Bruno thru Kepler
Bruno: (1548-1600) (Burned at the Stake in 1600)
In his cosmology, Bruno followed Lucretius and
Copernicus, but he developed the implications of the
Copernican system much further than Copernicus
himself had done (indeed, Copernicus really didn't do much at all!).
More than the other Italian philosophers who were his contemporaries, Bruno deserves to be called a forerunner, if not a founder, of modern science and philosophy.
What is different between these two representations
of the Universe ?
"This entire globe, this star, not being subject to death, and dissolution and annihilation being impossible
anywhere in Nature, from time to time renews itself by changing and altering all its parts. There is no absolute
up or down, as Aristotle taught; no absolute position in space; but the position of a body is relative to that of
other bodies. Everywhere there is incessant relative change in position throughout the universe, and the
observer is always at the center of things."
As to us on Earth, the Earth seems to be the center of the Universe, so to inhabitants of the Moon,
the Moon will appear as such http://abyss.uoregon.edu/~js. Each world has its center, each its up and down; these differences
are to be assigned relatively . . .
What is the main "science" concept that is being
Bruno followed Nicholas of Cusa in developing the concept of the
"acentric" Universe (there is no center). He also asserted that if homogeneity and isotropy are properties of such a
universe, then it is most logical that life would exist elsewhere as well
as on Earth.
This was so threatening to the Catholic church at the time that on
February 16, 1600 he was burned at the stake for heresy. Although his
life stands as a testimony to the drive for knowledge and truth his death
also stands as testimony to cultures that are imprisoned by fear of the
(aside: In 1992, after 12 years of deliberations, the
Roman Catholic Church grudgingly admitted that
Galileo Galilei had been right in supporting the
theories of Copernicus. The Holy Inquisition had
forced an aged Galileo to recant his ideas under
threat of torture in 1633. But no such admission
has been made in the case of Bruno. His writings
are still on the Vatican's list of forbidden texts.)
The French philosopher and mathematician Reni Descartes challenged old ways of thinking about
science. Descartes, for whom the Cartesian system of philosophy is named, argued that doubt and
reason are both necessary for determining truth, and that the world and everything in it operates
according to mechanical principles.
What is being expressed here?
- If I found any new truths in the sciences, I can say that they follow from, or depend on, five
or six principal problems which I succeeded in solving and which I regard as so many
battles where the fortunes of war were on my side.
- If we possessed a thorough knowledge of all the parts of the seed of any animal (e.g. man),
we could from that alone, be reasons entirely mathematical and certain, deduce the whole
conformation and figure of each of its members, and, conversely if we knew several
peculiarities of this conformation, we would from those deduce the nature of its seed.
And, in the context of this class, this is his most important thought:
By a method I mean certain and simple rules such that, if a man observe them accurately, he shall never assume
what is false is true.
What is being stated here?
Tycho Brahe 1546 - 1601
Classroom Parallax Demonstration
But first a bit more on Galileo:
Galileo's laws of Motion:
Aside from his numerous inventions, Galileo also laid down the first
accurate laws of motion for masses. Galileo measured that all bodies
accelerate at the same rate regardless of their size or mass.
Key among his investigations are:
- developed the concept of motion in terms of velocity (speed
and direction) through the use of inclined planes.
- developed the idea of force, as a cause for motion.
- determined that the natural state of an object is rest or uniform
motion, i.e. objects always have a velocity, sometimes that velocity has
a magnitude of zero = rest.
- objects resist change in motion, which is called inertia.
Kepler's (1571-1630) laws of Planetary Motion:
Kepler developed, using Tycho Brahe's observations, the first kinematic description of
orbits, Newton will develop a dynamic description that
involves the underlying influence (gravity)
Note: It was crucial to Kepler's method of checking possible orbits against observations that he have an idea of
what should be accepted as adequate agreement. From this arises the first explicit use of the concept of
Kepler's elliptical orbit for Mars
- 1st law (law of elliptic orbits): Each planet moves in an
elliptical orbit with the Sun at one focus.
2nd law (law of equal areas): a line connection the Sun and a
planet (called the radius vector) sweeps out equal areas in equal times
Objects travel fastest at the low point of their orbit, and travel
slowest at the high point of their orbit.
- 3rd law (law of harmonics): The square of a planet's orbital period
is proportional to its mean distance from the Sun cubed.
The 3rd law is used to
develop a ``yardstick'' for the Solar System, expressing the distance to
all the planets relative to Earth's orbit by just knowing their period
(timing how long it takes for them to go around the Sun).
Although successful, Kepler's laws remained a set of empirical rules without a dynamical basis. The link between these laws and the physical world would be established about 50 years later by Isaac Newton (1642-1727).