Lecture 0: A Philosophical and Historical Introduction to Astronomy

Don't Panic

Earthrise from Apollo 11, 1969jul16. Credit: NASA.

1. Caveat Emptor
2. Science in General
3. Physics
4. Physical Sciences
5. Astronomy

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Caveat Emptor

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Up from Earth's Centre through the Seventh Gate
rose, and on the Throne of Saturn sate;
And many a Knot unravel'd by the Road;
But not the Master-knot of Human Fate.

Rubaiyat of of Omar Khayyam, 5th edition, Verse XXXI by Omar Khayyam & Edward Fitzgerald

This lecture is somewhat idiosyncratic to the instructor as almost any ``philosophical'' discussion must be.

Everyone has their own take on things and their own nuances.

But on the other hand, the instructor doesn't think there is anything unusual or eccentric.

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Science in General

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Whole books are written about what science is: e.g., A. F. Chalmers' What is this thing called Science.

So offering a single short definition is always inadequate.

But how about:

The study of some set of objective objects and their relationships. OBJECTIVE meaning that the objects and relations are independent of the particular observers.

The study aims at a complete understanding which includes being able to predict the evolution of the systems of the objects to the past and the future.

Because a science studies objective things there is a GOLD STANDARD---the objective things themselves---against which theories in the science can tested.

This permits the scientific method.

A schematic diagram of the scientific method.

The diagram makes the scientific method look like a cycle, but it could also be regarded as an UPWARD SPIRAL.

[Note that scientific method in practice is history and full of messy contingencies.

In particular, the objective things are a GOLD STANDARD, but any given experiment can lie.

One should be as cautious about believing an experiment at the frontier of current understanding as about believing a speculative theory.

Experiments have to be confirmed, often many times, before one can be sure people arn't just making errors.

Think of cold fusion for example.

Some people thought they'd seen it for a little while before all the errors in their experiments were elucidated.]

On every sweep through the cycle, the theory and experiment/observation become more exact and/or more general and/or more far-reaching.

A science is thus PROGRESSIVE in that it approaches single objective goal.

Not all human endeavors are---not in the same sense anyway.

For example ART.

An artist may progress is realizing his/her vision.

Technique may progress: e.g., if you aim at painting with photographic realism, you can get closer.

But in general no: ART does not progress toward at single objective goal.

Is Neolithic cave art less progressed than Picasso?

Most people would probably say a comparison based on ``progressiveness'' is not relevant or enlightening.

Without being dogmatic, one could suggest that art evolves more like spreading out into different realms of experience and creation.

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Physics

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Physics, in brief, is the science of matter and motion.
[Light is usually not considered matter, but is considered in physics. But to be brief we can include light under matter. One could say ``stuff and motion,'' but that sounds weird and pedantic.]

The most exalted goal of physics is to find mathematically exact, eternal fundamental laws of nature.

FUNDAMENTAL in PHYSICS means JUST SO: i.e., something cannot be explained any further.

FUNDAMENTAL is a moving target though: over history laws that were originally posited as FUNDAMENTAL have been shown to be derivable or approximations to more FUNDAMENTAL LAWS.

We hope and believe that there is TRUE FUNDAMENTAL PHYSICS that we will discover---maybe in the not so distant future even---or maybe not---maybe never.

This TRUE FUNDAMENTAL PHYSICS is sometimes called the THEORY OF EVERYTHING or TOE---which is NOT a very good name, I think, since it is NOT a theory of everything as I explain below.

Most physicists are NOT involved in the study of FUNDAMENTAL PHYSICS, but in APPLIED PHYSICS in which physical laws are used to study actual systems and how they evolve.

ASTRONOMY can be described as a field of APPLIED PHYSICS.

Often the physical laws used in APPLIED PHYSICS are NOT the current fundamental laws.

Often we use NON-FUNDAMENTAL PHYSICAL LAWS that are sufficiently adequate for the system in question and are much SIMPLER to use that the current fundamental laws.

For example, Newtonian physics (which we will briefly cover in IAWL Lecture 5: Newton's Laws, Gravity, Orbits, Energy, Tides") is NOT fundamental---not any more that is---but for systems

1. much larger than atoms (which need quantum mechanics),
2. with speeds much less than the speed of light (which need special relativity),
3. with gravity much less intense than close to a black hole (which need general relativity),
4. and smaller than the observable universe (which need general relativity),

Newtonian physics is often completely adequate and is much simpler to use than MORE FUNDAMENTAL THEORIES.

I call Newtonian physics a true approximate theory: it is approximate, but within its realm of adequacy it is always right to some order of accuracy---often a very high order.

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Physical Sciences

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A PHYSICAL SCIENCE is one that is strongly dependent on physics which is itself the physical science par excellence.

Various kinds of APPLIED PHYSICS like ASTRONOMY could also be called PHYSICAL SCIENCES: the terminology is NOT rigid.

CHEMISTRY, GEOLOGY, METEOROLOGY are other important examples of PHYSICAL SCIENCES.

PHYSICAL SCIENCES often have to invoke laws or principles that are outside of physics: EXTRA-PHYSICAL PRINCIPLES to coin a new term.

Sometimes these EXTRA-PHYSICAL PRINCIPLES are just expedients because reducing some aspect of system to a description in term of PHYSICS is too difficult.

But some EXTRA-PHYSICAL PRINCIPLES are truly NOT reducible to PHYSICS in my opinion---and I think this is the common view.

I think the common term for such principles is emergent principles.

PHYSICS itself as it is defined actually contains what can be regarded as an important emergent principle: the 2ND LAW OF THERMODYNAMICS or the law of ENTROPY.

We will NOT do a deep description of this law, but we can say a few things.
1. An aphorism is that ``the 2ND LAW OF THERMODYNAMICS expresses the tendency of things left to themselves to go to heck.''

2. An important manifestation of the law is that heat always flows spontaneously from hot to cold and that left to itself a closed system tends to a state of THERMODYNAMIC EQUILIBRIUM: i.e., everything is at one temperature.

   You can make a reverse flow (e.g., in refrigerators), but that takes outside manipulation.

   This manifestation is very important in astronomy.

   Question: This is because:
   1. the universe is clearly badly out of thermodynamic equilibrium.
   2. the universe is clearly in thermodynamic equilibrium.

   
   
   Answer 1 is right.

   Stars are hot; space is cold: energy in the form of electromagnetic radiation is flowing from stars to space all the time.

3. 2ND LAW OF THERMODYNAMICS can be considered an emergent principle because it is believed it would apply in worlds (which might be called universe domains) with different true fundamental physics than our own. Such other universe domains may even exist is discussed in IAWL: Lecture 31: Cosmology.

Now there is probably no hard line, but most people would not regard BIOLOGY as a PHYSICAL SCIENCE even though BIOLOGY certainly depends on physics: living systems are made of matter and obey the laws of physics.

Certainly one argument against regarding BIOLOGY as a PHYSICAL SCIENCE is that emergent principles are so important in BIOLOGY.

A key---and sometimes controversial example---is the THEORY OF EVOLUTION BY NATURAL SELECTION.

Certainly this theory applies to physical bodies, but it could also apply in worlds that have different physics than our own.

THEORY OF EVOLUTION BY NATURAL SELECTION in computer calculations is used to find optimum solutions to problems where one treats the solutions as breeding entities.

The techniques are called genetic algorithm and genetic programming.

Both have seen considerable development and may well become very important both in future in scientific research, design, and solving everyday problems.

Other things that could be considered emergent principles are ``laws'' of consciousness, intelligence, ethics, the scientific method itself, and, perhaps, a lot of things.

A trivial, artificial example of emergent principles are the rules of CHESS.

All these principles are manifested by physical things, but one can imagine them manifested in worlds of quite different physics.

Emergent principles are often NOT expressible as exact mathematical statements. This is quite different from the laws of physics.

In my opinion---and I think it is not at all uncommon---the world cannot be reduced to PHYSICS.

This is why I think the TRUE FUNDAMENTAL PHYSICS should NOT be called the THEORY OF EVERYTHING: it is not a theory of everything.

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Astronomy

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ASTRONOMY is often cited as the oldest, empirical (i.e., based on observation), exact science.

One can quibble, but there really is no other candidate if one regards mathematics as an abstract science that is only applied in the empirical world.

In fact, historically the terms mathematician and astronomer (and astrologer too) were often regarded as near synomyns.

Up until the 19th century leading mathematicians were also often leading theoretical astronomers: e.g., Ptolemy (circa 100--175 CE), the greatest theoretical astronomer of Greco-Roman Antiquity, and Newton (1642/3--1727).

Ptolemy with an armillary sphere.

Newton of the Principia (1689).

How old is astronomy as an exact science?

Well there are moon-shaped cut marks on bones in groupings of order 30 from as long ago as 36,000 BCE that seem to be counts of days during a lunar month (No-xxiv).

[The mean lunar month is 29.53059 days (Cox-16). Thus a lunar month counted from first crescent to crescent could be 29 or 30 days or even longer if bad weather prevents one from seeing the actual first crescent.]

So plausibly exact astronomy---in a very modest sense---goes back tens of thousands of years.

Simple alignment astronomy is physically recorded in prehistoric monuments: the most famous is Stonehenge.

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Stonehenge as it remains.

Credit: Digital Imaging Project of Mary Ann Sullivan, Bluffton College; download site Digital Imaging Project's Stonehenge Gallery

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In ALIGNMENT ASTRONOMY you just record where objects rise or set over the horizon as seen from some specific place: e.g., the center of Stonehenge.

The ancient Britons were NOT literate, and so couldn't record there star lore any other way.

The ancient Mesopotamians could and have left extensive astronomical texts of observations and calculations: the most advanced of these come from circa 400 BCE--100 CE (Ne-30).

The calculations were to make predictions of astronomical phenomena which is something astronomers are still tasked with doing.

But we don't really know how the ancient Mesopotamians (or Babylonians) conceived of the universe.

Babylonian cosmos?

The ancient Greeks (circa 600 BCE -- 400 CE) also practiced astronomy and invented various models of the cosmos.

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The Parthenon seen from the west.

The Parthenon is on the Acropolis of Athens.

Credit: Digital Imaging Project of Mary Ann Sullivan, Bluffton College; download site Digital Imaging Project's Athenian Acropolis site.

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The dominant model of the cosmos was that of Aristotle (384--322 BCE) which became a philosophical dogma in Greco-Roman Antiquity, the Medieval Islamic and European societies, and in Europe up to the 17th century.

Aristotle, the supreme authority.

The ARISTOTELIAN COSMOS was completely vanquished by the NEWTONIAN MODEL OF THE SOLAR SYSTEM.

A cartoon of the Aristotelian cosmos.

In the course, of the 16th and 17th centuries we have the transformation to a heliocentric solar system and a quasi-infinite universe.

Newton's work was the completion of this transformation.

An important part of Newton's achievement was showing that the same physical laws that apply on Earth apply in space.

Question: This is:
1. obvious.
2. not at all obvious: on Earth, things fall down; in space from the perspective of the Earth, they move in circles.



Answer 2 is right in my opinion anyway.

Certainly, in the Aristotelian cosmos the physics of Earth and Heaven are different.

The unification of terrestrial and celestial physics finally made astronomy somewhat experimental.

We can NOT do experiments on stars, galaxies, etc.

But experiments on Earth do reveal aspects of the physics of space.

In fact, the unification of terrestrial and celestial physics is what has vastly increased the knowability of the universe.

[Further astronomical history can be found in IAWL Lecture 4: The History of Astronomy to Galileo.]