Welcome, everyone, to the study of physics.
In this course, you will be learning about the contributions of a few famous physicists
as well as many more people whose work
in mathematics, physics, and engineering did not bring them eternal fame. Of course, most of these people lived and
died long ago. There will be times, however, when the work of modern physicists
presents itself. Occasionally ,we may even get an inkling about the physics of
the next millennium.
Be warned however: understanding physics isn’t as hard as you think. How else to explain the way scientists have connected to physics to virtually every discipline? Long gone are the days (circa 1700 a.d.) when a recluse such as
So, what is physics exactly? Let’s start from the beginning of time. Actually, In the beginning there was nothing, or at least nothing much to write about. As time went on, things got more complex (or perhaps complexity increased and produced more things?). Eventually hairless and clawless human beings showed up and really added to the complexity of life. In our continual effort to stay alive in hostile environments, we created confusion by trying to explain everything. After doing this life-improvement work for a few hundred millennia, it got to be habit forming.
Pretty soon folks like Plato, Aristotle,
Copernicus, Galileo, Kepler,
Copernicus's Earth centered model of the cosmos led, 200 years later, to
In the 1920's Nils Bohr's theory of atomic energy levels, and Werner Heinsberg’s probability calculations ushered in the quantum revolution, and paved the way for the invention of transistors and high speed digital computers. Nowadays, physicists ponder the nature of apparently ghostlike particles called neutrinos, and space and time bending objects like black holes. In these cutting edge investigations, physicists are expectantly looking for than the tiniest flaw in our current theories, or the missing bit of data that proves an existing model correct. Its not at all obvious how these investigations might lead to practical innovation, but if history is any guide, they certainly will.
Recall that human beings have been trying to explain how and why things happen for quite some time. Before the advent of written language, we have little evidence of what those explanations were. It is the ancient Greeks who get considerable credit for starting the ball rolling (if you pardon the pun)--Partially because they were great writers, as well as great thinkers, Most of us are familiar with the names of Socrates, Plato, and Aristotle. While both Socrates and Plato shaped the questions that were asked and answers that could be given (the discourse of physics), it is Aristotle (384 - 322 BC) who gets most of the credit for asking and answering the questions that would form the basis for our understanding of the "natural" world.
Aristotle created a working model of the cosmos, placing the Earth at the center, and the sun, moon, planets, and stars on concentric spheres that revolved about the Earth. He also formed a "complete" theory of motion by separating all substances in four elementals: earth, air, fire, and water. Later a fifth element was proposed, the quintessence, or the "Aether" which filled all otherwise empty space. According to Aristotle, objects sought their natural place—period. Other than seeking their natural place, objects moved if they were in “violent motion,” meaning that they were pushed or pulled somehow.
The only detail was determining the natural place for the elementals. Well, water belonged in the ocean (and presumably in lakes), so water fell from the sky, ran downhill in rivers, and ended up in the ocean. Air (or any gas) belonged in the sky, so vapors trapped in the Earth, or released in a fire rose upward. Earth-like stuff (a rock for example) belonged in the Earth, so stones, hail, people, and puppy dogs fell downward. Fire is a tough one, but invariably went where it belonged.
Now imagine that you are student of
Aristotle, in the Lyceum in
imagine that it is one thousand five hundred years later. Aristotle's theories
are still in place. In fact, if you live in
At this point, you may be wishing that you lived in the second millennium AD. Well, lucky us! But perhaps we take some of the next 16 weeks or so to honor the courage and conviction of those to argued against the brilliant, but incorrect Aristotelian principles.
Skipping to 1543, Nicholas Copernicus
wrote a book describing the Heliocentric (sun centered) model of the
cosmos, with the Earth and all the known planets orbiting the sun, and only the
moon orbiting the Earth. As a monk, with good relations in a permissive wing of
the Catholic church, he was able to publish his work--with a couple of
safeguards in place of course. For one,
he wrote the book in Latin, so that only the scholarly community of
Ancient Greeks produced many enduring principles. While Aristotle's first four
elementals have bit the dust, so to speak, Archimedes principles of
geometry, leverage, buoyancy , and mechanics are part of our current catalog of
knowledge. In fact, you will study some of these later in the course to solve
some very modern problems. Using
geometry, Eratosthenes not only used geometrical reasoning to prove that
the Earth was spherical, but also measured its circumference in 235 BC. A few
years earlier, Aristarchus accurately determined the ratio of the
Earth's diameter to the Moon's diameter. If
Even earlier, Democritus, (about 400 BC) postulated that all matter was composed of small elementals, called atoms. Few people believed him at the time. But how to prove the existence of something you cannot see? In those parts of the world largely freed from ancient dogma, physicists got right to work on it, finally succeeding after the start of the 20th century.
makes a good theory?
These results and the methods that precede them, have withstood the test of time, which in science generally means “the unending scrutiny of scientists and mathematicians.” Nowadays, a scientific theory has to be both verifiable, and falsifiable. In other words, a "good" theory must be testable. If I propose, for example, that helium balloons rise in the air, not because helium gas is less dense than the air molecules outside the balloon, but rather because of invisible-undetectable gremlins that are attracted to helium balloons and invariably push them upward, then you, as a member of the literate scientific community, have every right to scoff. There is no way to test my theory.
By the same token, every good theory is out
there only so long as experimental evidence supports it.
about the 5th element?
What has replaced the Aristotelian idea of elementals seeking their natural place? Our Standard model now includes four different forces and associated “fields” that act at a distance, pulling baseballs to the ground, and electrons to the atom, protons and neutrons together within the nucleus, and governing the decay of the nucleons into more fundamental particles such as quarks and neutrinos. The except number, mass, and other properties of these fundamental particles are also key aspects of the Standard Model.
But gravity is still causing trouble. Most physics students have already heard that the Universe is expanding. This is old news, relativity speaking. An expanding universe can be explained with Einstein’s theory of gravity. The news of the day, however, is that the universe is expanding faster and faster—that it is accelerating. This possibility was not predicted by Einstein or anyone else! After lots of careful thought, however, theorists have come up with the “dark energy” model, which merges Einstein’s theory with the existence of a “quintessence” or dark energy that fills all of space and drives the expansion. Famously, Einstein himself adopted and then rejected the idea of a “cosmological constant” or quintessence-like Aether that kept the universe from collapsing in on itself. Aristotle of 225 BC would never have recognized his theory, but today’s young Aristotle’s are taking the idea at face value and testing its compatibility with increasingly accurate and unexpected data.
So remember, the Paradigm of physics is summarized in a Standard Model that includes all the verified particles and interactions between them, as well as the nature of space and time itself. However, these particles and interactions are subject to daily scrutiny. They hold as long as the data from experiments support them. We already know, for example, that parts of our main theories are not compatible with one another. What happens when massive objects shrink to the sizes of atoms, for example? New models are in the works, mainly to explain just such discrepancies, such as “string” and “brane” theory, which replace the very idea of particles in three or four dimensions with vibrations and interactions in multiple dimensions. We won’t be studying these theories here, but as you continue learning and reading, put new models in context as the best fit to available data—nothing more and definitely nothing less.