Robert P Crease wonders why physicists and philosophers can’t come to a common view on the concept of space
In a column last year I wrote about a book by the historian of science Jimena Canales (January 2016 p19). Entitled The Physicist and the Philosopher: Einstein, Bergson, and the Debate That Changed Our Understanding of Time, her book describes an encounter that took place in 1922 between Albert Einstein and the French philosopher Henri Bergson. The book was notable for dramatizing the gap between Einstein’s approach to “objective time” as quantitative and measurable, and Bergson’s notion of “experienced time” as a flux in which past, present and future are knitted together.
A century later, the gap in our thinking of time persists. But a similar gap also exists in notions of space, even if that divergence has never crystallized into a specific encounter as it did between Einstein and Bergson over time. Physicists are apt to explain the everyday experience of space as a smooth, 3D arena in which things always have definite positions as an illusion – a by-product of the limited sensory faculties of humans. As the German mathematician Hermann Minkowski proclaimed in 1908, “space by itself, and time by itself, are doomed to fade away into mere shadows”, for only 4D space–time can preserve “an independent reality”. In quantum mechanics, moreover, the uncertainty principle forbids things from having definite locations.
In more speculative theories, space is more complicated. Some versions of quantum-field theory picture a fluctuating space–time foam. In loop quantum gravity, meanwhile, space is quantized, with its patches unable to become infinitely small. As for string theorists, they insist on 10, 11 or 26 dimensions, with the extra ones closed or “compactified” so they are unseen even in current scientific experiments. The Columbia University theorist Brian Greene’s 2011 book The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos discusses no less than nine types of alternate universes.
Philosophers, by contrast, tend not to consider the ordinary experience of space illusory. They are more interested in features that make such experience possible – features that are not incidental or subjective but belong to the full reality of spatial experience. As the French philosopher Maurice Merleau-Ponty wrote in his 1945 book Phenomenology of Perception, these aspects are like “the darkness needed in the theatre to show up the performance”.
Philosophers, for instance, distinguish between “allocentric”, “perceptual” and “bodily” space. Allocentric space is an objective space in which locations and orientations can be defined – with a GPS, say – without reference to an observer’s location. Perceptual or “egocentric” space was identified in the 18th century by the German philosopher Immanuel Kant. It is based on the spatial orientation provided by an observer’s body – up and down, right and left, front and back – without which it would be impossible to locate something in allocentric space even with a compass or GPS device.
As for bodily or “proprioceptive” space, it was described by 20th-century philosophers (including Merleau-Ponty) as an awareness of the presence of your own body and its ability to move. It is the sense you have of your head and hands as you hold this magazine – or as you operate the phone or tablet you’re reading it on. Bodily space is the non-mathematical sense called upon in walking, playing and operating objects such as a GPS or a compass.
Given the gap between the physical and philosophical approaches to space, you might wonder why we don’t just assume that physicists and philosophers investigate different things: space and place, say, or Space and space.
That won’t work, because physics and philosophy are both ambitious disciplines; each aims to describe the world, not just a particular slice of it. As the physicist John Bell wrote: “To restrict quantum mechanics to be exclusively about piddling laboratory operations is to betray the great enterprise. A serious formulation will not exclude the big world outside the laboratory.”
That big world includes human experiences. The German philosopher Edmund Husserl, for example, denounced the “scientific fanaticism” of those who think they are studying the world when they rely on only what shows up in laboratories. Philosophy’s task, as Husserl saw it, is to investigate the basic features of all human activities, including science, and the experiences that make them possible. Both physicists and philosophers, then, insist that they are the ones talking about “Space” rather than “space” and grasp their relation.
What most divides physicists and philosophers on the issue of space seems to boil down to their answers to the question of whether consciousness is a fundamental feature of the world. Physicists begin with the assumption that what they study precedes and is independent of interactions with observers. Philosophers – or at least those who follow Husserl’s general starting point – begin with and never fully leave behind experiences of connections between humans and the world. That makes it hopeless either to try to reduce one starting point to the other, or to develop some larger conception of space to encompass both in an artificial compromise.
The critical point
Let’s adapt Bell’s image of the lab and the “big world”. Space that’s investigated in the lab – where there are trained staff, special assumptions, advanced equipment and controlled conditions – looks the way scientists find it to be, and it also can be used to describe much of what’s on the outside. Yet humans are born into and inhabit that “big world” first, and rely on the practical experience of space that philosophers address. That space is also found inside the lab, where scientists practically handle equipment and make measurements using perceptual and bodily space.
What’s in the lab is also in the big world, and what’s in the big world is also in the lab. Recognizing this multidimensionality makes space capacious enough for both physicists and philosophers alike.