Six Easy Pieces - Richard P. Feynman

"Each piece, or part, of the whole of nature is always merely an approximation to the complete truth, or the complete truth so far as we know it. In fact, everything we know is only some kind of approximation, because we know that we do not know all the laws as yet."

"all things are made of atoms - little particles that move around in perpetual motion, attracting each other when they are a little distant apart, but repelling upon being squeezed into one another."

"The most important hypothesis in all of biology, for example, is that everything that animals do, atoms do. In other words, there is nothing that living things do that cannot be understood from the point of view that they are made of atoms acting according to the laws of physics."

electrical force = likes repel, unlikes attract.

if we get very close, attraction rises, because the repulsion of likes and attraction of unlikes will tend to bring unlikes closer together and push likes farther apart. Then the repulsion is less than the attraction.

quantum mechanics = it is not possible to predict exactly what will happen in any circumstance.
"nature, as we understand it today, behaves in such a way that it is fundamentally impossible to make a precise prediction of exactly what will happen in a given experiment.

"the sole test of the validity of any idea is experiment."

"Now it is true that when the frequency is low(matter), the field aspect of the phenomenon is more evident,...But as the frequency increases (light), the particle aspects of the phenomenon become more evident..."

"We do not know how the universe got started, and we have never made experiments which check our ideas of space and time accurately, below some tiny distance, so we only know that our ideas work above that distance."

"The stuff of which we are made, was "cooked" once, in a star, and spit out....The furnace was like the stars, and so it is very likely that our elements were "made" in the stars and spit out in the explosions which we call novae and super-novae."

"The central problem of the mind, if you will, or the nervous system, is this: when an animal learns something, it can do something different than it could before, and its brain cell must have changed too, if it is made out of atoms. In what ways is it different? We do not know where to look, or what to look for, when something is memorized. We do not know what it means, or, what change there is in the nervous system, when a fact is learned."

"This is a very interesting subject which we have not the time to discuss further - the relationship between thinking and computing machines. It must be appreciated, of course, that this subject will tell us very little about the real complexities of ordinary human behavior. All human beings are so different."

"A poet once said, "The whole universe is in a glass of wine." We will probably never know in what sense he meant that, for poets do not write to be understood. But is true that if we look at a glass of wine closely enough we see the entire universe. There are the things of physics; the twisting liquid which evaporates depending on the wind and weather, the reflections in the glass, and our imagination adds the atoms. The glass is a distillation of the earth's rocks, and in its composition we see the secrets of the universe's age, and the evolution of the stars. What strange array of chemicals are in the wine? How did they come to be? There are the ferments, the enzymes, the substrates, and the products. There in wine is found the great generalization: all life is fermentation. Nobody can discover the chemistry of wine without discovering, as did Louis Pasteur, the cause of much disease. How vivid is the claret, pressing its existence into the consciousness that watches it! If our small minds, for some convenience, divide this glass of wine, this universe, into parts - physics, biology, geology, astronomy, psychology, and so on- remember that nature does not know it! So let us put it all back together, not forgetting ultimately what is for. Let it give us one more final pleasure: drink it and forget it all!"

conservation of energy = there is a certain quantity of energy that does not change.

It is important to realize that in physics today, we have no knowledge of what energy is.

"it is hard to exaggerate the importance of the effect on the history of science produced by this great success of the theory of gravitation. Compare the confusion, the lack of confidence, the incomplete knowledge that prevailed in the earlier ages, when there were endless debates and paradoxes, with the clarity and simplicity of this law-this fact that all the moons and planets and stars have such a simple rule to govern them, and further that man could understand it and deduce how the planets should move! This is the reason for the success of the sciences in the following years, for it gave hope that the other phenomena of the world might also have such beautifully simple laws."

"All we have done is to describe how the earth moves around the sun, but we have not said what makes it go. Newton made no hypotheses about this; he was satisfied to find what it did without getting into the machinery of it. No one has since given any machinery. It is characteristic of the physical laws that they have this abstract character. The law of conservation of energy is a theorem concerning quantities that have to be calculated and added together, with no mention of the machinery, and likewise the great laws of mechanics are quantitative mathematical laws for which no machinery is available. Why can we use math to describe nature without a mechanism behind it? No one knows."

"... No machinery has ever been invented that "explains" gravity without also predicting some other phenomenon that does not exist."

unified field theory = effort to unify electricity and gravity, force of electricity is a constant, with a minus sign, times the product of the charges, and varies inversely as the square of the distance. The two laws regarding electricity and gravity both involve the same square of the distance

"If we take, in some natural units, the repulsion of two electrons (mature's universal charge) due to electricity, and the attraction of two electrons due to their masses, we can measure the ratio of electrical repulsion to the gravitational attraction. The ratio is independent of the distance and is a fundamental constant of nature."

"It is a fact that the force of gravitation is proportional to the mass, the quantity which is fundamentally a measure of inertia - of how hard it is to hold something which is going around in a circle."

Einstein's law of gravitation = anything that has energy has mass.
mass - a thing attracted gravitationally. Even light, which has energy, must have a mass.

"The quantum-mechanical aspects of nature have not yet been carried over to gravitation. When the scale is so small that we need the quantum effects, the gravitational effects are so weak that the need for a quantum theory of gravitation has not yet developed."  

"We would like to emphasize a very important difference between classical and quantum mechanics. We've been talking about the probability that an electron will arrive in a given circumstance. We have implied that in our experimental arrangement (or even in the best possible one) it would be impossible to predict exactly what would happen. We can only predict the odds! This would mean, if it were true, that physics has given up on the problem of trying to predict exactly what will happen in a definite circumstance. Yes! Physics has given up. We do not know how to predict what would happen in a given circumstance, and we believe now that it is impossible, that the only thing that can be predicted is the probability of different events. It must be recognized that this is a retrenchment in our earlier ideal of understanding nature. It may be a backward step, but no one has seen a way to avoid it."