Reality Is Not What It Seems: The Journey to Quantum Gravity

by Carlo Rovelli

a journey out of our limited and parochial views of reality, toward an increasingly vast understanding of the structure of things.

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.

Science is made up of experiments, hypotheses, equations, calculations, and long discussions; but these are only tools, like the instruments of musicians.

from this moment onward, knowledge begins to grow at a vertiginous pace, nourished by past knowledge but at the same time by the possibility of criticism, and therefore improving knowledge and understanding.

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The Milesians had understood that the world can be comprehended using reason.

The only possibility, Democritus concludes, is that any piece of matter is made up of a finite number of discrete pieces that are indivisible, each one having finite size: the atoms.

Can we really cut a piece of string an arbitrary number of times? Do infinitely small amounts of time exist? This is precisely the problem that quantum gravity will have to face.

Mach publicly declared: “I do not believe that atoms exist!” This was in 1897.

From observations of granules drifting in fluids, from the measurement of how much these “drift”—that is, move away from a position—he calculates the dimensions of Democritus’s atoms, the elementary grains of which matter is made.

matter is granular.

religion is ignorance: reason is the torch that enlightens.

his discovery of the treatise on architecture by Vitruvius transformed the way in which fine buildings were designed and constructed.

De rerum natura

“To a wise man, the whole earth is open, because the true country of a virtuous soul is the entire universe.”

But the greatest result is still to come, and it will be Isaac Newton who will attain it.

We can follow his reasoning in terms of the “little moon,”

the force that causes the little moon to turn around its orbit must be the same as that which causes objects to fall to the ground on Earth.

So the universe, then, is a large space where bodies attract one another by means of forces;

The world of Newton is the world of Democritus, rendered mathematical.

Newton is deeming his very own masterwork to be absurd,

Today, Maxwell’s equations are used daily to describe all electric and magnetic phenomena,

these same equations are needed to explain how atoms function (they are held together by electrical forces),

He computes the speed at which the undulations of Faraday’s lines move, and the result turns out to be . . . the same as for light!

they have figured out what light is.

It isn’t true that we “do not see” Faraday lines. We only see vibrating Faraday lines.

Our entire current technology is founded on the use of a physical thing—electromagnetic waves—that was not discovered empirically: it was predicted by Maxwell, simply by searching for the mathematical description accounting for the intuition Faraday got from bobbins and needles. This is the outstanding power of theoretical physics.

Leer otras cosas que las que te dan en el colegio

You don’t get to new places by following established tracks.

Maxwell’s equations determine a velocity: the velocity of light. But Newton’s mechanics are not compatible with the existence of a fundamental velocity,

In Newton’s physics, velocity can only be velocity of something with respect to something else.

only one single law of conservation exists, not two.

What is conserved is the sum of mass and energy, not each separately.

Today, thanks to the intelligence of a rebellious young man who would not abide rules, we have the instruments to bring light to the homes of the ten billion human beings who will soon inhabit the planet. To travel in space toward other stars. Or to destroy one another and devastate the planet. It depends on our choices, on which leaders we call upon to decide for us.

Our intuitive idea of the present, the ensemble of all events happening “now” in the universe, is an effect of our blindness:

An illegitimate extrapolation from our parochial experience.

We would have realized that saying “here and now” makes sense, but that saying “now” to designate events “happening now” throughout the universe makes no sense.