Major Players
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History of Physics |
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"The sun rises. In that short phrase, in a single fact, is enough information to keep biology, physics, and philosophy busy for the rest of time."
Lyall Watson
When I say, "history of physics," what I mean is a span of time during which we humans have been engaged in seeking answers about our natural world.
It is impossible to create a linear map of the history of physics; too many developments occurred in parallel, too many paths could have led to the same result to assign a direct cause-effect relationship. Often, events required the contribution of a singular genius in order to advance. It is also impossible to include everything! However, if you'd like to see a particular topic make it onto the history pages, please just ask, and I'll do my best to make it available.
Early pioneers in physics were not physicists, as such. There were no specializations in the sciences, or even in learning in general. The learned person was simply expected to have a command of knowledge from many disciplines.
Archimedes
Archimedes is widely seen as one of the best mathematicians of all time, certainly the best mathematician up until the 17th century. He was from Syracuse, Sicily, born in around 287 BC. Archimedes was not only a mathematical genius, but also a brilliant engineer and inventor. Many of his devices were put to use as war machines in the defense of Syracuse. We'll explore one of these, because the ingenuity is simply awe inspiring! The Iron Claw was a device used extensively against the Roman ships attacking Syracuse. It was so successful, it helped keep the Romans at bay for over two years!
A lever basically allows you to multiply your available force. So, to lift a large rock that weighs twice what you could lift as dead weight, you need a lever whose "handle" end (the part you push on) is twice as long as the "contact" end (the part that sits under the rock), as measured from the fulcrum (the pivot). How many different lever systems can you find in this sketch? There are several! Pulleys are technically levers, too! The more pulleys you have connected to both the object and you, the more you multiply your force. For example, if you have a compound pulley system that doubles the ropes back and forth, for a total of 10 lines of rope, then you can exert 10 times the force as if pulling on a single line of rope. So what would happen is that the Roman ships would come in to unload soldiers, or to try to fire upon the Syracusan defensive towers, etc., but then the Syracuse soldiers would manipulate their Archimedes Claws to hook part of the ship. Then, once the ship was hooked, the soldiers would simply pull on the ropes! Or, they may have had larger animals of some sort do this (I'm not an expert on north African animal species...). The hooked ship had no choice but to be hoisted into the air, then unceremoneously dropped into the water and sunk. Simple yet effective, the hallmark of a brilliant design!
At the tail end of the 19th century, the scientific community more or less considered all problems of nature to be, in effect, solved. They considered their jobs now to simply extend experimental measurements a few additional decimal places! Oh, oh, oh. What surprises lay in store!
Albert Einstein
Einstein had a profound influence on the course of modern physics. You know, that may in fact be an understatement! Einstein was involved in pretty much everything. It's not a mystery why wicked smart folk are called "Einsteins."Einstein began his notable theoretical physics career (see the General Relativity section) with the publication of a paper on the photoelectric effect. He was, at the time, a patent clerk in Bern, Switzerland, after having a somewhat unsatisfying stint as a secondary school math teacher. He originally had wanted to teach at a university, but had not had much luck in acquiring such a position. But back to the photoelectric effect... For a full explanation, see the Terms and Units page. In brief, though, the photoelectric effect is when light is incident upon some material, and transfers energy to surface electrons allowing them to escape. In other words, when light shines on a metal, the metal's electrons can escape, and if the metal is part of an electrical circuit, we can measure a current when the electrons are escaping. The trick is, and what no one was able to explain before Einstein's paper, that the intensity of the incident light does not matter when we measure the energy of the ejected electrons. You'd think that a more intense beam (meaning more photons per unit time are hitting a particular area of the material) would eject electrons of higher energy, but this is not the case! Now, it is true that the current is larger, since more electrons are being ejected, but their individual energies are all the same. Remember that at this time, light was considered a wave, so the idea that multiple photons striking the material causing individual eletrons to dislodge was not really a possibility. But, Einstein reasoned that the light must be traveling in little bundles (i.e., quanta), otherwise a more intense light source would eject more energetic rather than more plentiful electrons. By the by, Einstein submitted a paper explaining all this in 1905. Also in 1905, Einstein wrote another paper, "On the Electrodynamics of Moving Bodies," that would become his theory of Special Relativity. Special Relativity (SR) involves two primary ideas. First is the Principle of Relativity, which states that physical laws hold in every inertial reference frame, and that there is no single preferred inertial frame. What's an inertial frame? It's a frame that is not accelerating with respect to our own. So, if we are traveling along in a car at a constant 65 mph on a straight, flat road, we are in an inertial reference frame with respect to the ground, and the ground is an inertial reference frame with respect to our car. This means that if you were performing some physics experiment (take your pick, they will all work) in your car, while someone on the side of the highway performed the same experiment, you would measure the same values of your experimental data. Second is the Constancy of the Speed of Light, which state that light travels at the same relative speed with respect to all inertial systems. Whoa... Take a second to let this digest, because it is freaky! Here's the situation: you are standing next to the train tracks while a train is moving slowly by at, say, 10mph. A friend is standing on a flat-bed train car and as she passes your position, throws a baseball. She can throw 35mph. What speed do you see the ball travel? Well, if she throws in the direction the train is moving, you'd see a 45mph throw. If she throws opposite the direction the train is moving, you'd see a 25mph throw. The point is that the velocities simply add up (or subtract). However, the speed of light does not obey this simple "add up the velocities" rule! We are answering the old question, "If you're traveling at the speed of light and turn on your headlights, what happens?" Well, you see the light travel away from you at the speed of light, since light always travels at the same speed relative to any inertial frame. And although you're moving very fast, you are still an inertial frame since you are not accelerating. But, someone standing on a nearby asteroid would not see the light coming from your ship at 2 times the speed of light (as you would guess from the old rule of "add them up"). Instead, they would see your ship cruise by at light speed, and nothing else. Ah, but shouldn't we always measure the same experimental data? Yes, but it takes time to perform an experiment, and from your asteroid bound friends perspective, time, for you, has stopped! Thus, how can you possibly turn on your headlights, since it takes time to perform that act? What do you mean, "time stops?" Oh, it's freaky, like I said. It turns out that the faster you travel, the slower your clocks will run. Yes, that includes atomic clocks, windup clocks, battery powered Star WarsTM radio clocks, and even your biological clock. Phooey, you say! This is just another example of how scientists are stupid and disconnected from reality, you say! Well, the experimental evidence is on the scientists side in this case, it is our intuition that is wrong. We are not accustomed to traveling at light speed, so how could we have any intuition about it? "They" did an experiment with four atomic clocks. They put two on an airplane, and left two on the tarmac. They synchronized the clocks, then flew the airplane around for a while at high altitude and high speed, then landed on the tarmac. Both clocks on the airplane were still synchronized, both clocks on the tarmac were still synchronized, but the clocks on the airplane showed less elapsed time than the clocks on the tarmac! The ones in motion had run more slowly. ... more to come ...
Ernest Rutherford... more to come ...
Neils Bohr... more to come ...
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This image is from Engineering in the Ancient World by J. G. Landels, University of California Press, Berkeley & Los Angeles, 1978. Notice the amazing use of leverage through the beams, and also through the use of pulleys. Archimedes studied statics very thoroughly, and he put his ideas to practical and devastating use in this machine!