Aristotle and Ptolemy believed in a universe that was divided into two parts. On the one hand was the earth, with water, fire and air. On the other hand, beyond the moon was a fifth element, called ether. In this realm of ether, things moved eternally in perfect circles. The original four elements, including earth, were thought to be stable and fixed. The movement of earthly bodies was thought of as a disruption from its natural state and the body's subsequent tendency to get back to this natural state. For example, since a stone is made of earth, it is supposed to be on the ground. A stone moves only when this natural state is disrupted, such as when it is thrown or kicked.
Dr. Bencivenga emphasizes the symbolism of Galileo's gesture of turning a telescope, which had been used only to look at the earth, to the heavens. Such a gesture indicates looking at the earth in a similar way to how we look at the other heavenly bodies. This is exactly the shift in scientific thinking that occurred when Galileo hypothesized that the earth is in motion just as other heavenly bodies are in motion.
Dr. Bencivenga notes that the common idea of modern science is that a super-human intelligence should be able to explain the movement of the entire universe with a single formula. It is only because human intelligence is limited that we cannot know everything. An unlimited intelligence could know everything. Dr. Bencivenga also notes that this conception of science is not faithful to current practice. Our next text, from Werner Heisenberg, will focus on the ways that science has changed in the last few hundred years.
In order to understand Heisenberg, we must understand the scientific context in which he was writing. Newton was very influential into the 18th century. Newton thought that the movement of light could be explained by particles. His system (Newtonian Mechanics) characterized physics for decades. At the outset of the 19th century, a famous experiment seemed to prove him wrong.
Thomas Young performed the two slit experiment. The experiment involves a source of light that goes through one screen with two slits onto a second blank screen. If light is made of particles, then some of these particles should go through either slit and hit the back screen. We would expect that the back screen will be illuminated by two spheres of light that overlap with a bright patch. But what we actually see is a series of strips, some brighter, some darker. This suggests that light is not made of particles but of waves. If waves travel through a slit, they can interfere with one another and either amplify or minimize the intensity of the light. The resulting display of light is an interference pattern.
Another change in science in the last couple hundred of years is how we conceive of motion. Aristotle, for example, thought that all motion is continuous. To travel from point A to point B means to travel on a continuous path between the two points, where all points on the path are met along the way. Max Planck thought that energy must travel in units of energy called quanta (or photons for light). Rather than moving in a continuous manner, energy makes giant leaps. Rather than passing by all points on a path, energy travels quantitative jumps from one place or value to another place or value.
Experiments about light in the early part of the 20th century seemed to indicate that both theories about light had some support in empirical evidence.
Heisenberg suggested that rather than conceiving of mechanical laws as equations for positions and velocities of electrons but for the frequencies and amplitudes. Frequencies themselves are the complex mixture of many different frequencies that occur at once. The extent to which a frequency is composed of other frequencies can be indicated with weighted measures. For example, a certain frequency, F, may be made of up 1/4 fA, 1/4 fB and 1/2 fC. So the equations are not fixed numbers but their value shifts depending on the complex event that is being described.
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