and move uniformly, not speeding or slowing. There was also the principle of motion, that objects naturally come to rest unless acted upon. Only agents can move continuously or spontaneously, which is where the teleology comes from.

Chapter 13: The Ptolemaic System

Ptolemy’s system from the Almagest was an Earth centered system that preserved the perfect circle and uniform motion “laws.” Ptolemy had most celestial bodies going in perfect circles around the Earth, although the Earth was not always in the exact center. Planets were a special case, so he had them traveling around an equant point. The travel also involved epicycles, a circle around a point which would revolve around the equant point in a circle itself. These epicycles added flexibility to the system to account for complex motions. There also had to be minor epicycles, cycles upon the epicycles, to account for further discrepancies.

Taking all these things into account led to a system that made predictions very close to observations.

Chapter 14: The Copernican System

1,400 years after Ptolemy, Copernicus came up with an alternate heliocentric system that still preserved the perfect circle and uniform motion “laws.” Copernicus could account for Mars’ retrograde motion in terms of the Earth passing Mars. Also the appearance of Venus near the sun was more easily explained by Venus’ close position.

The Copernican System was still basically the same in terms of complexity and predictive power.

Chapter 15: The Tychonic System

Tycho Brahe was convinced for reasons outlined above that the Earth is stationary, but he took many of Copernicus’ ideas into account. He had the sun and moon go around the earth, but the planets revolving around the sun. This solved at least some inconsistencies.

Chapter 16: Kepler’s System

Kepler took over Brahe’s data, and got rid of some basic assumptions, like the uniform motion and perfect circle “laws.” He came up with the ellipse shape to explain and predict the motion of the planets. He also created laws that were basically accurate, the first being that the planets revolve in an elliptical shape. His second law of planetary motion is that planets sweep out equal orbital areas in equal time. He did have a few more erroneous laws involving geometrical shapes in predicting the planetary orbits, but he got a lot right.

Chapter 17: Galileo and the Evidence from the Telescope

Galileo’s views were largely informed by information from the telescope. Importantly, none of the observations directly proved that the Earth is not stationary. Instead it challenged some basic assumptions and led to an abandoning of the Aristotelian worldview, opening the door for Newton.

Mountains on the moon and sunspots disproved the idea that celestial bodies are perfect. Saturn’s rings disproved the idea that planets, made of ether, must be perfect spheres. Moons around Jupiter answered the argument that the Earth around the sun plus the moon around the Earth would be awkward as a configuration. The phases of Venus was only explained if Venus is in closer orbit to the sun, because the phases align perfectly with this fact. The discovery of many more stars was evidence that the universe is more vast than previously thought.

Also worth noting is that the Catholic church, by and large, had a history of being tolerant of new scientific views. For example, for the most part the church was not opposed to the Copernican system. Of course, up until the new evidence from the telescope, the Copernican system was generally taken with an instrumentalist attitude, and as such was not contrary to scripture. But the point is that the church did not generally oppose new scientific views, and was generally willing to reinterpret scripture when required by new discoveries (3566).

Chapter 18: A Summary of Problems Facing the Aristotelian Worldview

If the issues from the above chapter show that the Earth is not the center of the galaxy, many long held ideas from the Aristotelian worldview are challenged. The tendency for objects to move toward the center of the universe no longer explains things falling. There has to be some explanation for Earth’s movement, and the fact that we don’t fly off the planet, or that things fall back in our hand when thrown upwards. Also challenged is the perfect sphere idea, and the relatively small universe.

All these issues and more opened the door for new explanations.

Chapter 19: Philosophical and Conceptual Connections in the Development of the New Science

In order to bridge the gap from Aristotelian to Newtonian worldviews, a few conceptual band-aids may have been necessary. An infinite or very large universe was wholly foreign. Thinkers like Giordano Bruno argued that an infinite universe was compatible with, or even necessitated by an infinite God. They also proposed the idea of atomism, which was more compatible with new ideas about inertia than Aristotelianism. This may have helped more people accept views that previously would have been unpalatable.

Chapter 20: Overview of the New Science and the Newtonian Worldview

Newton’s Principia marks the beginning of the New Science. The three laws of motion, as outlined in the Principia mark a significant departure from the Aristotelian worldview. First is the law of inertia- an object in motion tends to stay in motion; an object at rest tends to stay at rest unless acted upon by a force. Second, F=ma. Third, for any action there is an equal and opposite reaction.

Another “New Science” idea is universal gravitation. The force keeping the moon in orbit around the Earth is the same one that keeps the Earth in orbit around the sun and Jupiter’s moons in orbit around it.

Newton also marked a change from an essentialist and teleological view of the universe to a mechanistic view- the universe as a machine, or a clock.

Chapter 21: Philosophical Interlude- What is a Scientific Law?

Scientific laws are commonly seen as approximations of natural laws- fundamental features of the universe that make it work as it does.

Laws are commonly seen as being how things must behave without exception, not just how they happen to behave. They are also seen as objective, that is, in DeWitt’s view, independent of humans (I don’t really prefer this definition, but DeWitt acknowledges that there are different conceptions of the word). So according to him, chocolate mousse is subjective, but the orbit of Jupiter is objective.

Each of these aspects of scientific laws have some bizarre nuances.

Chapter 22: The Development of the Newtonian Worldview- 1700-1900

The more mechanistic Newtonian worldview worked its way into chemistry, biology, and electromagnetic theory in different ways over 1700-1900. Chemistry became less qualitative and more quantitative view in line with atomic theory. Biology abandoned vitalism, and embraced the idea that life broken into its elements is not different from non-life. Electricity and magnetism were unified. The Michelson-Morley experiments, black body radiation and x-rays all provided some early challenges to the so far hugely successful Newtonian worldview.

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