“What we observe is not nature itself, but nature expose to our method of questioning.” — Werner Heisenberg
How much can we know of the world? This, of course, is the central question for physics, and has been since the beginning not just of modern science as we know it, but of Western philosophy.
Around 650 BCE, Thales of Miletus first speculated on the basic material fabric of reality. The essential tension here is one of perception. To describe the world, we must see it, sense it, and go beyond, measuring it in all its subtle details. The problem is the “all.” We humans are necessarily blind to many aspects of physical reality, and those aspects that we do capture are necessarily colored through the lenses of our perception.
We can’t, not even in principle, begin to understand what “all of reality” means. With our instruments and tools of observation, we capture fragments of it, which we then describe through our mathematical models and theories the best way we can. To quote philosopher Thomas Nagel, there is no “view from nowhere,” the God’s-eye view of reality in all its detail. We may be able to imagine such a thing, but we cannot ever grasp it. There is no such thing as complete knowledge of anything, let alone of the natural world around us.
There are two main reasons for our shortsightedness. One is related to technology. The other to our physical, body-centered connection with nature. Even if our theories aim at a sort of universality of knowledge, we probe reality in a very human way.
A partially obscured view
Let’s start with technology. Data gathering depends on the accuracy of tools and instruments. What we “see” is contingent on the tools we use to see with. As a consequence, worldviews shift as our tools of exploration evolve. There is no perfectly clear snapshot of reality; we always get a partially obscured view.
An obvious example is that of astronomy, before and after the telescope—or that of biology before and after the microscope. Both inventions changed in irreversible ways how we think about the skies and about life. As telescopes and microscopes evolved from their initial 17th-century progenitors and became progressively more powerful and far-ranging, worldviews changed again and again. We’ve progressed from a static to an expanding universe dominated by dark energy and dark matter, and from cells to the genetic revolution based on the double-helix DNA model and, now, on DNA-sequencing technologies.
There is no question that as our tools of exploration advance, we are able to construct a more detailed picture of physical reality. The question of interest to us, however, is not one of progress but one of limits. Can technology advance to the point of gathering all the meaningful information about nature, so as to effectively exhaust it? Here is the snag: we can never know. Even as our tools become ever more powerful, picking up details at what is currently unimaginably small and large scales, we can’t ever be sure that we have reached the limit of what is “out there” in the world.
Perhaps a useful analogy is a fishnet. We can make it tighter and tighter, and thus capture smaller and smaller species of marine life. But there is a limit to how tight the net can be due to the composition of its fibers. At least for fishing. Life will certainly end below a certain scale, but there will be molecules and atoms and subatomic particles too, some of them requiring more sophisticated approaches to be “captured” and identified, as we move from fishing nets to optical microscopes to quantum tunneling microscopes to particle colliders and detectors.
The strange loop of reality
Unless one can prove a definite theorem demonstrating that subatomic particles reach a final lower level of irreducibility, or that there is an ontological shift in the fundamental nature of reality, as in string theory, there is no way of knowing where to stop the search.
And since the searching strategies depend on extrapolations from our current models, we reach a strange sort of loop, where we can only look for what we expect to see, like the fabled ouroboros closed on itself, while the rest of reality is “out there,” unreachable.
Of course, we are not driving completely blind here. As we move on to submicroscopic scales, fundamental physics does provide some guidance as to where the limits for material structure may be. The most essential of these limits is based on the Planck units, taken as the absolutes for the breakdown of our current descriptions of physical reality based on a differentiable spacetime and quantum fields.
Thus, we have the Planck length of 1.62 × 10−35 meters, the Planck time of 5.39 × 10−44 seconds, and the Planck energy of 1.22 × 1019 GeV. (A GeV is one billion electronvolts, the energy unit used in particle physics. If we divide it by the square of the speed of light—remember the E=mc2 formula—we get 1.78 x 10-27 kg, very close to the mass of a proton.) If this makes your eyes blurry, don’t worry, keep on reading for the punchline.
Even if we can’t establish for sure that the Planck units do represent an ultimate limit to physical description, assuming that they do we quickly realize that our current experimental knowledge of particle physics is about 15 orders of magnitude away. Physicists talk of a “desert” between these two energy scales, but how can we be sure? History has shown over and over again that every time we open a window into a new energy scale, we discover all sorts of marvels: from the visible realm to the cellular to nanoscopic, to molecular, to atomic, to nuclear to particles to . . .
We remain uncertain as to the ontological structure of nature, whether it is described by fundamental quantum fields and their related particle excitations, vibrating strings, or something completely different and unexpected.
Contrary to what one may think, this is not a bad thing at all: science is a collective effort to go into the unknown, exploring reality beyond its current limits. Curiosity and intellectual daring are its most essential fuels (together with financial backing of course), and we must take risks to move forward.
As we do, through our methods of questioning, we improve the map of what we call reality.