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An elementary structure of the world is emerging, generated by a swarm of quantum events, where time and space do not exist. Quantum fields draw together space, time, matter, and light, exchanging information between one event and another. Reality is a network of granular events; the dynamic that connects them is probabilistic; between one event and another, space, time, matter, and energy melt into a cloud of probability.
From time immemorial, or at least since humanity had left written texts that have come down to us, men had asked themselves how the world had come into being, what it was composed of, how it was ordered, and why natural phenomena occurred. For thousands of years, they had given themselves answers that all resembled one another: answers that referred to elaborate stories of spirits, deities, imaginary and mythological creatures, and other such similar things. From cuneiform tablets to ancient Chinese texts; from hieroglyphic writing in the pyramids to the myths of the Sioux; from the most
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the eighteenth-century Enlightenment. The ethical ideal of Democritus is that of a serenity of mind reached through moderation and balance, by trusting in reason and not allowing oneself to be overwhelmed by passions.
We are all sprung from heavenly seed. All alike have the same father, from whom all-nourishing mother earth receives the showering drops of moisture. Thus fertilized, she gives birth to smiling crops and lusty trees, to mankind and all the breeds of beasts. She it is that yields the food on which they all feed their bodies, lead their joyous lives and renew their race.15 There
“To a wise man, the whole earth is open, because the true country of a virtuous soul is the entire universe.”
But it is not only space that curves: time does too. Einstein predicts that time on Earth passes more quickly at higher altitude, and more slowly at lower altitude.
Everything attracts, therefore the only way for a finite universe not to collapse on itself is to be expanding:
Fourteen billion years ago, the universe was concentrated almost to a single, furiously hot point. From there it expanded in a colossal cosmic explosion,
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 world is not made up of fields and particles but of a single type of entity: the quantum field.
There are no longer particles that move in space with the passage of time, but quantum fields whose elementary events happen in spacetime.
I think that quantum mechanics has revealed three aspects of the nature of things: granularity, indeterminacy, and the relational structure of the world.
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 theory does not describe things as they “are”: it describes how things “occur,” and how they “interact with each other.” It doesn’t describe where there is a particle but how the particle shows itself to others. The world of existent things is reduced to a realm of possible interactions. Reality is reduced to interaction. Reality is reduced to relation.
Quantum mechanics extends this relativity in a radical way: all variable aspects of an object exist only in relation to other objects. It is only in interactions that nature draws the world.
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, with a beautiful phrase: “An object is a monotonous process.” A stone is a vibration of quanta that maintains its structure for a while, just as a marine wave maintains its identity for a while, before melting again into the sea.
quantum mechanics cannot deal with the curvature of spacetime, and general relativity cannot account for quanta. This is the problem of quantum gravity.
The central prediction of loop theory is therefore that space is not a continuum, it is not divisible ad infinitum, it is formed of “atoms of space,” a billion billion times smaller than the smallest of atomic nuclei.
It must not be claimed that anyone can sense time by itself apart from the movement of things. LUCRETIUS, De rerum natura
The passing of time is intrinsic to the world; it is born of the world itself, out of the relations between quantum events that are the world, and that themselves generate their own time.
At a fundamental level, there is no time. Our sense of the common passage of time is only an approximation that is valid for our macroscopic scale. It derives from the fact that we perceive the world in a coarse-grained fashion.
And even the great Einstein could go on to say (and he did so): “Ah . . . I made a mistake!” Science is the best strategy if we value reliability.
Clues put us on the right path toward a correct theory. Strong evidence is that which subsequently allows us to trust whether the theory we have built is a good one or not. Without clues, we search in the wrong directions. Without evidence, a theory is not reliable.
traveling to the past is difficult, but traveling to the future is easy: we need only to get close to a black hole with a spaceship, keep within its vicinity for a while, and then move away.
The pathological situations predicted by general relativity, where the theory gives infinite quantities, are called “singularities.” Quantum gravity places a limit to infinity and “cures” the pathological singularities of general relativity. The same happens at the center of black holes: the “singularity” that classic general relativity anticipated disappears as soon as we take quantum gravity into account.
It suggests that what we call “infinite” often is nothing more than something that we have not yet counted, or understood. I think this is true in general. “Infinite,” ultimately, is the name that we give to what we do not yet know. Nature appears to be telling us that there is nothing truly infinite.
The book of Ecclesiasticus, or Sirach, opens with a stupendous question:* Who can number the sand of the sea, and the drops of rain, and the days of eternity? Who can find out the height of heaven, and the breadth of the earth, and the deep, and wisdom? Not much longer after these lines were composed, another great text was written, with an opening that still resounds: Some think, O King Hiero, that the grains of sand cannot be counted. This is the opening of Psammites (The Sand Reckoner) by Archimedes, in which the greatest scientist of antiquity . . . counts the grains of sand in the
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a defiant cry of reason, which recognizes its own ignorance but refuses to delegate to others the source of knowledge.
The only truly infinite thing is our ignorance.
information is the measure of the number of possible alternatives for something.
The world isn’t, then, just a network of colliding atoms: it is also a network of correlations between sets of atoms, a network of real, reciprocal information between physical systems.
Entropy is “missing information,” that is, information with a minus sign. The total amount of entropy can only increase, because information can only diminish.*
Remember that a key result of quantum mechanics is precisely the fact that information is finite. The number of alternative results that we can obtain measuring a physical system* is infinite in classical mechanics; but thanks to quantum theory, we have understood that, in reality, it is finite. Quantum mechanics can be understood as the discovery that information in nature is always finite.
A physical system manifests itself only in interacting with another. The description of a physical system, then, is always given in relation to another physical system, the one with which it interacts. Any description of a system is therefore always a description of the information a system has about another system, that is to say, the correlation between the two systems. The mysteries of quantum mechanics become less dense if interpreted in this way, as the description of the information that physical systems have about one another.
The entire formal structure of quantum mechanics can be in large measure expressed in two simple postulates:1 The relevant information in any physical system is finite. You can always obtain new information on a physical system.
The first postulate characterizes the granularity of quantum mechanics: the fact that a finite number of possibilities exists. The second characterizes its indeterminacy: the fact that there is always something unpredictable that allows us to obtain new information. When we acquire new information about a system, the total relevant information cannot grow indefinitely (because of the first postulate), and part of the previous information becomes irrelevant, that is to say, it has no effect anymore upon predictions of the future. In quantum mechanics, when we interact with a system, we don’t
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Wheeler coined the phrase “It from bit” to express this idea, meaning that “everything is information.”
The salient characteristic of time is that it moves forward and not backward, that is to say, there are irreversible phenomena.
At the precise moment when heat is produced, the process is irreversible: the past differs from the future. It is always heat and only heat that distinguishes the past from the future.
This is universal. A burning candle is transformed into smoke, the smoke cannot transform into a candle—and a candle produces heat.
There is no preferred direction of time without heat.
Time is an effect of our overlooking the physical microstates of things. Time is information we don’t have. Time is our ignorance.
reality is this network of relations, of reciprocal information, that weaves the world. We slice up the reality surrounding us into “objects.” But reality is not made up of discrete objects. It is a variable flux.
We are complex nodes in a rich web of reciprocal information.
Awareness of the limits of our knowledge is also awareness of the fact that what we know may turn out to be wrong, or inexact. Only by keeping in mind that our beliefs may turn out to be wrong is it possible to free ourselves from wrong ideas, and to learn. To learn something, it is necessary to have the courage to accept that what we think we know, including our most rooted convictions, may be wrong, or at least naïve: shadows on the walls of Plato’s cave.
science is the search for the most credible answers available, not for answers pretending to certainty.
The nature of scientific thinking is critical, rebellious, and dissatisfied with a priori conceptions, reverence, and sacred or untouchable truth. The search for knowledge is not nourished by certainty: it is nourished by a radical distrust in certainty.
This means not giving credence to those who say they are in possession of the truth. For this reason, science and religion frequently find themselves on a collision course. Not because science pretends to know ultimate answers, but precisely for the opposite reason: because the scientific spirit distrusts whoever claims to be the one having ultimate answers or privileged access to Truth. This distrust is found to be disturbing in some religious quarters. It is not science that is disturbed by religion: there are certain religions that are disturbed by scientific thinking.
To accept the substantial uncertainty of our knowledge is to accept living immersed in ignoranc...
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There are some who prefer to believe in a story just because it was believed by the tribe’s ancestors, rather than bravely accept uncertainty.
