New Carlo Rovelli book challenges science's understanding of reality and the universe

I have a book on my shelf called Physics and Ultimate Reality. The title perfectly expresses the dream many physicists like me have when we begin our studies as young students. We yearn for perfect, objective knowledge of a perfectly knowable universe.

This "God's-eye view" is also what's claimed as the purpose and promise of physics in many popular books on the subject. But, now, comes a new book by physicist Carlo Rovelli that explicitly rejects any path to an ultimate reality. The force with which Rovelli -- one of the leading researchers and popularizers in the field – argues for this seemingly heretical view is what makes his On the Equality of All Things such a compelling, exciting and important read.

Rovelli begins with a simple and compelling point: We humans have access to a very limited set of experiences when it comes to the universe. Because we live on the solid surface of a planet, we think there are solid objects. Because that solid surface offers fixed reference points like mountain tops, we think solid objects can have fixed locations in space. And if those objects do move, we think we can use our fixed reference points to give us an absolute measure of that motion. In each case, however, modern physics has shown these assumptions to be illusions.

Albert Einstein's relativity revealed that measurements of time and space (including our sense of when two events are simultaneous) are relative. Quantum mechanics, our best theory of matter at the atomic level, showed us that the properties we can ascribe to things cannot be disentangled from how we measure them. In this way, Rovelli argues, modern physics began to erode the sense that physics gives us a perfect access to a world as seen from the outside (i.e. the God's-eye view).

Rovelli dedicates considerable space to a view of quantum mechanics called the relational interpretation. When quantum physics appeared in the early 20th century, it came as a shock to the physicists who were creating it. In the 250 years since Newton introduced his famous laws of motion, physicists had come to believe their equations described a reality that was entirely independent of human action or interpretation. The "stuff" described by Newton's laws, and the laws themselves existed "out there" in the "Ultimate Reality" that the book on my shelf points to. But in quantum mechanics it became difficult to speak of objects having properties before those properties were measured. This is the source of the famous Schrodinger's Cat parable where a cat in a box can be both dead and alive before the box is opened and a measurement is made.

For some physicists, it was so important to get that Ultimate Reality back that they invented interpretations of quantum physics that claimed the universe splits into separate parallel versions of itself when the box is opened. Rovelli thinks these attempts are nonsense. For him, the lesson of quantum mechanics is relationality. Everything exists only in relation to everything else. That means the properties of a system – any object – are always relational properties. There is no way to see them from an ultimate or absolute perspective because there are no ultimate or absolute perspectives. And in the absence of an ultimate perspective the power of physics to ultimately "explain everything" also falls apart.

As Rovelli puts it in his latest book, "Physics is often credited with a power it does not have: that of exhausting what can be known about the world. This is nonsense. Knowing the physical laws of the world does not amount to knowing the world."

This is a radical claim about physics, particularly for one of the world's most well-regarded physicists. Not only does it directly contradict the scientific triumphalism that one finds in many popular books about science, it's also a view that crashes against the perspectives of many contemporary philosophers of science. But as Rovelli writes, "we never leave the circle of perspectives." For him, this irreducibility of relationship is the central lesson of relativity and quantum mechanics.