Download Lecture Notes 6: The Idea of a Scientific Method

Philosophy 024: Big Ideas
Prof. Robert DiSalle ([email protected])
Talbot College 408, 519-661-2111 x85763
Office Hours: Monday and Wednesday 11:30-12:30 PM
Course Website:
http://instruct.uwo.ca/philosophy/024/
The idea of a scientific method
What is so great about science?
Does science have a way of looking at the world that makes it
superior to other ways in which humans look at the world?
Is science more objective than other ways of thinking?
Does science have a better grasp of the truth than other ways
of thinking?
Is there really a scientific method?
Galileo, by Tintoretto
The Cartesian idea of method:
To arrive at indubitable truths by conducting the reason
correctly
Everything that is true should be deducible from the
fundamental truths that are discovered by reasoning
Galileo’s idea of method:
To reach the truth about the sensible world by the study of
natural phenomena
To use mathematical ideas to describe precisely how nature
behaves
Descartes:
Reason should be able to reveal the underlying causes of all
physical phenomena
Galileo:
Reason can’t anticipate how the physical world must be, but
must prepared to be surprised by what empirical study will
reveal.
Combining mathematical and empirical reasoning will enable
us to describe how nature behaves-- not necessarily why.
Galileo’s conflict with the Church: Can questions about the
natural world be settled by the Bible? Or must they be settled
by the best empirical and mathematical methods of science?
Are we free to investigate nature, or must we be constrained by
religious authority?
The book of God: The history of God and his creation, written
in a language for general human comprehension
The book of Nature: The natural world itself, revealing its
laws in the phenomena---but written in the language of mathematics.
“Philosophy is written in this grand book, the
universe, which stands continually open to our gaze.
But this book cannot be understood unless one first
learns to comprehend the language and read the
letters in which it is composed. It is written in the
language of mathematics, and its characters are
triangles, circles, and other geometric figures
without which it is humanly impossible to
understand a single word of it; without these, one
wanders about in a dark labyrinth.”
(Galileo)
Galileo’s Abjuration before the Inquisition, 1633
…because I have been enjoined, by this Holy Office,
altogether to abandon the false opinion which maintains that
the sun is the center and immovable, and forbidden to hold,
defend, or teach, the said false doctrine in any manner…
therefore, with a sincere heart and unfeigned faith, I abjure,
curse, and detest the said errors and heresies, and generally
every other error and sect contrary to the said Holy Church;
and I swear that I will never more in future say, or assert
anything, verbally nor in writing, which may give rise to a
similar suspicion of me; but that if I shall know any heretic, or
any one suspected of heresy, I will denounce him to this Holy
Office, or to the Inquisitor and Ordinary of the place in which I
may be.
Galileo on science and Scripture:
I think it would be the part of wisdom not to allow any one to
apply passages of Scripture in such a way as to force them to
support as true any conclusions concerning nature, the contrary
of which may afterwards be revealed by the evidence of our
senses, or by actual demonstration. Who will set bounds to
man's understanding ? Who can assure us that every thing that
can be known in the world is known already ?
Galileo on science and Scripture (continued)
. . . I am inclined to think that Holy Scripture is intended to
convince men of those truths which are necessary for their
salvation, and which being far above man's understanding cannot
be made credible by any learning, or by any other means than
revelation. But that the same God who has endowed us with
senses, reason, and understanding, does not permit us to use
them, and desires to acquaint us in another way with such
knowledge as we are in a position to acquire for ourselves by
means of those faculties— that, it seems to me I am not bound to
believe…
Galileo vs. the Aristotelians on method:
Science can never appeal to the authority of any text, no
matter how great the philosopher who wrote it.
Aristotle himself did not accept the authority of anyone, but
judged for himself the opinions of his predecessors.
In matters of natural science, Aristotle himself never appealed
to authority, but relied on the evidence of his senses.
If Aristotle were alive in Galileo’s time, he would not believe
what he wrote in 350 BCE, but would revise his views on the
basis of all the accumulated evidence.
Galileo vs. the Aristotelians on the natural world:
The earth is not unique in the universe, and the celestial bodies
are made of the same basic stuff.
Falling to the earth is not a simple and natural motion, but a
compound of two motions, horizontal and vertical.
Because motions can be combined, we cannot tell whether the
earth is moving by observing bodies falling on it.
Speed of falling doesn’t depend on the weight of the body, but is
the same for all bodies.
Galileo’s telescope
What Galileo saw on the moon:
More views of the moon:
Why dropping a stone from a “stationary” tower is like
dropping a stone from the mast of a moving ship
The lesson of falling bodies:
We must rely on our senses, but it is a mistake to take what
they tell us at face value.
“The stone falls straight from the top of the tower to the
bottom” : that is not a statement of fact!
It is an interpretation of what we see.
If the earth is at rest, the stone falls in a straight line. But if the
earth is moving, the stone is falling in a parabola.
Science requires the combination of observation with
mathematical reasoning.
Some simple ideas about scientific method
Inductivism: Science proceeds by performing experiments
repeatedly, and accumulating observations.
Then it makes inductive generalizations from the accumulated
facts. These are the laws of science. (Francis Bacon)
Hypothetico-Deductivism: Science proceeds by devising
hypothetical models for how nature might really be organized.
Then it deduces the consequences of these models, and
compares them with observation. (Christiaan Huygens)
Kant’s questions about scientific method:
How has science achieved universal assent, while philosophy is
the subject of endless dispute?
What distinguishes scientific reasoning from philosophical
reasoning, so that the former leads to principles that are
necessary and universal, whereas the latter remains arbitrary and
particular?
How can philosophy start on “the secure path of a science”?
Kant’s “Copernican Revolution”:
The laws of nature don’t describe the way things are in
themselves; they describe conditions that our understanding
imposes upon experience.
“Every effect has a cause” is not a truth about things in
themselves. If it were, we would be right to doubt it.
Instead, it is a rule that the human understanding imposes on
the appearances, in order to submit them to a rule.
Without such rules experience would be impossible. The world
would be a chaos of sensory appearances.
Kant: Scientists like Galileo “comprehended that reason has
insight only into that which it produces itself after a plan of its
own...for otherwise, accidental observations, wth no
previously fixed plan, will never be made to yield a necessary
law….”
“Reason, holding in one had its principles…and in the other
hand the experiments it has devised according to those
principles, must approach nature in order to be taught by it. It
must not, however, do so in the manner of a pupil, who agrees
to everything the teacher says, but of an appointe judge, who
compels the witness to answer the questions which he himself
has phrased…”
The Newtonian method:
Instead of making up theories to explain the facts, compel the
facts to answer theoretical questions.
Example: Use the laws of motion to impose questions on the
world, such as, “what forces are at work?”
If the laws are assumed to be true, then every acceleration that
we see is telling us something about a force.
(F = MA, or “force equals mass times acceleration”: this means
that forces cause accelerations, and accelerations reveal the
action of a force.)
Newton’s laws of motion (The Mathematical
Principles of Natural Philosophy, 1687)
Law 1. Every body, left to itself, maintains its state of uniform
motion or rest until acted upon by a force.
Law 2. Acceleration is in the direction in which a forced is
impressed, and is proportional to the magnitude of the force and
the mass of the body.
Law 3. To every action there is an equal and opposite reaction.
Newton’s discovery of universal gravitation:
The accelerations of the planets answer all of our questions
about the masses and the forces that move them:
What is the magnitude of the force?
What is the center of the force?
What body exerts the force?
Where is the centre of mass of the system?
Kepler’s ellipse law: Planets orbit the sun in ellipses with the
sun at their common focus.
Kepler’s area law: The radius drawn from the sun to a planet
sweeps out equal areas in equal times.
Kepler’s “harmonic law”: The periodic time t and the mean
radius r of any planetary orbit are related as t2  r3.
Or,
t  r3/2
Or, for any two planets a and b,
Ta2 / Tb2 = Ra3 / Rb3
Because (by Law I) a body should naturally recede from any curve
along the tangent, the closed orbits of the planets should tell us that
a force is maintaining them in the curve, and should tell us
something about the magnitude and variation of that force.
The discovery of universal gravitation:
From the accelerations of the planets we infer:
1. The force holding them together is inverse-square, i.e.
proportional to 1/r2 (r is the radius of the orbit)
2. The force is directed to the sun, and the force on the moon
is toward the earth (and Jupiter’s moons to Jupiter, etc.)
3. The centre of mass is very close to the sun, since the sun
has most of the mass of the entire system.
4. The interplanetary force is the same as gravity, since
gravity is the same as the force that holds the moon in orbit
around the earth. (The falling of an apple is the same as
the falling of the moon.)
From this we can infer that the earth revolves around the sun,
rather than the sun revolving around the earth.
For all planets in the system revolve around their common centre
of gravity, and that is always near the center of the sun.
The big question: What is really moving in the solar system?
(i.e. who was right, Ptolemy or Copernicus?)
Before Newton: Choose the most reasonable hypothesis.
After Newton: Let the laws of physics turn this into an empirical
question, and let the facts decide.
Centre of gravity: Where do you put the fulcrum in order to
balance the sun against all the planets?
?
Answer: Because the Sun is so much more massive than all
the planets put together, the centre of gravity is never far from
the sun, even if all the planets happen to be on the same side.
To put the Earth in the centre makes as much sense as thinking
that the Earth’s mass can balance all the other masses together.
That makes as much physical sense as this picture: