Rovelli 6: It's all about information.

This is my sixth and final post on Carlo Rovelli's new book, Reality Is Not What It Seems. The first three posts were:

• From Democritus to Relativity to Quantum Mechanics
• Spacetime is Quantum
• Quanta of Space
• Time Does Not Exist
• Fundamental Constants of the Universe

1. Finished the book a few days ago. Chapters 12-13 look somewhat vaguely to the future. I frankly didn't get much out of them. In chapter 12 he tries to give a general sense of what he means by a "relational" interpretation of quantum mechanics (QM). He references this Stanford article. "The notion of the 'state' of a system refers, explicitly or implicitly, to another system" (253).

So he boils QM to two postulates: 1) The relevant information in any physical system is finite and 2) You can always obtain new information on a physical system. John Wheeler, the father of quantum gravity once said, "everything is information."

2. The main thing of interest is the question of time. He gives a "thermal" interpretation of time. All the processes of the universe are reversible (and thus time irrelevant) except for those that involve heat and entropy. "There is no preferred direction of time without heat" (251). "The origin of time may be similar to that of heat: it comes from averages of many microscopic variables" (250).

I did gain from this book, but it did leave me hanging. So I move on to more books...

Rovelli 5: Fundamental Constants of the Universe

This is my fifth post on Carlo Rovelli's new book, Reality Is Not What It Seems. The first three posts were:

• From Democritus to Relativity to Quantum Mechanics
• Spacetime is Quantum
• Quanta of Space
• Time Does Not Exist

1. Chapters 8-11 are fairly short. Some of it covers basic material from cosmology but there are some helpful synthetic thoughts too.

Chapter 8 fills in some gaps with regard to the Big Bang. He gives high praise to Georges Lemaître, a Belgian priest, for supporting the idea of a "primordial atom" even though Einstein strongly disagreed. Einstein's equations seemed to suggest that the universe was expanding, but he didn't want to believe it. In fact he added a "cosmological constant" to his equations to fix it (Λ). Lemaître turned out to be right about expansion.

Then Einstein lamented adding the cosmological constant and wanted to remove it. Again, Lemaître suggested he should leave it. Lemaître proved to be right again over Einstein. So in both cases Rovelli writes, "It doesn't fall to everyone to disprove Einstein" (204).

Then Lemaître stopped the Pope, apparently, from making the Big Bang official church belief. Again Rovelli says, "It is not given to everyone to disprove the pope" (205). This falls under the principle of not inserting God too dogmatically into your scientific theories, because theories change.

2. Rovelli favors something he calls "the Big Bounce." The idea here is that "our universe could be the collapse of a previous contracting universe passing across a quantum phase, where space and time are dissolved into probabilities" (208). This seems to me to be a form of the oscillating Big Bang theory.

I thought that the current sense of things was that there was not enough matter in the universe to pull everything back together and thus that the universe was headed for a "Big Rip" at the end of things. This is also different from the multiverse idea that other books I've read have suggested, namely, that our universe is just one of an infinite number of universe bubbles.

Meanwhile, Rovelli nicely, I think, counters Lee Smolin's sense that the universe is all there is by definition. Rovelli, much more soundly says, "The word 'universe' has assumed another meaning in cosmology: it refers to the spacetime continuum that we see directly around us, filled with galaxies and history of which we observe. There is no reason to be certain that, in this sense, this universe is the only one in existence" (208).

Take that Smolin, who says in the first chapter of Quantum Gravity, "By definition the universe is all there is" (17). Let's just say Rovelli is a much better philosopher, although I don't always agree with him.

The dissolution of spacetime into a cloud of possibilities when you have that much mass at a quantum size is an intriguing idea.

3. Chapter 9 asks if we have any experimental evidence for loop quantum gravity. A number of times he pushes back both against those who say you cannot talk about anything that you cannot now experimentally show and those who wildly speculate detached from current trajectories. To me this positioning makes perfect sense.

On the one hand, a theory should proceed to experimentation. "A theory lacking empirical confirmation is a theory that has not yet passed its exams" (212). On the other hand, he disagrees with wild hypotheses. "Many theoretical physicists are today looking for new theories by picking arbitrary hypotheses... I don't think that this way of doing science has ever produced good results" (215-16).

Rather, all the experimental evidence has been confirming the three cornerstones of modern physics: general relativity, quantum mechanics, and the Standard Model within quantum mechanics. The new findings have brought a complete absence of surprise. Hawking was disappointed.

The three big findings of this decade are 1) the confirmation of the Higgs boson, 2) the cosmic measurements of the Planck satellite, and 3) the detection of gravitational waves.

Also, the fact that CERN has not discovered supersymmetry is a blow to string theorists, which is why Sheldon on Big Bang Theory went looking for something else to study. :-)

4. Mapping of the cosmos has given us a sense of the lay of the background radiation left not too long after the so called Big Bang. The idea here is that it took some time for the universe to cool down enough for the light (photons) of creation to be released.

The remnants of this release are called "cosmic background radiation" (CBR), alleged to have happened some 380,000 years after the Big Bang.

Apparently, if LQG is correct (loop quantum gravity), then there should also be a gravitational background radiation. An experiment called LISA involving three satellites around the sun, might be able to test for these.

5. Chapter 10 looks at quantum black holes. There are black holes at the centers of most galaxies and, in at least one theory, they may account for what it otherwise called dark matter.

The horizon of a black hole is the point where you might stay out. Past that, nothing can get out. Time stops at the horizon. Stephen Hawking's claim to fame was his discovery that black holes slowly evaporate. Eugenio Bianchi showed that loop quantum gravity can also demonstrate Hawking's formula for the heat of a black hole.

What LQG would show is that, since spacetime is not infinitely divisible--since it never can reach a singularity--at some point a black hole should explode in a miniature version of the Big Bang. From our perspective outside a black hole, this would take billions years, even if it is only moments inside the black hole. Since the universe is allegedly 14 billion years old, we might find some of these. Rovelli suggests that some "fast radio bursts" detected by radio telescopes could be such.

6. Chapter 11 is called the end of infinity. The common sense of the suggestion here is so obvious I've thought of it for some time now and I'm not even a scientist. Why didn't Dirac and Feynman? Quantum mechanics and relativity are plagued with infinities. Feynman the pragmatist simply substituted the experimental values for certain infinities to get his equations to work.

But LQG, because it sees space as quantized, eliminates the infinities. This seems so obvious to me that it is surprising it is not a fundamental working assumption of modern physics.

"Putting a limit to infinity is a recurrent theme in modern physics. Special relativity may be summarized as the discovery that there exists a maximum velocity for all physical systems. Quantum mechanics can be summarized as the discovery that there exists a maximum of information for each physical system. The minimum length is the Planck length L_P, the maximum velocity is the speed of light c, and the total information is determined by the Planck constant h" (232).

Now we are getting somewhere. This is what I've been thinking and looking for someone to put succinctly like this. "The existence of these minimum and maximum values for length, velocity, and action fixes a natural system of units. Instead of measuring speed in kilometers per hour... we can measure it in fractions of the speed of light.. In the same way, we can posit L_P = 1 by definition and measure length in multiples of Planck's length. And we can posit h = 1 and measure actions in multiples of Planck's constant. In this way, we have a natural system of fundamental unities from which the others follow" (233).

One more seems to complete Rovelli's set, namely, the cosmological constant (Λ) used in relativity. I have a book called Just Six Numbers that is also on my reading list. I'm hoping it will help me understand the importance of the ratio between the cosmological constant and the Planck length.

My next post should finish the book.

Rovelli 4: Time Does Not Exist

This is my fourth post on Carlo Rovelli's new book, Reality Is Not What It Seems. The first three posts were:

• From Democritus to Relativity to Quantum Mechanics
• Spacetime is Quantum
• Quanta of Space

1. Chapter 7 is getting closer to theology. I have always been sympathetic to the medieval view that God is outside time. God immanent goes through time with us. God transcendent sees all of time in an eternal now. This construct provides a helpful way around the "Does omniscience imply determinism" debate.

I had the thought while reading this chapter, "God is quantumly entangled with the entirety of his creation." Quantum entanglement is the sense that when two paired particles go their separate way, their states remain connected. In Quantum Gravity, Smolin suggests that this connection can apply to particles inside and outside a black hole.

So I was playfully musing of God knowing every quanta of the universe from its connectness with him at the moment of creation. It's not a suggestion or completely satisfying. After all, this musing does not clearly relate to the future. It would only suggest an exhaustive knowledge of the present and the past.

2. One of the implications of general relativity is that "every object has its own time, running at a pace determined by the local gravitational field" (178). If I am traveling close to the speed of light and you are not, I will age much slower than you will. If you live on a planet with a much greater gravitational field than earth, you will age more slowly than me back on earth. In fact, someone who spends their whole life in Tibet will be a fraction of a second older than me, living my whole life at the Dead Sea, even if we were born at the same exact moment somewhere.

"Time" does not pass at the same rate everywhere.

One thing Rovelli has already mentioned is that, in some of the fundamental quantum gravity equations (e.g., Wheeler-DeWitt), there is no time variable. How is that possible? It gets back to a principle he has stated in his chapter on quantum mechanics. Reality is relational.

Quanta of gravity do not change "in time." Time is simply a counting of the interactions of quanta of gravity. The world is not something that changes "in time," for time does not exist. There is only process after process. "There is no longer space that 'contains' the world, and no longer time 'during the course of which' events occur" (183).

I am hoping I will have a better sense of what I am saying by the end of the book. :-)

3. So an event does not take place in spacetime. Rather, spacetime is part of the event. The event is a process with an initial and final state. And there is a boundary for the event.

"If quantum space has the structure of a spin network, what structure will spacetime have?" (186). Spacetime is the history of a spin network. This history of a spin network is apparently what Loop Quantum Gravity (LQG) physicists call "spinfoam."

I don't really like this word. The idea seems to be that the area of the node foams up to the beach of the line between nodes. And that beach is a spin line. I'm sure I'm massacring it.

"To compute the probability of a process, one must sum up over all the possible spinfoams within the box that have the same boundary in the process. The boundary of a spinfoam is a spin network and the matter on it" (187). This is what Feynman did to calculate the probability of a particle's trajectory.

4. So to sum up the chapter. "Space is a spin network whose nodes represent its elementary grains [of gravity], and whose links describe their proximity relations" (192). What we call spacetime is the transformation of these spin networks into and apart from one another, and the history of these spin networks is called "spinfoam."

So all reality is variations on quantum fields, fields one on top of the other. Another name for these are "covariant" quantum fields. These are, in Rovelli's mind, the fundamental reality that connects spacetime with quantum fields.

More to come...

Rovelli 3: Quanta of Space

This is my third post on Carlo Rovelli's new book, Reality Is Not What It Seems. The first two posts were:

• From Democritus to Relativity to Quantum Mechanics
• Spacetime is Quantum

1. This chapter is not long but it is getting at the things I am interested in right now. I re-skimed chapter 10 of Lee Smolin's Three Roads to Quantum Gravity to cross-reference their material. That chapter is called "Knots, Links, and Kinks." I see Smolin's coming out with a new edition.

Because I don't know the math, because they don't fully give the math, it's hard to get more than just an impression from these chapters. But I like the basic theses.

2. We already have the first key truth. Both space and time reduce to quanta. Space is not infinitesimally continuous. Time is not infinitesimally continuous. I like it.

Now here's another biggie. Gravity reduces to quanta, discrete units of gravity. The quanta of gravity are not in space. "They are themselves space" (172). "Quanta of gravity constitute space itself."

Using another picture, space reduces to discrete packets of volume, which we might call "nodes." "Volume is a property of the gravitational field, expressing 'how much gravitational field' there is" (163-64). The imaginary lines between these nodes are called "links," and a whole set of such intersecting lines is called a "graph."

Nodes, Links, and Graph (Rovelli)

3. There is an area associated with the lines between nodes, which is roughly the square of the Planck length mentioned in the previous post (8πL² times the square root of the spin times one plus the spin, with the spin coming in half integers). When we think of a larger three dimensional volume, the volume is the sum of the volumes of the nodes. Such a volume is a "spin network."

4. After writing all that, there is a danger of thinking that these nodes are space. But Rovelli and Smolin would both want to clarify that, like the electron, it is in the interaction of these gravitational quanta that space exists. Space is not in the node nor is the node space. Space is what happens when the nodes interact, if I understand correctly.

Rovelli 2: Spacetime is Quantum

This is my second post on Carlo Rovelli's new book, Reality Is Not What It Seems. The first post was:

• From Democritus to Relativity to Quantum Mechanics

1. My book has now been baptized in coffee, but is still readable. I suppose it was inevitable.

We now hit the problem edge of physics in chapter 5. Quantum mechanics works for things that are very small. General relativity works for things that are very big. They contradict each other.

Relativity says that spacetime is curved and continuous. Quantum mechanics says that space is flat and energy is discontinuous.

This contradiction is not a problem unless you are dealing with something that is both very small and yet has tremendous mass. In other words, black holes and the Big Bang.

2. A favorite scientist of Rovelli is clearly the Russian, Matvei Bronštejn, put to death under Stalin in 1938. He apparently suggested before his death that, following Heisenberg's uncertainty principle, the narrowness of location would require great ambiguity in momentum. The energy this would involve at a particular point would be so great as to create a black hole.

The bottom line, Bronštejn suggested that this thought experiment implied a limit to the divisibility of space. The minimum space is around:

This "Planck length" combines the three fundamental constants of nature. "H bar," as it is called, is fundamental to quantum mechanics. C is the speed of light from special relativity. And G is the gravitational constant from general relativity.

3. The next turn in the chapter is to John Wheeler, who coined the phrase black hole. It was not too long ago that many physicists were skeptical about their existence, but now it is overwhelmingly accepted.

Apparently, Wheeler and Bryce DeWitt come up with an equation for the "foaming" of space at the Planck level, the "Wheeler-DeWitt equation." Here I am beyond much acquaintance. What is most curious about the equation is that it does not have a time variable. How do you describe interactions on the most fundamental level of reality without a time component?

There will me more to come on this subject. I have some other sources that I may use to try to triangulate.

4. We are close to the birth of quantum loop gravity, the main contender with string theory for ultimate reality right now. In the late 80s, Abhay Ashtekar simplifies and rewrites the Wheeler-DeWitt equation. Lee Smolin tells the same story from his perspective in Three Roads to Quantum Gravity.

Smolin and a guy named Ted Jacobson find some solutions to this equation. The equation only has solutions when lines "loop" in space. Thus "loop quantum gravity" is born.

More to come...

Rovelli 1: Relativity and Quantum Mechanics

1. I only discovered Carlo Rovelli this last month. If you have followed my Brownian motion through science books, you will know that I have read parts of several books that have left me feeling rather empty. In the last few years I have started and not quite finished to varying degrees Tegmark's Our Mathematical Universe, Brian Greene's, The Fabric of the Cosmos, Roger Penrose's, The Road to Reality, and most recently, Lee Smolin's, Quantum Gravity. I read all but the last three chapters of Smolin's book last month, and it was he that set me on to Rovelli.

Maybe I'll go back and finish Smolin. He must decrease; Rovelli must increase.

In 2014 over spring break, I discovered The Perfect Theory: A Century of Geniuses and the Battle over General Relativity. It was fantastic. Since then I've been looking for the silver bullet to bring me up to speed on the edge of physics. I'm hoping to meet up with theology at the end. I did a MOOC that was wonderful, From the Big Bang to Dark Energy.

Since then (maybe even before then... I can't remember) I've had in mind a quasi-novel writing project called, "The First Day of Creation." I've been scrambling to read bits and pieces, trying to learn things I've been trying to learn since I was in high school. I've never gotten so far!! Schroedinger's equation is on the bucket list and is probably only a few hours of study away.

I can tell my mind is 50. I can remember how quick my mind used to be. It's depressing. I had coffee with a physics colleague of mine at IWU this week. He's just a little older than me but agreed that he could feel it.

BUT, I've never gotten this far. I've never understood so much. If only I'd have had someone to explain it to myself then!!!

2. I'm not done with Carlo Rovelli's Reality Is Not What It Seems. It came out this year. It is even better than The Perfect Theory. I don't think I've ever read anything so clear on these topics. Maybe it's just because I'm finally hitting a critical mass. I wanted to jot down notes on the first four chapters. They bring the reader up to speed with relativity and quantum mechanics.

It's so clear!! The rest of the book goes on to quantum gravity, the very edge of where physics is.

3.  I was annoyed with chapter 1. Maybe if I hadn't read so much I wouldn't have minded. He went back to Democritus and the ancient atomists. Epicurus, Lucretius. Yes, yes. Get on with it.

The nugget here was on Einstein and Brownian motion. In 1905 Einstein wrote three groundbreaking papers. One of them was on Brownian motion. It verified that matter was made up of atoms, whose vibrations knock a grain around on the surface of water.

4. Chapter two moved on to Newton in the 1600s and Faraday/Maxwell in the 1800s. Yes, yes. I've read most of this stuff before. Newton looks at space and time as the frameworks in which everything else moves. Rovelli at least likes that he subverts Plato and Aristotle. Well I do too. Half the Christian thinkers of the current age are still bemoaning that one.

Faraday and Maxwell come up with the idea of fields. You can act on things at a distance with electromagnetism. Maxwell's equations--on the bucket list and within striking distance.

5. Chapter 3. Finally. We get to relativity. I've given and continue to give some time to it. Sometime this fall I'm scheduled to do a Friday post on it. The post is already started.

One of Einstein's 1905 articles is the one where he announces special relativity to the world. Einstein solves a contradiction in the physics of his day. Normally, if you are on a train moving 40 miles an hour and throw a baseball forward at 30 miles per hour, it will seem to be going 70 miles an hour to me standing in a nearby field.

But it was discovered that the speed of light is 300,000,000 meters/second no matter where it is. If I shine a flashlight in the field, if you shine a flashlight on top of the train, if an ant on the baseball shines a light. No matter which one of us measures my, yours, the ants light speed, it will come out 300,000,000 meters per second.

Einstein's solution was brilliant. Spacetime appears to contract, depending on where you are standing. If you are moving close to the speed of light, you will seem to have shrunk and slowed down to me. And I will seem to have shrunk and slowed down to you.

6. But Einstein's general relativity has been called "the most beautiful of theories." He came out with it in 1915. I have a hunch David Hilbert really beat Einstein by a week, but as a gentleman he let Einstein take the credit. It is highly debated. Hilbert knew the math Einstein needed to finish the theory. Einstein had great difficulty getting his mind around it.

Hilbert said, "Any youngster on the streets of Goettingen understands geometry in four dimensions better than Einstein. And yet it was Einstein who completed the task" (92).

The main idea is that space curves around objects of great mass. Gravity is not a force. It is the curvature of space near a large object like the earth. So we are really simply moving along the curvature of space, not being pulled by the earth.

Rovelli goes on a fun tangent relating to Dante and the geometry of spheres. I kept telling myself. "He's Italian. Of course he's going to connect the story to its Italian connections." And, "man, this guy knows a lot more than physics." :-)

7. Chapter 4 is the best treatment of quantum mechanics I've ever read, and I've tried a number. Then again, I'm hitting a critical mass so it's bound to make more sense than ever.

Rovelli describes quantum mechanics in terms of three fundamentals. First, reality breaks down into quanta. Reality is granular. Energy breaks down into packets of photons. Matter breaks down into packets of fundamental particles like electrons, quarks, and neutrinos.

Again, I have been filling in gaps on the Standard Model these last five years. I read some in Richard Feynman. The confirmation of the Higgs boson has put the icing on the cake of the standard model. Now Rovelli can assume it.

By the way, Einstein's third paper in 1905 showed that, indeed, energy exists in quanta. Although Max Planck in 1900 is often said to be the father of quantum mechanics, he didn't really believe what he was seeing. Einstein again, showed quanta were real.

8. The second fundamental is that reality is indeterminate. This one has taken some time to convince me (Einstein was never convinced). I have disliked Heisenberg and the Copenhagen interpretation of quantum mechanics since my teens. I have a thick book by David Bohm I don't understand but hope one day to read. Like Einstein, he rejected indeterminacy.

But Rovelli has sealed the deal for me. Electrons have no positions until an event happens. This is his third point, the one I don't fully appreciate yet but am beginning to understand. Reality is a matter of events. The way he and Smolin put it is that "reality is relational." I'm sure that's better but let me start with what helps me.

"Quantum mechanics does not describe objects; it describes processes and events that are junction points between processes" (136).

The electron is only a possibility until it bumps into something. Rovelli has a great footnote where he says that Schroedinger's equation is not about reality. It only tells you the probability of where the particle will show up once an event happens. And when that happens, it is always at a point.

9. I'm not doing the chapter justice. I have known the players forever. I touched Dirac's door in Tallahassee in 1983, about a year before he died. But this chapter really moved me forward in understanding what these guys were really doing. How has this taken so long???

Heisenberg describes the appearance of electrons at a particular point as someone walking under lamp posts in the dark in Copenhagen, appearing for an instance under one only to disappear into the dark and then to mysteriously appear under another. Brilliant!

Dirac with Asperger's puts together the math, which I've realized is basically linear algebra, a new item on the bucket list. First we calculate the possible values an aspect of a particle can have ("calculation of the spectrum of a variable"). Then we calculate the probability of each possibility ("calculation of the amplitude of transition"). All those orbits we had to learn in chemistry are the possible solutions to Schroedinger's equation.

Dirac succeeds at combining quantum mechanics with special relativity. The challenge, what Rovelli is up to, is still to combine it with general relativity. That is the rest of the book.

10. Feynman also features in this chapter, connecting another strand I have not yet connected. His path to calculating the probability of a particular path is to add up all the possible paths. "It is as if the electron, in order to go from A to B, passed through all possible trajectories" (133).

11. I want to end with this chart, which is a brilliant encapsulation of the paradigm shifts that have taken place to this point in the book:

More to come...