Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum by Lee Smolin

Lee Smolin is a theoretical physicist who is dissatisfied with the state of theoretical physics. He is not alone in being dissatisfied. Physicists have two wonderful theories —  quantum mechanics (which deals with the very small) and general relativity (which deals with the very large) — that don’t fit together. Some of them have been trying for decades to reconcile the two theories. In addition, there is a lot about quantum mechanics that seems crazy or at least paradoxical. It’s been argued, therefore, that the theory is incomplete.

Smolin believes that there is a fundamental reality separate from our perceptions that underlies both quantum mechanics and general relativity. He would like to figure out what that reality is. He says this makes him a “realist”.

The first part of the book discusses what Smolin calls “anti-realist” views, primarily the so-called Copenhagen interpretation of quantum mechanics (sometimes referred to as the “shut up and calculate” view). He then outlines some competing views, such as Einstein’s, according to which quantum mechanics is incomplete.

In the final chapters, he offers the beginnings of his own theory. I won’t try to explain it, but he begins with an idea proposed by the brilliant German philosopher Gottfried Willhelm Leibniz (who died 300 years ago). Leibniz suggested that the universe is composed of an infinite number of simple substances called”monads”. The Wikipedia article on Leibniz says “each monad is like a little mirror of the universe”, i.e. a mirror reflecting all the other monads.

Near the end of the book, Smolin offers a one-sentence summary of his theory:

The universe consists of nothing but views of itself, each [view being from the perspective of] an event in [the universe’s] history, and the [universe’s] laws act to make these views as diverse as possible [271].

For Smolin, time is a fundamental feature of the universe. Space isn’t. Space emerges from events. Furthermore, the fact that space isn’t fundamental helps explain how two particles that are millions of miles away from each other can be “entangled”, so that an effect on one can immediately affect the other. That’s the idea of “non-locality” that Einstein called “spooky action at a distance”.

Smolin is sure that he doesn’t have all the answers, but he believes it’s worth trying to find them. If you’d like to know more, you’ll have to read the book or find someone else to explain it. There are diagrams and no math!

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

Carlo Rovelli is an Italian theoretical physicist whose previous book, Seven Brief Lessons on Physics, was a bestseller. In this one, he tells a familiar story: the history of physics from ancient Greece to the present day. But he tells it in such a charming and enlightening way that the story feels new.

One of the lessons from the book that will stick with me is that, according to current physics, the universe isn’t infinitely divisible. At some point, you’ll get to the bottom where the quanta (or tiniest pieces) are. The surprising part of that idea is that these quanta apparently include the quanta or tiny pieces of spacetime. But these tiniest pieces of spacetime aren’t in space or time. They compose space and time. Here’s how he sums it up at the end of the book:

 

The world is more extraordinary and profound than any of the fables told by our forefathers…. It is a world that does not exist in space and does not develop in time. A world made up solely of interacting quantum fields, the swarming of which generates — through a dense network of reciprocal interactions — space, time, particles, waves and light….

 

 

A world without infinity, where the infinitely small does not exist, because there is a minimum scale to this teeming, beneath which there is nothing. Quanta of space mingle with the foam of spacetime, and the structure of things is born from reciprocal information that weaves the correlations among the regions of the world. A world that we know how to describe with a set of equations. Perhaps to be corrected.

 

The biggest puzzle Rovelli and his colleagues are working on is how to reconcile the small-scale physics of quantum mechanics and the large-scale physics of general relativity. They aren’t consistent. Currently, the most popular way to resolve the inconsistency is string theory, but Rovelli’s preferred solution is loop quantum gravity. Unfortunately, his explanation of loop quantum gravity was the part of the book where he lost me. Maybe a second or third or fifteenth reading of that section would clear things up.

The other idea that will stick with me is from quantum field theory: among the fields that make up reality, such as the electron field and the Higgs boson field, is the gravitational field. But the gravitational field is just another name for spacetime. Spacetime is the gravitational field and vice versa. That’s what Rovelli claims anyway, although he ends the book by pointing out that all scientific conclusions are open to revision given new evidence and insights.