1. What is science?
2. How is it done these days?
3. The origins of modern science.

1. The nature of stonehenge
2. Occam's razor
3. Origins of astronomy
4. Models of  Ptolemy and Copernicus
5. Galileo: mechanics, speed, velocity, acceleration

• It is hard to say when science started but it has been suggested that it started with the astronomy work by Kepler sometime around 1600 AD.
• Astronomy, the study of the stars and the objects in the sky, has been on man’s mind for 1000’s of years. It might be because the stars are so bright at night. Imagine that 1000’s of years ago, with no artificial light sources, it got very dark at night and the heavens were filled with light. We know that the stars and constellations move slowly over the course of a year, rising and falling over the skyline, but repeating every year. The ancients no doubt saw the same thing and realized that the positions of objects in the sky could act as a timepiece.
• They studied the skies in order to establish a calendar. Evidence for such things include Stonehenge, which was built around 2800 BC. That’s almost 5000 years ago! It was built in such a way that the rising midsummer’s sun (June 21) and the setting midwinter's sun, (Dec 21) lines up with the center of the circles and the heel stone.

• It is actually hard to say why it was built, what we can guess is that it served as a calendar, used to notify when planting must be done.
• The accuracy of the calendar is such that it still is correct. This required much observation and a fundamental belief that nature is periodic, predictable, and quantifiable. The builders of Stonehenge certainly followed parts of the scientific method. (So, why isn't this considered the start of the scientific method?)
• Some think that aliens built Stonehenge. We do not need to resort to this sort of hypothesis since there exists a simpler argument. Man built it by pulling large rocks, probably over the snow, and set it up (max is 500 men).

• This brings up Occam’s razor. Occam was a 14th century Englishman who stated that "given a choice of possible solutions to a problem, the simplest is probably correct".

• So we have established that astronomy is one of the oldest of the sciences.
• When you look up at the stars at night, you can see the moon and the planets. Does anyone not know where?
• Careful record keeping shows that the planets move in very peculiar ways relative to the position of the stars. If we think of the stars as providing a fixed backdrop, the planets by-and-large seem to move to the east. But every so often they go in the opposite direction called retrograde.
• The moon also seems to move to the east, but it never goes into retrograde.
• A great deal of time was spent trying to understand this peculiar behavior, and to be able to predict it.

• The first plausible solution was due to Ptolemy (200 AD), an Egyptian born Greek astronomer.
• He assumed that the earth was in the center of the universe and that all objects circled around it. The origin of the first assumption was religious, and also supported by the observation that heavy bodies fall to their natural place, the Earth, which must then be the center of the universe. The stars, planets, moon and sun were objects that Ptolemy thought were positioned on concentric rotating spheres. The planets, furthermore, were planets because they existed on smaller rotating spheres that rolled on the surfaces of the larger spheres. His model worked very well and was used for 1500 years to predict the positions of the heavenly bodies.
• He assumed that the earth was in the center because religion said it was. He also assumed spheres because of their perfection.
• This was the model of choice till Copernicus (~1500 AD). He suggested that another reasonable model would have the Sun at the center of the universe, with the planets circling around and the stars real far away. He still assumed circles. His model was able to accurately predict the positions of the heavenly bodies just about as good as Ptolemy. Actually Ptolemy’s was better, but much more complicated.
• Copernicus put the sun at the center of the universe for philosphical reasons: "At the middle of all things lies the sun. As the location of this luminary in the cosmos, that most beautiful temple, would there be any other place or any better place than the centre, from which it can light up everything at the same time? Hence the sun is not inappropriately called by some the lamp of the universe, by others its mind, and by others its ruler."

• Now astronomers had two models to think about. The philosophical differences were enormous. The test between these two models would shape our perception of the nature of God. The existing measurements were too crude to actually determine which model was more accurate.
• Tycho Brahe spent 25 years recording the positions of the planets and stars with new instruments that he designed, and with a greater accuracy than ever before observed.
• When he died his assistant took over. This was Kepler, who was a mathematician around 1600 AD. He analyzed Brahe’s data. He determined that the planets revolved around the Sun in elliptical motion. This completely described all the planetary movement recorded by Brahe, and with a more accurate prediction than the other theories. And it was simpler!

• This example illustrates that sometimes science can only advance once a instrument is designed to be accurate enough to separate error from noise.
• With Kepler’s results we now knew how the planets moved, but we did not know why.
• It is interesting that it is after this study that modern science developed. Many call it the birth of modern science. It may be that we needed to eliminate the concept of the earth at the center of the universe. This caused many problems with religious leaders. But there is no doubt that the birth of science was associated with this event.

• Galileo was an Italian who was very clever at inventing things, such as the telescope, the thermometer, and the pendulum clock. He believed in the idea that the planets revolved about the Sun and wrote a book about this in everyday Latin, accessible to the educated public. The Catholic Church warned him not to do this. So, he wrote another book in which he criticized the Church for holding onto old views and made the pope look like a simpleton. A trial was finally held when he was older and he recanted all that he had written, saying that he did not believe it. He died, an old man under house arrest. In 1992 the Catholic Church reopened the case and declared him not guilty.
• His greatest work however, had to do with the subject of mechanics.
• Mechanics is the study of how objects move.
• The Greeks reasoned that heavier objects fall with greater speed than lighter objects; but, of course, they never tested this idea. Galileo measured the falling speed of various objects (in the 1620’s) and showed that all objects fall at the same speed, no matter how heavy they are. In order to do this he had to learn how to measure distance and time very accurately.
• Define 3 words:
1. Speed: distance traveled by an object divided by the time it took to travel that distance.
2. Velocity: same numerical value as speed, but it includes direction. Eg, 30 mph north.
3. Acceleration: measures the rate of change of velocity. M/s², or feet/s², e.g. suppose your car could go from 0 to 60 miles/hour in 5 seconds, then you would say it accelerates 60 mph/5 sec = 15 mphps.
• If an object changes speed or direction then it is accelerating. Slowing down is a form of acceleration.
• Galileo found that every object, independent of weight or mass, falls exactly with the same acceleration: 32 feet/s². This means that after 1 sec it is going 32 ft/s (22 mph), after 2 sec it is going 64 ft/s, etc. Because the longer it falls the faster it falls, a penny thrown off the Empire State building can go through a car and kill you. If you jump off a building that is 32 feet high, then you will fall for 1 sec, and hit the ground going 22 mph.
• People still believe that heavy objects fall faster than lighter ones. Why?
• A fundamental reason why Galileo was so important to the history of science is that he addressed the issue of falling objects. Many people believed that the earth was the center of the universe because all objects appear to fall to the earth. He quantified the observations, preparing the way for Newton.