Cosmology and the Origin of Life

A Scientific Perspective:

Three biases from this perspective:

Scientific models are only validated through observation and prediction

Science itself is a process which maps out the unknown. It is not a process that converts the unknown to the known nor is it a method to discover the "truth".

There is nothing perfect about SCIENCE. Its beauty and truth lie in its intrinsic uncertainty.

So lets' start around 600 BC. By this time Greek Culture was quite well defined and the idea of Law, as a means of establishing order was firmly in place. If society itself could be "governed" by a set of rational laws, then clearly Nature must be similarly governed.

Hellenistic Culture(~600 B.C.):

The ancient Greeks inherited astronomical records from the Babylonians and applied the data to construct a cosmological framework. Data was not just used for practical goals, such as navigation, but also to think of new experiments = natural philosopher.

Fine Tuning the Cosmos: Identifying its essential Ingredients

600 BC Greeks start to dissect the world into component pieces:

ORIGINAL IDEA ALERT:
• All the world can be understood as an interaction between 4 primal elements (variation on the earlier theme)

• Air, Earth, Fire, Water

  • Thales Water: world floats in primordial sea
  • Anaximenes Air is ultimate: stars are fires in the sky

Now we have CAUSE and EFFECT and the first hints of the physical nature of the Universe.

There are three components to cause and effect:

• contiguity in space
• temporal priority of the cause (i.e. its first)
• necessary connection

An Alternative to the idea that something is most important:

500 BC:

Democritus: The Universe consists of atoms and the Void; all else is opinion and illusion

Collisions between atoms formed the Universe

The Universe runs by Itself

ORIGINAL IDEA ALERT

Quantum Mechanics has just been expressed. That is, the universe can exist without anyone in it

The Greeks constructed their whole theory of the Universe on the concepts of numbers and shape, arithmetic and geometry. An example of this was when Empedocles discovered that there exist only 5 regular solids. This ultimately leads to Plato's Theory of Forms .

Plato, so impressed by the elgence of this discovery, then proposed that four of these solids correspond to the four atomic elements in the Universe (earth, water, air and fire). The fifth element corresponds to the Cosmos:

Now comes geometry and the concepts of perfection. Culturally this seems like a natural harmonious meld with the Cosmos:

Pythagoras Geometry! a² + b² = c²

• Earth is a sphere (which is a perfect figure)
• Planetary Motion is governed by geometric laws
• Geometry begets Harmony

To Plato, making a model for Astronomy seemed relatively simple. All one had to do was to provide an explanation which would account for the highly ordered motions of the planets as observed from the Earth.

Over time this lead to Aristotle's Cosmology of the Crystalline Spheres:

Aristotle and Plato:

In the center of the painting are Aristotle and Plato, Aristotle's hand level to the Earth symbolizing his realism view of Nature; Plato's hand pointed towards the heaven symbolizing the mystical nature to his view of the Universe.

Aristotle stands in the Greek philosophical tradition which asserts that nature is understandable. This tradition, opposed to the idea that nature is under the control of capricious deities which are to be appeased rather than understood, is one of the roots of science.

However, one must be careful to assert that nature is not completely understandable

Aristotle constructed his view of the Universe based on a intuitive feeling of holistic harmony. Central to this philosophy was the concept of teleology or final causation. He supposed that individual objects (e.g. a falling rock) and systems (e.g. the motion of the planets) subordinate their behavior to an overall plan or destiny.

His theory of motion flows from his understanding of matter as constituted of four elements: air, earth, fire, and water. Objects, being solid like earth, would tend to clump together with other solids (earth), so objects tend to fall to earth, their natural place. Thus, falling is a natural motion.

To avoid the idea that their is an infinite chain of causes, Aristotle argued that there must be an "unmoved mover," something which can initiate motion without itself being set in motion today we might call this gravity!

Aristotle introduces the Two Sphere Universe. This is a FINITE Universe that you can now draw the Universe on a piece of paper!

We have come a long way from the world view that everything had a common origin (e.g. the Cosmic Womb in the Mythic Universe):

The Earth lies at the Center of the Two Sphere Universe and everything revolves around it Huge Cultural Bias.

Furthermore, Aristotle tells us that the Universe is perfect and unchanging.

Clearly, imagination has now vanished. We have a deterministic model of the Universe (e.g. two spheres) and we think that all is figured out!

Now all is in harmony, the earth is at the center of the universe and the cosmos revolves around us in perfect contentment

Elements of the Universe at this time (Aristotle):

• Geocentric Cosmology and the Earth is Immobile.
• Stars and planets on perfect crystalline spheres that rotate around the Earth.
• Universe is perfect and Changeless

But there are observational problems:

• observed transient phenomena (comets, novae, variable stars) attributed to disturbances in the upper atmosphere of the earth

• Periodic changes in the brightness of the planets this had to be attributed to something intrinsic to the planet because the earth - planet distance did not vary under the the crystalline sphere model.

• Aristotelian model makes a definite prediction all planets and stars should move in the same direction . This means that any planet should always move in the same direction, with respect to the background stars (which are the coordinate system here). But Mars was known at that time to sometimes move in the opposite direction for a brief period of time (this is known as retrograde motion)

  Yet, the retrograde motion of Mars was well known at the time.

  

  Mars generally moves west to east (right to left) on the background of stars. But every 780 days it goes through period of 83 days during which it moves east to west against the stars, the retrograde motion.

  The retrograde period is centered around the time when Mars is in opposition - Mars is directly opposite the Sun. Thus, this phenomena could be established as repeatable and realiable after only a decade's worth of observations.

  

  Plato gave his students a major problem to work on.

  Their task was to find a geometric explanation for the apparent motion of the planets, especially the strange retrograde motion.

  One key observations is that near and during the time of retrograde motion, Mars appears significantly brighter in the sky than at other times What might this mean?

  Plato and his students were, of course, also guided by the Pythagorean Paradigm. This meant that regardless of the scheme they came up with, the Earth should be at the unmoving center of the planet motions.

  One student named Aristarchus violated that rule and developed a model with the Sun at the center. His model was not accepted because of the obvious observations against a moving Earth.

  
  
  Ptolemy to the Rescue?
  
  

  In order to preserve the geocentric cosmology of the time and to account for retrograde motion, Ptolemy had to make a model of epicycles. This makes the orbits of planets very complicated and violates the scientific search for simplicity.

  A visualation of epicycles:

  

  Thought Question: This model makes a prediction. What is that prediction?

  Full Animated Epicycle
  
  

  The Ptolemaic Moment will stand for about 1500 years with this model for planetary orbits remains unchallenged, partly because Ptolemy's model did improve the precision to which planetary positions could be predicted. Remember, however, the precision at measuring planetary positions was quite poor and therefore there was a large random error involved when comparing predictions with observations.

  The Ptolomaic model represents an excellent example of "cultural" bias in science. Most citizens of the cultural wanted to accept the idea of the Earth being the center of the Universe (i.e. the earth was special) and therefore observations were molded in such a way so as to preserve that cultural norm. (Things may not be very different today).

  Recall, there was a competing model of the time, that of Aristarchus of Samos (280 BC):

  ( Aristarchus of Samos (c. 310-230 BC), Greek astronomer, first to maintain that the Earth rotates and revolves around the Sun. On this ground, Cleanthes the Stoic declared that he ought to be indicted for impiety.

  Aristarchus' advanced ideas on the movement of the Earth are known from Archimedes and Plutarch; his only extant work is a short treatise, "On the Sizes and Distances of the Sun and Moon." The values he obtained, by using geometry, are inaccurate, because of faulty observations. Aristarchus found a more precise value for the length of the solar year.)

  
  

  Aristarchus was extremely clever and also figured out a way to determine the ratio of distances between the earth and the moon and the earth and the sun. While wrong, at least he reasoned that the sun was much farther from the earth than the moon.

  Problems for heliocentric theory:

  • Earth in motion??? can't feel it
  • no parallax seen in stars

    

  • geocentric = ego-centric = more "natural"

  Measuring the Circumference of the Earth:

  Eratosthenes (220 B.C.) - The early Greeks knew the Earth was a sphere based on the shadow of Earth on the Moon during lunar eclipses. Eratosthenes proceeded to use this information to measure circumference of Earth in the following manner; he knew that on a certain date that a stick placed in the ground at Syene cast no shadow. Whereas, a stick at Alexandria has a small shadow. Using simple ratios he showed the following:

  

  Geocentric model was so popular that it stood for 1500 years.