How science proceeds

Observations hypothesis theory

– Hypotheses must make testable predictions…

– Science can only disprove, not prove…

– Theories that survive, become more respected…

– Simpler theories are preferred (Occam’s Razor).

Bogus science

Signposts of bogosity:1) Being hopelessly complicated.

- Complicated does not mean accurate.

2) It is a traditional belief.- Because your parents did it, does not make it right.

3) Explaining one observation by introducing another rule.- This is simply restating the observation as an assumption

4) Observations are not repeatable.- It may be correct, but it is unproven.

5) You must be a believer to understand it.- Ha ha ha.

Progression of science: Greeks to geeks

Solar system models

• Geocentric model;

• Heliocentric model.

The players

• Tycho;

• Kepler;

• Galileo.

Physics

• Newton;

• Einstein.

The Geocentric Model:

Ptolemy (~90-168 AD)

His work builds upon Aristotle’s;

Based upon a geocentric model;

Involves circular orbits, uniform speeds;

In initial conception, simple and beautiful;

Codified in the Almagest.

The Heliocentric Model:

Copernicus (1473-1543)

His work builds upon Aristarchus’;

Based upon a heliocentric model;

Involves circular orbits, uniform speeds;

In initial conception, simple and beautiful;

De Revolutionibus, published at his death

Problems with both models

Retrograde motion: Mars clearly travels BACKWARDS in the sky, for a few months, every year!

Stellar parallax: if the Earth shifted its position, surely we would see the stars shifting in the sky!

The geocentric mess

In order to explain nonuniform speeds of objects in the sky, complicated patches were added to the geocentric model.

Model smack-down

Geocentric

+ Aristotle said so;

+ Feels good;

+ Accurate at first;

- Decreasing accuracy;

- Complicated;

- Retrograde motion

Heliocentric

+ Retrograde motion;

+ Simple;

- No improved accuracy;

- No parallax for stars.

Tycho

1546-1601

(Yin)

TychoDanish bon vivant;

Fabulous parties (including jesters and elk);

Metal nose;

Extraordinary observer;

Observed supernova (1572), no parallax;

Observed comet (1577), further than the moon;

KeplerGerman astrologer;

Geek among geeks;

Avoided distractions.

Kepler

1571-1630

(Yang)

The odd couple

Tycho

1546-1601

(Yin)

K1: All objects orbit on elliptical paths, with the central object at one “focus” — i.e., does not require circles!

Kepler

1571-1630

(Yang)

Kepler’s three laws:

Tycho

1546-1601

(Yin)

K2: All objects orbit so that they sweep out equal areas in equal times — i.e., does not require constant speed!

Kepler

1571-1630

(Yang)

Kepler’s three laws:

Tycho

1546-1601

(Yin)

Kepler

1571-1630

(Yang)

K3: The square of the orbital period is proportional to the cube of the semi-major axis (~radius) of the orbit:

P2=a3

Kepler’s three laws:

Galileo’s (1564-1642) observations

Some of Galileo’s key discoveries

– Jupiter has four satellites;(a case of something orbiting an object other than the Earth)

– The Moon seems to be a world, with craters and mountains;(the planets were supposedly celestial orbs)

– The Sun has spots;(how could it be imperfect?)

– Venus has phases and a varying size.(it cannot be orbiting the Earth)

Galileo’s troubles– He broke with Ptolemaic ideas of harmony of science, theology, poetry and music

that all fit together in the Renaissance system. French theologian and mathematician Blaise Pascal, said, "The eternal silence of these infinite spaces fills me with dread.“

– It challenged the church's commitment to geocentricism.

– Galileo began a crusade to change the Church’s policy toward geocentricism. He expected people to accept his authority.

– Sarcastic attacks on those who refused to look through his telescopes.

– He denied Kepler a scope.

– He dismissed church authorities who asked for more definitive proof.

– Galileo was forbidden (1616) from teaching Copernican theory as fact—“Dialogue on the Two Chief World Systems: Ptolemaic and Copernican” (1632).

– Simplicio utters a text from a letter from Pope Urban VIII.

– The Inquisition convicted Galileo of heresy (1633) using forged minutes.

– Ultimately placed in house arrest for the last 9 years of his life.

Newton (1643-1727)

Some definitions

Position – where something is;

Speed – change in position;

Velocity – change in position or direction;

Acceleration – change in velocity;

Mass – how much stuff is in something;

Force – how hard something pushes/pulls.

Newton (1643-1727)

N1: An object at rest will stay at rest, while an object in motion will stay in motion with no change in its velocity (unless acted upon by an outside force).

N2: If an object (with mass=m) is affected by a force (force=F), it will respond by accelerating (a):

F=ma

N3: For every force being applied, there is an equal and opposite counter force.

Newton (1643-1727)

NG: Two objects of mass (M, m), separated by a distance (R), will have a mutually attractive gravitational force, an action at a distance:

Fg=GMm/R2

Grandmaster Geek:

Einstein (1879-1955)

Explored the affects of velocities near the speed of light (Special Relativity).

Developed concepts of space-time, to redefine how we think of gravity (General Relativity).