Certainly, some difficult topics to wrap ones head around. Feynman does a marvelous job teaching these difficult to teach subjects. One can't help but wonder what the world would be like if we were able to grow up with professors such as he in our lives. Thankfully these books and his lectures exist. They are marvelous. I'm certain I'll return to this book over and over as I try to grasp the ideas on deeper levels.

Unico errore: scrivere una legge di trasformazione della massa tra sistemi inerziali. In fisica si assume la massa costante in tutti i sistemi di riferimento, tanto che è utilizzata come etichetta per le particelle.

Minus two stars for my own mathematical and equation lack of knowledge. So many equations and symbols! I don't remember the names for most of the Greek symbols/letters used. But I did enjoy reading about the different laws and what happens in curved space-time.

"Another example in which the laws are not symmetrical, that we know quite well, is this: a system in rotation at a uniform angular velocity does not give the same apparent laws as one that is not rotating. If we make an experiment and then put everything in a spaceship and have the spaceship spinning in empty space all alone at a constant angular velocity, the apparatus will not work the same way because, as we know, things inside the equipment will be thrown to the outside, and so on, by the centrifugal or Coriolis forces, etc. In fact, we can tell that the earth is rotating by using a so-called Foucault pendulum, without looking inside." pg. 28 [The Coriolis effect/force was also mentioned in To Sleep in a Sea of Stars, which I'm currently also reading, so this was more of a book coincidence, but I wanted to gather the context around the Coriolis effect/force to better understand it. Also is this the same Foucault who talked about surveillance?]

"The symmetries of the physical laws are very interesting at this level, but they turn out, in the end, to be even more interesting and exciting when we come to quantum mechanics. For a reason which we cannot make clear at the level of the present discussion--a fact that most physicists still find somewhat staggering, a most profound and beautiful thing, is that, in quantum mechanics, for each of the rules of symmetry there is a corresponding conservation law; there is a definite connection between the laws of the conservation and the symmetries of physical laws. We can only state this at present, without any attempt at explanation.
The fact, for example, that the laws are symmetrical for translation in space when we add the principles of quantum mechanics turns out to mean that momentum is conserved.
That the laws are symmetrical under translation in time means, in quantum mechanics, that energy is conserved.
Invariance under rotation through a fixed angle in space corresponds to the conservation of angular momentum. These connections are very interesting and beautiful things, among the most beautiful and profound things in physics." pg. 29

"The principle of relativity was first stated by Newton, in one of his corollaries to the laws of motion: 'The motions of bodies included in a given space are the same among themselves, whether that space is at rest or moves uniformly forward in a straight line.' This means, for example, that if a spaceship is drifting along at a uniform speed, all experiments performed in the spaceship and all the phenomena in the spaceship will appear the same as if the ship were not moving, provided, of course, that one does not look outside. That is the meaning of the principle of relativity. This is a simple enough idea, and the only question is whether it is true that in all experiments performed inside a moving system the laws of physics will appear the same as they would if the system were standing still." pg. 50-51

"Given the fact that the velocity of light is 186,000 mi/sec, one will find few philosophers who will calmly state that it is self-evident that if light goes 186,000 mi/sec inside a car, and the car is going 100,000 mi/sec, that the light also goes 186,000 mi/sec past an observer on the ground. That is a shocking fact to them; the very ones who claim it is obvious find, when you give them a specific fact, that it is not obvious." pg. 75

"The mass of the object which is formed when two equal objects collide must be twice the mass of the objects which come together. You might say, 'Yes, of course, that is the conservation of mass.' But not 'Yes, of course,' so easily, because these masses have been enhanced over the masses that they would be if they were standing still, yet they still contribute, to the total M, not the mass they have when standing still, but more. Astonishing as that may seem, in order for the conservation of momentum to work when two objects come together, the mass that they form must be greater than the rest masses of the objects, even though the objects are at rest after the collision!" pg. 88

"Now the interesting thing about all the rest of space-time, i.e. region 1, is that we can neither affect it now from O, nor can it affect us now at O, because nothing can go faster than the speed of light. Of course, what happens at R can affect us later; that is, if the sun is exploding 'right now,' it takes eight minutes before we know about it, and it cannot possibly affect us before then.
What we mean by 'right now' is a mysterious thing which we cannot define and we cannot affect, but it can affect us later, or we could have affected it if we had done something far enough in the past. When we look at the star Alpha Centauri, we see it as it was four years ago; we might wonder what it is like 'now.' 'Now' means at the same time from our special coordinate system. We can only see Alpha Centauri by the light that has come from our past, up to four years ago, but we do not know what it is doing 'now'; it will take four years before what it is doing 'now' can affect us. Alpha Centauri 'now' is an idea or concept of our mind; it is not something that is really definable physically at the moment, because we have to wait to observe it; we cannot even define it right 'now.' Furthermore, the 'now' depends on the coordinate system. If, for example, Alpha Centauri were moving, an observer there would not agree with us because he would put his axes at an angle, and his 'now' would be a different time. We have already talked about the fact that simultaneity is not a unique thing." pg. 100-101

Book: borrowed from SSF Main Library.

Richard Feynman - a legend in the field of Physics and even a better lecturer. Great book if you have an interest for astrophysics and want to take a dive into more complex physical scenarios.

C'è chi ha il dono di rendere facili anche le cose più difficili. Chi è capace di trasmettere poesia tramite le formule di trasformazione. Feynman è capace di tutto questo e anche di più. Un saggio da non perdere se si può contare su solide basi matematiche e fisiche.

Hilaaa diya!!!

A beautiful book. This is a selection from Feynman's lectures specifically covering Einstein's Special and General Theories of Relativity. The treatment is involved; not at an unreachable technical level but one needs to take some paper with pencil to enjoy the content as Feynman explains some profound and extraordinary physics.

In a time of excessive work, night reads like this give a glimpse of something far more eternal and magnificent than what can be seen in normal life. And I am grateful for it.

(Last read this book in 2005)

Feynman, Six Not-So-Easy Pieces - another six chapters from Feynman’s great physics textbook, quite a bit more technical than the “easy” pieces, but the reward is proper physical insight into special relativity, spacetime, and curved space.

4/5

Another clear book by Feynman. The so-called not-so-easy pieces are made easy through his explications, and some solutions to problems mentioned are innovative. Highly recommended.

Just like the title says, not as accessible as the first book. I enjoyed the first two chapters about symmetry even if I didn't get all of the specifics. Then relativity required too much work for me right now. Maybe I'll come back to it when I have more motivation.

"Not so easy" is right! Feynman designed these lectures so that, he hoped, physics non-majors would be able to grasp the concepts, while majors would get a sense of the excitement of physics and maintain their interest.

There is a lot of math in the book, but one can ignore most of it (as I did), and try to understand the ideas from Feynman's very clear and simple language. But, simple as Feynman's language is, these concepts are hard for even a smart person to get his or her head around. We have grown up in a 3-dimensional world that we understand somewhat, and it's not easy to grasp relativity, curved space, of space-time, let alone curved space-time. I did my best, and Feynman is always a joy to read, but I probably won't remember much about these topics tomorrow.

Feynman è sempre molto bravo nel fornire una descrizione dei fenomeni fisici che vada oltre le formule matematiche e colga il senso fisico.
Suppongo però che le parti matematiche che per me sono ovvie per i non addetti ai lavori siano un po' ostiche , quindi non lo consiglio ad un lettore che ricerchi un testo divulgativo.
Sul fronte specialistico non mi piace il fatto che Feynman, come quasi tutti negli anni 60, sostenga e utilizzi il concetto di massa relativistica che varia con la velocità, concetto ormai accantonato e sostituito dall'idea che la quantità di moto e l'energia dipendano dalla velocità mentre la massa sia un invariante esattamente come la carica elettrica o il numero leptonico, per questo motivo 4 stelle e non 5.