Reality Is Not What It Seems: The Journey to Quantum Gravity in Science and Inquiry

Apr 26, 2017 Charlene rated it it was amazing

Shelves: constructs, space, mindgasms, physics, information-theory

This book is a modern day, On the Nature of Things. Like Lucretius himself, Rovelli is a poet who, with his words, constructs beautiful images of the true nature of reality.

The key message in this book is that everything comes down to geometry and the geometry of space is much more interesting than we probably suppose. Energy has morphed into various shapes as it traveled from the radiation of the hot, dense, atom sized ball it was when it was young, to elements and forms seen in the cooler, ex This book is a modern day, On the Nature of Things. Like Lucretius himself, Rovelli is a poet who, with his words, constructs beautiful images of the true nature of reality.

The key message in this book is that everything comes down to geometry and the geometry of space is much more interesting than we probably suppose. Energy has morphed into various shapes as it traveled from the radiation of the hot, dense, atom sized ball it was when it was young, to elements and forms seen in the cooler, expanding, vast universe of today. The laws of thermodynamics have ensured that various geometrical shapes occur and those geometrical shapes are forced to interact with other thermodynamically created geometrical shapes. What a symphony!

Rovelli detailed the most exquisitely beautiful history of how humans have come to understand the geometry of space itself, the matter that populates space, and how that geometry translates into motion of objects on Earth and in the universe at large. For example, Newton came to understand, and subsequently helped the rest of humanity understand, that because of Earth's shape and size, it would exert a strong gravitational pull on an apple and the apple would exert a small pull on Earth. Humanity could then finally understand how they would remain solidly planted to the ground if the earth were to rotate. It was perfectly reasonable before Newton to assume a human would fall off Earth if it spun upside down.

However, Newton himself could not understand the implication of his own theory. What physical material could do the action of pulling one object to another-- something Einstein later called "spooky action at a distance."? Without this substance, Newton could not understand how gravity could cause the large object to pull the smaller object physically toward it.

Michael Faraday was able to shed some light on this problem when he came to understand that the electric field and magnetic field were one in the same, the electromagnetic field, which can be thought of as lines in space that fill all of space, that attract elements toward each other. But, how then could this fully explain the gravitational pull of a large object like the sun pulling Earth toward it or a black hole pulling whole solar systems toward it?

(As an aside: I love all histories of Faraday. I cannot help but constantly play a voice inside my head that says, "Michael Faraday, May The Force be with you!" This is so stupid and has nothing to do with the actual force in the universe; and yet, I cannot help saying it in my head every time I read about Faraday.)

With his theories of special and general relativity, Einstein helped humanity understand how forms with large masses could pull smaller masses toward them. Einstein came to understand how spacetime itself was not just populated with Faraday's field lines; spacetime itself was warped by large objects. That is, large objects bend and stretch the fabric of spacetime such that nearby smaller objects have their spacetime bent too. The spacetime bends so the large object is always at the bottom of a hill and all the objects around it are higher up and fall toward it. The density of the object is what bends the spacetime and acts to lower the energy needed for other objects to fall toward it. (it really isn't that different from an enzyme in living systems). This is why Caleb Sharf (who was not mentioned in this book) called black holes "Gravity's Engines." They power the motion of the universe.

Rovelli argues that, like Faraday's field lines, gravity has its own lines. But, and this is the crucial but, gravity does not make up lines in space, gravitational lines *are* space. They construct the actual space upon which Faraday's lines can exist. John Wheeler's equations show that these gravitational lines close in on themselves. Thus, they are a loop; and thus, they are quantized loops of gravity. According to this theory, these quantized loops of gravity are what makeup spacetime itself.

These quantum loops of gravity have some important and fascinating implications. Since each loop is a specific quanta of space, it affects how we understand the singularity of the beginning of the universe or the singularity of black holes. General relativity tells us that gravity in a black hole will pull objects into it to smaller and smaller spaces, to a point of infinite density. But, and this is an important but, quantum gravity says that nothing can be condensed indefinitely. Things being pulled into a black hole can only be pulled in to a *finite* density. This is because *space itself* is quantized. Space itself can only get so small (the size of each loop of gravity). So, an object can only be condensed to the size of the smallest size of space itself (the loop).

I love the idea of each loop being a node in a web, but I would eventually like a more solid explanation of how that can be. I suspect that the universe works that way, but that is based on nothing except for the my love of networks. I need a little more convincing before I buy the whole argument, but I have to say, it is by far my favorite argument for how the universe works.

At the end, Rovelli eluded to Jeremy England's work on dissipation of energy in living systems (thermodynamically driven evolution, which is a continuation of Schrodinger's work) but didn't really do much other than gloss over it. Still, I was happy to see it included. ...more

18 likes · Like · see review

Apr 19, 2018 Barb rated it it was amazing · review of another edition

Shelves: own-it

I started off reading this very slowly, trying to understand it completely. I soon realized there are ideas here I’ll never completely understand! This was still an excellent book. The author seems to be a big fan of Democritus I don’t recall ever hearing of Democritus before reading this book! There were a lot of mind blowing ideas presented in this book. I had no idea that Dante, in The Divine Comedy describes the universe as a 3-sphere. I’m still struggling to picture a 3-sphere but the descr ...more

2 likes · Like · see review

Jan 31, 2023 Tomislav rated it it was amazing · review of another edition

Shelves: science, history, 5-stars

For the past century, theoretical physicists have struggled to reconcile general relativity with quantum mechanics, and a recent theory has been Loop Quantum Gravity (LQG). This introductory book by one of the leading researchers in LQG eloquently presents the background, concepts, and implications through plain analogy. If I may, I will give a bumper-sticker definition now. LQG interprets our curved spacetime as a quantized gravitational field. Considering spacetime at the smallest level to be For the past century, theoretical physicists have struggled to reconcile general relativity with quantum mechanics, and a recent theory has been Loop Quantum Gravity (LQG). This introductory book by one of the leading researchers in LQG eloquently presents the background, concepts, and implications through plain analogy. If I may, I will give a bumper-sticker definition now. LQG interprets our curved spacetime as a quantized gravitational field. Considering spacetime at the smallest level to be made of tiny irreducible quanta eliminates some issues that Einstein’s continuous spacetime has with infinity. But it also changes our understanding of how the universe behaves around singularities like the big bang and black holes.

The book begins in classical Greek times with Democritus, whose works have all been totally lost, but is known to us only through references made to him by others. Democritus is generally credited with the formulation of atomism – that all matter is made up of fundamental indivisible atoms. After deploring the thousand years of suppressed science that was the Roman Empire and the Dark Ages, the text quickly runs through the development of astronomy and physics up to the time of Einstein. And then a significant amount of page count is dedicated to Einstein’s work and on the development of quantum mechanics. Anybody who has read the history of science already knows all this. But because his purpose here is to foreshadow LQG, Rovelli describes concepts in ways I found fresh and accessible. This would enhance my understanding even if the second half of the book weren’t there.

In the second half, Rovelli explains what LQG is, how it unifies general relativity with quantum mechanics, and describes some of the problems it eliminates. There are a few shots taken at String Theory, LQG’s rival for Theory of Everything. For example the disappointing lack of supersymmetric particles by the new Large Hadron Collider at CERN. Without the math, and with scant experimental evidence in either case, all I can say personally is that the idea that spacetime is a quantized field, just as electromagnetism and everything else seems to be quantized, appeals to my aesthetic sense.

Finally, he looks at some of the cosmological implications of LQG, and this is where we realize that if accepted it would change more than just be a replacement of String Theory. Because there is a finite minimum length of spacetime, the Big Bang does not work back to an infinitesimal point, but rather no smaller than a single atomic element of spacetime, of size 1 Planck length. From there it re-expands. So rather than a Big Bang, we have a Big Bounce. Likewise, when matter enters a black hole rather than compressing to an infinitesimal point, it compresses only to that same minimum size, and then re-expands. Of course, due to time dilation, we may not witness the subsequent explosion for a really long time.

It's going to be interesting to watch the unification theories play out. I recommend this book for anyone interested in the problems of 20th and 21st century physics, even if Rovelli seems a little self-aggrandizing. I read a 2016 translation to English, made from the original 2014 Italian. ...more

1 like · Like · see review