出版社: Riverhead Books
副标题: The Journey to Quantum Gravity
译者: Erica Segre
出版年: 2017124
页数: 288
定价: USD 26.00
装帧: Hardcover
ISBN: 9780735213920
内容简介 · · · · · ·
What are time and space made of?
Where does matter come from?
And what exactly is reality?
Theoretical physicist Carlo Rovelli has spent his whole life exploring these questions and pushing the boundaries of what we know. Here he explains how our image of the world has changed over the last few dozen centuries.
In elegant and accessible prose, Rovelli takes us on a wondrous jou...
What are time and space made of?
Where does matter come from?
And what exactly is reality?
Theoretical physicist Carlo Rovelli has spent his whole life exploring these questions and pushing the boundaries of what we know. Here he explains how our image of the world has changed over the last few dozen centuries.
In elegant and accessible prose, Rovelli takes us on a wondrous journey from Aristotle to Albert Einstein, from Michael Faraday to the Higgs boson, and from classical physics to his own work in quantum gravity. As he shows us how the idea of reality has evolved over time, Rovelli offers readers a deeper understanding of the theories he introduced so concisely in Seven Brief Lessons on Physics. His evocative explanations invite us to imagine, beyond our everchanging idea of reality, a whole new world that has yet to be discovered.
作者简介 · · · · · ·
Carlo Rovelli,
an Italian theoretical physicist, is the head of the quantum gravity group at the Centre de Physique Théorique of AixMarseille Université. He is one of the founders of the loop quantum gravity theory and the author of the international bestseller Seven Brief Lessons on Physics. Rovelli lives in Marseille, France.
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Reality Is Not What It Seems的书评 · · · · · · ( 全部 89 条 )
《现实不似你所见》思维导图
这篇书评可能有关键情节透露
《现实不似你所见——量子引力之旅》思维导图，专门选了一个配色和书封面颜色差不多的主题来做。内容不多的一本小书，能够记下来的东西不多，一部分是广为人知的物理学发展史，没有记录其中。此书给人印象最深刻的就是对于科学的推崇和信赖，对为科学做出贡献的科学家们的致敬... (展开)挑战读者的想象力与理解力
这篇书评可能有关键情节透露
目前理论物理学的发展目标，就是争取把《广义相对论》、《量子物理学》、《宇宙标准模型》三大门学科的理论合二为一，找出所谓的万物理论，以书中所描述的最新发展来看，路漫漫其修远兮。 相对论是大家耳熟能详的东西，然而能真正理解的并不多，不信，尝试理解一下这个，地球... (展开)一场优雅的物理图像旅行
这篇书评可能有关键情节透露
我们儿时或许都或多或少地做过一个梦，梦想有一天能够窥破渺茫宇宙的本质，笔尖流淌出描绘世间万象的绝学。 此书就是一本这样的书。且语言之优美，逻辑之清晰，深感叹服。作为目前研究量子相关（光与物质相互作用，cQED基础的量子计算）的一名小博士生，自觉还是稍微有资格点评... (展开)当对物理毫无概念的我翻开了这本书
这篇书评可能有关键情节透露
半个月前的一天，我在鹅组闲逛，偶然看到一个关于巨物恐惧症的帖子，点进去是B站的“当太阳系的各个行星在月球的位置上会是什么样”的视频。我发现在手机上看完还不过瘾，就投屏到60寸电视上再享受了一把窒息感，紧随起来的是一种莫名其妙的快乐和释放。在刷完B站各种固定或者... (展开)> 更多书评 89篇
读书笔记 · · · · · ·
我来写笔记
一些摘录： 1 An ‘expanded present’ Between the past and the future of an event (for example, between the past and the future for you, where you are, and in the precise moment in which you are reading) there exists an ‘intermediate zone’, an ‘expanded present’; a zone that is neither past nor future. This is the discovery made with special relativity. ... on Mars, there are events that in ...
20210616 09:35:41
一些摘录：
1 An ‘expanded present’
Between the past and the future of an event (for example, between the past and the future for you, where you are, and in the precise moment in which you are reading) there exists an ‘intermediate zone’, an ‘expanded present’; a zone that is neither past nor future. This is the discovery made with special relativity.
... on Mars, there are events that in this precise moment have already happened, events that are yet to happen, but also a quarter of an hour during which things occur that are neither in our past nor in our future.
2 There is no need to add space as an extra ingredient.
The world is not made up of space + particles + electromagnetic field + gravitational field. The world is made up of particles + fields, and nothing else; there is no need to add space as an extra ingredient. Newton’s space is the gravitational field. Or vice versa, which amounts to saying the same thing: the gravitational field is space.
But, unlike Newton’s space, which is flat and fixed, the gravitational field, by virtue of being a field, is something which moves and undulates, subject to equations...
3 The border of the universe
the universe can be finite and at the same time have no boundary. How?
Just as the surface of the Earth is not infinite but does not have a boundary either, where it ‘ends’. This can happen, naturally enough, if something is curved: the surface of the Earth is curved. And in the theory of general relativity, of course, threedimensional space can also be curved. Consequently, our universe can be finite but borderless.
On the surface of the Earth, if I were to keep walking in a straight line, I would not advance ad infinitum: I would eventually get back to the point I started from. Our universe could be made in the same way: if I leave in a spacecraft and journey always in the same direction, I fly around the universe and eventually end up back on Earth. A threedimensional space of this kind, finite but without boundary, is called a 3sphere.
The best way of describing a 3sphere is not to try to ‘see it from the outside’, but rather to describe what happens when moving within it.
Our culture is foolish to keep science and poetry separated: they are two tools to open our eyes to the complexity and beauty of the world.
Dante’s 3sphere is only an intuition within a dream. Einstein’s 3sphere has mathematical form and follows from the theory’s equations. The effect of each is different. Dante moves us deeply, touching the sources of our emotions. Einstein opens a road towards the unsolved mysteries of our universe. But both count among the most beautiful and significant flights that the mind can achieve.
4 Light is made up of small grains, particles of light
Today we call these packets of energy ‘photons’, from the Greek word for light: ϕώς. Photons are the grains of light, its ‘quanta’. In the article Einstein writes:
It seems to me that the observations associated with blackbody radiation, fluorescence, the production of cathode rays by ultraviolet light, and other related phenomena connected with the emission or transformation of light are more readily understood if one assumes that the energy of light is discontinuously distributed in space. In accordance with the assumption to be considered here, the energy of a light ray spreading out from a point source is not continuously distributed over an increasing space but consists of a finite number of ‘energy quanta’ which are localized at points in space, which move without dividing, and which can only be produced and absorbed as complete units.
These simple and clear lines are the real birth certificate of quantum theory. Note the wonderful initial ‘It seems to me …’, ... True genius is aware of the momentousness of the steps it is taking, and is always hesitant …
5 Electrons don’t always exist. They exist when they interact.
Colour is the speed at which Faraday’s lines vibrate, and this is determined by the vibrations of the electric charges which emit light. These charges are the electrons that move inside the atoms. Therefore, studying spectra, we can understand how electrons move around nuclei.
... But then why does the light emitted by an atom not contain all colours, rather than just a few particular ones? Why are atomic spectra not a continuum of colours, instead of just a few separate lines? Why, in technical parlance, are they ‘discrete’ instead of continuous?
Bohr makes the hypothesis that electrons can exist only at certain ‘special’ distances from the nucleus, that is, only on certain particular orbits...
Heisenberg returns home gripped by feverish emotion, and plunges into calculations. He emerges, some time later, with a disconcerting theory: a fundamental description of the movement of particles, in which they are described not by their position at every moment but only by their position at particular instants: the instants in which they interact with something else.
This is the second cornerstone of quantum mechanics, its hardest key: the relational aspect of things. Electrons don’t always exist. They exist when they interact. They materialize in a place when they collide with something else. The quantum leaps from one orbit to another constitute their way of being real: an electron is a combination of leaps from one interaction to another.
6 As Heisenberg had recognized: no variable of the object is defined between one interaction and the next.
The venerable Bohr said of him, ‘Of all physicists, Dirac has the purest soul.’ ... For him, the world is not made of things, it’s constituted of an abstract mathematical structure which shows us how things appear and how they behave when manifesting themselves. It’s a magical encounter between logic and intuition.
Dirac’s quantum mechanics is the mathematical theory used today by any engineer, chemist or molecular biologist. In it, every object is defined by an abstract space and has no property in itself, apart from those that are unchanging, such as mass. Its position and velocity, its angular momentum and its electrical potential, and so on, acquire reality only when it collides – ‘interacts’– with another object. It is not just its position which is undefined, as Heisenberg had recognized: no variable of the object is defined between one interaction and the next. The relational aspect of the theory becomes universal.
7 Chance operates at the atomic level
We do not know with certainty where the electron will appear, but we can compute the probability that it will appear here or there. This is a radical change from Newton’s theory, where it is possible, in principle, to predict the future with certainty. Quantum mechanics brings probability to the heart of the evolution of things. This indeterminacy is the third cornerstone of quantum mechanics: the discovery that chance operates at the atomic level. While Newton’s physics allows for the prediction of the future with exactitude, if we have sufficient information about the initial data and if we can make the calculations, quantum mechanics allows us to calculate only the probability of an event. This absence of determinism at a small scale is intrinsic to nature. An electron is not obliged by nature to move towards the right or the left; it does so by chance. The apparent determinism of the macroscopic world is due only to the fact that the microscopic randomness cancels out on average, leaving only fluctuations too minute for us to perceive in everyday life.
The probability of finding an electron or any other particle at one point or another can be imagined as a diffuse cloud, denser where the probability of seeing the particle is stronger. Sometimes it is useful to visualize this cloud as if it were a real thing. For instance, the cloud that represents an electron around its nucleus indicates where it is more likely that the electron appears if we look at it.
8 There are no longer particles which move in space with the passage of time, but quantum fields whose elementary events happen in spacetime.
Quantum mechanics, with its fields/particles, offers today a spectacularly effective description of nature. The world is not made up of fields and particles but of a single type of entity: the quantum field. There are no longer particles which move in space with the passage of time, but quantum fields whose elementary events happen in spacetime. The world is strange, but simple.
9 Some conclusions about what it is, precisely, that quantum mechanics tells us about the world.
Quanta 1: Information is finite the existence of a limit to the information that can exist within a system: a limit to the number of distinguishable states in which a system can be. This limitation upon infinity – this granularity of nature glimpsed by Democritus – is the first central aspect of the theory.
Quanta 2: Indeterminacy
An electron, a quantum of a field or a photon does not follow a trajectory in space but appears in a given place and at a given time when colliding with something else. When and where will it appear? There is no way of knowing with certainty. Quantum mechanics introduces an elementary indeterminacy to the heart of the world.
If we look at a stone, it stays still. But if we could see its atoms, we would observe them constantly spread here and there, and in ceaseless vibration. Quantum mechanics reveals to us that, the more we look at the detail of the world, the less constant it is. The world is not made up of tiny pebbles. It is a world of vibrations, a continuous fluctuation, a microscopic swarming of fleeting microevents.
The atomism of antiquity had anticipated also this aspect of modern physics: the appearance of laws of probability at a deep level. ...
... all trajectories from A to B contribute: it is as if the electron, in order to go from A to B, passed ‘through all possible trajectories’, or, in other words, unfurled into a cloud in order then to converge mysteriously on point B, where it collides again with something else.
Quanta 3: Reality is relational
It is only in interactions that nature draws the world.
In the world described by quantum mechanics there is no reality except in the relations between physical systems. It isn’t things that enter into relations but, rather, relations that ground the notion of ‘thing’. The world of quantum mechanics is not a world of objects: it is a world of events. Things are built by the happening of elementary events: as the philosopher Nelson Goodman wrote in the 1950s, in a beautiful phrase, ‘An object is a monotonous process.’ ... What is a wave, which moves on water without carrying with it any drop of water? A wave is not an object, in the sense that it is not made of matter that travels with it. The atoms of our body, as well, flow in and away from us. We, like waves and like all objects, are a flux of events; we are processes, for a brief time monotonous …
To summarize, quantum mechanics is the discovery of three features of the world: Granularity (figure 4.8). The information in the state of a system is finite, and limited by Plank’s constant.
Indeterminacy. The future is not determined unequivocally by the past. Even the more rigid regularities we see are, ultimately, statistical.
Relationality. The events of nature are always interactions. All events of a system occur in relation to another system. Quantum mechanics teaches us not to think about the world in terms of ‘things’ which are in this or that state but in terms of ‘processes’ instead. A process is the passage from one interaction to another. The properties of ‘things’manifest themselves in a granular manner only in the moment of interaction, that is to say, at the edges of the processes, and are such only in relation to other things. They cannot be predicted in an unequivocal way but only in a probabilistic one.
I think that the obscurity of the theory is not the fault of quantum mechanics but, rather, is due to the limited capacity of our imagination.
10 The gravitational field at a point is not well defined, when taking quanta into account.
The gravitational field at a point is not well defined, when taking quanta into account.
There is an intuitive way of understanding what happens. Suppose we want to observe a very, very, very small region of space. To do this, we need to place something in this area, to mark the point that we wish to consider. Say we place a particle there. Heisenberg had understood that you can’t locate a particle at a point in space for long. It soon escapes. The smaller the region in which we try to locate a particle, the greater the velocity at which it escapes. (This is Heisenberg’s uncertainty principle.) If the particle escapes at great speed, it has a great deal of energy. Now let us take Einstein’s theory into account. Energy makes space curve. A lot of energy means that space will curve a great deal. A lot of energy in a small region results in curving space so much that it collapses into a black hole, like a collapsing star. But if a particle plummets into a black hole, I can no longer see it. I can no longer use it as a reference point for a region of space. I can’t manage to measure arbitrarily small regions of space, because if I try to do this these regions disappear inside a black hole.
未完待续 （慢慢再补
回应 20210616 09:35:41

一些摘录： 1 An ‘expanded present’ Between the past and the future of an event (for example, between the past and the future for you, where you are, and in the precise moment in which you are reading) there exists an ‘intermediate zone’, an ‘expanded present’; a zone that is neither past nor future. This is the discovery made with special relativity. ... on Mars, there are events that in ...
20210616 09:35:41
一些摘录：
1 An ‘expanded present’
Between the past and the future of an event (for example, between the past and the future for you, where you are, and in the precise moment in which you are reading) there exists an ‘intermediate zone’, an ‘expanded present’; a zone that is neither past nor future. This is the discovery made with special relativity.
... on Mars, there are events that in this precise moment have already happened, events that are yet to happen, but also a quarter of an hour during which things occur that are neither in our past nor in our future.
2 There is no need to add space as an extra ingredient.
The world is not made up of space + particles + electromagnetic field + gravitational field. The world is made up of particles + fields, and nothing else; there is no need to add space as an extra ingredient. Newton’s space is the gravitational field. Or vice versa, which amounts to saying the same thing: the gravitational field is space.
But, unlike Newton’s space, which is flat and fixed, the gravitational field, by virtue of being a field, is something which moves and undulates, subject to equations...
3 The border of the universe
the universe can be finite and at the same time have no boundary. How?
Just as the surface of the Earth is not infinite but does not have a boundary either, where it ‘ends’. This can happen, naturally enough, if something is curved: the surface of the Earth is curved. And in the theory of general relativity, of course, threedimensional space can also be curved. Consequently, our universe can be finite but borderless.
On the surface of the Earth, if I were to keep walking in a straight line, I would not advance ad infinitum: I would eventually get back to the point I started from. Our universe could be made in the same way: if I leave in a spacecraft and journey always in the same direction, I fly around the universe and eventually end up back on Earth. A threedimensional space of this kind, finite but without boundary, is called a 3sphere.
The best way of describing a 3sphere is not to try to ‘see it from the outside’, but rather to describe what happens when moving within it.
Our culture is foolish to keep science and poetry separated: they are two tools to open our eyes to the complexity and beauty of the world.
Dante’s 3sphere is only an intuition within a dream. Einstein’s 3sphere has mathematical form and follows from the theory’s equations. The effect of each is different. Dante moves us deeply, touching the sources of our emotions. Einstein opens a road towards the unsolved mysteries of our universe. But both count among the most beautiful and significant flights that the mind can achieve.
4 Light is made up of small grains, particles of light
Today we call these packets of energy ‘photons’, from the Greek word for light: ϕώς. Photons are the grains of light, its ‘quanta’. In the article Einstein writes:
It seems to me that the observations associated with blackbody radiation, fluorescence, the production of cathode rays by ultraviolet light, and other related phenomena connected with the emission or transformation of light are more readily understood if one assumes that the energy of light is discontinuously distributed in space. In accordance with the assumption to be considered here, the energy of a light ray spreading out from a point source is not continuously distributed over an increasing space but consists of a finite number of ‘energy quanta’ which are localized at points in space, which move without dividing, and which can only be produced and absorbed as complete units.
These simple and clear lines are the real birth certificate of quantum theory. Note the wonderful initial ‘It seems to me …’, ... True genius is aware of the momentousness of the steps it is taking, and is always hesitant …
5 Electrons don’t always exist. They exist when they interact.
Colour is the speed at which Faraday’s lines vibrate, and this is determined by the vibrations of the electric charges which emit light. These charges are the electrons that move inside the atoms. Therefore, studying spectra, we can understand how electrons move around nuclei.
... But then why does the light emitted by an atom not contain all colours, rather than just a few particular ones? Why are atomic spectra not a continuum of colours, instead of just a few separate lines? Why, in technical parlance, are they ‘discrete’ instead of continuous?
Bohr makes the hypothesis that electrons can exist only at certain ‘special’ distances from the nucleus, that is, only on certain particular orbits...
Heisenberg returns home gripped by feverish emotion, and plunges into calculations. He emerges, some time later, with a disconcerting theory: a fundamental description of the movement of particles, in which they are described not by their position at every moment but only by their position at particular instants: the instants in which they interact with something else.
This is the second cornerstone of quantum mechanics, its hardest key: the relational aspect of things. Electrons don’t always exist. They exist when they interact. They materialize in a place when they collide with something else. The quantum leaps from one orbit to another constitute their way of being real: an electron is a combination of leaps from one interaction to another.
6 As Heisenberg had recognized: no variable of the object is defined between one interaction and the next.
The venerable Bohr said of him, ‘Of all physicists, Dirac has the purest soul.’ ... For him, the world is not made of things, it’s constituted of an abstract mathematical structure which shows us how things appear and how they behave when manifesting themselves. It’s a magical encounter between logic and intuition.
Dirac’s quantum mechanics is the mathematical theory used today by any engineer, chemist or molecular biologist. In it, every object is defined by an abstract space and has no property in itself, apart from those that are unchanging, such as mass. Its position and velocity, its angular momentum and its electrical potential, and so on, acquire reality only when it collides – ‘interacts’– with another object. It is not just its position which is undefined, as Heisenberg had recognized: no variable of the object is defined between one interaction and the next. The relational aspect of the theory becomes universal.
7 Chance operates at the atomic level
We do not know with certainty where the electron will appear, but we can compute the probability that it will appear here or there. This is a radical change from Newton’s theory, where it is possible, in principle, to predict the future with certainty. Quantum mechanics brings probability to the heart of the evolution of things. This indeterminacy is the third cornerstone of quantum mechanics: the discovery that chance operates at the atomic level. While Newton’s physics allows for the prediction of the future with exactitude, if we have sufficient information about the initial data and if we can make the calculations, quantum mechanics allows us to calculate only the probability of an event. This absence of determinism at a small scale is intrinsic to nature. An electron is not obliged by nature to move towards the right or the left; it does so by chance. The apparent determinism of the macroscopic world is due only to the fact that the microscopic randomness cancels out on average, leaving only fluctuations too minute for us to perceive in everyday life.
The probability of finding an electron or any other particle at one point or another can be imagined as a diffuse cloud, denser where the probability of seeing the particle is stronger. Sometimes it is useful to visualize this cloud as if it were a real thing. For instance, the cloud that represents an electron around its nucleus indicates where it is more likely that the electron appears if we look at it.
8 There are no longer particles which move in space with the passage of time, but quantum fields whose elementary events happen in spacetime.
Quantum mechanics, with its fields/particles, offers today a spectacularly effective description of nature. The world is not made up of fields and particles but of a single type of entity: the quantum field. There are no longer particles which move in space with the passage of time, but quantum fields whose elementary events happen in spacetime. The world is strange, but simple.
9 Some conclusions about what it is, precisely, that quantum mechanics tells us about the world.
Quanta 1: Information is finite the existence of a limit to the information that can exist within a system: a limit to the number of distinguishable states in which a system can be. This limitation upon infinity – this granularity of nature glimpsed by Democritus – is the first central aspect of the theory.
Quanta 2: Indeterminacy
An electron, a quantum of a field or a photon does not follow a trajectory in space but appears in a given place and at a given time when colliding with something else. When and where will it appear? There is no way of knowing with certainty. Quantum mechanics introduces an elementary indeterminacy to the heart of the world.
If we look at a stone, it stays still. But if we could see its atoms, we would observe them constantly spread here and there, and in ceaseless vibration. Quantum mechanics reveals to us that, the more we look at the detail of the world, the less constant it is. The world is not made up of tiny pebbles. It is a world of vibrations, a continuous fluctuation, a microscopic swarming of fleeting microevents.
The atomism of antiquity had anticipated also this aspect of modern physics: the appearance of laws of probability at a deep level. ...
... all trajectories from A to B contribute: it is as if the electron, in order to go from A to B, passed ‘through all possible trajectories’, or, in other words, unfurled into a cloud in order then to converge mysteriously on point B, where it collides again with something else.
Quanta 3: Reality is relational
It is only in interactions that nature draws the world.
In the world described by quantum mechanics there is no reality except in the relations between physical systems. It isn’t things that enter into relations but, rather, relations that ground the notion of ‘thing’. The world of quantum mechanics is not a world of objects: it is a world of events. Things are built by the happening of elementary events: as the philosopher Nelson Goodman wrote in the 1950s, in a beautiful phrase, ‘An object is a monotonous process.’ ... What is a wave, which moves on water without carrying with it any drop of water? A wave is not an object, in the sense that it is not made of matter that travels with it. The atoms of our body, as well, flow in and away from us. We, like waves and like all objects, are a flux of events; we are processes, for a brief time monotonous …
To summarize, quantum mechanics is the discovery of three features of the world: Granularity (figure 4.8). The information in the state of a system is finite, and limited by Plank’s constant.
Indeterminacy. The future is not determined unequivocally by the past. Even the more rigid regularities we see are, ultimately, statistical.
Relationality. The events of nature are always interactions. All events of a system occur in relation to another system. Quantum mechanics teaches us not to think about the world in terms of ‘things’ which are in this or that state but in terms of ‘processes’ instead. A process is the passage from one interaction to another. The properties of ‘things’manifest themselves in a granular manner only in the moment of interaction, that is to say, at the edges of the processes, and are such only in relation to other things. They cannot be predicted in an unequivocal way but only in a probabilistic one.
I think that the obscurity of the theory is not the fault of quantum mechanics but, rather, is due to the limited capacity of our imagination.
10 The gravitational field at a point is not well defined, when taking quanta into account.
The gravitational field at a point is not well defined, when taking quanta into account.
There is an intuitive way of understanding what happens. Suppose we want to observe a very, very, very small region of space. To do this, we need to place something in this area, to mark the point that we wish to consider. Say we place a particle there. Heisenberg had understood that you can’t locate a particle at a point in space for long. It soon escapes. The smaller the region in which we try to locate a particle, the greater the velocity at which it escapes. (This is Heisenberg’s uncertainty principle.) If the particle escapes at great speed, it has a great deal of energy. Now let us take Einstein’s theory into account. Energy makes space curve. A lot of energy means that space will curve a great deal. A lot of energy in a small region results in curving space so much that it collapses into a black hole, like a collapsing star. But if a particle plummets into a black hole, I can no longer see it. I can no longer use it as a reference point for a region of space. I can’t manage to measure arbitrarily small regions of space, because if I try to do this these regions disappear inside a black hole.
未完待续 （慢慢再补
回应 20210616 09:35:41

一些摘录： 1 An ‘expanded present’ Between the past and the future of an event (for example, between the past and the future for you, where you are, and in the precise moment in which you are reading) there exists an ‘intermediate zone’, an ‘expanded present’; a zone that is neither past nor future. This is the discovery made with special relativity. ... on Mars, there are events that in ...
20210616 09:35:41
一些摘录：
1 An ‘expanded present’
Between the past and the future of an event (for example, between the past and the future for you, where you are, and in the precise moment in which you are reading) there exists an ‘intermediate zone’, an ‘expanded present’; a zone that is neither past nor future. This is the discovery made with special relativity.
... on Mars, there are events that in this precise moment have already happened, events that are yet to happen, but also a quarter of an hour during which things occur that are neither in our past nor in our future.
2 There is no need to add space as an extra ingredient.
The world is not made up of space + particles + electromagnetic field + gravitational field. The world is made up of particles + fields, and nothing else; there is no need to add space as an extra ingredient. Newton’s space is the gravitational field. Or vice versa, which amounts to saying the same thing: the gravitational field is space.
But, unlike Newton’s space, which is flat and fixed, the gravitational field, by virtue of being a field, is something which moves and undulates, subject to equations...
3 The border of the universe
the universe can be finite and at the same time have no boundary. How?
Just as the surface of the Earth is not infinite but does not have a boundary either, where it ‘ends’. This can happen, naturally enough, if something is curved: the surface of the Earth is curved. And in the theory of general relativity, of course, threedimensional space can also be curved. Consequently, our universe can be finite but borderless.
On the surface of the Earth, if I were to keep walking in a straight line, I would not advance ad infinitum: I would eventually get back to the point I started from. Our universe could be made in the same way: if I leave in a spacecraft and journey always in the same direction, I fly around the universe and eventually end up back on Earth. A threedimensional space of this kind, finite but without boundary, is called a 3sphere.
The best way of describing a 3sphere is not to try to ‘see it from the outside’, but rather to describe what happens when moving within it.
Our culture is foolish to keep science and poetry separated: they are two tools to open our eyes to the complexity and beauty of the world.
Dante’s 3sphere is only an intuition within a dream. Einstein’s 3sphere has mathematical form and follows from the theory’s equations. The effect of each is different. Dante moves us deeply, touching the sources of our emotions. Einstein opens a road towards the unsolved mysteries of our universe. But both count among the most beautiful and significant flights that the mind can achieve.
4 Light is made up of small grains, particles of light
Today we call these packets of energy ‘photons’, from the Greek word for light: ϕώς. Photons are the grains of light, its ‘quanta’. In the article Einstein writes:
It seems to me that the observations associated with blackbody radiation, fluorescence, the production of cathode rays by ultraviolet light, and other related phenomena connected with the emission or transformation of light are more readily understood if one assumes that the energy of light is discontinuously distributed in space. In accordance with the assumption to be considered here, the energy of a light ray spreading out from a point source is not continuously distributed over an increasing space but consists of a finite number of ‘energy quanta’ which are localized at points in space, which move without dividing, and which can only be produced and absorbed as complete units.
These simple and clear lines are the real birth certificate of quantum theory. Note the wonderful initial ‘It seems to me …’, ... True genius is aware of the momentousness of the steps it is taking, and is always hesitant …
5 Electrons don’t always exist. They exist when they interact.
Colour is the speed at which Faraday’s lines vibrate, and this is determined by the vibrations of the electric charges which emit light. These charges are the electrons that move inside the atoms. Therefore, studying spectra, we can understand how electrons move around nuclei.
... But then why does the light emitted by an atom not contain all colours, rather than just a few particular ones? Why are atomic spectra not a continuum of colours, instead of just a few separate lines? Why, in technical parlance, are they ‘discrete’ instead of continuous?
Bohr makes the hypothesis that electrons can exist only at certain ‘special’ distances from the nucleus, that is, only on certain particular orbits...
Heisenberg returns home gripped by feverish emotion, and plunges into calculations. He emerges, some time later, with a disconcerting theory: a fundamental description of the movement of particles, in which they are described not by their position at every moment but only by their position at particular instants: the instants in which they interact with something else.
This is the second cornerstone of quantum mechanics, its hardest key: the relational aspect of things. Electrons don’t always exist. They exist when they interact. They materialize in a place when they collide with something else. The quantum leaps from one orbit to another constitute their way of being real: an electron is a combination of leaps from one interaction to another.
6 As Heisenberg had recognized: no variable of the object is defined between one interaction and the next.
The venerable Bohr said of him, ‘Of all physicists, Dirac has the purest soul.’ ... For him, the world is not made of things, it’s constituted of an abstract mathematical structure which shows us how things appear and how they behave when manifesting themselves. It’s a magical encounter between logic and intuition.
Dirac’s quantum mechanics is the mathematical theory used today by any engineer, chemist or molecular biologist. In it, every object is defined by an abstract space and has no property in itself, apart from those that are unchanging, such as mass. Its position and velocity, its angular momentum and its electrical potential, and so on, acquire reality only when it collides – ‘interacts’– with another object. It is not just its position which is undefined, as Heisenberg had recognized: no variable of the object is defined between one interaction and the next. The relational aspect of the theory becomes universal.
7 Chance operates at the atomic level
We do not know with certainty where the electron will appear, but we can compute the probability that it will appear here or there. This is a radical change from Newton’s theory, where it is possible, in principle, to predict the future with certainty. Quantum mechanics brings probability to the heart of the evolution of things. This indeterminacy is the third cornerstone of quantum mechanics: the discovery that chance operates at the atomic level. While Newton’s physics allows for the prediction of the future with exactitude, if we have sufficient information about the initial data and if we can make the calculations, quantum mechanics allows us to calculate only the probability of an event. This absence of determinism at a small scale is intrinsic to nature. An electron is not obliged by nature to move towards the right or the left; it does so by chance. The apparent determinism of the macroscopic world is due only to the fact that the microscopic randomness cancels out on average, leaving only fluctuations too minute for us to perceive in everyday life.
The probability of finding an electron or any other particle at one point or another can be imagined as a diffuse cloud, denser where the probability of seeing the particle is stronger. Sometimes it is useful to visualize this cloud as if it were a real thing. For instance, the cloud that represents an electron around its nucleus indicates where it is more likely that the electron appears if we look at it.
8 There are no longer particles which move in space with the passage of time, but quantum fields whose elementary events happen in spacetime.
Quantum mechanics, with its fields/particles, offers today a spectacularly effective description of nature. The world is not made up of fields and particles but of a single type of entity: the quantum field. There are no longer particles which move in space with the passage of time, but quantum fields whose elementary events happen in spacetime. The world is strange, but simple.
9 Some conclusions about what it is, precisely, that quantum mechanics tells us about the world.
Quanta 1: Information is finite the existence of a limit to the information that can exist within a system: a limit to the number of distinguishable states in which a system can be. This limitation upon infinity – this granularity of nature glimpsed by Democritus – is the first central aspect of the theory.
Quanta 2: Indeterminacy
An electron, a quantum of a field or a photon does not follow a trajectory in space but appears in a given place and at a given time when colliding with something else. When and where will it appear? There is no way of knowing with certainty. Quantum mechanics introduces an elementary indeterminacy to the heart of the world.
If we look at a stone, it stays still. But if we could see its atoms, we would observe them constantly spread here and there, and in ceaseless vibration. Quantum mechanics reveals to us that, the more we look at the detail of the world, the less constant it is. The world is not made up of tiny pebbles. It is a world of vibrations, a continuous fluctuation, a microscopic swarming of fleeting microevents.
The atomism of antiquity had anticipated also this aspect of modern physics: the appearance of laws of probability at a deep level. ...
... all trajectories from A to B contribute: it is as if the electron, in order to go from A to B, passed ‘through all possible trajectories’, or, in other words, unfurled into a cloud in order then to converge mysteriously on point B, where it collides again with something else.
Quanta 3: Reality is relational
It is only in interactions that nature draws the world.
In the world described by quantum mechanics there is no reality except in the relations between physical systems. It isn’t things that enter into relations but, rather, relations that ground the notion of ‘thing’. The world of quantum mechanics is not a world of objects: it is a world of events. Things are built by the happening of elementary events: as the philosopher Nelson Goodman wrote in the 1950s, in a beautiful phrase, ‘An object is a monotonous process.’ ... What is a wave, which moves on water without carrying with it any drop of water? A wave is not an object, in the sense that it is not made of matter that travels with it. The atoms of our body, as well, flow in and away from us. We, like waves and like all objects, are a flux of events; we are processes, for a brief time monotonous …
To summarize, quantum mechanics is the discovery of three features of the world: Granularity (figure 4.8). The information in the state of a system is finite, and limited by Plank’s constant.
Indeterminacy. The future is not determined unequivocally by the past. Even the more rigid regularities we see are, ultimately, statistical.
Relationality. The events of nature are always interactions. All events of a system occur in relation to another system. Quantum mechanics teaches us not to think about the world in terms of ‘things’ which are in this or that state but in terms of ‘processes’ instead. A process is the passage from one interaction to another. The properties of ‘things’manifest themselves in a granular manner only in the moment of interaction, that is to say, at the edges of the processes, and are such only in relation to other things. They cannot be predicted in an unequivocal way but only in a probabilistic one.
I think that the obscurity of the theory is not the fault of quantum mechanics but, rather, is due to the limited capacity of our imagination.
10 The gravitational field at a point is not well defined, when taking quanta into account.
The gravitational field at a point is not well defined, when taking quanta into account.
There is an intuitive way of understanding what happens. Suppose we want to observe a very, very, very small region of space. To do this, we need to place something in this area, to mark the point that we wish to consider. Say we place a particle there. Heisenberg had understood that you can’t locate a particle at a point in space for long. It soon escapes. The smaller the region in which we try to locate a particle, the greater the velocity at which it escapes. (This is Heisenberg’s uncertainty principle.) If the particle escapes at great speed, it has a great deal of energy. Now let us take Einstein’s theory into account. Energy makes space curve. A lot of energy means that space will curve a great deal. A lot of energy in a small region results in curving space so much that it collapses into a black hole, like a collapsing star. But if a particle plummets into a black hole, I can no longer see it. I can no longer use it as a reference point for a region of space. I can’t manage to measure arbitrarily small regions of space, because if I try to do this these regions disappear inside a black hole.
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0 有用 泰洛丹 20220514 08:08:59
说得很明白。感恩。
6 有用 ichbinluz 20170710 02:13:15
书的前半部分由Democritus讲至Einstein，可能我先前读过好几本物理科普都不超过这个范围，所以读起来挺轻松易懂。——”懂”仅指字面含义上读懂了作者所说的话，但不包括背后原理及推演过程乃至应用层面的含义。书的后半部分着重于loop quantum gravity，就真的有点难了，需要多了解一点费曼图和黎曼函数的基本知识。 作者的文风还是很棒的，科普书里面不乱给比喻真是难能可贵。虽然作者引... 书的前半部分由Democritus讲至Einstein，可能我先前读过好几本物理科普都不超过这个范围，所以读起来挺轻松易懂。——”懂”仅指字面含义上读懂了作者所说的话，但不包括背后原理及推演过程乃至应用层面的含义。书的后半部分着重于loop quantum gravity，就真的有点难了，需要多了解一点费曼图和黎曼函数的基本知识。 作者的文风还是很棒的，科普书里面不乱给比喻真是难能可贵。虽然作者引用了Einstein说的，想象一下软体动物般的柔性参考体系，觉得这画面感尤其尴尬，我想到的都是做成了食物的鱿鱼花。一个“好的”公式应当（简洁优美到）能在一件Tshirt上写完，下次可以不穿E=mC^2 这么常见的啦。 (展开)
1 有用 树叶的叶 20161209 12:59:04
R4 read by Mark Meadows. Fiat Lux, The Most Beautiful of Theories, The Quantum Leap, The Dances of Time, Beyond Space and Time. Quantum gravity
0 有用 未时 20220222 11:38:21
感觉没太看懂（有空再来一次…
0 有用 Roseanna 20190929 08:26:33
扯白也旁征博引的样子～
0 有用 Ray 20220605 19:21:59
用整个物理学史来佐证一件事：在认知世界本质这方面，人类的直觉相当靠不住。
0 有用 泰洛丹 20220514 08:08:59
说得很明白。感恩。
0 有用 danphy 20220412 18:16:48
一本非常好的科普书，很喜欢作者的写作风格，科学发现、历史时间线、名人轶事、科学观等等，而且读完也确实理解了“现实不似你所见”。有两点唤起了跟语言学的平行性，第一个是作为没有数学基础的我读物理似乎总像隔靴搔痒，少了坚实的感觉，就很像做句法却不懂形式语义带来的无力感，但作者说爱因斯坦虽然数学没有物理好，但同时期竞争的数学家Hilbert还是比爱因斯坦晚一步算出公式，作者认为爱因斯坦是用公式描绘脑海中的... 一本非常好的科普书，很喜欢作者的写作风格，科学发现、历史时间线、名人轶事、科学观等等，而且读完也确实理解了“现实不似你所见”。有两点唤起了跟语言学的平行性，第一个是作为没有数学基础的我读物理似乎总像隔靴搔痒，少了坚实的感觉，就很像做句法却不懂形式语义带来的无力感，但作者说爱因斯坦虽然数学没有物理好，但同时期竞争的数学家Hilbert还是比爱因斯坦晚一步算出公式，作者认为爱因斯坦是用公式描绘脑海中的vision而Hilbert是在推导公式；另一个有趣的是big bang theory这个名字起初是对这种观点的嘲笑，没想到后来学界接受，让我想起给猩猩起名叫Nim Chimpsky那个实验是想推翻Noam Chomsky结果实验结果却证实了他的想法。时间空间都是宏观的感知，是人有限的感知。 (展开)
0 有用 未时 20220222 11:38:21
感觉没太看懂（有空再来一次…
0 有用 菜豹 20211106 16:34:58
语言优美的科普小品，大概需要高中物理以上的水平去理解…短评里居然有人说看完更迷糊了😂不至于不至于