Pedro Lilienfeld

In late 19th century, the prevailing view of scientists, especially physicists, was that science had, at last, reached a full understanding of the laws governing natural phenomena and that we needed to simply work out some details, i.e., “dot the is”. This was, in retrospect, a complete misreading of the status of extant knowledge. I can cite at least three fundamental unresolved quandaries of that time: 1. How light propagates in empty space; 2. How gravitation exerts its force at a distance, apparently instantaneously; and 3. What is the age of the Earth and the Solar System.

Let us look at each of those above unresolved problems of the second half of the 19th century.

Throughout the 19th century the wave nature of light had been fully confirmed as well as the laws governing its propagation, the latter a brilliant mathematical construct by the Scottish physicist James Clerk Maxwell in 1865. It was then hypothesized that this propagation, being undulatory, required a medium through which light and any other electromagnetic radiation would be transmitted through space. This hypothetical medium was called aether and whose presence remained   purportedly indispensable but was, after all, an ad hoc substance. To prove its existence, American physicists Albert A. Michelson and Edward W. Morley carried out a crucial optical experiment in 1887 that surprisingly and unequivocally disproved the existence of any light carrying medium, i.e., the aether did not exist.

1. Through the notable efforts of Johannes Kepler, in what is now Germany, during the early 17th century and, especially, Isaac Newton in 1687, it became possible to fully define and quantify the planetary motions of our Solar system. This mathematical construct was based on the existence of gravitational forces that operated at a distance but whose properties and nature remained a mystery.
2. A conflict arose within several branches of science in the late 19th century. Geologists and Darwinian evolutionary biologists had reached the conclusion that the Earth had to be at least a billion years old. However, thermodynamicists such as William Thompson, 1st Baron Kelvin, had concluded in 1895 that the Earth was only about 20 to 40 million years old. He based his estimate on the time that the Sun could had been radiating its energy from combustion sources or any other then known source of heat.
3. The solution to all three quandaries was provided, over a period of about 10 years, between 1905 and 1915, by a young physicist, working as a humble patent examiner in Zurich, Switzerland. His name was Albert Einstein. He determined that light is constituted by minuscule packets of energy, photons, that always move through space at a constant and fixed velocity, regardless of the velocity of its source or its receiver. Einstein, concurrently, uncovered the enormous energy equivalence of matter that explained the source of energy required for a multibillion-year age of the Sun and the corresponding age of the Earth. Finally, through the Generalized Theory of Relativity he explained the properties and nature of gravity; it is a distortion of the space-time continuum caused by the presence of matter.

I contend that physics is facing a somewhat similar crossroads at present.

There are several fundamental unresolved questions. I can cite three of them, although I believe that the number of such unanswered questions is more extensive. The first two of these perplexing matters are cosmological. The third is about the fundamentals of matter. Here they are: The nature of dark energy; the nature of dark matter; and the incompatibility between gravitation and quantum mechanics. The first two of these unresolved questions have arisen in the last 3 or 4 decades and imply that we only understand about 5% of the constituents of the universe, i.e., baryonic or ordinary matter.

Several years ago I attended a lecture (I believe by the astrophysicist Sara Seager) wherein she touted our extant knowledge about the makeup of the cosmos, based on the Standard Model of particle physics. At the end of lecture I expressed the opinion that if science can only explain 5% of the constituents of the universe, our theoretical understanding of it leaves a lot to be desired. The lecturer dismissed my comment as being unjustified. Are we witnessing a new version of the late 19th century hubris about the completeness of our knowledge? In fact, the nonconformity between gravity and quantum physics is equally important and fundamental.

The precedent discussion raises in my mind the basic philosophical question of whether advances in science and our understanding of nature are inevitably accompanied by the creation of new unresolved questions, and that our pursuit of knowledge is, in the end, a quasi-Sisyphean undertaking. I prefer to view this process as asymptotic, ever advancing, closer and closer to the ultimate truth without ever fully achieving that nirvana, provided humanity survives unscathed.