Happy Pi Day everyone.
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:
The orbit of every planet is an ellipse with the sun at a focus.
A line joining a planet and the sun sweeps out equal areas during equal intervals of time.
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.
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 Newton’s Laws of Gravitation have not been replaced by Einstein’s General Theory of relativity.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.
Guest blogger LisaJ over at PZ Myers blog Pharyngula wishes she were a paleontologist. I understand why. She has this to say:
Imagine you’re a paleontologist, digging through the Sahara desert looking for dinosaur bones and you stumble, instead, upon this wondrous find:
That’s exactly what happened to Paleontologist Paul Sereno and his team back in 2000, and they have announced their findings from their excavations of this region in Northern Niger in National Geographic this week. This team unexpectedly unearthed 200 human burials on the shores of a long dried up lake, representing two very distinct cultures spanning 5000 years (between 4500 to about 9000 years ago). The image shown above is of their ‘most striking discovery’, and depicts a woman and two children, ages 5 and 8, holding hands. They also found pollen in the grave, suggesting that they may have been laid on a bed of flowers.
What an evocative image that is. It is most likely a mother and her two children lovingly laid together hands clasped on a bed of flowers. The unknown tale behind this tragedy will never be revealed. My heart missed a beat when I first saw that image.
It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less-improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
Today is Darwin Day and we celebrate the birth of Charles Robert Darwin on 12th February 1809. This gentleman naturalist is one of the most influential individuals in the history of science. His Theory of Evolution is (though controversial in certain religious circles) almost universally accepted as fact by the scientific community.