"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." (Carlo Rovelli, "The Order of Time", 2018)
"Continuity is only a mathematical technique for approximating very finely grained things. The world is subtly discrete, not continuous." (Carlo Rovelli, "The Order of Time", 2018)
"For a moving object, time contracts. Not only is there no single time for different places - there is not even a single time for any particular place. A duration can be associated only with the movement of something, with a given trajectory." (Carlo Rovelli, "The Order of Time", 2018)
"Granularity is ubiquitous in nature: light is made of photons, the particles of light. The energy of electrons in atoms can acquire only certain values and not others. The purest air is granular, and so, too, is the densest matter. Once it is understood that Newton’s space and time are physical entities like all others, it is natural to suppose that they are also granular. Theory confirms this idea: loop quantum gravity predicts that elementary temporal leaps are small, but finite." (Carlo Rovelli, "The Order of Time", 2018)
"In the elementary equations of the world, the arrow of time appears only where there is heat. The link between time and heat is therefore fundamental: 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." (Carlo Rovelli, "The Order of Time", 2018)
"It is not possible to think of duration as continuous. We must think of it as discontinuous: not as something that flows uniformly but as something that in a certain sense jumps, kangaroo-like, from one value to another. In other words, a minimum interval of time exists. Below this, the notion of time does not exist - even in its most basic meaning." (Carlo Rovelli, "The Order of Time", 2018)
"Nature, for its part, is what it is - and we discover it very gradually. If our grammar and our intuition do not readily adapt to what we discover, well, too bad: we must seek to adapt them.
"Nothing is valid always and everywhere. Sooner or later, we always come across something that is new." (Carlo Rovelli, "The Order of Time", 2018)
"[...] our vision of the world is blurred because the physical interactions between the part of the world to which we belong and the rest are blind to many variables. This blurring is at the heart of Boltzmann's theory. From this blurring, the concepts of heat and entropy are born - and these are linked to the phenomena that characterize the flow of time. The entropy of a system depends explicitly on blurring. It depends on what I do not register, because it depends on the number of indistinguishable configurations. The same microscopic configuration may be of high entropy with regard to one blurring and low in relation to another." (Carlo Rovelli, "The Order of Time", 2018)
"Physics does not describe how things evolve 'in time' but how things evolve in their own times, and how 'times' evolve relative to each other." (Carlo Rovelli, "The Order of Time", 2018)
"Spacetime is a physical object like an electron. It, too, fluctuates. It, too, can be in a 'superposition' of different configurations.
"The basic units in terms of which we comprehend the world are not located in some specific point in space. They are - if they are at all - in a where but also in a when. They are spatially but also temporally delimited: they are events." (Carlo Rovelli, "The Order of Time", 2018)
"The entire evolution of science would suggest that the best grammar for thinking about the world is that of change, not of permanence. Not of being, but of becoming." (Carlo Rovelli, "The Order of Time", 2018)
"The entropy of the world does not depend only on the configuration of the world; it also depends on the way in which we are blurring the world, and this depends on what the variables of the world are that we interact with. That is to say, on the variables with which our part of the world interacts. [...] The difference between past and future does not lie in the elementary laws of motion; it does not reside in the deep grammar of nature. It is the natural disordering that leads to gradually less particular, less special situations."" (Carlo Rovelli, "The Order of Time", 2018)
"The entropy of the world in the far past appears very low to us. But this might not reflect the exact state of the world: it might regard the subset of the world's variables with which we, as physical systems, have interacted. It is with respect to the dramatic blurring produced by our interactions with the world, caused by the small set of macroscopic variables in terms of which we describe the world, that the entropy of the universe was low." (Carlo Rovelli, "The Order of Time", 2018)
"The relation of 'temporal precedence' is a partial order
made of cones. Special relativity is the discovery that the temporal structure
of the universe is like the one established by filiation: it defines an order
between the events of the universe that is partial, not complete. The expanded
present is the set of events that are neither past nor future: it exists, just
as there are human beings who are neither our descendants nor our forebears. […]
Every event has its past, its future, and a part of the universe that is
neither past nor future, just as every person has forebears, descendants, and
others who are neither forebears nor descendants. Light travels along the
oblique lines that delimit these cones."
"The world without a time variable is not a complicated one. It’s a net of interconnected events, where the variables in play adhere to probabilistic rules that, incredibly, we know for a good part how to write. And it’s a clear world, windswept and full of beauty as the crests of mountains; aridly beautiful as the cracked lips of the adolescent you loved." (Carlo Rovelli, "The Order of Time", 2018)
"Thermal agitation is like a continual shuffling of a pack of cards: if the cards are in order, the shuffling disorders them. In this way, heat passes from hot to cold, and not vice versa: by shuffling, by the natural disordering of everything. The growth of entropy is nothing other than the ubiquitous and familiar natural increase of disorder." (Carlo Rovelli, "The Order of Time", 2018)
"We cannot draw a complete map, a complete geometry, of
everything that happens in the world, because such happenings - including among them
the passage of time - are always triggered only by an interaction with, and with
respect to, a physical system involved in the interaction. The world is like a
collection of interrelated points of view. To speak of the world “seen from
outside” makes no sense, because there is no “outside” to the world.
"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."
No comments:
Post a Comment