The Riemann hypothesis is the most notorious unsolved problem in all of mathematics. Ever since it was first proposed by Bernhard Riemann in 1859, the conjecture has maintained the status of the “Holy Grail” of mathematics. In fact, the person who solves it will win a $1 million prize from the Clay Institute of Mathematics. So, what is the Riemann hypothesis? Why is it so important? What can it tell us about the chaotic universe of prime numbers? And why is its proof so elusive? Alex Kontorovich, professor of mathematics at Rutgers University, breaks it all down in this comprehensive explainer.

A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself. Wikipedia

Johann Carl Friedrich Gauss was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Wikipedia

Johann Carl Friedrich Gauss was born on 30 April 1777** **in Brunswick (Braunschweig), in the Duchy of Brunswick-Wolfenbüttel (now part of Lower Saxony, Germany), to poor, working-class parents.^{[6]} His mother was illiterate and never recorded the date of his birth, remembering only that he had been born on a Wednesday, eight days before the Feast of the Ascension (which occurs 39 days after Easter). Gauss later solved this puzzle about his birthdate in the context of finding the date of Easter, deriving methods to compute the date in both past and future years.^{[7]} He was christened and confirmed in a church near the school he attended as a child.^{[8]}

Gauss was a child prodigy. In his memorial on Gauss, Wolfgang Sartorius von Waltershausen says that when Gauss was barely three years old he corrected a math error his father made; and that when he was seven, he confidently solved an arithmetic series problem (commonly said to be 1 + 2 + 3 + … + 98 + 99 + 100) faster than anyone else in his class of 100 students.^{[9]} Many versions of this story have been retold since that time with various details regarding what the series was – the most frequent being the classical problem of adding all the integers from 1 to 100.^{[10]}^{[11]}^{[12]} There are many other anecdotes about his precocity while a toddler, and he made his first groundbreaking mathematical discoveries while still a teenager. He completed his magnum opus, *Disquisitiones Arithmeticae*, in 1798, at the age of 21—though it was not published until 1801.^{[13]} This work was fundamental in consolidating number theory as a discipline and has shaped the field to the present day.

Gauss’s intellectual abilities attracted the attention of the Duke of Brunswick,^{[10]}^{[5]} who sent him to the Collegium Carolinum (now Braunschweig University of Technology),^{[10]} which he attended from 1792 to 1795,^{[14]} and to the University of Göttingen from 1795 to 1798.^{[13]} While at university, Gauss independently rediscovered several important theorems.^{[15]} His breakthrough occurred in 1796 when he showed that a regular polygon can be constructed by compass and straightedge if the number of its sides is the product of distinct Fermat primes and a power of 2.^{[a]} This was a major discovery in an important field of mathematics; construction problems had occupied mathematicians since the days of the Ancient Greeks, and the discovery ultimately led Gauss to choose mathematics instead of philology as a career. Gauss was so pleased with this result that he requested that a regular heptadecagon be inscribed on his tombstone. The stonemason declined, stating that the difficult construction would essentially look like a circle.^{[16]}

The year 1796 was productive for both Gauss and number theory. He discovered a construction of the heptadecagon on 30 March.^{[13]}^{[17]} He further advanced modular arithmetic, greatly simplifying manipulations in number theory. On 8 April he became the first to prove the quadratic reciprocity law. This remarkably general law allows mathematicians to determine the solvability of any quadratic equation in modular arithmetic. The prime number theorem, conjectured on 31 May, gives a good understanding of how the prime numbers are distributed among the integers.

Gauss also discovered that every positive integer is representable as a sum of at most three triangular numbers on 10 July and then jotted down in his diary the note: “ΕΥΡΗΚΑ! num = Δ + Δ’ + Δ”. On 1 October he published a result on the number of solutions of polynomials with coefficients in finite fields, which 150 years later led to the Weil conjectures.

### Later years and death

Gauss on his deathbed (1855)Gauss’s gravesite at Albani Cemetery in Göttingen, Germany

Gauss remained mentally active into his old age, even while suffering from gout and general unhappiness.^{[18]} For example, at the age of 62, he taught himself Russian.^{[18]}

In 1840, Gauss published his influential *Dioptrische Untersuchungen*,^{[19]} in which he gave the first systematic analysis on the formation of images under a paraxial approximation (Gaussian optics).^{[20]} Among his results, Gauss showed that under a paraxial approximation an optical system can be characterized by its cardinal points^{[21]} and he derived the Gaussian lens formula.^{[22]}

In 1845, he became an associated member of the Royal Institute of the Netherlands; when that became the Royal Netherlands Academy of Arts and Sciences in 1851, he joined as a foreign member.^{[23]}

In 1854, Gauss selected the topic for Bernhard Riemann‘s inaugural lecture “Über die Hypothesen, welche der Geometrie zu Grunde liegen” (*About the hypotheses that underlie Geometry*).^{[24]} On the way home from Riemann’s lecture, Weber reported that Gauss was full of praise and excitement.^{[25]}

On 23 February 1855, Gauss died of a heart attack in Göttingen (then Kingdom of Hanover and now Lower Saxony);^{[6]}^{[18]} he is interred in the Albani Cemetery there. Two people gave eulogies at his funeral: Gauss’s son-in-law Heinrich Ewald, and Wolfgang Sartorius von Waltershausen, who was Gauss’s close friend and biographer. Gauss’s brain was preserved and was studied by Rudolf Wagner, who found its mass to be slightly above average, at 1,492 grams, and the cerebral area equal to 219,588 square millimeters^{[26]}(340.362 square inches). Highly developed convolutions were also found, which in the early 20th century were suggested as the explanation of his genius.^{[27]}

### Religious views

Gauss was a Lutheran Protestant, a member of the St. Albans Evangelical Lutheran church in Göttingen.^{[28]} Potential evidence that Gauss believed in God comes from his response after solving a problem that had previously defeated him: “Finally, two days ago, I succeeded—not on account of my hard efforts, but by the grace of the Lord.”^{[29]} One of his biographers, G. Waldo Dunnington, described Gauss’s religious views as follows:

For him science was the means of exposing the immortal nucleus of the human soul. In the days of his full strength, it furnished him recreation and, by the prospects which it opened up to him, gave consolation. Toward the end of his life, it brought him confidence. Gauss’s God was not a cold and distant figment of metaphysics, nor a distorted caricature of embittered theology. To man is not vouchsafed that fullness of knowledge which would warrant his arrogantly holding that his blurred vision is the full light and that there can be none other which might report the truth as does his. For Gauss, not he who mumbles his creed, but he who lives it, is accepted. He believed that a life worthily spent here on earth is the best, the only, preparation for heaven. Religion is not a question of literature, but of life. God’s revelation is continuous, not contained in tablets of stone or sacred parchment. A book is inspired when it inspires. The unshakeable idea of personal continuance after death, the firm belief in a last regulator of things, in an eternal, just, omniscient, omnipotent God, formed the basis of his religious life, which harmonized completely with his scientific research.

^{[30]}

Apart from his correspondence, there are not many known details about Gauss’s personal creed. Many biographers of Gauss disagree about his religious stance, with Bühler and others considering him a deist with very unorthodox views,^{[31]}^{[32]}^{[33]} while Dunnington (though admitting that Gauss did not believe literally in all Christian dogmas and that it is unknown what he believed on most doctrinal and confessional questions) points out that he was, at least, a nominal Lutheran.^{[b]}

In connection to this, there is a record of a conversation between Rudolf Wagner and Gauss, in which they discussed William Whewell‘s book *Of the Plurality of Worlds*. In this work, Whewell had discarded the possibility of existing life in other planets, on the basis of theological arguments, but this was a position with which both Wagner and Gauss disagreed. Later Wagner explained that he did not fully believe in the Bible, though he confessed that he “envied” those who were able to easily believe.^{[31]}^{[c]} This later led them to discuss the topic of faith, and in some other religious remarks, Gauss said that he had been more influenced by theologians like Lutheran minister Paul Gerhardt than by Moses.^{[34]} Other religious influences included Wilhelm Braubach, Johann Peter Süssmilch, and the New Testament. Two religious works which Gauss read frequently were Braubach’s *Seelenlehre* (Giessen, 1843) and Süssmilch‘s *Gottliche* (Ordnung gerettet A756); he also devoted considerable time to the New Testament in the original Greek.^{[35]}

Dunnington further elaborates on Gauss’s religious views by writing:

Gauss’s religious consciousness was based on an insatiable thirst for truth and a deep feeling of justice extending to intellectual as well as material goods. He conceived spiritual life in the whole universe as a great system of law penetrated by eternal truth, and from this source he gained the firm confidence that death does not end all.

^{[28]}

Gauss declared he firmly believed in the afterlife, and saw spirituality as something essentially important for human beings.^{[36]} He was quoted stating: *“The world would be nonsense, the whole creation an absurdity without immortality,”*^{[37]}and for this statement he was severely criticized by the atheist Eugen Dühring who judged him as a narrow superstitious man.^{[38]}

Though he was not a church-goer,^{[39]} Gauss strongly upheld religious tolerance, believing “that one is not justified in disturbing another’s religious belief, in which they find consolation for earthly sorrows in time of trouble.”^{[5]} When his son Eugene announced that he wanted to become a Christian missionary, Gauss approved of this, saying that regardless of the problems within religious organizations, missionary work was “a highly honorable” task.^{[40]}

### Family

Gauss’s daughter Therese (1816–1864)

On 9 October 1805,^{[41]} Gauss married Johanna Osthoff (1780–1809), and had two sons and a daughter with her.^{[41]}^{[42]} Johanna died on 11 October 1809,^{[41]}^{[42]}^{[43]}and her most recent child, Louis, died the following year.^{[41]} Gauss plunged into a depression from which he never fully recovered. He then married Minna Waldeck (1788–1831)^{[41]}^{[42]} on 4 August 1810,^{[41]} and had three more children.^{[42]} Gauss was never quite the same without his first wife, and he, just like his father, grew to dominate his children.^{[42]} Minna Waldeck died on 12 September 1831.^{[41]}^{[42]}

Gauss had six children. With Johanna (1780–1809), his children were Joseph (1806–1873), Wilhelmina (1808–1846) and Louis (1809–1810). With Minna Waldeck he also had three children: Eugene (1811–1896), Wilhelm (1813–1879) and Therese (1816–1864). Eugene shared a good measure of Gauss’s talent in languages and computation.^{[44]} After his second wife’s death in 1831 Therese took over the household and cared for Gauss for the rest of his life. His mother lived in his house from 1817 until her death in 1839.^{[5]}

Gauss eventually had conflicts with his sons. He did not want any of his sons to enter mathematics or science for “fear of lowering the family name”, as he believed none of them would surpass his own achievements.^{[44]} Gauss wanted Eugene to become a lawyer, but Eugene wanted to study languages. They had an argument over a party Eugene held, for which Gauss refused to pay. The son left in anger and, in about 1832, emigrated to the United States. While working for the American Fur Company in the Midwest, he learned the Sioux language. Later, he moved to Missouri and became a successful businessman. Wilhelm also moved to America in 1837 and settled in Missouri, starting as a farmer and later becoming wealthy in the shoe business in St. Louis. It took many years for Eugene’s success to counteract his reputation among Gauss’s friends and colleagues. See also the letter from Robert Gauss to Felix Klein on 3 September 1912.

### Personality

Gauss was an ardent perfectionist and a hard worker. He was never a prolific writer, refusing to publish work which he did not consider complete and above criticism. This was in keeping with his personal motto *pauca sed matura* (“few, but ripe”). His personal diaries indicate that he had made several important mathematical discoveries years or decades before his contemporaries published them. Scottish-American mathematician and writer Eric Temple Bell said that if Gauss had published all of his discoveries in a timely manner, he would have advanced mathematics by fifty years.^{[45]}

Though he did take in a few students, Gauss was known to dislike teaching. It is said that he attended only a single scientific conference, which was in Berlin in 1828. However, several of his students became influential mathematicians, among them Richard Dedekind and Bernhard Riemann.

On Gauss’s recommendation, Friedrich Bessel was awarded an honorary doctor degree from Göttingen in March 1811.^{[46]}Around that time, the two men engaged in a correspondence.^{[47]} However, when they met in person in 1825, they quarrelled; the details are unknown.^{[48]}

Before she died, Sophie Germain was recommended by Gauss to receive an honorary degree; she never received it.^{[49]}

Gauss usually declined to present the intuition behind his often very elegant proofs—he preferred them to appear “out of thin air” and erased all traces of how he discovered them.^{[citation needed]} This is justified, if unsatisfactorily, by Gauss in his *Disquisitiones Arithmeticae*, where he states that all analysis (i.e., the paths one traveled to reach the solution of a problem) must be suppressed for sake of brevity.

Gauss supported the monarchy and opposed Napoleon, whom he saw as an outgrowth of revolution.

Gauss summarized his views on the pursuit of knowledge in a letter to Farkas Bolyai dated 2 September 1808 as follows:

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, stretches out his arms for others.

^{[50]}

WE&P by EZorrilla.