Why Physics Needs to Ask Questions

File:Schopenhauer.jpgThe German Philosopher Arthur Schopenhauer once said that thequestion “Why?” is the mother of all sciences. In our era of modernity, physics offers a lot of answers, almost every day. These answers however, refer to sophisticated questions that presuppose a lot of “established” concepts. What bothers me is that some more basic problems seem to have been forgotten in this process. I want to illustrate that with two examples from particle physics and astrophysics.

Today’s neutrino experiments deliver data about the so-called mixing angles, which represent the probabilities of the three neutrino flavors (elecron, muon, tau) being transformed into each other. This is an experimental answer on the `top level’, but the underlying question “Why do three types of neutrinos exist?” (once raised by Emilio Segre) is about to fade. Today’s physicists would be even less likely to bother with the question “Why do neutrinos exist at all?”, though one may justifiably wonder why Nature had created such peculiar and elusive objects. To address such questions properly, one has to study a little bit of history (in this case, Wolfgang Pauli’s ideas of around 1930). This would lead to the still more basic question of whether energy has to be conserved during the beta decay – as discussed at the time by Niels Bohr. Also, there is still another fundamental question which seems to have been forgotten by the overwhelming importance of radioactivity in physics (indeed, its discovery triggered its biggest revolution). Why did Nature invent radioactivity after all, and why in different types? Couldn’t one just think of a world with stable nuclei? Is the very existence of radioactivity just a superfluous whim of Nature? Or is there something we still fail to understand?

When one follows the latest news in cosmology, it appears that the acceleration rate of the universe is changing (“How much?” would be the question) – in the jargon, this is called the time dependence of the cosmological constant or of dark energy. However, we have barely digested the very existence of dark energy (2011′s Nobel prize), as it means asking: “Why is the expansion of the universe accelerating?” This is a worthwhile problem to ponder, however, but on a still more basic level we can ask: “Why is the universe expanding?” Of course, Edwin Hubble’s observation of 1930 is now interpreted as indicating such expansion and there is no reason to warm up the `steady state’ model which was popular in the 1960s. However, a good reason for why the universe must expand does not seem to exist (I shall come back later to an idea of Robert Dicke in 1957). Theorists would immediately argue that Einstein’s equations do allow only for contracting or expanding solutions, which is true. But this does not answer the question in terms of a logical necessity, as Einstein used to phrase it: “I want to know if he [the creator] had a choice”.

I do not think that going to ever more sophisticated levels of questions and answers, while leaving behind the important ones, will advance physics in the long run. And surely, the pragmatic approach “Well it is as it is, let’s continue to collect more data” cannot be said to be a wise one.

What Einstein Said About Fundamental Constants

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Reality and Scientific Truth: Discussions with Einstein,von Laue and Planck is a collection of conversations between Einstein and Ilse Rosenthal-Schneider, a lady who took a PhD in philosophy in Berlin around 1920. After fleeing the Nazi regime in 1938 and settling in Australia, she continued her discussions with Einstein by letter. The book is a unique source of the views Einstein held about the fundamental constants of physics. It is worthwhile to compare them with some modern opinions on the subject.

In a letter dated May 11th, 1945, Einstein wrote that he believed that numbers “arbitrarily chosen by God” do not exist and that their “alleged existence relies on our incomplete understanding”. Similarly, he contended in a letter of March 24th 1950 that “dimensionless constants in the laws of nature, which, from a rational point of view, could have other values as well, shouldn’t exist”.

Such a statement obviously refers to numbers such as the inverse of the fine structure constant (which is about 137), which is reminiscent of Richard Feynman, who forty years later wrote in a very similar vein: “It’s one of the greatest damn mysteries of physics: a magic number that comes to us with no understanding by man. You might say, ‘the hand of God’ wrote this number, and we don’t know how He pushed his pencil.” At the same time, Feynman advised his colleagues that: “All good theoretical physicists put this number up on their wall and worry about it.”

It is interesting that both Einstein and Feynman seemed to be convinced that this was a puzzle to be tackled while at the same time being aware that such a conviction was not testable in a strict sense. Einstein, in another letter from Oct 13th, 1945, wrote: “Obviously, I can’t prove that. But I cannot imagine a reasonable unified theory which contains a number that could have been chosen differently by a whim of the creator.”

Since then, the attitude of physicists toward fundamental constants seems to have changed. Modern cosmology, for example, has terrific data, and Michael Turner of the University of Chicago explained in 2010 in Munich how these observations are accommodated using a couple of parameters by the current ‘concordance model’ of cosmology. After the talks at the Siemens foundation, there is always an ample possibility for discussion (and a very nice buffet). Turner, as he admitted frankly to me, is not very interested in the initial conditions of the universe such as density, photon to baryon ratio or similar stuff. He would be happy to find the correct equations that would make the world go, rather than bothering with how it got started. No doubt, however, these initial conditions (although Einstein would have been delighted by the data) are numbers he would have sought to explain using the theory. All these numbers make the world a little more complicated than it should be in principle. “A theoretical construction has little chance to be successful, unless it is very simple” Einstein wrote on April 23rd, 1949, and here he was certainly in agreement with Isaac Newton’s credo: “Truth is ever to be found in simplicity, and not in the multiplicity and confusion of things.”

Antiblog: The Current vs the Relevant

Blogging is largely against my own convictions. Fundamental physics has a slow pace, and there is no need to comment on its progress on a daily basis. Rather I believe that overestimating the news of the day, a habit that was called “arrogance of the presentˮ by the Swiss writer Max Frisch, is a serious problem in physics, if not in all sciences. The danger is that important questions may fall into oblivion, rather than that something fundamental will be overloooked in the stream of news. You probably won’t miss very much if you don’t scan the arXiv for a couple of months.

Secondly, and probably owing to the fact I’ve written three books now, I believe that blogs are on average a superficial kind of text. By definition, they miss the maturation of ideas that comes after several rounds of rewriting and correcting. A book is a much more elaborate and refined piece of work. Somebody has invested to maximize the ouput for you, the reader. The bestselling author Nassim Taleb (The Black Swan, Antifragile) doesn’t read any newspapers or journals (and I infer, no blogs either), just books. He says that the job of a scholar is to ignore insignificant current affairs. So, you may ask, why this blog?

The purpose is to focus on the relevant, not on the current, to dig out the forgotten gems of physics, rather than commenting on fashionable events. Physics is no sport where we have to rush about. Einstein, in his memoir The world as I see it, wrote on the development of general relativity:

“The years of anxious searching in the dark, with their intense longing, alternating between confidence and fatigue, and their eventual breakthrough to truth – only those who have experienced it can understand that.”

Maxwell, Newton and Kepler needed decades to arrive at their revolutional findings. It’s worth looking at how they got there. The history of physics is not boring stuff, you need to deal with if you want to evaluate the current state of affairs. Thus there will be a lot of history, intriguing problems, and hopefully stuff that will get you to reflect on the fundamental questions of physics.