Reading - The Code of Time (continuous updating)
Enjoy the book and when I did the extracts - almost became a reward after completing other assignments! I enjoy the logic of the book and also understanding the logic of the world running. As the logic or to say the convincing storytelling, it usually answers my question as soon as I came up with.
「He looked for a plausible explanation and found one by imagining that the sun and the Earth do not attract each other directly but that each of the two gradually acts on that which is between them. And since what lies between them is only space and time, he imagined that the sun and the Earth each modified the space and the time that surrounded them, just as a body immersed in water displaces the water around it.
“Modification of the structure of time”: a mass slows down time around itself. The Earth is a large mass and slows down time in its vicinity. It does so more in the plains and less in the mountains, because the plains are closer to it.
If things fall, it is due to this slowing down of time. Where time passes uniformly, in interplanetary space, things do not fall. The movement of things inclines naturally toward where time passes more slowly, as when we run down the beach into the sea and the resistance of water on our legs make us fall headfirst into the waves. Things fall downward because, down there, time is slowed by the Earth.
Hence, even though we cannot easily observe it, the slowing down of time nevertheless has crucial effects: things fall because of it, and it allows us to keep our feet firmly on the ground. If our feet adhere to the pavement, it is because our whole body inclines naturally to where time runs more slowly - and time passed more slowly for your feet than it does for your head.」
It's a very poetic and romantic expression. It seems that time is so precious to us that we are reluctant to stay where it flows faster. Not only for human beings, but for all the creatures and lifeless objects. Also, found another reason that I prefer low house than buildings. But I'm confused by the logic behind it. According to the law of universal gravitation, every particle attracts every other particle in the universe with a force. Why the "slowing down time" is not a phenomenon but the reasons for "things falling"? Can every object that has the quality modify the structure of time? When I searched for the general relativity and special relativity, I recalled the memory that having learnt it in middle school - felt sad for the exam-oriented education - teacher only asked us to mechanically remember the definition and formula in books, hoping that teacher could recommend such book so that more people may think physics was not that bad at my middle school days.
Things are transformed one into another according to necessity,
and render justice to one another
according to the order of time. - Anaximander
From one of the crucial, initial moments of natural science there remains nothing but these obscure, arcanely resonant words, this appeal to the "order of time."
In antiquity, astronomy described the movements of stars in time. The equations of physics describe how things change in time. From the equations of Newton, which establish the foundations of mechanics, to those of Maxwell for electromagnetic phenomena; from Schrodinger's equation describing how quantum phenomena evolve, to those of quantum field theory for the dynamics of subatomic particles: the whole of our physics, and science in general, is about how things develop "according to the oder of time."
There is no "truer" time; there are two times and they change relative to each other. Neither is truer than the other.
Times are legion: a different one for every point in space. There is no single time; there is a vast multitude of them.
We do not describe how the world evolves in time: we describe how things evolve in local time. The world is not like a platoon advancing at the pace of a single commander. It's a network of events affecting each other.
Physics does not describe how things evolve in “time” but how things evolve in their own times, and how “time” evolve relative to each other.
I didn't realize I also learnt it in middle school until I saw the equation: t(table) - t(ground) = gh/c²t
Time took my memory away...
It became more vivid image in my mind when he describes the world "a network of events affecting each other". Every event owns a time - is it we live in time, or time lives in us? If time lives in us, how our brains figure out which is the past and which is the future? Why we can only remember the past? Does future already exist?
What is a "proper time"?
The things of this world interweave dances made to different rhythms. If the world is upheld by the dancing Shiva, there must be ten thousand such dancing Shivas, like the dancing figures painted by Matisse…
So fun! different rhythms
In the elementary equations of the world, the arrow of time appears only where there is heat.
Only where there is heat is there a distinction between past and future. - frictions & thoughts!
Every time a difference is manifested between the past and the future, heat is involved. In every sequence of events that becomes absurd if projected backward, there is something that is heating up.
The equation for time’s arrow.
delta S >= 0
It is the only equation of fundamental physics that knows any difference between past and future.
...throwing us into one of our most dizzying dives toward understanding the intimate grammar of our world.
Have done so many exercises using this equation and really haven't think about that!
The instability of his character was real enough, oscillating as it did between elation and depression.
This is what Boltzmann understood. The difference between past and future lies in the natural disordering that leads to gradually less particular, less special situations.
Why, in one of the two directions of time - the one we call past - were things more ordered? ... Why, in the past, was entropy lower?
But why do the phenomena that we observe around us in the cosmos begin in a state of lower entropy in the first place?
But notice that it is particular if we look at the color of the cards - red or black. It is particular because I am looking at the color. ... If we think about it carefully, every configuration is particular, every configuration is singular, if we look at all of its detail, since every configuration always has something about it that characterizes it in a unique way.
The notion of "particularity" is born only at the moment we begin to see the universe in a blurred and approximate way.
Is it right? But we still can tell which one is relatively more unique or particular. Isn't it too idealism？
Boltzmann has shown that entropy exists because we describe the world in a blurred fashion. He has demonstrated that entropy is precisely the quantity that counts how many are the different configurations that our blurred vision does not distinguish between. Heat, entropy, and the lower entropy of the past are notions that belong to an approximate, statistical description of nature.
The difference between past and future is deeply linked to this blurring... So if I could take into account all the details of the exact, microscopic state of the world, would the characteristic aspects of the flowing of time disappear?
Yes. If I observe the microscopic state of things, then the difference between past and future vanishes. The future of the world, for instance, is determined by its present state - though neither more nor less than is the past.(That is to say, in a deterministic manner if you overlook quantum mechanics, and in a probabilistic manner if you take account of quantum mechanics instead. In both cases, in the same way for the future as for the past.) p33
I'm totally confused! In a micro world, time does not exit?
We often say that causes precede effects and yet, in the elementary grammar of things, there is no distinction between "cause" and "effect". There are regularities, represented by what we call physical laws, that link events of different times, but they are symmetric between future and past. In a microscopic description, there can be no sense in which the past is different from the future.
This is the disconcerting conclusion that emerges from Boltzmann's work: the difference between the past and the future refers only to our own blurred vision of the world. It's a conclusion that leaves us flabbergasted: is it really possible that a perception so vivid, basic, existential - my perception of the passage of time - depends on the fact that I cannot apprehend the world in all of its minute detail?
...Is it possible that I have as much knowledge of the past - or ignorance of it - as I do of the future?
What does it mean by saying that there is no difference between the past and the future? The "difference" is defined by whom? We now differentiate past and future because it stands in different locations in a timetable. How does it make sense when events are linked within different time but there is no difference between past and future? Is it because "present" does not exit? - Truly disconcerting!
...the evidence id overwhelming: all the phenomena that characterize the flowing of time are reduced to a "particular" state in the world's past, the "particularity" of which may be attributed to the blurring of our perspective. ... entropy, as Boltzmann fully understood, is nothing other than the number of microscopic states that our blurred vision of the world fails to distinguish.
以前从没把热力学和量子力学或是时间结合起来想过，就像它们在物理书上是完全seperated的两章一样。Really tried hard to remember Boltzmann constant in middle school to remember nothing but a number:(
Many young students of physics go to visit his tomb, and linger there to ponder. And sometimes the odd elderly professor of physics as well.
Appointed a university professor at just twenty-five years old; received at court by the emperor at the apex of his success; severely criticized by the majority of the academic world, which did not understand his ideas; always precariously balanced between enthusiasm and depression: the "dear sweet chubby one", Ludwig Boltzmann, will end his life by hanging himself.
(speed also slows down time)Einstein had read this within the equation of electromagnetism, by taking them seriously.
What is your sister doing now on Proxima b? ----- like asking "What is here in Beijing?" when we are in Venice.
By take care: if you look like your sister, you are receiving light that travels from her to your eyes. ... Therefore, you are not quite seeing what she is doing now but what she was doing a few nanoseconds ago.
If your sister is on Proxima b, however, light takes four years to reach you from there. Hence if you look at her through a telescope, or receive a radio communication from her, you know what she was doing four years ago rather than what she is doing now.
It's so easy to understand why "now" means nothing!
Oh my god, I was just about to say 「so perhaps you can say that your sister is doing now is what she will be doing four years after the moment that you see her through the telescope」
“simultaneity”: our different speeds define different surfaces of simultaneity. Not even in this way do we obtain a notion of a common "present".
There is no special moment on Proxima b that corresponds to what constitutes the present here and now.
So, narrow the range from the distance between the Earth and Proxima b to the distance between you and I, we don't share a "present"? ---------once again he answers me! So amazingly strange!!!
The notion of "the present" refers to things that are close to us, not to anything that is far away.
Our "present" does not extend throughout the universe. It is like a bubble around us.
How far does this bubble extend? It depends on the precision with which we determine time. If by nanoseconds, the present is defined only over a few meters; if by milliseconds, it is defined over thousands of kilometers. As humans, we distinguish tenths of a second only with great difficulty; we can easily consider our entire planet to be like a single bubble where we can speak of the present as if it were an instant shared by us all. This is as far as we can go.
So we still "own" the present on this planet right?
There is our past: all the events that happened before what we can witness now. There is our future: the events that will happen after the moment from which we can see the here and now. Between this past and this future there is an interval that is neither past nor future and still has a duration: fifteen minutes on Mars; lightyears on Proxima b; millions of years in the Andromeda galaxy. It is the expanded present. It is perhaps the greatest and strangest of Einstein's discoveries.
The "present of the universe" is meaningless.