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.


Bruno's Cosmology


Copernicus's Cosmology

What is different between these two representations of the Universe ?

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.

What is being expressed here?

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:


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.

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

    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).