27th December 1571 – Johannes Kepler born

27 December 2008

Johannes Kepler (1571-1630) played a major role in the scientific revolution. He is best known as the discoverer of the three Laws of Planetary Motion. He did this by studying the observations made by Tycho Brahe (1546-1601) of planetary motion.

Kepler was instrumental in replacing our Geocentric – Earth centered –  view of the Universe with a heliocentric – Sun centered – view. This heliocentric view would later fall. Two major mileposts on our way towards a modern view of our Universe.

Kepler’s three laws are stated in our times thus:
First Law:
The orbit of every planet is an ellipse with the sun at a focus.
Second Law:
A line joining a planet and the sun sweeps out equal areas during equal intervals of time.
Third Law:
The square of the orbital period of a planet is directly proportional to the third power of the semi-major axis of its orbit. Moreover, the constant of proportionality has the same value for all planets.

The first law describes the shape of a planet orbit. The second law tells us that a planet moves faster when closer to the Sun than when further away. The third law tells us that the length of a planet’s year depends on its distance from the Sun. The further out a planet orbits the Sun; the longer its year is.

Isaac Newton was later able to derive these laws using his Theory of Gravitation.

Start rant…

Did you notice that a Scientific Law describes how natural phenomenon behave?

A Scientific Theory on the other hand explains why things follow the laws they are observed to follow.

The scientific use of the words law and theory differ from the common use of these words.  In common use a Law is a rule agreed upon by common agreement and a theory is an untested idea that has not been proved. In common use a theory is weaker than a law. In science the opposite is true.

Note that scientific theories are never proved to be true. Theories can either be proved false (rare) or (more commonly) replaced by a new theory that explains natural phenomenon even better.  Newton’s Laws of Gravitation have not been replaced by Einstein’s General Theory of relativity. Relativity is just more accurate than Newton’s Theory in extreme situations.  When sending a probe to the Moon; Newton’s Theory of Gravitation works just fine. Sending a probe into orbit round a black hole on the other hand would require use of Einstein’s General Theory of Relativity because the velocities in question are much closer to the speed of light and therefore more extreme.

…end rant.


20th December 2005 – cdesign proponentsist day

20 December 2007

Quote from Wikipedia for today:

US District Court Judge John E. Jones III rules against mandating the teaching “intelligent design” in his ruling of Kitzmiller v. Dover Area School District.

My first encounter with an evolution denier happened in my late teens. I was talking to a new acquaintance. In telling him things about myself I made a passing comment that took for granted that the theory of evolution was as much a fact as things scientific ever are. My new acquaintance stunned me by telling me he did not believe in evolution. To me this was the equivalent of denying that the theory of gravitation was true. I was shocked that someone could refuse to accept a theory that has stood the test of time since 1859. This person was obviously smart yet his faith seemed to me to be in direct conflict with reality.

Later in life I came across Niven’s Laws the 14th of which seems to cover this:

There exist minds that think as well as you do, but differently.


Word for the day – theory

27 July 2007

The Bad Astronomer posted an article just over a week ago on his irritation with the argument that “evolution is just a theory”. He says:

It’s like saying the Eiffel Tower is just a tower.

His article links to this site which explains what scientists mean when they use the word theory.

In everyday use, theory means a guess or a hunch, something that maybe needs proof. In science, a theory is not a guess, not a hunch. It’s a well-substantiated, well-supported, well-documented explanation for our observations. It ties together all the facts about something, providing an explanation that fits all the observations and can be used to make predictions. In science, theory is the ultimate goal, the explanation. It’s as close to proven as anything in science can be.

So by saying “evolution is just a theory” what you are saying scientifically speaking is that evolution is as close to being proved as it can be. Which is what mainstream scientist have been confirming for the last 150 years.