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.

Bruno's Cosmology

Copernicus's Cosmology

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 developed here?

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 unknown.

(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.

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:

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 observational error.

• 1st law (law of elliptic orbits): Each planet moves in an elliptical orbit with the Sun at one focus.

Kepler's elliptical orbit for Mars

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).