My new favorite book, until a fresh one arrives from Amazon, is Carlo Rovelli's Reality is Not What It Seems: The Journey to Quantum Gravity.
Rovelli is an Italian theoretical physicist who, not surprisingly given the title of his book, is focused on resolving the mismatch between relativity theory and quantum mechanics. The key to doing this is to find a theory of gravity that is more fundamental than Einstein's general relativity, which describes gravity as the warping of space-time and isn't compatible with quantum mechanics.
That's a fascinating subject, made more fascinating by Rovelli's impressive writing ability, albeit in an English translation.
I've only just begun the book but am already liking it a lot. Rovelli starts off with a chapter about the atomic theory of ancient Greek thinkers such as Democritus. They broke away from the superstitions and religions of their time by extolling the ability of reason and observation to lay bare the secrets of the universe, which is still the basic scientific approach.
I found Rovelli's description of how Democritus concluded that reality had to be composed of discrete parts enlightening, having never heard it put this way before.
Democritus observed that matter could not be a continuous whole, because there is something contradictory in the proposition that it should be so. We know of Democritus's reasoning because Aristotle reports it.
Imagine, says Democritus, that matter is infinitely divisible, that is to say, that it may be broken down an infinite number of times. Imagine then that you break up a piece of matter ad infinitum. What would be left?
Could small particles of extended dimension remain? No, because if this were the case, the piece of matter would not yet be broken up to infinity. Therefore, only points without extension would remain.
But now let us try to put together the piece of matter starting from these points: by putting together two points without extension, you cannot obtain a thing with extension, nor can you with three, or even with four. No matter how many points you put together, in fact, you never have extension, because points have no extension.
Therefore we cannot think that matter is made of points without extension, because no matter how many of these we manage to put together, we never obtain something with an extended dimension.
The only possibility, Democritus concludes, is that any piece of matter is made up of a finite number of discrete pieces that are indivisible, each one having a finite size: the atoms.
Pretty damn brilliant. Just through clear thinking, around 450 BCE Democritus was able to come up with an atomic theory of what matter consists of that has stood the test of time. Sadly, all of Democritus' writings were destroyed by Christian emperors who didn't like that his ideas conflicted with Christian dogma.
So we're left with indirect mentions of Democritus' teachings. A Latin poet, Lucretius, says Rovelli, "adheres to the philosophy of Epicurus, a pupil of a pupil of Democritus." Here's how Rovelli describes how Lucretius viewed reality, comparing it to medieval notions that were much farther removed from modern science,
The medieval cosmos so marvelously sung by Dante was interpreted on the basis of a hierarchical organization of the universe that reflected the hierarchical organization of European society: a spherical cosmic structure with Earth at its center; the irreducible separation between Earth and heavens; finalistic and metaphorical explanations of natural phenomena; fear of God, fear of death; little attention to nature; the idea that forms preceding things determine the structure of the world; the idea that the source of knowledge could only be the past, in revelation and tradition.
There is none of this in the world of Democritus as sung by Lucretius. There is no fear of the gods; no ends or purposes in the world; no cosmic hierarchy; no distinction between Earth and heavens. There is a deep love of nature, a serene immersion within it; a recognition that we are profoundly part of it; that men, women, animals, plants, and clouds are organic threads of a marvelous whole, without hierarchies. There is a feeling of deep universalism, in the wake of the splendid words of Democritus: "To a wise man, the whole earth is one, because the true country of a virtuous soul is the entire universe."
There is, too, the ambition of being able to think about the world in simple terms. Of being able to investigate and understand the secrets of nature. To know more than our parents. And there are extraordinary conceptual tools on which Galileo, Kepler, and Newton will build: the idea of free and rectilinear motion in space; the idea of elementary bodies and their interactions, out of which the world is constructed; the idea of space as a container of the world.
And there is the simple idea of the finite divisibility of things. The granular quality of the world The idea that stops the infinite between our fingers. This idea is at the root of the atomic hypothesis, but it will also return with augmented force with quantum mechanics, and today is revealing itself to be powerful again -- as the keystone of quantum gravity.