Pedro Lilienfeld

Recently I came across the following quote by the famous German physicist Werner Heisenberg:

“We have to remember that what we observe is not nature in itself but nature exposed to our method of questioning”.

This statement provokedmy thinking because I found it quite profound and all-encompassing and yet, potentially subject itself, to questioning.

First of all, we should consider that Heisenberg expressed the above thought during the first half of the 20th century, a period during which the physical sciences underwent the momentous revolution embodied by both relativity and quantum mechanics. These fields gave us a totally new perspective on nature, one that was, heretofore, essentially unsuspected. These entirely new directions revealed that our classical model of nature was only a convenient mirage that fit our perceptions and preconceptions.

I would like to address this situation from the point of view of our knowledge about the universe, a cosmological perspective. Let me center this perspective on two recent periods: the 1930s — Heisenberg’s apogee —  and the present — the 2020s. Our understanding of the universe during the earlier of these two periods was based exclusively on a very narrow band of the electromagnetic spectrum, i.e., the visible band, that limited window of atmospheric absorption which very nearly coincides, through Darwinian evolution, with our optical perception of light. The vast remaining spectrum of electromagnetic radiation from the cosmos consisting of cosmic radiation, X-rays, ultraviolet radiation, infrared and radio waves, impinging on the outer layers of Earth’s atmosphere, was barred from our “method of questioning”. Thus, “what we observe”, in Heisenberg’s words, was defined by a constrained loophole through which we learned about the universe. It is worth reflecting that that limitation had persisted, largely unaltered, for centuries ever since Galileo looked through his humble telescope in 1609.

That situation has been radically altered during the last decades. Our “method of questioning” has now been broadened to encompass practically the entire electromagnetic spectrum by means of space telescopes, complemented by physical exploration of our Solar System by space probes, landers, rovers, etc. In addition, entirely newly minted  methodologies have been added: neutrino astronomy and gravitational wave detection. The net result of this technological revolution has been that our cosmological understanding, rather than limited but our methods of questioning has been broadened enormously by widely expanded techniques that had not been known by Heisenberg .

Although this remarkable expansion in methods to probe the cosmos has resulted in a stupendous growth in our insight about the universe, there is no question that many new questions have arisen as a result of that probing. Some of these are fundamental such as the nature of dark matter and dark energy, the Big Bang itself, the source of the preponderance of matter over antimatter, etc. That these new questions have arisen, however, is unlikely to undergird a fundamental impossibility to eventually elucidate them.

I believe that the same arguments can be made in what concerns other fields of knowledge, e.g., nuclear physics, biology, the origin of life, etc.

Each of these are, at present, at differing levels of understanding largely corresponding to the level of their methods of probing.

The preceding discussion, however, should not be interpreted as a an outright rejection of Heisenberg’s dictum. There could well be an ultimate limit to our full understanding of nature which, at this point, we are unable to identify. This raises the question whether there is an ultimate limit to our ability to assess the entirety of nature. This question enters the realm of philosophy of science. My view on this fundamental matter is that we have the tool to validate the results of observations, Heisenberg’s “method”: If what we observe coincides with the predictions of theory, that observation does, indeed, reflect nature. In other words, if a theoretical prediction is confirmed by observation, we are revealing reality itself and not just our perception of nature. This implies that theory transcends the limitations imposed by the technological tools that are applied to confirm theoretical predictions.

This latter test sequence is exemplified by the iconic validation of Einstein’s General Theory of Relativity by the observation, during a total solar eclipse, of the gravitationally induced deflection of starlight grazing the surface of the Sun. Similarly, the existence of gravitational waves was confirmed by an entirely indirect method, the gradual slowing down of the of the rate of rotation of pulsars in binary star systems. Again, in this latter case, theory was validated by observation.

My humble view of the basic quandary propounded by Heisenberg is that the boundaries of our understanding of nature itself are not fixed but gradually recede as our methods of probing expand and improve. I view this progression as following a quasi asymptotic process where our understanding of nature itself becomes ever more valid and complete.