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

by Carlo Rovelli

*

Whoa!

*

Newton makes the simple calculation, and the result is . . . 9.8 meters per second per second!

And so: 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.

We call “gravity” the force causing objects to fall.

Newton understands that it is this same gravity that makes the little m...

Without this gravity, it would run away in a...

But then also the real moon must orbit Earth because of gravity! And the moons that orbit Jupiter are attracted by Jupiter, and the planets that turn around the sun are attracted by the sun! Without this attraction, every celestial body would move in a straight line. 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.

This literally is interdependence

simple calculation with the little moon allows Newton to deduce how the force of gravity changes with distance, and to determine its strength, given by what we call today “Newton’s Constant,” indicated by the letter G for gravity.

*

It’s a subversion of the conceptual structure of the Aristotelian world, the dominant vision of the world throughout the Middle Ages.

The world of Newtonian mechanics is simple and is summarized in figures 2.1 and 2.2. It is the world of Democritus reborn.

world made of a vast undifferentiated space, always equal to itself, where particles run forever and act upon one another—and nothing else.

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

Utterly Fascinating

The power of the new Newtonian intellectual framework proves to be beyond all expectation. The entire technology of the nineteenth century and of our own modern world rests largely upon Newton’s formulas.

The modern world would not have been born without passing by way of Newton’s little moon.

Newton knew that his equations do not describe all the forces that exist in nature.

This had to wait until the nineteenth century, and it led to two surprises.

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 “elect...

It is this force that holds together the matter that forms solid bodies; holds together atoms in mole...

This is what makes chemistry and livin...

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.

"May the Force be with you...-

The second and biggest surprise, crucial to the story I’m telling, is that understanding this force requires an important modification to the world of Newton: the modification out of which modern physics was born, and the most important notion to keep in focus, to understand the rest of this book: the notion of “field.” The understanding of how electromagnetic force works was made by another Briton, or rather by two, science’s oddest couple: Michael Faraday and James Clerk Maxwell.

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.

Without knowing mathematics, he writes one of the best books of physics ever written, virtually devoid of equations.

He sees physics with his mind’s eye, and with his mind’s ...

Maxwell is a rich Scottish aristocrat, and one of the greatest mathemat...

Despite being separated by a gulf in intellectual style as well as social origin, they succeed in ...

together, combining two kinds of genius, they open the way...

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 that is modified by electric and magnetic bodies and that, in turn, acts upon (pushes and pulls) the bodies.

This entity, whose existence Faraday intuits, is today c...

Maxwell quickly realizes the value of this idea. He translates Faraday’s insight, which Faraday explains only verbally, into a page of equations.* These are Maxwell’s equations. They describe the behavior of the electric and the magnetic fields, the mathematical version of the “Faraday lines.”

Maxwell’s equations are used daily to describe all electric and magnetic phenomena, and to design antennae, radios, electric engines, and computers. And this is not all: these same equations are needed to explain how atoms function (they are held together by electrical forces), and why the particles of the material that forms a stone adhere together, or how the sun works.

Almost everything that we witness taking place, with the exception of gravity and little else besides, is well d...

Maxwell’s equations tell us what light is.

Maxwell realizes that his equations predict that Faraday’s lines can tremble and undulate, just like the waves of the sea. 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! Why? Maxwell understands: because light is nothing other than this rapid trembling of Faraday’s lines! Not only have Faraday and Maxwell figured out how electricity and magnetism work, but with the same stroke, as a collateral effect, they have figured out what light is.

Holy shit! Now gravity also travels at the speed of light. Maybe quantum gravity fixes 'realative time' to a light force that is our soul? What if our soul's 'light force' engages with quantum gravity to manifest a uniqe human being; allowing our sixth sense, to indulge in the earthly five senses.

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.

I wonder how Maxwell felt when he realized that his equations—written to describe bobbins, small cages, and little needles in Faraday’s lab—turned out to explain the nature of light and color.

To wonder is to begin to understand

To “see” is to perceive light, and light is the movement of the Faraday lines.

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?

Maxwell recognizes that the equations foresee that Faraday’s lines can also vibrate at much lower frequencies, that is to say slower than light. Therefore there must be other waves that nobody had ever yet seen, produced by the movement of electrical charges, and that in turn move electrical charges.

All modern communications technology—radio, television, telephones, computers, satellites, WI-FI, the Internet, and the like—is an application of Maxwell’s prediction; the Maxwell equations are the basis for all calculations of telecommunications engineers.

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. Figure 2.6 What is the world made of?

In this part of the book, I describe the two theories in some detail, trying to clarify their core meaning, and highlight the conceptual revolution they brought about. It’s here that the magic of twentieth-century physics begins. Studying and trying to understand them in depth is a bewitching adventure.

These two theories—relativity and the quanta—provide the basis on which we are today building a quantum theory of gravity.

In fact there are two theories of relativity. The envelope sent by the twenty-five-year-old Einstein contained the exposition of the first of these, the theory known today as “special relativity.” This is an important clarification of the structure of space and time, which I illustrate here before turning to the other, and the most important of Einstein’s theories, general relativity.

The theory shows, for the first time, that in the Newtonian vision of the world there isn’t just something missing: rather, it must be radically modified—in a way that goes completely against common sense. It is the first real leap into the revision of our most intuitive understanding of the world.