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January 20 - February 6, 2018
The more we learn about the world, the more we are amazed by its variety, beauty and simplicity.
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 space, time, matter and light, exchanging information between one event and another. Reality is a network of granular events; the dynamic which connects them is probabilistic; between one event and another, space, time, matter and energy melt in a cloud of probability.
We are all in the depths of a cave, chained by our ignorance, by our prejudices, and our weak senses reveal to us only shadows. If we try to see further, we are confused: we are unaccustomed. But we try. This is science.
The incompleteness and the uncertainty of our knowledge, our precariousness, suspended over the abyss of the immensity of what we don’t know, does not render life meaningless: it makes it interesting and precious.
Science is about reading the world from a gradually widening point of view.
Everything else is nothing but a by-product, random and accidental, of this movement and this combining of atoms.
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.
The universe is granular, not continuous.
He provides, after 2,300 years, the proof of the accuracy of Democritus’s insight: matter is granular.
Do you not see that nature is clamouring for two things only, a body free from pain, a mind released from worry and fear for the enjoyment of pleasurable sensations?
There is none of this in the world of Democritus as sung by Lucretius. There is no fear of the gods; no ends or purposes in the world; no cosmic hierarchy; no distinction between Earth and heavens. There is a deep love of nature, a serene immersion within it; a recognition that we are profoundly part of it; that men, women, animals, plants and clouds are organic threads of a marvellous whole, without hierarchies. There is a feeling of deep universalism in the wake of the splendid words of Democritus: ‘To a wise man, the whole earth is open, because the true country of a virtuous soul is the
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He absorbed and distilled its useful message: mathematics is the language best adapted to understand and describe the world. The reach of this insight is immense; it is one of the reasons for the success of Western science.
His intuition is this: we must not think of forces acting directly between distant objects, as Newton presumed. We must instead think that there exists an entity diffused throughout space, which is modified by electric and magnetic bodies and which, in turn, acts upon (pushes and pulls) the bodies. This entity, whose existence Faraday intuits, is today called the field.
general relativity and quantum mechanics. Both demand a daring re-evaluation of our conventional ideas about the world: space and time in relativity; matter and energy in quantum theory.
You don’t get to new places by following established tracks.
The theories of Newton and of Maxwell appear to contradict each other in a subtle way. Maxwell’s equations determine a velocity: the velocity of light. But Newton’s mechanics is not compatible with the existence of a fundamental velocity, because what enters Newton’s equations is acceleration, not velocity. In Newton’s physics, velocity can only be velocity of something with respect to something else.
the minimum amount of time we perceive with our senses – which is somewhere in the order of a tenth of a second.
The present is like the flatness of the Earth: an illusion.
Einstein predicts that time on Earth passes more quickly at higher altitude, and more slowly at lower altitude.
Place a watch on the floor and another on a table: the one on the floor registers less passing of time than the one on the table. Why? Because time is not universal and fixed, it is something which expands and shrinks, according to the vicinity of masses: the Earth, like all masses, distorts spacetime, slowing time down in its vicinity.
That is to say, the idea is to describe a curved space not as ‘seen from the outside’, stating how it curves in an external space, but instead in terms of what may be experienced by somebody within that space, who is moving and always remaining within it. For
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.
relates how the theory came into being and the three aspects of reality it has unveiled: granularity, indeterminism and relationality.
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.
its hardest key: the relational aspect of things. Electrons don’t always exist. They exist when they interact.
The equations of the theory, written by Dirac, account for the granular nature of light, which Planck and Einstein had intuited.
Photons are the quanta of the electromagnetic field.
The general form of quantum theory compatible with special relativity is thus called quantum field theory, and it forms the basis of today’s particle physics. Particles are quanta of a field, just as photons are quanta of light. All fields display a granular structure in their interactions.
Against expectations, however, all of its predictions have been confirmed. For more than thirty years, every single experiment of particle physics has done nothing but repeatedly reconfirm the standard model.
Instead, quantum mechanics tells us that between five and six centimetres there is a finite number of possible values of the amplitude, hence our missing information about the pendulum is finite.
Therefore, the first meaning of quantum mechanics is 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. Planck’s constant h measures the elementary scale of this granularity.
Quantum mechanics introduces an elementary indeterminacy to the heart of the world. The future is genuinely unpredictable. This is the second fundamental lesson learned with quantum mechanics.
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 micro-events.
Lucretius says this in beautiful words: this deviation occurs ‘incerto tempore … incertisque loci’:3 at an uncertain place, at an uncertain time.
The same randomness, the same appearance of probability at an elementary level, is the second key discovery about the world that quantum mechanics expresses.
This technique for computing the probability of a quantum event is called Feynman’s sum over paths,fn27 and we shall see that it plays a role in quantum gravity.
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.4
Aristotle was first to emphasize that we only perceive relative speed. On a ship, for example, we talk of our speed relative to the ship; on land, relative to the Earth.
Galileo understood that this is the reason why the Earth can move with respect to the Sun without us feeling the movement. Speed is not a property of an object on its own: it is the property of the motion of an object with respect to another object.
Einstein extended the notion of relativity to time: we can say that two events are simultaneous only rel...
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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 ...
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The world of quantum mechanics is not a world of objects: it is a world of events.
We, like waves and like all objects, are a flux of events; we are processes, for a brief time monotonous …
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.
But they remain mysterious: they do not describe physical systems but only how physical systems interact with and affect one another. What does this mean?
In my opinion, its dramatic empirical success should compel us to take it seriously, and to ask ourselves not what there is to change in the theory – but rather what is limited about our intuition that makes it seem so strange to us.
When, a few years later, Bohr in turn died, someone took a photograph of the blackboard in his study. There’s a drawing on it. It represents the ‘box of light’ of Einstein’s thought experiment. To the very last, the desire to debate, to understand more. To the very last, doubt. This permanent doubt, the deep source of science.
An example is the interior of black holes. Another is what happened to the universe during the Big Bang. In more general terms, we do not know how time and space behave at very small scale.
In other words, it is in the nodes of the graph, not in the lines, that the volume of space ‘resides’.
