The Quantum Dice

L.I Ponomarev, I.V Kurchatov

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000157277
• Edition: 1
• Topic: Ciencias físicas
• Subtopic: Teoría cuántica

"Real black magic calculus" is how Albert Einstein described quantum mechanics in a letter in 1925. Quantum mechanics is now rather more widely understood by physicists, but still many "outsiders" are unaware of what quantum mechanics is, how it has changed the course of development of physics and how it affects their everyday lives. This book gives a fascinating account of the evolution of the ideas and concepts of quantum theory and modern physics, written by an "insider" but aimed specifically at the general science reader. Many anecdotes from famous past physicists give an insight into their work and personalities. The many illustrations are an important and attractive feature of the book.
Leonid Ponomarev is a leading theoretical physicist. His deep understanding of the subject is allied with his wide knowledge of history, literature and philosophy to produce this history of the development of modern physics and its impact on our lives.

1.

Origins

DOI: 10.1201/9781003062950-1

Science! true daughter of Old Time thou art

Who alterest all things with thy peering eyes.

Why prayest thou thus upon the poet’s heart,

Vulture, whose wings are dull realities?

How should he love thee? or how deem thee wise,

Who wouldst not leave him in his wandering

To seek for treasure in the jewelled skies,

Albeit he soared with an undaunted wing?

Edgar Allan Poe Sonnet — To Science

Chapter One

Atoms • Waves • Quanta

DOI: 10.1201/9781003062950-2

Quantum mechanics is the science of the structure and properties of quantum objects and phenomena.

Everything is correct in this definition — and yet it is useless unless we explain what the phrases “quantum phenomena” and “quantum object” mean.

The word “quantum” means “how much”, “quantity”, “share”, “portion”, and so on. If we place it in front of the words “object” or “phenomenon”, we will have something like “quantity phenomenon” or “portion object”, i.e., a piece of nonsense, if taken at face value.

Those who have ever learned foreign languages will easily see the reason behind this incongruity: “quantum phenomenon”, “quantum object” — just like “quantum physics” for that matter — are idioms, which are not to be taken literally. To grasp their true meaning, you must first get acquainted with the customs and culture of the country whose language you are learning.

Quantum physics is a vast country with a rich and deep culture. If all you know about it is that it has “unravelled the age-old enigma of the mysterious country of the microworld”, and also brought about an “upheaval in our entire view of the world”, then you know as much about it as tourists know about an unfamiliar country whose culture is foreign to them and whose language they do not understand. Their memory will only retain some highlights — for instance, bright neon signs and posters.

The language of quantum physics is peculiar although in essence it is not different from a conventional language. Like any language it cannot be absorbed overnight. What is needed is patience and method. At first one should memorise some common words and try to construct simple phrases from them, without paying too much attention to grammar. Later on come the ease and fluency which reward the student with the satisfaction and joy of having a firm command of the language.

In order to get used to the language and logic of quantum physics you must start with some seemingly unrelated concepts. To fit them into some sort of consistent picture will take a lot of correlation and speculation. The process of perceiving quantum ideas can be likened to the process of dissolving salt in water: if you drop a pinch of salt into a glass of water it will disappear without trace, but as you add more salt you reach a point where it is sufficient merely to add one more speck for a large regular crystal of salt to start to grow.

This book is a story of the origins, ideas and findings of quantum physics. It will introduce you to its array of images and will illustrate them with some applications. At first you will have to dissolve in your mind some initial concepts, to learn those few, but necessary, words without which you will be unable to construct even a single meaningful “quantum phrase”. These words are atoms, waves, and quanta.

Atoms

There are few people nowadays who do not accept the reality of atoms as they do, say, the motion of the Earth around the Sun. Atoms normally predicate something minute and indivisible. What is the meaning given by today’s science to the concept of the atom? What were the origins of this concept, what did the ancients read into it? How did the atomic concept evolve? And why did it have to wait for quantum mechanics to make its appearance to be promoted from just a speculative scheme to a workable theory?

The father of the atomic concept, it is widely believed, was the ancient Greek philosopher Democritus (c. 460-370 BC), although history also mentions his teacher Leucippus and, with less certainty, the ancient Hindu philosopher Kanada. Our knowledge of Democritus’s life and personality is scarce. We know that he was born in Abdera on the Thracian shore of the Mediterranean; that he was a disciple of Leucippus and studied under some Chaldean scholars and the Persian Magi; that he travelled widely and knew much; that he lived to a great age and was given a public burial by the citizens of his native city, who held him in great esteem. Generations of artists depicted Democritus as a tall man with a short beard wearing a white Grecian tunic and sandals on his bare feet.

Legend has it that one fine morning Democritus sat on a stone by the sea, stared at an apple in his hand, and reasoned: “If I cut this apple in half I will have two halves; if then I cut one half in two I will have two fourths. Now if I keep on dividing the remaining parts in the same way, will I continue to obtain one eighth, one sixteenth, one thirty-second, etc., of an apple? Or will I, at some time in the process, reach a point where the divided parts will no longer possess the properties of an apple?” It turned out subsequently that Democritus’s doubt (as do almost all disinterested doubts) contained a grain of truth. The philosopher came to the conclusion that a limit to divisibility does exist. He named the ultimate, indivisible particle ατoµoαį the atom (from the Greek for “indivisible”). He published his views in a book entitled Little World System. Behold what was written more than 2000 years ago:

“The Universe is made up, in reality, of nothing but atoms and the void; all the rest exists only in the mind. There are countless worlds and each has a beginning and an end in time. And nothing is ever begotten of nothing, nor can anything be destroyed and reduced to nothing. And the atoms are innumerable in size and quantity, moving in all directions in a void, colliding and forming vortices in which all complex substances arise: fire, water, air and earth. The fact is that these, in essence, are but combinations of certain atoms. Atoms are indestructible and unchangeable owing to their hardness.”

When Democritus died, Aristotle, the future mentor of Alexander the Great, was fourteen. He was spare, short, and had extremely refined manners. The esteem in which he was held knew no sensible bounds. There were good reasons for this: he commanded the full range of knowledge of that time. Aristotle taught the opposite: an apple can be divided into smaller and smaller pieces indefinitely, at least in principle. (For fairness’s sake it should be admitted that the idea of the infinite divisibility of matter for an unsophisticated mind appears as being more natural than the idea that there exists in principle a limit to the divisibility of matter.) Aristotle’s views prevailed. Democritus was forgotten for many centuries and his works were ruthlessly destroyed. This is why his writings have come down to us only in fragments and the comments of his contemporaries. Democritus became known in Europe from the poem De Rerum Natura (“On the Nature of Things”) by Titus Lucretius Carus (c. 95-55 BC).

We should not blame the ancients for preferring Aristotle’s views to Democritus’s; for them both systems were equally reasonable and acceptable. They viewed science not as a means of obtaining some practical applications (which embarrassed them) but rather as a means of reaching by speculation that feeling of harmony of the world that one derives from any consummate philosophy.

It took 2000 years to shake off the erroneous views of the great authority. Physics as a science came into existence in the seventeenth century and quickly replaced ancient natural philosophy.

The new science was based on experiments and mathematics rather than on pure speculation. Instead of merely observing nature, people began to study it around them, i.e., to stage experiments to check hypotheses and to record the results of these experiments in the form of numbers. Aristotle’s idea could not pass such a test, whereas Democritus’s hypothesis received support and started atomic theory.

After twenty centuries of oblivion the idea of atoms was resurrected by the French philosopher and sage Pierre Gassendi (1592-1655). In 1647 he published a book devoted to the ideas of atomism. In those days this was fraught with definite risks, for in medieval times scientists were persecuted not only for various hypotheses but also for rigorous facts, if these facts were at variance with universally recognized dogmata. (In Paris, for example, teaching about atoms was prohibited in 1626 under pain of death.)

Nonetheless, the atomistic hypothesis was accepted by all the prominent scientists of the day. Even Newton, with his famous motto Hypotheses non fingo (“I frame no hypotheses”) accepted and expounded it in his peculiar way at the end of the third volume of his Opticks.

It was a compelling hypothesis; yet until it had been verified by experiment it was doomed to remain just a hypothesis.

The first graphic proof that Democritus was right came from the Scottish botanist Robert Brown (1773-1858). In 1827 he was the middle-aged keeper of the department of botany at the British Museum. In his youth he spent four years travelling on expeditions in Australia and brought back about 4000 species of plants. Twenty years later, he was still studying the collections. In the summer of 1827, Brown observed that the finest pollen grains of plants suspended in water move about in an irregular manner due to the action of some unknown forces. He immediately published a paper with a title very typical of that unhurried age: “A Brief Account of Microscopical Observations Made in the Months of June, July and August, 1827, on the Particles Contained in the Pollen of Plants; and on the General Existence of Active Molecules in Organic and Inorganic Bodies.”

At first his experiment gave rise to perplexity, which was aggravated by Brown himself, who made an attempt to explain the phenomenon as the result of some “vital force” inherent in all organic molecules. Such a primitive explanation of the Brownian motion could not satisfy scientists, and so they undertook new efforts to study its details. Especially successful were the Belgian Ignace Carbonnelle (1880) and the Frenchman Louis George Gouy (1888). They devised careful experiments and found that Brownian motion did not depend upon such factors as the time of year or day, the addition of salts, or the kind of pollen used, and that “it is observed equally well at night on a subsoil in the country as during the day near a populous street where heavy vehicles pass.” It does not depend even upon the type of particles but only on their size and, what is most important, it never ceases.” (Nearly twenty centuries before Brown these properties of Brownian motion were pictured by the imagination of Lucretius Carus, who described them in...