On Randomness II (Trivia II)

“From a purely operational point of viewpoint […] the concept of randomness is so elusive as to cease to be viable." (Mark Kac, 1983)

“The popular image of mathematics as a collection of precise facts, linked together by well-defined logical paths, is revealed to be false. There is randomness and hence uncertainty in mathematics, just as there is in physics.” (Paul Davis, “The Mind of God”, 1992)

“Randomness, chaos, uncertainty, and chance are all a part of our lives. They reside at the ill-defined boundaries between what we know, what we can know, and what is beyond our knowing. They make life interesting.” (Ivars Peterson, “The Jungles of Randomness: A Mathematical Safari”, 1998)

“[…] we underestimate the share of randomness in about everything […]  The degree of resistance to randomness in one’s life is an abstract idea, part of its logic counterintuitive, and, to confuse matters, its realizations nonobservable.” (Nassim N Taleb, “Fooled by Randomness”, 2001)

“Mathematics, far from being stymied by this situation, finds enormous value in it. The fecundity of ‘randomness’ is astounding; it is an inexhaustible source of scientific riches. Could ‘randomness’ be such a rich notion because of the inner contradiction that it contains, not despite it? The depth we sense in ‘randomness’ comes from something that lies behind any specific mathematical definition.” (William Byers, “How Mathematicians Think”, 2007)

“A Black Swan is a highly improbable event with three principal characteristics: It is unpredictable; it carries a massive impact; and, after the fact, we concoct an explanation that makes it appear less random, and more predictable, than it was. […] The Black Swan idea is based on the structure of randomness in empirical reality. [...] the Black Swan is what we leave out of simplification.” (Nassim N Taleb, “The Black Swan”, 2007)

“The key to understanding randomness and all of mathematics is not being able to intuit the answer to every problem immediately but merely having the tools to figure out the answer.” (Leonard Mlodinow, “The Drunkard’s Walk: How Randomness Rules Our Lives”, 2008)

"The randomness which lies at the very foundations of pure mathematics of necessity permeates every human description of nature" (Joseph Ford)

“Our concept of randomness is merely an attempt to characterize and distinguish the sort of series which bamboozles the most people. […] It is thus irrelevant whether a series has been made up by a penny, a calculating machine, a Geiger counter or a practical joker. What matters is its effect on those who see it, not how it was produced.” (Spencer Brown)

5 Books 10 Quotes V: Randomness IV

Ivars Peterson, "The Jungles of Randomness: A Mathematical Safari", 1998
	"Often, we use the word random loosely to describe something that is disordered, irregular, patternless, or unpredictable. We link it with chance, probability, luck, and coincidence. However, when we examine what we mean by random in various contexts, ambiguities and uncertainties inevitably arise. Tackling the subtleties of randomness allows us to go to the root of what we can understand of the universe we inhabit and helps us to define the limits of what we can know with certainty."
"We use mathematics and statistics to describe the diverse realms of randomness. From these descriptions, we attempt to glean insights into the workings of chance and to search for hidden causes. With such tools in hand, we seek patterns and relationships and propose predictions that help us make sense of the world."
Leonard Mlodinow, "The Drunkard’s Walk: How Randomness Rules Our Lives", 2008
	"The theory of randomness is fundamentally a codification of common sense. But it is also a field of subtlety, a field in which great experts have been famously wrong and expert gamblers infamously correct. What it takes to understand randomness and overcome our misconceptions is both experience and a lot of careful thinking."
"Why is the human need to be in control relevant to a discussion of random patterns? Because if events are random, we are not in control, and if we are in control of events, they are not random. There is therefore a fundamental clash between our need to feel we are in control and our ability to recognize randomness. That clash is one of the principal reasons we misinterpret random events."
Deborah J Bennett, "Randomness", 1998
	"Is a random outcome completely determined, and random only by virtue of our ignorance of the most minute contributing factors? Or are the contributing factors unknowable, and therefore render as random an outcome that can never be determined? Are seemingly random events merely the result of fluctuations superimposed on a determinate system, masking its predictability, or is there some disorderliness built into the system itself?"
"Can randomness result from nonrandom situations? Is randomness merely the human inability to recognize a pattern that may in fact exist? Or is randomness a function of our inability, at any point, to predict the result?” (Deborah J. Bennett, "Randomness", 1998)
William Byers, "How Mathematicians Think", 2007
	"What is randomness? At the level of our everyday life experience we call it ‘chance’, something with which that we all feel familiar. It refers to something unexpected, something caused by luck or fortune, that is, without any apparent cause. Randomness is, in a sense, the opposite of determinism. It reflects the ordinary sense that some things are too complicated to admit of a simple explanation or even any explanation at all."
"[…] it would seem that randomness and order are both inevitable parts of any description of reality. When we try to understand some particular phenomenon we are, in effect, banishing disorder. Before a piece of mathematics is understood it stands as a random collection of data. After it is understood, it is ordered, manageable. […] Both properties - the randomness and the order - are present simultaneously. This is what should be called complexity. Complexity is ordered randomness."
Edward Beltrami, "Chaos and Order in Mathematics and Life", 1999
	"Randomness is the very stuff of life, looming large in our everyday experience. […] The fascination of randomness is that it is pervasive, providing the surprising coincidences, bizarre luck, and unexpected twists that color our perception of everyday events."
"The subject of probability begins by assuming that some mechanism of uncertainty is at work giving rise to what is called randomness, but it is not necessary to distinguish between chance that occurs because of some hidden order that may exist and chance that is the result of blind lawlessness. This mechanism, figuratively speaking, churns out a succession of events, each individually unpredictable, or it conspires to produce an unforeseeable outcome each time a large ensemble of possibilities is sampled." Previous Post <<||>> Next Post

Random Numbers

“A random sequence is a vague notion embodying the idea of a sequence in which each term is unpredictable to the uninitiated and whose digits pass a certain number of tests traditional with statisticians and depending somewhat on the uses to which the sequence is to be put.” (Derrick H Lehmer, 1951)

“Any one who considers arithmetical methods of producing random digits is, of course, in a state of sin. For, as has been pointed out several times, there is no such thing as a random number - there are only methods to produce random numbers, and a strict arithmetic procedure of course is not such a method.” (John von Neumann, "Various techniques used in connection with random digits", 1951)

"[A] sequence is random if it has every property that is shared by all infinite sequences of independent samples of random variables from the uniform distribution." (J. N. Franklin (1962)

“[…] random numbers should not be generated with a method chosen at random. Some theory should be used.” (Donald E. Knuth, “The Art of Computer Programming” Vol. II, 1968)

"The generation of random numbers is too important to be left to chance." (Robert R. Coveyou, 1969)

“What will prove altogether remarkable is that some very simple schemes to produce erratic numbers behave identically to some of the erratic aspects of natural phenomena.” (Mitchell Figenbaum, “Universal Behavior in Nonlinear Systems”, 1980)

“[In statistics] you have the fact that the concepts are not very clean. The idea of probability, of randomness, is not a clean mathematical idea. You cannot produce random numbers mathematically. They can only be produced by things like tossing dice or spinning a roulette wheel. With a formula, any formula, the number you get would be predictable and therefore not random. So as a statistician you have to rely on some conception of a world where things happen in some way at random, a conception which mathematicians don’t have.” (Lucien LeCam, [interview] 1988)

"It is evident that the primes are randomly distributed but, unfortunately, we don't know what 'random' means.'' (Rob C Vaughan, 1990)

"According to the narrower definition of randomness, a random sequence of events is one in which anything that can ever happen can happen next. Usually it is also understood that the probability that a given event will happen next is the same as the probability that a like event will happen at any later time. [...] According to the broader definition of randomness, a random sequence is simply one in which any one of several things can happen next, even though not necessarily anything that can ever happen can happen next." (Edward N Lorenz, "The Essence of Chaos", 1993)

“Suppose that we think of the integers lined up like dominoes. The inductive step tells us that they are close enough for each domino to knock over the next one, the base case tells us that the first domino falls over; the conclusion is that they all fall over. The fault in this analogy is that it takes time for each domino to fall and so a domino which is a long way along the line won't fall over fora long time. Mathematical implication is outside time.” (Peter J Eccles, “An Introduction to Mathematical Reasoning”, 1997)

“Sequences of random numbers also inevitably display certain regularities. […] The trouble is, just as no real die, coin, or roulette wheel is ever likely to be perfectly fair, no numerical recipe produces truly random numbers. The mere existence of a formula suggests some sort of predictability or pattern.” (Ivars Peterson, “The Jungles of Randomness: A Mathematical Safari”, 1998)

“The practical definitions of randomness - a sequence is random by virtue of how many and which statistical tests it satisfies and a sequence is random by virtue of the length of the algorithm necessary to describe it [...].” (Deborah J. Bennett, “Randomness”, 1998)

On Randomness I (Trivia I)

“When a rule is extremely complex, that which conforms to it passes for irregular (random).” (Gottfried Leibniz, “Discourse on Metaphysics”, 1686)

“The tissue of the world is built from necessities and randomness; the intellect of men places itself between both and can control them; it considers the necessity and the reason of its existence; it knows how randomness can be managed, controlled, and used.” (Goethe)

“The very events which in their own nature appear most capricious and uncertain, and which in any individual case no attainable degree of knowledge would enable us to foresee, occur, when considerable numbers are taken into account, with a degree of regularity approaching to mathematical.” (John S Mills, “A System of Logic”, 1862)

“The definition of random in terms of a physical operation is notoriously without effect on the mathematical operations of statistical theory because so far as these mathematical operations are concerned random is purely and simply an undefined term.” (Walter A Shewhart and W. Edwards “Deming, Statistical Method from the Viewpoint of Quality Control”, 1939)

“Perhaps randomness is not merely an adequate description for complex causes that we cannot specify. Perhaps the world really works this way, and many events are uncaused in any conventional sense of the word.” (Stephen Jay Gould,"Hen's Teeth and Horse's Toes”, 1983).

“If you perceive the world as some place where things happen at random - random events over which you have sometimes very little control, sometimes fairly good control, but still random events - well, one has to be able to have some idea of how these things behave. […] People who are not used to statistics tend to see things in data - there are random fluctuations which can sometimes delude them - so you have to understand what can happen randomly and try to control whatever can be controlled. You have to expect that you are not going to get a clean-cut answer. So how do you interpret what you get? You do it by statistics.” (Lucien LeCam, [interview] 1988)

“Events may appear to us to be random, but this could be attributed to human ignorance about the details of the processes involved.” (Brain S Everitt, “Chance Rules”, 1999)

“While in theory randomness is an intrinsic property, in practice, randomness is incomplete information.” (Nassim N Taleb, “The Black Swan”, 2007)

“The fact that randomness requires a physical rather than a mathematical source is noted by almost everyone who writes on the subject, and yet the oddity of this situation is not much remarked.” (Brian Hayes, “Group Theory in the Bedroom”, 2008)

“Randomness might be defined in terms of order - its absence, that is. […] Everything we care about lies somewhere in the middle, where pattern and randomness interlace.” (James Gleick, “The Information: A History, a Theory, a Flood”, 2011)

Life and Probability

"Probability is the very guide of life." (Marcus Tullius Cicero, "De Natura Deorum" ["On the Nature of the Gods"], 45 BC)

"In practical life we are compelled to follow what is most probable; in speculative thought we are compelled to follow truth. […] we must take care not to admit as true anything, which is only probable. For when one falsity has been let in, infinite others follow." (Baruch Spinoza, [letter to Hugo Boxel, 1674)

"[…] to us, probability is the very guide of life." (Joseph Butler, "The Analogy of Religion, Natural and Revealed, to the Constitution and Course of Nature", 1736)

"The laws of probability, so true in general, so fallacious in particular." (Edward Gibbon, "Memoirs of My Life", 1774)

"The most important questions of life are indeed, for the most part, really only problems of probability." (Pierre-Simon Laplace,  "Analytical Theory of Probability, 1812)

"The theory of probabilities is at bottom nothing but common sense reduced to calculus; it enables us to appreciate with exactness that which accurate minds feel with a sort of instinct for which of times they are unable to account." (Pierre-Simon Laplace, "Analytical Theory of Probability, 1812)

"Life is a school of probability. " (Walter Bagehot, 1855)

"The essence of life is statistical improbability on a colossal scale." (Richard Dawkins, "The Blind Watchmaker", 1986)

"We can never achieve absolute truth but we can live hopefully by a system of calculated probabilities. The law of probability gives to natural and human sciences - to human experience as a whole - the unity of life we seek." (Agnes E Meyer,  "Education for a New Morality", 1957)

On Probability ( - 300 AD)

"God's dice always have a lucky roll." (Sophocles, 5th century BC)

"It is a part of probability that many improbable things will happen." (Agathon, 5th century BC)

"No human being will ever know the Truth, for even if they happen to say it by chance, they would not even known they had done so." (Xenophanes, 5th century BC)

"Nothing occurs at random, but everything for a reason and by necessity" (Leucippus, 5th century BC)

"The art of war teaches us to rely not on the likelihood of the enemy's not coming, but on our own readiness to receive him; not on the chance of his not attacking, but rather on the fact that we have made our position unassailable." (Sun Tzu, "The Art of War", 5th century BC)

"Everything existing in the universe is the fruit of chance." (Democritus, 4th century BC)

"For that which is probable is that which generally happens." (Aristotle, "The Art of Rhetoric", 4th century BC)

"I know too well that these arguments from probabilities are imposters, and unless great caution is observed in the use of them, they are apt to be deceptive." (Plato," Phaedo" [On the Soul], 4th century BC)

"All human actions have one or more of these seven causes: chance, nature, compulsions, habit, reason, passion, desire." (Aristotle, 4th century BC)

"If in a discussion of many matters […] we are not able to give perfectly exact and self-consistent accounts, do not be surprised: rather we would be content if we provide accounts that are second to none in probability." (Plato, "Timaeus", cca. 360 BC)

"A likely impossibility is always preferable to an unconvincing possibility. The story should never be made up of improbable incidents; there should be nothing of the sort in it." (Aristotle, "Poetics", cca. 335 BC)

"How often things occur by the mearest chance." (Terence, "Phormio", 2nd century BC)

"Suam habet fortuna rationem.’

"Chance has its reasons." (Gaius Petronius, "Satryicon liber" ["The Book of Satyrlike Adventures"], 1st century BC)

"Probability is the very guide of life." (Cicero, "De Natura Deorum" ["On the Nature of the Gods"], 45 BC)

"Valor is of no service, chance rules all, and the bravest often fall by the hands of cowards." (Cornelius Tacitus, cca. 69-100 AD)

The Joy of Mathematics

"It is not knowledge, but the act of learning, not possession but the act of getting there, which grants the greatest enjoyment. When I have clarified and exhausted a subject, then I turn away from it, in order to go into darkness again; the never satisfied man is so strange if he has completed a structure, then it is not in order to dwell in it peacefully, but in order to begin another. I imagine the world conqueror must feel thus, who, after one kingdom is scarcely conquered, stretched out his arms for others." (Carl F Gauss, [Letter to Farkas Bolyai] 1808)

“Practically everyone can understand and enjoy mathematics and appreciate its role in modem society. More generally, I feel that we develop only a small part of our potential, not only in mathematics but also in art, carpentry, cooking, drawing, singing, and so on. We close up too soon. Each of us can reach a higher level than we imagine if we are willing to explore the world and ourselves.” (Sherman K Stein, “Strength in Numbers: Discovering the Joy and Power of Mathematics in Everyday Life”, 1996)

"A great discovery solves a great problem but there is a grain of discovery in the solution of any problem. Your problem may be modest; but if it challenges your curiosity and brings into play your inventive faculties, and if you solve it by your own means, you may experience the tension and enjoy the triumph of discovery." (George Polya, “How to solve it”, 1944)

 “Is it possible to breach this wall, to present mathematics in such a way that the spectator may enjoy it? Cannot the enjoyment of mathematics be extended beyond the small circle of those who are ‘mathematically gifted’? Indeed, only a few are mathematically gifted in the sense that they are endowed with the talent to discover new mathematical facts. But by the same token, only very few are musically gifted in that they are able to compose music. Nevertheless, there are many who can understand and perhaps reproduce music, or who at least enjoy it. We believe that the number of people who can understand simple mathematical ideas is not relatively smaller than the number of those who are commonly called musical, and that their interest will be stimulated if only we can eliminate the aversion toward mathematics that so many have acquired from childhood experiences.” (Hans Rademacher & Otto Toeplitz, “The Enjoyment of Mathematics”, 1957)

"I think the thing which makes mathematics a pleasant occupation are those few minutes when suddenly something falls into place and you understand. Now a great mathematician may have such moments very often. Gauss, as his diaries show, had days when he had two or three important insights in the same day. Ordinary mortals have it very seldom. Some people experience it only once or twice in their lifetime. But the quality of this experience - those who have known it - is really joy comparable to no other joy.” (Lipman Bers)

"The joy of suddenly learning a former secret and the joy of suddenly discovering a hitherto unknown truth are the same to me - both have the flash of enlightenment, the almost incredibly enhanced vision, and the ecstasy and euphoria of released tension." (Paul R Halmos, “I Want to Be a Mathematician”, 1985)

“To experience the joy of mathematics is to realize mathematics is not some isolated subject that has little relationship to the things around us other than to frustrate us with unbalanced check books and complicated computations. Few grasp the true nature of mathematics - so entwined in our environment and in our lives.” (Theoni Pappas, “The Joy of Mathematics” Discovering Mathematics All Around You”, 1986)

“Mathematics is amazingly compressible: you may struggle a long time, step by step, to work through some process or idea from several approaches. But once you really understand it and have the mental perspective to see it as a whole, there is a tremendous mental compression. You can file it away, recall it quickly and completely when you need it, and use it as just one step in some other mental process. The insight that goes with this compression is one of the real joys of mathematics.” (William P Thurston, “Mathematical education”, Notices AMS 37, 1990)

On Numbers: Perfect Numbers I

“A perfect number is that which is equal to the sum of its own parts.” (Euclid, “Elements”, cca. 300 BC)

“If as many numbers as we please beginning from a unit be set out continuously in double proportion, until the sum of all becomes a prime, and if the sum multiplied into the last make some number, the product will be perfect.” (Euclid, “Elements”, cca 300 BC)

“Among simple even numbers, some are superabundant, others are deficient: these two classes are as two extremes opposed to one another; as for those that occupy the middle position between the two, they are said to be perfect. And those which are said to be opposite to each other, the superabundant and the deficient, are divided in their condition, which is inequality, into the too much and the too little.” (Nicomachus of Gerasa, “Introductio Arithmetica”, cca. 100 AD)

"There exists an elegant and sure method of generating these numbers, which does not leave out any perfect numbers and which does not include any that are not; and which is done in the following way. First set out in order the powers of two in a line, starting from unity, and proceeding as far as you wish: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096; and then they must be totalled each time there is a new term, and at each totaling examine the result, if you find that it is prime and non-composite, you must multiply it by the quantity of the last term that you added to the line, and the product will always be perfect. If, otherwise, it is composite and not prime, do not multiply it, but add on the next term, and again examine the result, and if it is composite leave it aside, without multiplying it, and add on the next term. If, on the other hand, it is prime, and non-composite, you must multiply it by the last term taken for its composition, and the number that results will be perfect, and so on as far as infinity." (Nicomachus of Gerasa, “Introductio Arithmetica”, cca. 100 AD)

"Six is a number perfect in itself, and not because God created all things in six days; rather, the converse is true. God created all things in six days because the number is perfect." (Saint Augustine, "The City of God", 426 AD)

“We should not leave unmentioned the principal numbers […] those which are called ‘perfect numbers’. These have parts which are neither larger nor smaller than the number itself, such as the number six, whose parts, three, two, and one, add up to exactly the same sum as the number itself. For the same reason twenty-eight, four hundred ninety-six, and eight thousand one hundred twenty-eight are called perfect numbers.” (Hrotsvit of Gandersheim, “Sapientia”, 10th century)

"[…] I think I am able to prove that there are no even numbers which are perfect apart from those of Euclid; and that there are no odd perfect numbers, unless they are composed of a single prime number, multiplied by a square whose root is composed of several other prime number. But I can see nothing which would prevent one from finding numbers of this sort. For example, if 22021 were prime, in multiplying it by 9018009 which is a square whose root is composed of the prime numbers 3, 7, 11, 13, one would have 198585576189, which would be a perfect number. But, whatever method one might use, it would require a great deal of time to look for these numbers […]" (René Descartes, [a letter to Marin Mersenne] 1638)

“The existence of an odd perfect number – its escape, so to say, from the complex web of conditions which hem it in on all sides – would be little short of a miracle.” (James J Sylvester)

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Resources:
Wikipedia (2018) List of perfect numbers [Online] Available from: https://en.wikipedia.org/wiki/List_of_perfect_numbers

On Numbers: Odd and Even Numbers

“I can show you that the art of computation has to do with odd and even numbers in their numerical relations to themselves and to each other.” (Plato, “Charmides”, cca. 5 century BC)

“Uneven numbers are the god’s delight” (Virgil, “The Eclogues”, cca. 40 BC)

“Why do we believe that in all matters the odd numbers are more powerful […]?” (Pliny the Elder, “Natural History”, cca. 77-79 AD)

“Numbers are called prime which can be divided by no number; they are seen to be not ‘divisible’ by the monad but ‘composed’ of it: take, for example, the numbers live, seven, eleven, thirteen, seventeen, and others like them. No number can divide these numbers into integers. So, they are called `prime,' since they arise from no number and are not divisible into equal proportions. Arising in themselves, they beget other numbers from themselves, since even numbers are begotten from odd numbers, but an odd number cannot be begotten from even numbers. Therefore, prime numbers must of necessity be regarded as beautiful.” (Martianus Capella, cca. 400 AD)

“Number is divided into even and odd. Even number is divided into the following: evenly even, evenly uneven, and unevenly uneven. Odd number is divided into the following: prime and incomposite, composite, and a third intermediate class (mediocris) which in a certain way is prime and incomposite but in another way secondary and composite.” (Isidore of Seville, Etymologies, Book III, cca. 600)

“There is divinity in odd numbers, either in nativity, chance, or death.” (William Shakespeare, “The Merry Wives of Windsor”, 1602)

"For any number there exists a corresponding even number which is its double. Hence the number of all numbers is not greater than the number of even numbers, that is, the whole is not greater than the part." (Gottfried W Leibniz, “De Arte Combinatoria”, 1666)

“We know that there is an infinite, and we know not its nature. As we know it to be false that numbers are finite, it is therefore true that there is a numerical infinity. But we know not of what kind; it is untrue that it is even, untrue that it is odd; for the addition of a unit does not change its nature; yet it is a number, and every number is odd or even (this certainly holds of every finite number). Thus, we may quite well know that there is a God without knowing what He is.” (Blaise Pascal, “Pensées”, 1670)

On Complex Numbers V

“It is generally true, that wherever an imaginary expression occurs the same results will follow from the application of these expressions in any process as would have followed had the proposed problem been possible and its solution real.” (Augustus de Morgan, “On the Study and Difficulties of Mathematics”, 1898) 

“What could be more beautiful than a deep, satisfying relation between whole numbers. How high they rank, in the realms of pure thought and aesthetics, above their lesser brethren: the real and complex numbers.” (Manfred Schroeder, “Number Theory in Science and Communication”, 1984)

“The attitudes of mathematicians can be found not only in what they wrote, but in what they did not write. It is possible to divide mathematicians into those who gave complex numbers some kind of coverage, and those who sometimes or always ignored them.” (Diana Willment, “Complex Numbers from 1600 to 1840” [Masters thesis], 1985)

“The lack of a visual representation for √-1 had a profound influence on attitudes to it, and complex numbers were not widely accented until after the invention of the Argand diagram.” (Diana Willment, “Complex Numbers from 1600 to 1840” [Masters thesis], 1985)

“The square roots of negative numbers! If negative numbers were false, absurd or fictitious, it is hardly to be wondered at that their square roots were described as 'imaginary'.” (David Wells, “The Penguin Dictionary of Curious and Interesting Numbers”, 1986)

“The original purpose and immediate objective in introducing complex numbers into mathematics is to express laws of dependence between variables by simpler operations on the quantities involved. If one applies these laws of dependence in an extended context, by giving the variables to which they relate complex values, there emerges a regularity and harmony which would otherwise have remained concealed.” (Heinz-Dieter Ebbinghaus et al, “Numbers”, 1990)

"The number ‘i’ is evidence that much real progress can result from the positing of imaginary entities. Theologians who have built elaborate systems on much flimsier analogies should perhaps take heart." (John A Paulos, “Beyond Numeracy”, 1991)

“If we think of square roots in the geometric manner, as we have just done, to ask for the square root of a negative quantity is like asking: ‘What is the length of the side of a square whose area is less than zero?’ This has more the ring of a Zen koan than of a question amenable to a quantitative answer.” (Barry Mazur, “Imagining Numbers”, 2003)

“To have the courage to think outside the square, we need to be intrigued by a problem. This intrigue will encourage us to use our imaginations to find solutions which are beyond our current view of the world. This was the challenge that faced mathematicians as they searched for a solution to the problem of finding meaning for the square root of a negative number, in particular √-1.” (Les Evans, “Complex Numbers and Vectors”, 2006)

“Unfortunately, if we were to use geometry to explore the concept of the square root of a negative number, we would be setting a boundary to our imagination that would be difficult to cross. To represent -1 using geometry would require us to draw a square with each side length being less than zero. To be asked to draw a square with side length less than zero sounds similar to the Zen Buddhists asking ‘What is the sound of one hand clapping?’” (Les Evans, “Complex Numbers and Vectors”, 2006)

See also:
5 Books 10 Quotes: Complex Numbers V
Complex Numbers III
Complex Numbers II
Complex Numbers I