In Reality is not what it seem, Dalio weaves the beautiful thread of atomicism from when it was first conceived by philosophers of antiquity (Democritus), through banishment under Christain Roman Empire to Renaissense and modern time. The book was both historical and scientific.

From an early age of human civilization people have been tempted to understand the nature of surrounding reality. Without sophisticated mathematical and engineering tools, ancient philosophers reflect and reason about phenomena observed in nature. They asked hypothetical questions such as Zeno’s Achille and turtle paradox). The book has proved that, more than once in history, the sheer force of intuition and imagination led original thinkers to catch glimpses of the world view that mordern science would arrive at. Thinkers like Democritus, Anexamandria, thought of the world as swarm of indivisible grains just like quantas making up the world in mordern physics.Or the poet Dante who imagined a finite world but without limit.

As the book progresses, our own daily perception of reality with space, time and particles in space, emerges into a singular unified concept of covariant quantum fields. No longer is space a vacuum box in which objects occupy. Space is now mesh of gravitational field which curves nearer to objects. Time is no longer the underlying objective flow by which clock ticks and events unfold. Rather, it is the succession of events that create time. And in fact, we never really measure time itself. We instead count one thing with respect to other, like number of quartz viberations per clock tick, angle a clock hand moves versus movement of the sun… The macroscopic world is static. A rock is standing still. A person is a stable whole. The microscopic world, on the contrary, is a spider of never ceasing events. We are constantly losing and gaining quanta from the surrounding.

The book summarises quantum gravity with these three important characteristics:

1. Granualarity

There is a limit to divisibility. Electron orbits around nucleus at certain energy levels rather than any random distance. If we keep dividing a piece of paper by half, it won’t go on forever. Analog signal is not continuous, it is digital signal with very tiny sampling interval. The specific number that a thing can assume value is determined by Eigenvalue equation.

2. Indeterminacy.

The most important point is the picture of a world which is probabilistic at its core. Observing an electron moving in its orbit, we are not certain it will move left or right next. Only thing we know is how probable a path is. Laplace’s demon wouldn’t be able to see the future with 100 percent certainty, even if he perceived the state of the present down to atoms.

3. Relational.

Properties such as velocity and angular momentum are not intrinsic to particles. Quanta like electron acquire those properties only at collision with each other. Outside those interactions, quanta are cloud of possibility to realize at the next interaction. Some other articles refer to this relational nature as electron having a property only when we look at it. (Wow, isn’t it scary to say that we exist only when somebody looks at us? This reminds me of profit/loss in stock investing, which only takes value when we look at our portfolio :D). Relativity is nothing new in science. Newton said that speed is relative between moving object and the observer. Direction is relative. Moving up and down is relative to the observer. Time is measured by counting occurences of one events relative to another.

The book moves on to current frontier of mordern physics, which is to reconcicle general gravity and quantum mechanics. Can anything be both field and particle. Just like light are undulations of electronmagnetic field as much as swarm of photons. And the suggested way forward should be a combination of general relativity, quantum mechanics and thermal time.

This is a crude summary of what I learned. There are definitely more to the book. For example, it’s fascinating reading about how we could travel to a distant future by staying close to the surface of a blackhole, around which space curves and time passes slowly. This idea has been used in science fiction story such as Winter’s King by Ursula Le Guin. Maybe we will be able to do that one day. (But i’m not sure who would be willing to go to an uncertain future without any mean of coming back.)