Predictions about universe a blind scientist’s bluff ?

[KashifAsrar]

An article in ToI dated 23 April 2007.
Kashif



The lighter side of science

Let’s get physical

Predictions about universe a blind scientist’s bluff ?​

Sunil Mukhi




An engineer, a physicist and a mathematician are taking a walk in the Scottish highlands when they spot a black sheep. “Ah” says the engineer, “so the sheep in the Scottish highlands are black”. “Not necessarily,” responds the physicist, “But there is at least one black sheep in Scotland.” The mathematician reflects for a while and delivers this solemn verdict: “All we are entitled to conclude is that the animal we are observing appears to be black on the side facing us.”
This joke was obviously penned by a physicist, for it is he (or she, perhaps) who comes across as the reasonable member in the trio. The engineer is portrayed as someone who jumps to conclusions, while at the other extreme is the mathematician, apparently pedantic and unwilling to accept a common-sense fact. But let us try to overlook the physics-chauvinism implicit in the joke (though I fear some of my colleagues will not be so generous) and examine the intended moral: if it is bad to believe too much without sufficient evidence, it is equally bad to believe too little. The notion that scientific theories must be tested experimentally is fundamental to the doctrine of positivism, which also requires that theories must always deal with quantities that are observable. From this point of view, the mathematician in our story is a true positivist, unwilling to admit that the sheep is black on its other side because the other side has not yet been viewed. But Steven Weinberg, a Nobel Laureate and one of the greatest living physicists, asserts that “positivism has done as much harm as good”. To make this point, which he develops at length in his excellent book Dreams of a Final Theory, he argues that it was positivism that kept a number of scientists from believing in atoms, in electrons and much later, in quarks. Weinberg supports his claim with a comparison of two scientists. The British physicist JJ Thomson is credited with the discovery of the electron, but Walter Kaufman in Germany performed the same experiment independently at the same time, and even managed a more precise measurement of the electron’s properties. While Thomson reported the discovery of a new particle, which he named the electron, Kaufman merely reported the phenomenon he had observed (the bending of cathode rays). He did not assume it corresponded to a new particle. We can see echoes of our sheep story here — the physicist believed he was seeing a black sheep, while the positivist mathematician refused to go so far based on the limited observation that had been made.
The negativity of the positivist, if I may describe it thus, manifested itself with a vengeance when in the 1960s it was suggested that protons and neutrons — the particles at the heart of the atomic nucleus — are made up of smaller particles called quarks. Many properties of protons and neutrons, as well as other particles, could be satisfactorily explained on the hypothesis that they were made of three quarks each. But some physicists continued to maintain that the quarks were not “real” and that the quark-based explanation of the proton was at best some sort of mathematical trick. The fact that quarks were not produced in any experiment added fuel to their scepticism and the matter remained undecided for a decade. Then in the early 1970s the situation was clarified. The force between quarks increases, rather than decreases, with their separation (two objects attached by a rubber band have the same property). As a result, they are permanently “confined” and cannot be released from a proton however hard we try to knock them out. But they are as real as any other elementary particle, and we can see them if we agree to enter the “cage” in which they are confined, in practice by sending in highly sensitive probe particles. If a certain human being was never seen to leave home, but was always available to meet visitors at home, we would not doubt his existence, would we?
Today, even positivists believe in quarks. One could argue in their defence that their initial reticence was the reasoned scepticism of a scientific mind wary of being drawn to a false hypothesis. But there is an opposite argument that I personally find more compelling. Supposing one was deluded by a hypothesis and pursued it to its end. If it was false, its flaws would show up very quickly. On the other hand, a sceptic would not be motivated to pursue anything in particular, and scientific progress would be considerably delayed. So, on balance, for a physicist it is better to be deluded than sceptical.
A physicist and a mathematician have different imperatives, so it would not be correct to condemn the mathematician’s positivist response to the sheep. Mathematics is a towering structure of abstract results, each built upon the previous one. Without rock-solid certainty, or rigorous proof, at each stage, the entire structure could collapse at any time. Without evidence, a mathematician cannot assume that a sheep is the same colour on both sides, or even that it has two sides.
(The writer is a theoretical
physicist)