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mata kuliah English for Physics

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UNIVERSITAS JEMBER2013

GALILEO GALILEI

1. Brief Biography

Galileo was born on February 15, 1564 in Pisa. By the time he died on January 8,

1642 . He was as famous as any person in Europe. Moreover, when he was born there was

no such thing as ‘science’, yet by the time he died science was well on its way to becoming

a discipline and its concepts and method a whole philosophical system.

Galileo and his family moved to Florence in 1572. He started to study for the

priesthood, but left and enrolled for a medical degree at the University of Pisa. He never

completed this degree, but instead studied mathematics notably with Ostilio Ricci, the

mathematician of the Tuscan court. Later he visited the mathematician Christopher Clavius

in Rome and started a correspondence with Guildobaldo del Monte. He applied and was

turned down for a position in Bologna, but a few years later in 1589, with the help of

Clavius and del Monte, he was appointed to the chair of mathematics in Pisa.

In 1592 he was appointed, at a much higher salary, to the position of

mathematician at the University of Padua. While in Padua he met Marina Gamba, and in

1600 their daughter Virginia was born. In 1601 they had another daughter Livia, and in

1606 a son Vincenzo.

It was during his Paduan period that Galileo worked out much of his mechanics

and began his work with the telescope. In 1610 he published The Starry Messenger, and

soon after accepted a position as Mathematician and Philosopher to the Grand Duke of

Tuscany (and a non-teaching professorship at Pisa). He had worked hard for this position

and even named the moons of Jupiter after the Medici. There were many reasons for his

move but he says he did not like the wine in the Venice area and he had to teach too many

students. Late in 1610, the Collegio Romano in Rome, where Clavius taught, certified the

results of Galileo's telescopic observations. In 1611 he became a member of what is

perhaps the first scientific society, the Academia dei Lincei.

In 1612 Galileo published a Discourse on Floating Bodies, and in 1613, Letters on

the Sunspots. In this latter work he first expressed his position in favor of Copernicus. In

1614 both his daughters entered the Franciscan convent of Saint Mathew, near Florence.

Virginia became Sister Maria Celeste and Livia, Sister Arcangela. Marina Gamba, their

mother, had been left behind in Padua when Galileo moved to Florence.

In 1613 Galileo entered into discussions of Copernicanism through his student

Benedetto Castelli, and wrote a Letter to Castelli. In 1616 he transformed this into the

Letter to the Grand Duchess Christina. In February 1616, the Scared Congregation of the

Index condemned Copernicus' book On the Revolution of the Heavenly Orbs, pending

correction. Galileo then was called to an audience with Cardinal Robert Bellarmine and

advised not to teach or defend Copernican theory.

In 1623 Galileo published The Assayer dealing with the comets and arguing they

were sublunary phenomena. In this book, he made some of his most famous

methodological pronouncements including the claim the book of nature is written in the

language of mathematics.

The same year Maffeo Barberini, Galileo's supporter and friend, was elected Pope

Urban VIII. Galileo felt empowered to begin work on his Dialogues concerning the Two

Great World Systems. It was published with an imprimatur from Florence in 1632. Shortly

afterwards the Inquisition banned its sale, and Galileo was ordered to Rome for trial. In

1633 he was condemned.

In 1634, while Galileo was under house arrest, his daughter, Maria Celeste died. At

this time he began work on his final book, Discourses and Mathematical Demonstrations

concerning Two New Sciences. This book was smuggled out of Italy and published in

Holland. Galileo died early in 1642. Due to his conviction, he was buried obscurely until

1737.

2. Introduction and Background

For most people, in the 17th Century as well as today, Galileo was and is seen as the

‘hero’ of modern science. Galileo discovered many things with his telescope, he first saw

the moons of Jupiter and the mountains on the Moon; he determined the parabolic path of

projectiles and calculated the law of free fall on the basis of experiment. He is known for

defending and making popular the Copernican system, using the telescope to examine the

heavens, inventing the microscope, dropping stones from towers and masts, playing with

pendula and clocks, being the first ‘real’ experimental scientist, advocating the relativity of

motion, and creating a mathematical physics. His major claim to fame probably comes

from his trial by the Catholic Inquisition and his purported role as heroic rational, modern

man in the subsequent history of the ‘warfare’ between science and religion.

Since his death in 1642, Galileo has been the subject of manifold interpretations

and much controversy. The use of Galileo's work and the invocations of his name make a

fascinating history.

Philosophically, Galileo has been used to exemplify many different themes, usually

as a side bar to what the particular writer wished to make the hallmark of the scientific

revolution or the nature of good science. Whatever was good about the new science or

science in general, it was Galileo who started it. One early 20th Century tradition of

Galileo scholarship used to divvy up Galileo's work into three or four parts: (1) his

physics, (2) his astronomy, and (3) his methodology, which could include his method of

Biblical interpretation and his thoughts about the nature of proof or demonstration. In this

tradition, typical treatments dealt with his physical and astronomical discoveries.

Yet most everyone in this tradition seemed to think the three areas—physics,

astronomy and methodology were somewhat distinct and represented different Galilean

endeavors. More recent historical research has followed contemporary intellectual fashion

and shifted foci bringing new dimensions to our understanding of Galileo by studying his

rhetoric, the power structures of his social milieu, his personal quest for acknowledgment

and more generally has emphasized the larger social and cultural history, specifically the

court and papal culture, in which Galileo functioned.

In an intellectualist recidivist mode, this entry will outline his investigations in

physics, astronomy and exhibit, in a new way, how these all cohered in a unified inquiry.

At the end of his life, Galileo felt compelled (in some sense of necessity) to write the

Discourses Concerning the Two New Sciences, which stands as a true completion of his

overall project and is not just a reworking of his earlier research that he reverted to after

his trial, when he was blind and under house arrest.

3. Galileo's Scientific Story

The philosophical thread that runs through Galileo's intellectual life is a strong and

increasing desire to find a new conception of what constitutes natural philosophy and how

natural philosophy ought to be pursued. Galileo signals this goal clearly when he leaves

Padua in 1611 to return to Florence and the court of the Medici and asks for the title

Philosopher as well as Mathematician. This was not just a status-affirming request, but

also a reflection of his large-scale goal. What Galileo accomplished by the end of his life

in 1642 was a reasonably articulated replacement for the traditional set of analytical

concepts connected with the Aristotelian tradition of natural philosophy. He offered, in

place of the Aristotelian categories, a set of mechanical concepts that were accepted by

most everyone who afterwards developed the ‘new sciences’, and which in some form or

another, became the hallmark of the new philosophy. His way of thinking became the way

of the scientific revolution (and yes, there was such a ‘revolution’.

Some scholars might wish to describe what Galileo achieved in psychological

terms as an introduction of new mental models.However phrased, Galileo's main move

was to dethrone the Aristotelian physical categories of the one celestial (the aether or fifth

element) and four terrestrial elements (fire, air, water and earth) and their differential

directional natures of motion (circular,  and up and down). In their place he left only one

element, corporeal matter, and a different way of describing the properties and motions of

matter in terms of the mathematics of the equilibria of proportional relations (Palmieri

2001) that were typified by the Archimedian simple machines the balance, the inclined

plane, the lever, and includes the pendulum.In doing so Galileo changed the acceptable

way about matter and its motion, and so ushered in the mechanical tradition that

characterizes so much of modern science.

As a main focus underlying Galileo's accomplishments, it is useful to see him as

being interested in finding a unified theory of matter, a mathematical theory of the material

stuff that constitutes the whole of the cosmos. Perhaps he didn't realize that this was his

grand goal until the time he actually wrote the Discourses on the Two New Sciences in

1638. Despite working on problems of the nature of matter from 1590 onwards, he could

not have written his final work much earlier than 1638, certainly not before Starry

Messenger of 1610, and actually not before the Dialogues on the Two Chief World Systems

of 1632. Before 1632, he did not have the theory and evidence he needed to support his

claim about unified, singular matter. He had thought deeply about the nature of matter

before 1610 and had tried to work out how best to describe matter, but the idea of unified

matter theory had to wait on the establishment of principles of matter's motion on a

moving earth.

Galileo began his critique of Aristotle in the 1590 manuscript, De Motu. The first

part of this manuscript deals with terrestrial matter and argues that Aristotle's theory has it

wrong. For Aristotle, sublunary or terrestrial matter is of four kinds [earth, air, water, and

fire] and has two forms, heavy and light, which by nature are different principles of

(natural) motion, down and up. Galileo, using an Archimedian model of floating bodies

and later the balance, argues that there is only one principle of motion, the heavy

(gravitas), and that lightness (or levitas) is to be explained by the heavy bodies moving.So

on his view heaviness (or gravity) is the cause of all natural terrestrial motion. But this left

him with a problem as to the nature of the heavy, the nature of gravitas? In De Motu, he

argued that the moving arms of a balance could be used as a model for treating all

problems of motion. In this model heaviness is the proportionality of weight of one object

on one arm of a balance to that of the weight of another body on the other arm of the

balance. In the context of floating bodies, weight is the ‘weight’ of one body minus weight

of the medium.

Galileo realized quickly these characterizations were insufficient, and so began to

explore how heaviness was relative to the different specific gravities of bodies having the

same volume. He was trying to figure out what is the concept of heaviness that is

characteristic of all matter. What he failed to work out, and this was probably the reason

why he never published De Motu. There seemed to be no way to find standard measures of

heaviness that would work across different substances. So at this point he did not have

useful replacement categories.

A while later, in his 1600 manuscript, Le Mecaniche (Galileo 1600/1960) he

introduces the concept of momento, a quasi force concept that applies to a body at a

moment and which is somehow proportional to weight or specific gravity. Still, he has no

good way to measure or compare specific gravities of bodies of different kinds and his

notebooks during this early 17th century period reflect his trying again and again to find a

way to bring all matter under a single proportional measuring scale. He tries to study

acceleration along an inclined plane and to find a way to think of what changes

acceleration brings. In this regard and during this period he attempts to examine the

properties of percussive effect of bodies of different specific gravities, or how they have

differential impacts. Yet the details and categories of how to properly treat weight and

movement elude him.

One of Galileo's problems was that the Archimedian simple machines that he was

using as his model of intelligibility, especially the balance, are not easily conceived of in a

dynamic way. Except for the inclined plane, time is not a property of the action of simple

machines that one would normally attend to. In discussing a balance, one does not

normally think about how fast an arm of the balance descends nor how fast a body on the

opposite arm is rising.The converse is also true. It is difficult to model ‘dynamic’

phenomena that deal with the rate of change of different bodies as problems of balance

arms moving upwards or downwards because of differential weights. So it was that

Galileo's classic dynamic puzzle about how to describe time and the force of percussion, or

the force of body's impact, would remain unsolved, He could not, throughout his life find

systematic relations among specific gravities, height of fall and percussive forces. In the

Fifth Day of the Discouses, he presciently explores the concept of the force of percussion.

This concept will become, after his death, one of the most fecund ways to think about

matter.

In 1603, Galileo worked long at doing experiments on inclined planes and most

importantly with pendula. The pendulum again exhibited to Galileo that acceleration and,

therefore, time is a crucial variable. Moreover, isochrony equal times for equal lengths of

string, despite different weights someway towards showing that time is a possible form for

describing the equilibrium (or ratio) that needs to be made explicit in representing motion.

It also shows that in at least one case time can displace weight as a crucial variable. Work

on the force of percussion and inclined planes also emphasized acceleration and time, and

during this time. he wrote a little treatise on acceleration that remained unpublished.

We see from this period that Galileo's law of free fall arises out of this struggle to

find the proper categories for his new science of matter and motion. Galileo accepts,

probably as early as the 1594 draft of Le Mecaniche, that natural motions might be

accelerated. But that accelerated motion is properly measured against time is an idea

enabled only later, chiefly through his failure to find any satisfactory dependence on place

and specific gravity. Galileo must have observed that the speeds of bodies increase as they

move downwards and perhaps, do so naturally, particularly in the cases of the pendulum,

the inclined plane, in free fall, and during projectile motion. Also at this time he begins to

think about percussive force, the force that a body acquires during its motion that shows

upon impact. For many years he thinks that the correct science of these changes should

describe how bodies change according to where they are on their paths. Specifically, it

seems that height is crucial. Percussive force is directly related to height and the motion of

the pendulum seems to involve essentially equilibrium with respect to the height of the bob

(and time also, but isochrony did not lead directly to a recognition of time's importance.)

The law of free fall, expressed as time squared, was discovered by Galileo through

the inclined plane experiments, but he attempted to find an explanation of this relation and

the equivalent mean proportional relation, through a velocity-distance relation. His later

and correct definition of natural acceleration as dependent on time is an insight gained

through recognizing the physical significance of the mean proportional relation.Yet

Galileo would not publish anything making time central to motion until 1638, in

Discourses on the Two New Sciences .

In 1609 Galileo begins his work with the telescope. Many interpreters have taken

this to be an interlude irrelevant to his physics. The Starry Messenger, which describes his

early telescopic discoveries, was published in 1610. There are many ways to describe

Galileo's findings but for present purposes they are remarkable as his start at dismantling

of the celestial/terrestrial distinction.Perhaps the most unequivocal case of this is when he

analogizes the mountains on the moon to mountains in Bohemia. The abandonment of the

heaven/earth dichotomy implied that all matter is of the same kind, whether celestial or

terrestrial. Further, if there is only one kind of matter there can be only one kind of natural

motion, one kind of motion that this matter has by nature. So it has to be that one law of

motion will hold for earth, fire and the heavens. This is a far stronger claim than he had

made back in 1590. In addition, he described of his discovery of the four moons circling

Jupiter, which he called politically the Medicean stars (after the ruling family in Florence,

his patrons). In the Copernican system, the earth having a moon revolve around it was

unique and so seemingly problematic. Jupiter's having planets made the earth-moon

system non-unique and so again the earth became like the other planets.  Some fascinating

background and treatments of this period of Galileo's life and motivations have recently

appeared.

A few years later in his Letters on the Sunspots (1612), Galileo enumerated more

reasons for the breakdown of the celestial/terrestrial distinction. Basically the ideas here

were that the sun has spots (maculae) and rotated in circular motion, and most importantly

Venus had phases just like the moon, which was the spatial key to physically locating

Venus as being between the Sun and the earth, and as revolving around the Sun. In these

letters he claimed that the new telescopic evidence supported the Copernican theory.

Certainly the phases of Venus contradicted the Ptolemaic ordering of the planets.

Later in 1623, Galileo argued for a quite mistaken material thesis. In The Assayer,

he tried to show that comets were sublunary phenomena and that their properties could be

explained by optical refraction. While this work stands as a masterpiece of scientific

rhetoric, it is somewhat strange that Galileo should have argued against the super-lunary

nature of comets, which the great Danish astronomer Tycho Brahe had demonstrated

earlier.

Yet with all these changes, two things were missing. First, he needed to work out

some general principles concerning the nature of motion for this new unified matter.

Specifically, given his Copernicanism, he needed to work out, at least qualitatively, a way

of thinking about the motions of matter on a moving earth. The change here was not just

the shift from a Ptolemaic, Earth centered planetary system to a Sun centered Copernican

model. For Galileo, this shift was also from a mathematical planetary model to a

physically realizable cosmography. It was necessary for him to describe the planets and the

earth as real material bodies. In this respect Galileo differed dramatically from Ptolemy,

Copernicus, or even Tycho Brahe, who had demolished the crystalline spheres by his

comets-as-celestial argument and flirted with physical models. So on the new Galilean

scheme there is only one kind of matter, and it may have only one kind of motion natural

to it. Therefore, he had to devise (or shall we say, discover) principles of local motion that

will fit a central sun, planets moving around that sun, and a daily whirling earth.

This he did by introducing two new principles. In Day One of his Dialogues on the

Two Chief World Systems (Galileo 1632) Galileo argued that all natural motion is circular.

Then, in Day Two, he introduced his version of the famous principle of the relativity of

observed motion. This latter held that motions in common among bodies could not be

observed. Only those motions differing from a shared common motion could be seen as

moving. The joint effect of these two principles was to say that all matter shares a common

motion, circular, and so only motions different from the common, say up and down

motion, could be directly observed. Of course, neither of the principles originated with

Galileo. They had predecessors. But no one needed them for the reasons that he did,

namely that they were necessitated by a unified cosmological matter.

In Day Three, Galileo dramatically argues for the Copernican system. Salviati, the

persona of Galileo, has Simplicio, the ever astounded Aristotelian, make use of

astronomical observations, especially the facts that Venus has phases and that Venus and

Mars are never far from the Sun, to construct a diagram of the planetary positions. The

resulting diagram neatly corresponds to the Copernican model. Earlier in Day One, he had

repeated his claims from The Starry Messenger, noting that the earth must be like the

moon in being spherical, dense and solid, and having rugged mountains. Clearly the moon

could not be a crystalline sphere as held by some Aristotelians.

In the Dialogues, things are more complicated than I have just sketched. Galileo, as

noted, argues for a circular natural motion, so that all things on the earth and in the

atmosphere revolve in a common motion with the earth so that the principle of the

relativity of observed motion will apply to phenomena such as balls dropped from the

masts of moving ships. Yet he also introduces at places a straight-line natural motion. For

example, in Day Three, he gives a quasi account for a Coriolis-type effect for the winds

circulating about the earth by means of this straight-line motion. Further, in Day Four,

when he is giving his proof of the Copernican theory by sketching out how the three way

moving earth mechanically moves the tides, he nuances his matter theory by attributing to

the element water the power of retaining an impetus for motion such that it can provide a

reciprocal movement once it is sloshed against a side of a basin. This was not Galileo's

first dealing with water. In fact a large part of this debate turned on the exact nature of

water as matter, and what kind of mathematical proportionality could be used to correctly

describe it and bodies moving in it.

The final chapter of Galileo's scientific story comes in 1638 with the publication of

Discourses of the Two New Sciences. The second science, discussed (so to speak) in the

last two days, dealt with the principles of local motion. These have been much commented

upon in the Galilean literature. Here is where he enunciates the law of free fall, the

parabolic path for projectiles and his physical “discoveries”. But the first two days, the

first science, has been much misunderstood and little discussed. This first science,

misleadingly, has been called the science of the strength of materials, and so seems to have

found a place in history of engineering, since such a course is still taught today. However,

this first science is not about the strength of materials. It is Galileo's attempt to provide a

mathematical science of his unified matter. Galileo realizes that before he can work out a

science of the motion of matter, he must have some way of showing that the nature of

matter may be mathematically characterized. Both the mathematical nature of matter and

the mathematical principles of motion he believes belong to the science of mechanics,

which is the name he gives for this new way of philosophizing.

So it is in Day One that he begins to discuss how to describe, mathematically (or

geometrically), the causes of how beams break. He is searching for the mathematical

description of the essential nature of matter. He rules out certain questions that might use

infinite atoms as basis for this discussion, and continues on giving reasons for various

properties that matter has. Among these are questions of the constitution of matter,

properties of matter due to its heaviness, the properties of the media within which bodies

move and what is the cause of a body's coherence as a single material body. The most

famous of these discussions is his account of acceleration of falling bodies, that whatever

their weight would fall equally fast in a vacuum. The Second Day lays out the

mathematical principles concerning how bodies break. He does this all by reducing the

problems of matter to problems of how a lever and a balance function. Something he had

begun back in 1590, though this time he believes he is getting it right, showing

mathematically how bits of matter solidify and stick together, and do so by showing how

they break into bits. The ultimate explanation of the “sticking” eluded him since he felt he

would have to deal with infinitesimals to really solve this problem.

The sketch above provides the basis for understanding Galileo's changes. He has a

new science of matter, a new physical cosmography, and a new science of local motion. In

all these he is using a mathematical mode of description based upon, though somewhat

changed from, the proportional geometry of Euclid, Book VI and Archimedes The second

science, Days Three and Four of Discorsi, dealt with proper principles of local motion, but

this was now motion for all matter (not just sublunary stuff) and it took the categories of

time and acceleration as basic. Interestingly Galileo, here again, revisited or felt the need

to include some anti-Aristotelian points about motion as he had done back in 1590. The

most famous example of his doing this, is his “beautiful thought experiment”, whereby he

compares two bodies of the same material of different sizes and points out that according

to Aristotle they fall at different speeds, the heavier one faster. Then, he says, join the

bodies together. In this case the lightness of the small one ought to slow down the faster

larger one, and so they together fall as a speed less than the heavy fell in the first

instance.But one might also conceive of the two bodies joined as being one larger body, in

which case it would fall even more quickly. So there is a contradiction in the Aristotelian

position. His projected Fifth Day would have treated the grand principle of the power of

matter in motion due to impact. He calls it the force of percussion, which deals with two

bodies interacting. This problem he does not solve, and it won't be solved until Descartes,

probably following Beeckman, turns the problem into finding the equilibrium points for

colliding bodies.

It is in this way that Galileo developed the new categories of the mechanical new

science, the science of matter and motion. His new categories utilized some of the basic

principles of traditional mechanics, to which he added the category of time and so

emphasized acceleration. But throughout, he was working out the details about the nature

of matter so that it could be understood as uniform and treated in a way that allowed for

coherent discussion of the principles of motion. That a unified matter became accepted and

its nature became one of the problems for the ‘new science’ that followed was due to

Galileo. Thereafter, matter really mattered.

4. Galileo and the Church

No account of Galileo's importance to philosophy can be complete if it does not

discuss Galileo's condemnation and the Galileo affair. The end of the episode is simply

stated, in late 1632, after publishing Dialogues on the Two Chief World Systems, Galileo

was ordered to go to Rome to be examined by the Holy Office of the Inquisition. In

January 1633, a very ill Galileo made an arduous journey to Rome. Finally, in April 1633

Galileo was called before the Holy Office. This was tantamount to a charge of heresy, and

he was urged to repent. Specifically, he had been charged with teaching and defending the

Copernican doctrine that holds that the Sun is at the center of the universe and that the

earth moves. This doctrine had been deemed heretical in 1616, and Copernicus' book had

placed on the index of prohibited books, pending correction.

Galileo was called four times for a hearing; the last was on June 21, 1633. The next

day, 22 June, Galileo was taken to the church of Santa Maria sopra Minerva, and ordered

to kneel while his sentence was read. It was declared that he was “vehemently suspect of

heresy”. Galileo was made to recite and sign a formal abjuration:

“I have been judged vehemently suspect of heresy that is, of having held and believed that

the sun in the centre of the universe and immoveable, and that the earth is not at the center

of same, and that it does move. Wishing however, to remove from the minds of your

Eminences and all faithful Christians this vehement suspicion reasonably conceived

against me, I abjure with a sincere heart and unfeigned faith, I curse and detest the said

errors and heresies, and generally all and every error, heresy, and sect contrary to the Holy

Catholic Church.

Galileo was not imprisoned but had his sentence commuted to house arrest. In

December 1633 he was allowed to retire to his villa in Arcetri, outside of Florence. During

this time he finished his last book, Discourses on the Two New Sciences, which was

published in 1638, in Holland, by Louis Elzivier. He died on January 8, 1642.

There has been much controversy over the events leading up to Galileo's trial, and

it seems that each year we learn more about what actually happened. There is also

controversy over the legitimacy of the charges against Galileo, both in terms of their

content and judicial procedure. The summary judgment about this latter point is that the

Church most probably acted within its authority and on ‘good’ grounds given the

condemnation of Copernicus, and, as we shall see, the fact that Galileo had been warned

by Cardinal Bellarmine earlier in 1616 not to defend or teach Copernicanism. The were

also a number of political factors given the Counter Reformation, the 30 Years War and

the problems with the papacy of Urban VIII that served as further impetus to Galileo's

condemnation. It has even been argued that the charge of Copernicanism was a

compromise plea bargain to avoid the truly heretical charge of atomism. Though this latter

hypothesis has not found many willing supporters.

Legitimacy of the content, that is of the condemnation of Copernicus, is much more

problematic. Galileo had addressed this problem in 1615, when he wrote his Letter to

Castelli (which becomes known as the Letter to the Grand Duchess Christina). In this

letter he had argued that, of course, the Bible was an inspired text, yet two truths could not

contradict one another. So in cases where it was known that science had achieved a true

result, the Bible ought to be interpreted in such a way that makes it compatible with this

truth. The Bible, he argued, was an historical document written for common people at an

historical time, and it had to be written in language that would make sense to them and

lead them towards the true religion.

Much philosophical controversy, before and after Galileo's time, revolves around

this doctrine of the two truths and their seeming incompatibility. Which of course, leads us

right to such questions as: “What is truth?” and “How is truth known or shown?”

Cardinal Bellarmine was willing to countenance scientific truth if it could be

proven or demonstrated. But Bellarmine held that the planetary theories of Ptolemy and

Copernicus (and presumably Tycho Brahe) were only hypotheses and due to their

mathematical, purely calculatory character were not susceptible to physical proof. This is a

sort of instrumentalist, anti-realist position. There are any number of ways to argue for

some sort of instrumentalism. Duhem (1985) himself argued that science is not

metaphysics, and so only deals with useful conjectures that enable us to systematize the

phenomena. Subtler versions, without an Aquinian metaphysical bias, of this position have

been argued subsequently and more fully by van Fraassen (1996) and others. Less

sweepingly, it could reasonably be argued that both Ptolemy and Copernicus' theories were

primarily mathematical, and that what Galileo was defending was not Copernicus' theory

per se, but a physical realization of it. In fact, it might be better to say the Copernican

theory that Galileo was constructing was a physical realization of parts of Copernicus'

theory, which, by the way, dispensed with all the mathematical trappings (eccentrics,

epicycles, Tusi couples and the like). Galileo would be led to such a view by his concern

with matter theory. Of course, put this way we are faced with the question of what

constitutes identity conditions for a theory, or being the same theory. There is clearly a

way in which Galileo's Copernicus is not Copernicus and most certainly not Kepler.

The other aspect of all this which has been hotly debated is: what constitutes proof

or demonstration of a scientific claim? In 1616, the same year that Copernicus' book was

placed on the Index of Prohibited Books, Galileo was called before Cardinal Robert

Bellarmine, head of the Holy Office of the Inquisition and warned not to defend or teach

Copernicanism. During this year Galileo also completed a manuscript, On the Ebb and

Flow of the Tides. The argument of this manuscript will turn up 17 years later as day Four

of Galileo's Dialogues concerning the Two Chief World Systems. This argument, about the

tides, Galileo believed provided proof of the truth of the Copernican theory. But insofar as

it possibly does, it provides an argument for the physical plausibility of Galileo's

Copernican theory.

Galileo argues that the motion of the earth (diurnal and axial) is the only physical

cause for the reciprocal regular motion of the tides. He restricts the possible class of causes

to mechanical motions, and so rules out Kepler's attribution of the moon as a cause. How

could the moon without any connection to the seas cause the tides to ebb and flow. Such

an explanation would be the invocation of magic or occult powers. So the motion of the

earth causes the waters in the basins of the seas to slosh back and forth, and since the

earth's diurnal and axial rotation is regular, so are the periods of the tides; the backward

movement is due to the residual impetus built up in the water during its slosh. Differences

in tidal flows are due to the differences in the physical conformations of the basins in

which they flow.

Albeit mistaken, Galileo's commitment to mechanically intelligible causation

makes this is a plausible argument. One can see why Galileo thinks he has some sort of

proof for the motion of the earth, and therefore for Copernicanism. Yet one can also see

why Bellarmine and the instrumentalists would not be impressed. First, they do not accept

Galileo's restriction of possible causes to mechanically intelligible causes. Second, the

tidal argument does not directly deal with the annual motion of the earth about the sun.

And third, the argument does not touch anything about the central position of the sun or

about the periods of the planets as calculated by Copernicus. So at its best, Galileo's

argument is an inference to the best partial explanation of one point in Copernicus' theory.

Yet when this argument is added to the earlier telescopic observations that show the

improbabilities of the older celestial picture, to the fact that Venus has phases like the

moon and so must revolve around the sun, to the principle of the relativity of perceived

motion which neutralizes the physical motion arguments again a moving earth, it was

enough for Galileo to believe that he had the necessary proof to convince the Copernican

doubters. Unfortunately, it was not until after Galileo's death and the acceptance of a

unified material cosmology, utilizing the presuppositions about matter and motion that

were published in the Discourses on the Two New Sciences, that people were ready for

such proofs. But this could occur only after Galileo had changed the acceptable parameters

for gaining knowledge and theorizing about the world.

Source : http://plato.stanford.edu/entries/galileo/

TERMS IN THIS ARTICLE

1. Acceleration = Percepatan

2. The Incline Plane = Bidang miring

3. Sun Spots = Bintik-binti matahari

4. Crystalline Spheres = Bola kristal

5. Balance = Keseimbangan

6. In Free Fall = Jatuh bebas

7. Projectile Motion = Gerak peluru

8. Refraction = Pembiasan