Carlo Rovelli, Penguin Books, ISBN 978-0-141-98496-4
In the universe there is the possibility of time and space. Masses of bodies modify the structure of the possible space and time between them: closer to a mass there is less time. dpb: if this concerns how much time passes, then does this mean that the grain of the structure of time is finer closer to a mass than further removed? And does that mean that closer to a mass more steps are needed compared to farther away? Time is different at every locus: it is relative and it has no unity.
In the laws of physics there is no inherent difference between past and future. Why is the past so different from the future to us? Based on Carnots proposition, Clausius posits that, if everything else remains equal, heat cannot pass from a cold body to a hot one. Rovelli writes: ‘This is the only basic law of physics that distinguishes the past from the future‘. None of the others do so’ Not Newton, Maxwell, Einstein, Heisenberg, Dirac, Schrodinger or elementary particle scientists. But dpb: is this indeed the only asymmetry known to physics? Or the only time related one?
The link between time and heat is fundamental: ‘In every sequence of events that becomes absurd if projected backwards, there is something that is heating up‘ (p 23). This means it is the only irreversible one, all the others are reversible. dpb: Is it conceivable that irreversible change occurs without something heating up? Chaos theory teaches us that even deterministic systems can produce irreversible unpredictability. If a system has started to reverse its behavior at some point it is likely to deviate from its trajectory back to the beginning of the observation in unpredictable ways, and hence to be irreversible. Another source of irreversibility is complexity, especially life, because what higher level of organization emerges will resist reversal to a previous, less organized state. Take e.g an autopoietic system that seeks to maintain its operational closure and its present organization (configuration). It will last longer than expected (Schrodinger).
Clausius formulated the 2nd law, namely dS=>0, implying that heat never passes from cold to hot bodies. But e.g. Popper (??) argues that heat gets passed from colder to warmer bodies all the time and that entropy is not homogeneous over different locations and is a stochastic parameter. Boltzmann: entropy production is growing disorder into less particular less special situations. dpb: to what is the order and its decrease attributed when entropy increases? Or in other words: what are these situations and what are their changes?
Take the example of sunlight, a source of low entropic energy, cast on a stone. The atoms that compose the stone are agitated by the high-grade energy of the sunlight. Caused by the agitation the atoms heat up and the temperature of the entire stone rises. The amount of energy carried by the stone increases with what was carried by the sunlight. However, that energy dissipates and becomes less special, aka less capable of work: entropy is produced. At night, when the air cools, the heat carried by the stone (or rather by its agitated atoms) is transferred to the atoms of the air surrounding it. They become agitated and the energy of the atoms in the stone is transferred to the atoms in the air. Entropy is produced and the energy carried in the agitated air atoms is capable of still less work, becoming even less special.
dpb: Take the example when the atoms composing a cat are agitated when sunlight is cast on the cat. The cat is a self-referencing (autopoietic) system which is organized such that its body temperature is kept in bounds such that it keeps functioning. The temperature of the entire cat rises, until the cat reacts by taking physiological measures to cool its body sweating through its soles. The molecules in the surrounding soil and air are agitated, heating it. Entropy is produced and the same amount of energy as initially input by the sunlight into the atoms of the cat is capable of ever less work, entering a less special state.
dpb: The state of a system becomes less special when entropy is produced: the system becomes less ordered, aka less organized, and the ignorance of the observer regarding the likelihood of future states increases. The stone and the cat are defined by us as we observe the processes and their relations taking place within their physical boundaries. But they are determined by their organization as a stone and a cat respectively. The incoming sun(light) and the atoms composing the air are external.
dpb: Thus, entropy is produced regardless of the level of organization of the discussed systems. While they produce entropy their organizations don’t change: the organization of the stone and the cat remain the same. What does it mean to say that the level of organization decreases when entropy is produced but the organization of the stone and the cat remain the same?
However, the amount of uncertainty regarding the future states – in phase space – of these systems increases. This explains the production of entropy in an existing system. If an organism emerges – appears for the first time – the order of what are (post-hoc) its components increases into their organization as the observed system, but the entropy increases nonetheless. The appearance of organisms does not reverse entropy production!
Increasing (dis)order is on account of the observer. When entropy is maximum all the possible next states are equally special, it is observed. The notion of particularity only comes to be if we see things in a blurred and approximate way. dpb: the states become less particular from the perspective of someone taking a blurred view. Does blurred mean that e.g. a person cannot distinguish atoms? Can there also be a relation between blurring and emergence, because observing an emerged system we are incapable to reduce its behavior at the larger scale to that of its components at the smaller scale?
According to Rovelli, blurring means that we are incapable of seeing the microscopic level where there is no difference between past and present, and between cause and effect. An observer is required for that! There is a loss of direction, because there is no intrinsic difference between past and future.
Time passes more slowly for what moves. dpb: I understand this effect in the same way as (potential) time slows down closer to a mass. The dimensions of the squares (grains) of the grid onto which time is canvassed become smaller on the topology closer to a mass and at high relative speed.
There is no single or absolute time and every point in space has a proper time. ‘Now’ is meaningless, because there is no present anywhere corresponding to any other. The question of the present of the universe is therefore improper. The temporal structure of the universe can be said to be made of partially ordered cones. Each approximate generation roughly followed by another. The structure of space-time is not stratified but scattered, and without common direction (wobbly). There is no universal present.
Aristotle suggests that time is the measure of change. He includes the thinking of change as change also measured as time. Newton suggests that even if nothing happens, time (of some kind) still passes. Leibniz defends the former idea that time results from counting of events, but the latter has caught on and is the more widely accepted. Until the end of the 19th century every place had its proper time, only later local time was replaced with global time schedules. This is less removed from the notion of relativity of time than the wide spread absolute interpretations.
dpb: events are grained or quanted into the space-time grid that of potential space and time. A thing is required to occupy space and time. When closer to a mass or moving, the time grid particular to it is finer grained and the thing is therefore observed to move slower.
Aristotle suggests that the position of a thing in space and time is identified by what surrounds it. There is no ‘empty’ space or time. dpb: this connects with the idea of a rhizome spanning up its own dimensions plus the ones required to describe it by the observer.
What does it mean when space and time can be void i.e nothing is there as Newton suggests? Not even electromagnetic fields or other things imperceptible to people. Einstein suggest that time and space are like canvasses on which reality (substances) comes to exist as fields. Gravity, one of these fields, determines the topology of space-time. Space-time is the gravitational field. dpb: Time and space are not absolute but relative, suggesting they interpenetratingly depend on adjacent elements. It means that space and time remain potential until something occupies them. Is it fair to say that they substantiate from a potential (virtual;) to the real, or that they become?
If we move on to consider quantum properties of space and of time, then in addition to individualized, localized and independent as previously described, time is also distributed. This leads to the aspects pf granularity, indeterminacy, and relativity which further break down our understanding of time.
Quantum effects occur at Planck time scales of 10E-44. Below that there is no time. Also time assumes only special discrete values: most times do not exist. Hence time is not continuous but granular, leapfrogging from one to another instance separated by intermittencies at the Planck scale.
Time is indeterminate: it is in a superposition and its present state is unknown. Something may take place before and after something else does. It is resolved at an interaction. The only point where it becomes concrete is in the relation with the ones it interacts with. Instead of uniformly for the rest of the universe. In this view, the world is made up of events not things. This takes place in a disorderly way as processes. Events are short-lived, and things persist.
The notion of the event as the basic unity of reality fits well with how we experience the world, because it is spatially and temporally delimited. Objects in this view are long events. In this sense time equals happening.
Thus, the idea of presentism, that reality moves from one present to the next no longer works. The world is not a single linear succession of presents. The opposite idea of eternalism (block universe), that past, present and future are equally real means that change is an illusion realistically can’t be true. The point is that the present develops in a disorderly distributed and indeterminate way. But our grammar isn’t suitable: ‘In the world there is change, there is a temporal structure of relations between events that is anything but illusory’ (p 100).
We do not need the time variable to describe the world, but the variables that describe it, and how they change relative to each other. If a number of these relations are established then we might say when an event takes place: ‘.. what the relations are between these variables’ (p 103). dpb: or in other words these are differences (relations) between two series of differences (variables), aka assemblages. The differences should have the adjective comparable to indicate the potential of correlations between correlations.
Fields become manifest in granular form. The grains are not immersed in space but they form it, its structure is granular. Spatiality is the web of interactions between these grains. They exist only during those interactions. The latter are the happening of the world, the development of reality.
‘Time emerges from a world without time, ..’ (p 117). dpb: will this be the link to blurring and approximation Rovelli mentions early on in the text as an insight of Boltzmann?
The conventional view is that time determines energy determines macro state. An opposing view is that the macro state determines energy determines time, whereby the macro state equals the blurred view of systems and their behavior. Or in other words: time becomes determined because / as an effect of the blurring, namely the incompleteness of the description of the corresponding micro-states. dpb: Rovelli refers to this notion as thermal time, because it corresponds to the probabilistic notion of entropy at the macro scale.
Measurement of speed and position of a particle are non-commutative. The order of the interactions (measuring) matter causing a primitive form of time to develop. Time developing in changing macro states (thermal) and time developing in changing quantum states (quantum) are very similar. Rovelli suggests that this is the time we know, whereby quantum indeterminacy and the large quantities of particles cause the blurring. Time is ignorance. dpb: There are a number of examples of emergence in physical systems and I was hoping there was expressed a stronger connection link to emergence &c.
So, again: what is blurring? We, and every physical system, interact with a limited number of other systems. We interact with them through only a limited number of variables (aka correlations, assemblages). The configurations we do not notice seem to be equivalent to us. Thus our – and other physical systems’ – vision of the world is blurred.
Thus, blurring is the pivot of the theory of Boltzmann: entropy is the number of configurations of a system we are not aware of. This can of course vary per observed system as well as per observing system, because what is not visible for one can be visible for another. Blurring is not only mental, because interactions with the micro-systems exist. Entropy is relative to the observer aka the one interacting with the system in hand, like speed a property of the object relative to others.
The entropy of the world depends on its configuration as well as on our (or in general physical systems’) blurring of them. This depends on which variables of the world – our part of the world – we interact with.
Thus, the seemingly low entropy in the far past may be a result of the limited set of variables we interacted with and our blurring of them. Our interactions are limited to a small number of macroscopic variables. The microscopic configurations are blurred. Since we are responsible for that, with the supposed low entropy as a result. In this view the arrow of time is not universal but it depends on the physical system doing the viewing, us in this case, from our ‘special corner’ of the universe.
Indexicality refers to words which assume a different meaning depending on their use. dpb: like a variable? Indexing makes the perspective of its use explicit. It is not possible to say anything from outside the world. Existence takes place from within (so as the map is useful if we know our position versus it). Thus, time is not external to us (or any physical system) but we are situated within it, seeing time from the inside.
Any energy goes to thermal energy. Low entropy goes to high: production. Without entropy there is no past and no future. dpb: this is becoming a sort of blind spot! Entropy production is increasing disorder. But evolution of organisms increases order by way of organization while entropy is still produced. What is the subject of entropy? The relevant one is the change of order in phase space (not real space). Even though there are temporary pockets of order in the grand scheme (e.g of evolution), the very grand scheme is of increasing disorder.
The past leaves traces in the future. CR suggests that this is because of low entropy into he past, because there is nothing else to separate the past from the future. dpb: blind spot. Common causes in the past of current phenomena point at low entropy in the past, because of the increasing improbability of their occurring together? ‘In a state of thermal equilibrium, or in a purely mechanical system, there isn’t a direction to time identified by causality‘ (p 146). dpb: but it isn’t just causality but irreversibility.
Time is related to us. What are we? We are not individual entities, but relational identities. What produces this:1) point of view 2) in connection with the working of our brain, we categorize vis-a-vis other humans (the reflection of us we get back from our kind) 3) memory links our histories through narratives.
The mind can see traces of the past left in the brain. But threading them as an interpretation of the flow of time is an internal process of the mind. It is integral to the mind. The mind constitutes (a representation of) time through the retention of traces on the brain of past events (Husserl).
‘Time opens up our limited access to the world. Time, then, is the form in which we beings whose brains are made up essentially of memory and foresight interact with the world: it is the source of our identity‘ (p 164).