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

by Carlo Rovelli

For Aristotle, physics works as follows: first, it is necessary to distinguish between the heavens and Earth. In the heavens, everything is made up of a crystalline substance that moves in a circular motion and turns eternally around Earth in great concentric circles, with the spherical Earth at the center of everything. On Earth, on the other hand, it is necessary to distinguish between forced motion and natural motion. Forced motion is caused by a thrust and ends when the thrust ends. Natural motion is vertical—upward or downward—and depends both on the substance and the location. Each substance has a “natural place,” that is to say, a proper altitude to which it always returns; earth at the bottom, water a little way above it, air a little higher still, and fire even higher. When you pick up a stone and let it fall, the stone moves downward because it wants to return to its natural level. Air bubbles in water, fire in the air, or children’s flying balloons move upward instead, again seeking their natural place.

Aristotle's elemental theory

So the universe, then, is a large space where bodies attract one another by means of forces; and there is a universal force, gravity: every body attracts every other body.

Whaaaat

the world consists only of a great infinite space where, as time passes, particles move and attract one another by means of forces. We can write precise equations that describe these forces.

Beautiful

The first surprise is that almost all phenomena we see are governed by a single force, other than gravity: the force that today we call “electromagnetism.”

Important

It is this force that holds together the matter that forms solid bodies; holds together atoms in molecules, and electrons in atoms. This is what makes chemistry and living matter work. It is this force that operates in the neurons of our brain and governs our processing of the information on the world we perceive, and the way we think. And it’s always this force that creates the friction that stops a sliding object, that softens the landing of a parachutist, that turns electric motors and combustion engines,* or that allows us to turn on lights and listen to the radio.

The same force that holds atoms together is the same force that makes our brains and bodies work

the notion of “field.”

Michael Faraday is an impoverished Londoner without formal education who works first in a bookbindery, then in a laboratory, where he excels, gains his master’s confidence, and grows into the most brilliant experimenter of nineteenth-century physics, and its greatest visionary.

What was known about electricity and magnetism at the beginning of the eighteenth century consisted of little more than a few amusing sideshow tricks: glass rods that attract pieces of paper, magnets that repel and attract. The study of electricity

Right and mary shelley used basic electrical understanding to invent frankenstein

Newton is deeming his very own masterwork to be absurd, the very same work that was to be praised for centuries to come as the ultimate achievement of science! He understands that behind the action at a distance of his theory, there must be something else, but he has no idea what, and leaves the question . . . “to the Consideration of my Readers”!

Maybe a connection to camus

It is characteristic of genius to be aware of the limitations of its own findings, even in the case of such momentous outcomes as Newton’s discovery of the laws of mechanics and universal gravity.

Newton’s theory worked so well, it turned out to be so useful, that for two centuries no one bothered any longer to question it.

Is that also the nature of genius, that it blows everyones mind so much no one dares question it?

We see the world around us in color. What is color? Put simply, it is the frequency (the speed of oscillation) of the electromagnetic wave light is. If the wave vibrates more rapidly, the light is bluer. If it vibrates a little more slowly, the light is redder. Color as we perceive it is our psychophysical reaction of the nerve signal generated by the receptors of our eyes, which distinguish electromagnetic waves of different frequencies.

Good explanation but kinda painful too

Light is thus nothing more than a rapid vibration of the spiderweb of Faraday’s lines, which ripple like the surface of a lake as the wind blows. It isn’t true that we “do not see” Faraday lines. We only see vibrating Faraday lines.

Fuck you, man, I see what I want

If we see a child playing on the beach, it is only because between him and ourselves there is this lake of vibrating lines that transport his image to us. Is the world not marvelous?

No, it is terrifying

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

Between the past and the future of an event (for example, between the past and the future for you, where you are, and in the precise moment in which you are reading), there exists an “intermediate zone,” an “extended present”; a zone that is neither past nor future. This is the discovery made with special relativity. The duration of this “intermediate zone,”* which is neither in your past nor in your future, is very small and depends on where an event takes place relative to you, as illustrated in figure 3.2: the greater the distance of the event from you, the longer the duration of the extended present. At a distance of a few meters from your nose, the duration of what for you is the “intermediate zone,” neither past nor future, is no more than a few nanoseconds: next to nothing (the number of nanoseconds in a second is the same as the number of seconds in thirty years). This is much less than we could possibly notice. On the other side of the ocean, the duration of this “intermediate zone” is a thousandth of a second, still well below the threshold of our perception of time, the minimum amount of time we perceive with our senses, which is somewhere on the order of a tenth of a second. But on the moon, the duration of the “extended present” is a few seconds, and on Mars it is a quarter of an hour. This means we can say that on Mars there are events that in this precise moment have already happened, events that are yet to happen, but also a quarter-of-an-hour of events dur...

Special relativity

The present is like the flatness of Earth: an illusion. We imagined a flat Earth because of the limitations of our senses, because we cannot see much beyond our own noses. Had we lived on an asteroid of a few kilometers in diameter, like Antoine de Saint-Exupéry’s Little Prince, we would have easily realized we were on a sphere. Had our brain and our senses been more precise, had we easily perceived time in nanoseconds, we would never have made up the idea of a “present” extending everywhere. We would have easily recognized the existence of the intermediate zone between past and future. 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. It is like asking whether our galaxy is “above or below” the galaxy of Andromeda: a question that makes no sense, because “above” or “below” has meaning on the surface of Earth, not in the universe. There isn’t an “up” and a “down” in the universe. Similarly, there isn’t always a “before” and an “after” between two events in the universe. The resulting knitted structure that space and time form together, depicted in figures like 3.2 and 3.3, is what physicists call “spacetime” (figure 3.4). Figure 3.4 What is the world made of?

So this is the power of now, recognizing it doesn't exist?

The present is like the flatness of Earth: an illusion. We imagined a flat Earth because of the limitations of our senses, because we cannot see much beyond our own noses. Had we lived on an asteroid of a few kilometers in diameter, like Antoine de Saint-Exupéry’s Little Prince, we would have easily realized we were on a sphere. Had our brain and our senses been more precise, had we easily perceived time in nanoseconds, we would never have made up the idea of a “present” extending everywhere. We would have easily recognized the existence of the intermediate zone between past and future. 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. It is like asking whether our galaxy is “above or below” the galaxy of Andromeda: a question that makes no sense, because “above” or “below” has meaning on the surface of Earth, not in the universe. There isn’t an “up” and a “down” in the universe. Similarly, there isn’t always a “before” and an “after” between two events in the universe. The resulting knitted structure that space and time form together, depicted in figures like 3.2 and 3.3, is what physicists call “spacetime” (figure 3.4). Figure 3.4 What is the world made of?

General relativity

The present is like the flatness of Earth: an illusion. We imagined a flat Earth because of the limitations of our senses, because we cannot see much beyond our own noses. Had we lived on an asteroid of a few kilometers in diameter, like Antoine de Saint-Exupéry’s Little Prince, we would have easily realized we were on a sphere. Had our brain and our senses been more precise, had we easily perceived time in nanoseconds, we would never have made up the idea of a “present” extending everywhere. We would have easily recognized the existence of the intermediate zone between past and future. 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. It is like asking whether our galaxy is “above or below” the galaxy of Andromeda: a question that makes no sense, because “above” or “below” has meaning on the surface of Earth, not in the universe. There isn’t an “up” and a “down” in the universe. Similarly, there isn’t ...

Special relativity

Democritus himself, who had placed empty space at the basis of his world where atoms course, certainly wasn’t crystal clear on the issue: he wrote that empty space is something “between being and non-being”:

Democritus understood bullshit

No one has ever understood what Newton meant by God’s sensorium, perhaps not even Newton himself.

An exciting mystery

Einstein, who read philosophers, was well aware of them.

We are not contained within an invisible, rigid scaffolding: we are immersed in a gigantic, flexible mollusk (the metaphor is Einstein’s).

Figure 3.6 Earth turns around the sun because spacetime around the sun is curved, rather like a bead that rolls on the curved wall of a funnel.

Whoa ok

phantasmagorical

Well: believe it or not, a ball thrown upward falls downward for the same reason: it “gains time” moving higher up, because time passes at a different speed up there.

believe it or not, a ball thrown upward falls downward for the same reason: it “gains time” moving higher up, because time passes at a different speed up there.

Earth in late 2015, and the announcement, given in early 2016, has once again left the world speechless.

"The world"? Seriously? A rather unscientific assertion, no?

Dirac’s quantum mechanics thus allows us to do two things. First, to calculate which values a physical variable may assume. This is called “calculation of the spectrum of a variable”; it captures the granular nature of things. When an object (atom, electromagnetic field, molecule, pendulum, stone, star, and the like) interacts with something else, the values computed are those that its variables can assume in the interaction (relationism). The second thing that Dirac’s quantum mechanics allows us to do is to compute the probability that this or that value of a variable appears at next interaction. This is called “calculation of an amplitude of transition.” Probability expresses the third feature of the theory: indeterminacy, the fact that it does not give unique predictions, only probabilistic ones.

Two things qm gives us: relationism and indeterminism