Английская Википедия:Fermat's Last Theorem

Содержание

Текст

Текст

Текст

Текст

Текст

Текст

Текст

Текст

Текст

Шаблон:Short description Шаблон:For-multi Шаблон:Use dmy dates Шаблон:Infobox mathematical statement In number theory, Fermat's Last Theorem (sometimes called Fermat's conjecture, especially in older texts) states that no three positive integers Шаблон:Math, Шаблон:Math, and Шаблон:Math satisfy the equation Шаблон:Math for any integer value of Шаблон:Math greater than Шаблон:Math. The cases Шаблон:Math and Шаблон:Math have been known since antiquity to have infinitely many solutions.

The proposition was first stated as a theorem by Pierre de Fermat around 1637 in the margin of a copy of Arithmetica. Fermat added that he had a proof that was too large to fit in the margin. Although other statements claimed by Fermat without proof were subsequently proven by others and credited as theorems of Fermat (for example, Fermat's theorem on sums of two squares), Fermat's Last Theorem resisted proof, leading to doubt that Fermat ever had a correct proof. Consequently, the proposition became known as a conjecture rather than a theorem. After 358 years of effort by mathematicians, the first successful proof was released in 1994 by Andrew Wiles and formally published in 1995. It was described as a "stunning advance" in the citation for Wiles's Abel Prize award in 2016. It also proved much of the Taniyama–Shimura conjecture, subsequently known as the modularity theorem, and opened up entire new approaches to numerous other problems and mathematically powerful modularity lifting techniques.

The unsolved problem stimulated the development of algebraic number theory in the 19th and 20th centuries. It is among the most notable theorems in the history of mathematics and prior to its proof was in the Guinness Book of World Records as the "most difficult mathematical problem", in part because the theorem has the largest number of unsuccessful proofs.

Overview

Pythagorean origins

The Pythagorean equation, Шаблон:Nowrap, has an infinite number of positive integer solutions for x, y, and z; these solutions are known as Pythagorean triples (with the simplest example being 3, 4, 5). Around 1637, Fermat wrote in the margin of a book that the more general equation Шаблон:Nowrap had no solutions in positive integers if n is an integer greater than 2. Although he claimed to have a general proof of his conjecture, Fermat left no details of his proof, and no proof by him has ever been found. His claim was discovered some 30 years later, after his death. This claim, which came to be known as Fermat's Last Theorem, stood unsolved for the next three and a half centuries.

The claim eventually became one of the most notable unsolved problems of mathematics. Attempts to prove it prompted substantial development in number theory, and over time Fermat's Last Theorem gained prominence as an unsolved problem in mathematics.

Subsequent developments and solution

Шаблон:More citations needed The special case Шаблон:Math, proved by Fermat himself, is sufficient to establish that if the theorem is false for some exponent n that is not a prime number, it must also be false for some smaller n, so only prime values of n need further investigation. Over the next two centuries (1637–1839), the conjecture was proved for only the primes 3, 5, and 7, although Sophie Germain innovated and proved an approach that was relevant to an entire class of primes. In the mid-19th century, Ernst Kummer extended this and proved the theorem for all regular primes, leaving irregular primes to be analyzed individually. Building on Kummer's work and using sophisticated computer studies, other mathematicians were able to extend the proof to cover all prime exponents up to four million, but a proof for all exponents was inaccessible (meaning that mathematicians generally considered a proof impossible, exceedingly difficult, or unachievable with current knowledge).

Separately, around 1955, Japanese mathematicians Goro Shimura and Yutaka Taniyama suspected a link might exist between elliptic curves and modular forms, two completely different areas of mathematics. Known at the time as the Taniyama–Shimura conjecture (eventually as the modularity theorem), it stood on its own, with no apparent connection to Fermat's Last Theorem. It was widely seen as significant and important in its own right, but was (like Fermat's theorem) widely considered completely inaccessible to proof.

In 1984, Gerhard Frey noticed an apparent link between these two previously unrelated and unsolved problems. An outline suggesting this could be proved was given by Frey. The full proof that the two problems were closely linked was accomplished in 1986 by Ken Ribet, building on a partial proof by Jean-Pierre Serre, who proved all but one part known as the "epsilon conjecture" (see: Ribet's Theorem and Frey curve). These papers by Frey, Serre and Ribet showed that if the Taniyama–Shimura conjecture could be proven for at least the semi-stable class of elliptic curves, a proof of Fermat's Last Theorem would also follow automatically. The connection is described below: any solution that could contradict Fermat's Last Theorem could also be used to contradict the Taniyama–Shimura conjecture. So if the modularity theorem were found to be true, then by definition no solution contradicting Fermat's Last Theorem could exist, which would therefore have to be true as well.

Although both problems were daunting and widely considered to be "completely inaccessible" to proof at the time, this was the first suggestion of a route by which Fermat's Last Theorem could be extended and proved for all numbers, not just some numbers. Unlike Fermat's Last Theorem, the Taniyama–Shimura conjecture was a major active research area and viewed as more within reach of contemporary mathematics. However, general opinion was that this simply showed the impracticality of proving the Taniyama–Shimura conjecture. Mathematician John Coates' quoted reaction was a common one: Шаблон:Blockquote

On hearing that Ribet had proven Frey's link to be correct, English mathematician Andrew Wiles, who had a childhood fascination with Fermat's Last Theorem and had a background of working with elliptic curves and related fields, decided to try to prove the Taniyama–Shimura conjecture as a way to prove Fermat's Last Theorem. In 1993, after six years of working secretly on the problem, Wiles succeeded in proving enough of the conjecture to prove Fermat's Last Theorem. Wiles's paper was massive in size and scope. A flaw was discovered in one part of his original paper during peer review and required a further year and collaboration with a past student, Richard Taylor, to resolve. As a result, the final proof in 1995 was accompanied by a smaller joint paper showing that the fixed steps were valid. Wiles's achievement was reported widely in the popular press, and was popularized in books and television programs. The remaining parts of the Taniyama–Shimura–Weil conjecture, now proven and known as the modularity theorem, were subsequently proved by other mathematicians, who built on Wiles's work between 1996 and 2001. For his proof, Wiles was honoured and received numerous awards, including the 2016 Abel Prize.

Equivalent statements of the theorem

There are several alternative ways to state Fermat's Last Theorem that are mathematically equivalent to the original statement of the problem.

In order to state them, we use the following notations: let Шаблон:Math be the set of natural numbers 1, 2, 3, ..., let Шаблон:Math be the set of integers 0, ±1, ±2, ..., and let Шаблон:Math be the set of rational numbers Шаблон:Math, where Шаблон:Mvar and Шаблон:Mvar are in Шаблон:Math with Шаблон:Math. In what follows we will call a solution to Шаблон:Math where one or more of Шаблон:Mvar, Шаблон:Mvar, or Шаблон:Mvar is zero a trivial solution. A solution where all three are nonzero will be called a non-trivial solution.

For comparison's sake we start with the original formulation.

• Original statement. With Шаблон:Mvar, Шаблон:Mvar, Шаблон:Mvar, Шаблон:Mvar ∈ Шаблон:Math (meaning that n, x, y, z are all positive whole numbers) and Шаблон:Math, the equation Шаблон:Math has no solutions.

Most popular treatments of the subject state it this way. It is also commonly stated over Шаблон:Math:

• Equivalent statement 1: Шаблон:Math, where integer Шаблон:Mvar ≥ 3, has no non-trivial solutions Шаблон:Mvar, Шаблон:Mvar, Шаблон:Mvar ∈ Шаблон:Math.

The equivalence is clear if Шаблон:Mvar is even. If Шаблон:Mvar is odd and all three of Шаблон:Math are negative, then we can replace Шаблон:Math with Шаблон:Math to obtain a solution in Шаблон:Math. If two of them are negative, it must be Шаблон:Mvar and Шаблон:Mvar or Шаблон:Mvar and Шаблон:Mvar. If Шаблон:Math are negative and Шаблон:Mvar is positive, then we can rearrange to get Шаблон:Math resulting in a solution in Шаблон:Math; the other case is dealt with analogously. Now if just one is negative, it must be Шаблон:Mvar or Шаблон:Mvar. If Шаблон:Mvar is negative, and Шаблон:Mvar and Шаблон:Mvar are positive, then it can be rearranged to get Шаблон:Math again resulting in a solution in Шаблон:Math; if Шаблон:Mvar is negative, the result follows symmetrically. Thus in all cases a nontrivial solution in Шаблон:Math would also mean a solution exists in Шаблон:Math, the original formulation of the problem.

• Equivalent statement 2: Шаблон:Math, where integer Шаблон:Math, has no non-trivial solutions Шаблон:Math.

This is because the exponents of Шаблон:Math and Шаблон:Mvar are equal (to Шаблон:Mvar), so if there is a solution in Шаблон:Math, then it can be multiplied through by an appropriate common denominator to get a solution in Шаблон:Math, and hence in Шаблон:Math.

• Equivalent statement 3: Шаблон:Math, where integer Шаблон:Math, has no non-trivial solutions Шаблон:Math.

A non-trivial solution Шаблон:Mvar, Шаблон:Mvar, Шаблон:Mvar ∈ Шаблон:Math to Шаблон:Math yields the non-trivial solution Шаблон:Math, Шаблон:Math ∈ Шаблон:Math for Шаблон:Math. Conversely, a solution Шаблон:Math, Шаблон:Math ∈ Шаблон:Math to Шаблон:Math yields the non-trivial solution Шаблон:Math for Шаблон:Math.

This last formulation is particularly fruitful, because it reduces the problem from a problem about surfaces in three dimensions to a problem about curves in two dimensions. Furthermore, it allows working over the field Шаблон:Math, rather than over the ring Шаблон:Math; fields exhibit more structure than rings, which allows for deeper analysis of their elements.

• Equivalent statement 4 – connection to elliptic curves: If Шаблон:Mvar, Шаблон:Mvar, Шаблон:Mvar is a non-trivial solution to Шаблон:Math, Шаблон:Mvar odd prime, then Шаблон:Math (Frey curve) will be an elliptic curve without a modular form.

Examining this elliptic curve with Ribet's theorem shows that it does not have a modular form. However, the proof by Andrew Wiles proves that any equation of the form Шаблон:Math does have a modular form. Any non-trivial solution to Шаблон:Math (with Шаблон:Mvar an odd prime) would therefore create a contradiction, which in turn proves that no non-trivial solutions exist.

In other words, any solution that could contradict Fermat's Last Theorem could also be used to contradict the modularity theorem. So if the modularity theorem were found to be true, then it would follow that no contradiction to Fermat's Last Theorem could exist either. As described above, the discovery of this equivalent statement was crucial to the eventual solution of Fermat's Last Theorem, as it provided a means by which it could be "attacked" for all numbers at once.

Mathematical history

Pythagoras and Diophantus

Pythagorean triples

Шаблон:Main In ancient times it was known that a triangle whose sides were in the ratio 3:4:5 would have a right angle as one of its angles. This was used in construction and later in early geometry. It was also known to be one example of a general rule that any triangle where the length of two sides, each squared and then added together Шаблон:Nowrap, equals the square of the length of the third side Шаблон:Nowrap, would also be a right angle triangle. This is now known as the Pythagorean theorem, and a triple of numbers that meets this condition is called a Pythagorean triple; both are named after the ancient Greek Pythagoras. Examples include (3, 4, 5) and (5, 12, 13). There are infinitely many such triples, and methods for generating such triples have been studied in many cultures, beginning with the BabyloniansШаблон:Sfn and later ancient Greek, Chinese, and Indian mathematicians. Mathematically, the definition of a Pythagorean triple is a set of three integers Шаблон:Nowrap that satisfy the equationШаблон:Sfn <math>a^2 + b^2 = c^2.</math>

Diophantine equations

Fermat's equation, xⁿ + yⁿ = zⁿ with positive integer solutions, is an example of a Diophantine equation,Шаблон:Sfn named for the 3rd-century Alexandrian mathematician, Diophantus, who studied them and developed methods for the solution of some kinds of Diophantine equations. A typical Diophantine problem is to find two integers x and y such that their sum, and the sum of their squares, equal two given numbers A and B, respectively:

<math>A = x + y</math>

<math>B = x^2 + y^2.</math>

Diophantus's major work is the Arithmetica, of which only a portion has survived. Fermat's conjecture of his Last Theorem was inspired while reading a new edition of the Arithmetica,Шаблон:Sfn that was translated into Latin and published in 1621 by Claude Bachet.Шаблон:Sfn

Diophantine equations have been studied for thousands of years. For example, the solutions to the quadratic Diophantine equation Шаблон:Nowrap are given by the Pythagorean triples, originally solved by the Babylonians (Шаблон:Circa).Шаблон:Sfn Solutions to linear Diophantine equations, such as Шаблон:Nowrap, may be found using the Euclidean algorithm (c. 5th century BC).Шаблон:Sfn Many Diophantine equations have a form similar to the equation of Fermat's Last Theorem from the point of view of algebra, in that they have no cross terms mixing two letters, without sharing its particular properties. For example, it is known that there are infinitely many positive integers x, y, and z such that Шаблон:Nowrap, where n and m are relatively prime natural numbers.

Fermat's conjecture

Файл:Diophantus-II-8.jpg

Problem II.8 in the 1621 edition of the Шаблон:Lang of Diophantus. On the right is the margin that was too small to contain Fermat's alleged proof of his "last theorem".

Problem II.8 of the Шаблон:Lang asks how a given square number is split into two other squares; in other words, for a given rational number k, find rational numbers u and v such that Шаблон:Nowrap. Diophantus shows how to solve this sum-of-squares problem for Шаблон:Nowrap (the solutions being Шаблон:Nowrap and Шаблон:Nowrap).Шаблон:Sfn

Around 1637, Fermat wrote his Last Theorem in the margin of his copy of the Шаблон:Lang next to Diophantus's sum-of-squares problem:Шаблон:SfnШаблон:Sfn

After Fermat's death in 1665, his son Clément-Samuel Fermat produced a new edition of the book (1670) augmented with his father's comments. Although not actually a theorem at the time (meaning a mathematical statement for which proof exists), the marginal note became known over time as Fermat's Last Theorem,Шаблон:Sfn as it was the last of Fermat's asserted theorems to remain unproved.Шаблон:Sfn

It is not known whether Fermat had actually found a valid proof for all exponents n, but it appears unlikely. Only one related proof by him has survived, namely for the case Шаблон:Nowrap, as described in the section Шаблон:Slink.

While Fermat posed the cases of n = 4 and of n = 3 as challenges to his mathematical correspondents, such as Marin Mersenne, Blaise Pascal, and John Wallis, he never posed the general case. Moreover, in the last thirty years of his life, Fermat never again wrote of his "truly marvelous proof" of the general case, and never published it. Van der Poorten suggests that while the absence of a proof is insignificant, the lack of challenges means Fermat realised he did not have a proof; he quotes Weil as saying Fermat must have briefly deluded himself with an irretrievable idea. The techniques Fermat might have used in such a "marvelous proof" are unknown.

Wiles and Taylor's proof relies on 20th-century techniques. Fermat's proof would have had to be elementary by comparison, given the mathematical knowledge of his time.

While Harvey Friedman's grand conjecture implies that any provable theorem (including Fermat's last theorem) can be proved using only 'elementary function arithmetic', such a proof need be 'elementary' only in a technical sense and could involve millions of steps, and thus be far too long to have been Fermat's proof.

Proofs for specific exponents

Файл:Diophantus-VI-24-20-Fermat.png

Fermat's infinite descent for Fermat's Last Theorem case n=4 in the 1670 edition of the Arithmetica of Diophantus (pp. 338–339).

Exponent = 4

Only one relevant proof by Fermat has survived, in which he uses the technique of infinite descent to show that the area of a right triangle with integer sides can never equal the square of an integer.Шаблон:SfnШаблон:Sfn His proof is equivalent to demonstrating that the equation

<math>x^4 - y^4 = z^2</math>

has no primitive solutions in integers (no pairwise coprime solutions). In turn, this proves Fermat's Last Theorem for the case Шаблон:Nowrap, since the equation Шаблон:Nowrap can be written as Шаблон:Nowrap.

Alternative proofs of the case Шаблон:Nowrap were developed later by Frénicle de Bessy (1676), Leonhard Euler (1738), Kausler (1802), Peter Barlow (1811), Adrien-Marie Legendre (1830), Schopis (1825), Olry Terquem (1846), Joseph Bertrand (1851), Victor Lebesgue (1853, 1859, 1862), Théophile Pépin (1883), Tafelmacher (1893), David Hilbert (1897), Bendz (1901), Gambioli (1901), Leopold Kronecker (1901), Bang (1905), Sommer (1907), Bottari (1908), Karel Rychlík (1910), Nutzhorn (1912), Robert Carmichael (1913), Hancock (1931), Gheorghe Vrănceanu (1966), Grant and Perella (1999), Barbara (2007), and Dolan (2011).

Other exponents

After Fermat proved the special case Шаблон:Nowrap, the general proof for all n required only that the theorem be established for all odd prime exponents. In other words, it was necessary to prove only that the equation Шаблон:Nowrap has no positive integer solutions Шаблон:Nowrap when n is an odd prime number. This follows because a solution Шаблон:Nowrap for a given n is equivalent to a solution for all the factors of n. For illustration, let n be factored into d and e, n = de. The general equation

aⁿ + bⁿ = cⁿ

implies that Шаблон:Nowrap is a solution for the exponent e

(a^d)^e + (b^d)^e = (c^d)^e.

Thus, to prove that Fermat's equation has no solutions for Шаблон:Nowrap, it would suffice to prove that it has no solutions for at least one prime factor of every n. Each integer Шаблон:Nowrap is divisible by 4 or by an odd prime number (or both). Therefore, Fermat's Last Theorem could be proved for all n if it could be proved for Шаблон:Nowrap and for all odd primes p.

In the two centuries following its conjecture (1637–1839), Fermat's Last Theorem was proved for three odd prime exponents p = 3, 5 and 7. The case Шаблон:Nowrap was first stated by Abu-Mahmud Khojandi (10th century), but his attempted proof of the theorem was incorrect.Шаблон:Sfn In 1770, Leonhard Euler gave a proof of p = 3, but his proof by infinite descent contained a major gap.Шаблон:SfnШаблон:Sfn However, since Euler himself had proved the lemma necessary to complete the proof in other work, he is generally credited with the first proof.Шаблон:SfnШаблон:Sfn Independent proofs were published by Kausler (1802), Legendre (1823, 1830), Calzolari (1855), Gabriel Lamé (1865), Peter Guthrie Tait (1872), Siegmund Günther (1878), Gambioli (1901), Krey (1909), Rychlík (1910), Stockhaus (1910), Carmichael (1915), Johannes van der Corput (1915), Axel Thue (1917), and Duarte (1944).

The case Шаблон:Nowrap was proved independently by Legendre and Peter Gustav Lejeune Dirichlet around 1825.Шаблон:SfnШаблон:Sfn Alternative proofs were developed by Carl Friedrich Gauss (1875, posthumous), Lebesgue (1843), Lamé (1847), Gambioli (1901), Werebrusow (1905),Шаблон:Full citation needed Rychlík (1910),Шаблон:DubiousШаблон:Full citation needed van der Corput (1915), and Guy Terjanian (1987).

The case Шаблон:Nowrap was provedШаблон:SfnШаблон:Sfn by Lamé in 1839. His rather complicated proof was simplified in 1840 by Lebesgue, and still simpler proofs were published by Angelo Genocchi in 1864, 1874 and 1876. Alternative proofs were developed by Théophile Pépin (1876) and Edmond Maillet (1897).

Fermat's Last Theorem was also proved for the exponents n = 6, 10, and 14. Proofs for Шаблон:Nowrap were published by Kausler, Thue, Tafelmacher, Lind, Kapferer, Swift, and Breusch. Similarly, Dirichlet and Terjanian each proved the case n = 14, while Kapferer and Breusch each proved the case n = 10. Strictly speaking, these proofs are unnecessary, since these cases follow from the proofs for n = 3, 5, and 7, respectively. Nevertheless, the reasoning of these even-exponent proofs differs from their odd-exponent counterparts. Dirichlet's proof for n = 14 was published in 1832, before Lamé's 1839 proof for Шаблон:Nowrap.Шаблон:Sfn

All proofs for specific exponents used Fermat's technique of infinite descent,Шаблон:Citation needed either in its original form, or in the form of descent on elliptic curves or abelian varieties. The details and auxiliary arguments, however, were often ad hoc and tied to the individual exponent under consideration.Шаблон:Sfn Since they became ever more complicated as p increased, it seemed unlikely that the general case of Fermat's Last Theorem could be proved by building upon the proofs for individual exponents.Шаблон:Sfn Although some general results on Fermat's Last Theorem were published in the early 19th century by Niels Henrik Abel and Peter Barlow,Шаблон:Sfn the first significant work on the general theorem was done by Sophie Germain.

Early modern breakthroughs

Sophie Germain

In the early 19th century, Sophie Germain developed several novel approaches to prove Fermat's Last Theorem for all exponents. First, she defined a set of auxiliary primes <math>\theta</math> constructed from the prime exponent <math>p</math> by the equation <math>\theta = 2hp + 1</math>, where <math>h</math> is any integer not divisible by three. She showed that, if no integers raised to the <math>p</math>th power were adjacent modulo <math>\theta</math> (the non-consecutivity condition), then <math>\theta</math> must divide the product <math>xyz</math>. Her goal was to use mathematical induction to prove that, for any given <math>p</math>, infinitely many auxiliary primes <math>\theta</math> satisfied the non-consecutivity condition and thus divided <math>xyz</math>; since the product <math>xyz</math> can have at most a finite number of prime factors, such a proof would have established Fermat's Last Theorem. Although she developed many techniques for establishing the non-consecutivity condition, she did not succeed in her strategic goal. She also worked to set lower limits on the size of solutions to Fermat's equation for a given exponent <math>p</math>, a modified version of which was published by Adrien-Marie Legendre. As a byproduct of this latter work, she proved Sophie Germain's theorem, which verified the first case of Fermat's Last Theorem (namely, the case in which <math>p</math> does not divide <math>xyz</math>) for every odd prime exponent less than <math>270</math>,Шаблон:Sfn and for all primes <math>p</math> such that at least one of <math>2p + 1</math>, <math>4p + 1</math>, <math>8p + 1</math>, <math>10p + 1</math>, <math>14p + 1</math> and <math>16p + 1</math> is prime (specially, the primes <math>p</math> such that <math>2p + 1</math> is prime are called Sophie Germain primes). Germain tried unsuccessfully to prove the first case of Fermat's Last Theorem for all even exponents, specifically for <math>n = 2p</math>, which was proved by Guy Terjanian in 1977. In 1985, Leonard Adleman, Roger Heath-Brown and Étienne Fouvry proved that the first case of Fermat's Last Theorem holds for infinitely many odd primes <math>p</math>.

Ernst Kummer and the theory of ideals

In 1847, Gabriel Lamé outlined a proof of Fermat's Last Theorem based on factoring the equation Шаблон:Math in complex numbers, specifically the cyclotomic field based on the roots of the number 1. His proof failed, however, because it assumed incorrectly that such complex numbers can be factored uniquely into primes, similar to integers. This gap was pointed out immediately by Joseph Liouville, who later read a paper that demonstrated this failure of unique factorisation, written by Ernst Kummer.

Kummer set himself the task of determining whether the cyclotomic field could be generalized to include new prime numbers such that unique factorisation was restored. He succeeded in that task by developing the ideal numbers.

(Note: It is often stated that Kummer was led to his "ideal complex numbers" by his interest in Fermat's Last Theorem; there is even a story often told that Kummer, like Lamé, believed he had proven Fermat's Last Theorem until Lejeune Dirichlet told him his argument relied on unique factorization; but the story was first told by Kurt Hensel in 1910 and the evidence indicates it likely derives from a confusion by one of Hensel's sources. Harold Edwards says the belief that Kummer was mainly interested in Fermat's Last Theorem "is surely mistaken".Шаблон:Sfn See the history of ideal numbers.)

Using the general approach outlined by Lamé, Kummer proved both cases of Fermat's Last Theorem for all regular prime numbers. However, he could not prove the theorem for the exceptional primes (irregular primes) that conjecturally occur approximately 39% of the time; the only irregular primes below 270 are 37, 59, 67, 101, 103, 131, 149, 157, 233, 257 and 263.

Mordell conjecture

In the 1920s, Louis Mordell posed a conjecture that implied that Fermat's equation has at most a finite number of nontrivial primitive integer solutions, if the exponent n is greater than two.Шаблон:Sfn This conjecture was proved in 1983 by Gerd Faltings, and is now known as Faltings's theorem.

Computational studies

In the latter half of the 20th century, computational methods were used to extend Kummer's approach to the irregular primes. In 1954, Harry Vandiver used a SWAC computer to prove Fermat's Last Theorem for all primes up to 2521. By 1978, Samuel Wagstaff had extended this to all primes less than 125,000. By 1993, Fermat's Last Theorem had been proved for all primes less than four million.

However, despite these efforts and their results, no proof existed of Fermat's Last Theorem. Proofs of individual exponents by their nature could never prove the general case: even if all exponents were verified up to an extremely large number X, a higher exponent beyond X might still exist for which the claim was not true. (This had been the case with some other past conjectures, and it could not be ruled out in this conjecture.)

Connection with elliptic curves

The strategy that ultimately led to a successful proof of Fermat's Last Theorem arose from the "astounding"Шаблон:Rp Taniyama–Shimura–Weil conjecture, proposed around 1955—which many mathematicians believed would be near to impossible to prove,Шаблон:Rp and was linked in the 1980s by Gerhard Frey, Jean-Pierre Serre and Ken Ribet to Fermat's equation. By accomplishing a partial proof of this conjecture in 1994, Andrew Wiles ultimately succeeded in proving Fermat's Last Theorem, as well as leading the way to a full proof by others of what is now known as the modularity theorem.

Taniyama–Shimura–Weil conjecture

Around 1955, Japanese mathematicians Goro Shimura and Yutaka Taniyama observed a possible link between two apparently completely distinct branches of mathematics, elliptic curves and modular forms. The resulting modularity theorem (at the time known as the Taniyama–Shimura conjecture) states that every elliptic curve is modular, meaning that it can be associated with a unique modular form.

The link was initially dismissed as unlikely or highly speculative, but was taken more seriously when number theorist André Weil found evidence supporting it, though not proving it; as a result the conjecture was often known as the Taniyama–Shimura–Weil conjecture.Шаблон:Rp

Even after gaining serious attention, the conjecture was seen by contemporary mathematicians as extraordinarily difficult or perhaps inaccessible to proof.Шаблон:Rp For example, Wiles's doctoral supervisor John Coates states that it seemed "impossible to actually prove",Шаблон:Rp and Ken Ribet considered himself "one of the vast majority of people who believed [it] was completely inaccessible", adding that "Andrew Wiles was probably one of the few people on earth who had the audacity to dream that you can actually go and prove [it]."Шаблон:Rp

Ribet's theorem for Frey curves

In 1984, Gerhard Frey noted a link between Fermat's equation and the modularity theorem, then still a conjecture. If Fermat's equation had any solution Шаблон:Nowrap for exponent Шаблон:Nowrap, then it could be shown that the semi-stable elliptic curve (now known as a Frey-Hellegouarch)

y² = x(x − a^p)(x + b^p)

would have such unusual properties that it was unlikely to be modular. This would conflict with the modularity theorem, which asserted that all elliptic curves are modular. As such, Frey observed that a proof of the Taniyama–Shimura–Weil conjecture might also simultaneously prove Fermat's Last Theorem.Шаблон:Sfn By contraposition, a disproof or refutation of Fermat's Last Theorem would disprove the Taniyama–Shimura–Weil conjecture.

In plain English, Frey had shown that, if this intuition about his equation was correct, then any set of four numbers (a, b, c, n) capable of disproving Fermat's Last Theorem, could also be used to disprove the Taniyama–Shimura–Weil conjecture. Therefore, if the latter were true, the former could not be disproven, and would also have to be true.

Following this strategy, a proof of Fermat's Last Theorem required two steps. First, it was necessary to prove the modularity theorem, or at least to prove it for the types of elliptical curves that included Frey's equation (known as semistable elliptic curves). This was widely believed inaccessible to proof by contemporary mathematicians.Шаблон:Rp Second, it was necessary to show that Frey's intuition was correct: that if an elliptic curve were constructed in this way, using a set of numbers that were a solution of Fermat's equation, the resulting elliptic curve could not be modular. Frey showed that this was plausible but did not go as far as giving a full proof. The missing piece (the so-called "epsilon conjecture", now known as Ribet's theorem) was identified by Jean-Pierre Serre who also gave an almost-complete proof and the link suggested by Frey was finally proved in 1986 by Ken Ribet.

Following Frey, Serre and Ribet's work, this was where matters stood:

• Fermat's Last Theorem needed to be proven for all exponents n that were prime numbers.
• The modularity theorem—if proved for semi-stable elliptic curves—would mean that all semistable elliptic curves must be modular.
• Ribet's theorem showed that any solution to Fermat's equation for a prime number could be used to create a semistable elliptic curve that could not be modular;
• The only way that both of these statements could be true, was if no solutions existed to Fermat's equation (because then no such curve could be created), which was what Fermat's Last Theorem said. As Ribet's Theorem was already proved, this meant that a proof of the modularity theorem would automatically prove Fermat's Last theorem was true as well.

Wiles's general proof

Файл:Andrew wiles1-3.jpg

British mathematician Andrew Wiles

Ribet's proof of the epsilon conjecture in 1986 accomplished the first of the two goals proposed by Frey. Upon hearing of Ribet's success, Andrew Wiles, an English mathematician with a childhood fascination with Fermat's Last Theorem, and who had worked on elliptic curves, decided to commit himself to accomplishing the second half: proving a special case of the modularity theorem (then known as the Taniyama–Shimura conjecture) for semistable elliptic curves.Шаблон:Sfn

Wiles worked on that task for six years in near-total secrecy, covering up his efforts by releasing prior work in small segments as separate papers and confiding only in his wife.Шаблон:Rp His initial study suggested proof by induction,Шаблон:Rp and he based his initial work and first significant breakthrough on Galois theoryШаблон:Rp before switching to an attempt to extend horizontal Iwasawa theory for the inductive argument around 1990–91 when it seemed that there was no existing approach adequate to the problem.Шаблон:Rp However, by mid-1991, Iwasawa theory also seemed to not be reaching the central issues in the problem.Шаблон:RpШаблон:Sfn In response, he approached colleagues to seek out any hints of cutting-edge research and new techniques, and discovered an Euler system recently developed by Victor Kolyvagin and Matthias Flach that seemed "tailor made" for the inductive part of his proof.Шаблон:Rp Wiles studied and extended this approach, which worked. Since his work relied extensively on this approach, which was new to mathematics and to Wiles, in January 1993 he asked his Princeton colleague, Nick Katz, to help him check his reasoning for subtle errors. Their conclusion at the time was that the techniques Wiles used seemed to work correctly.Шаблон:RpШаблон:Sfn

By mid-May 1993, Wiles was ready to tell his wife he thought he had solved the proof of Fermat's Last Theorem,Шаблон:Rp and by June he felt sufficiently confident to present his results in three lectures delivered on 21–23 June 1993 at the Isaac Newton Institute for Mathematical Sciences.Шаблон:Sfn Specifically, Wiles presented his proof of the Taniyama–Shimura conjecture for semistable elliptic curves; together with Ribet's proof of the epsilon conjecture, this implied Fermat's Last Theorem. However, it became apparent during peer review that a critical point in the proof was incorrect. It contained an error in a bound on the order of a particular group. The error was caught by several mathematicians refereeing Wiles's manuscript including Katz (in his role as reviewer),Шаблон:Sfn who alerted Wiles on 23 August 1993.

The error would not have rendered his work worthless: each part of Wiles's work was highly significant and innovative by itself, as were the many developments and techniques he had created in the course of his work, and only one part was affected.Шаблон:Rp However, without this part proved, there was no actual proof of Fermat's Last Theorem. Wiles spent almost a year trying to repair his proof, initially by himself and then in collaboration with his former student Richard Taylor, without success. By the end of 1993, rumours had spread that under scrutiny, Wiles's proof had failed, but how seriously was not known. Mathematicians were beginning to pressure Wiles to disclose his work whether it was complete or not, so that the wider community could explore and use whatever he had managed to accomplish. But instead of being fixed, the problem, which had originally seemed minor, now seemed very significant, far more serious, and less easy to resolve.

Wiles states that on the morning of 19 September 1994, he was on the verge of giving up and was almost resigned to accepting that he had failed, and to publishing his work so that others could build on it and fix the error. He adds that he was having a final look to try and understand the fundamental reasons for why his approach could not be made to work, when he had a sudden insight: that the specific reason why the Kolyvagin–Flach approach would not work directly Шаблон:Em meant that his original attempts using Iwasawa theory could be made to work, if he strengthened it using his experience gained from the Kolyvagin–Flach approach. Fixing one approach with tools from the other approach would resolve the issue for all the cases that were not already proven by his refereed paper.Шаблон:Sfn He described later that Iwasawa theory and the Kolyvagin–Flach approach were each inadequate on their own, but together they could be made powerful enough to overcome this final hurdle.

On 24 October 1994, Wiles submitted two manuscripts, "Modular elliptic curves and Fermat's Last Theorem" and "Ring theoretic properties of certain Hecke algebras", the second of which was co-authored with Taylor and proved that certain conditions were met that were needed to justify the corrected step in the main paper. The two papers were vetted and published as the entirety of the May 1995 issue of the Annals of Mathematics. The proof's method of identification of a deformation ring with a Hecke algebra (now referred to as an R=T theorem) to prove modularity lifting theorems has been an influential development in algebraic number theory.

These papers established the modularity theorem for semistable elliptic curves, the last step in proving Fermat's Last Theorem, 358 years after it was conjectured.

Subsequent developments

The full Taniyama–Shimura–Weil conjecture was finally proved by Diamond (1996), Conrad et al. (1999), and Breuil et al. (2001) who, building on Wiles's work, incrementally chipped away at the remaining cases until the full result was proved. The now fully proved conjecture became known as the modularity theorem.

Several other theorems in number theory similar to Fermat's Last Theorem also follow from the same reasoning, using the modularity theorem. For example: no cube can be written as a sum of two coprime nth powers, Шаблон:Nowrap. (The case Шаблон:Nowrap was already known by Euler.)

Relationship to other problems and generalizations

Fermat's Last Theorem considers solutions to the Fermat equation: Шаблон:Math with positive integers Шаблон:Math, Шаблон:Math, and Шаблон:Math and an integer Шаблон:Math greater than 2. There are several generalizations of the Fermat equation to more general equations that allow the exponent Шаблон:Math to be a negative integer or rational, or to consider three different exponents.

Generalized Fermat equation

The generalized Fermat equation generalizes the statement of Fermat's last theorem by considering positive integer solutions a, b, c, m, n, k satisfying Шаблон:NumBlk In particular, the exponents m, n, k need not be equal, whereas Fermat's last theorem considers the case Шаблон:Math

The Beal conjecture, also known as the Mauldin conjecture and the Tijdeman-Zagier conjecture, states that there are no solutions to the generalized Fermat equation in positive integers a, b, c, m, n, k with a, b, and c being pairwise coprime and all of m, n, k being greater than 2.

The Fermat–Catalan conjecture generalizes Fermat's last theorem with the ideas of the Catalan conjecture. The conjecture states that the generalized Fermat equation has only finitely many solutions (a, b, c, m, n, k) with distinct triplets of values (a^m, bⁿ, c^k), where a, b, c are positive coprime integers and m, n, k are positive integers satisfying Шаблон:NumBlk The statement is about the finiteness of the set of solutions because there are 10 known solutions.

Inverse Fermat equation

When we allow the exponent Шаблон:Math to be the reciprocal of an integer, i.e. Шаблон:Math for some integer Шаблон:Math, we have the inverse Fermat equation <math>a^{1/m} + b^{1/m} = c^{1/m}.</math> All solutions of this equation were computed by Hendrik Lenstra in 1992. In the case in which the mth roots are required to be real and positive, all solutions are given by

<math>a=rs^m</math>

<math>b=rt^m</math>

<math>c=r(s+t)^m</math>

for positive integers r, s, t with s and t coprime.

Rational exponents

For the Diophantine equation <math>a^{n/m} + b^{n/m} = c^{n/m}</math> with n not equal to 1, Bennett, Glass, and Székely proved in 2004 for Шаблон:Nowrap, that if n and m are coprime, then there are integer solutions if and only if 6 divides m, and <math>a^{1/m}</math>, <math>b^{1/m},</math> and <math>c^{1/m}</math> are different complex 6th roots of the same real number.

Negative integer exponents

n = −1

All primitive integer solutions (i.e., those with no prime factor common to all of a, b, and c) to the optic equation <math>a^{-1} + b^{-1} = c^{-1}</math> can be written asШаблон:Sfn

<math>a = mk + m^2,</math>

<math>b = mk + k^2,</math>

<math>c = mk</math>

for positive, coprime integers m, k.

n = −2

The case Шаблон:Nowrap also has an infinitude of solutions, and these have a geometric interpretation in terms of right triangles with integer sides and an integer altitude to the hypotenuse. All primitive solutions to <math>a^{-2} + b^{-2} = d^{-2}</math> are given by

<math>a = (v^2 - u^2)(v^2 + u^2),</math>

<math>b = 2uv(v^2 + u^2),</math>

<math>d = 2uv(v^2 - u^2),</math>

for coprime integers u, v with Шаблон:Nowrap. The geometric interpretation is that a and b are the integer legs of a right triangle and d is the integer altitude to the hypotenuse. Then the hypotenuse itself is the integer

<math>c = (v^2 + u^2)^2,</math>

so Шаблон:Nowrap is a Pythagorean triple.

n < −2

There are no solutions in integers for <math>a^n + b^n = c^n</math> for integers Шаблон:Nowrap. If there were, the equation could be multiplied through by <math>a^{|n|} b^{|n|} c^{|n|}</math> to obtain <math>(bc)^{|n|} + (ac)^{|n|} = (ab)^{|n|}</math>, which is impossible by Fermat's Last Theorem.

abc conjecture

Шаблон:Main The abc conjecture roughly states that if three positive integers a, b and c (hence the name) are coprime and satisfy Шаблон:Nowrap, then the radical d of abc is usually not much smaller than c. In particular, the abc conjecture in its most standard formulation implies Fermat's last theorem for n that are sufficiently large. The modified Szpiro conjecture is equivalent to the abc conjecture and therefore has the same implication. An effective version of the abc conjecture, or an effective version of the modified Szpiro conjecture, implies Fermat's Last Theorem outright.

Prizes and incorrect proofs

In 1816, and again in 1850, the French Academy of Sciences offered a prize for a general proof of Fermat's Last Theorem.Шаблон:Sfn In 1857, the academy awarded 3,000 francs and a gold medal to Kummer for his research on ideal numbers, although he had not submitted an entry for the prize.Шаблон:Sfn Another prize was offered in 1883 by the Academy of Brussels.

In 1908, the German industrialist and amateur mathematician Paul Wolfskehl bequeathed 100,000 gold marks—a large sum at the time—to the Göttingen Academy of Sciences to offer as a prize for a complete proof of Fermat's Last Theorem.Шаблон:Sfn On 27 June 1908, the academy published nine rules for awarding the prize. Among other things, these rules required that the proof be published in a peer-reviewed journal; the prize would not be awarded until two years after the publication; and that no prize would be given after 13 September 2007, roughly a century after the competition was begun. Wiles collected the Wolfskehl prize money, then worth $50,000, on 27 June 1997. In March 2016, Wiles was awarded the Norwegian government's Abel prize worth €600,000 for "his stunning proof of Fermat's Last Theorem by way of the modularity conjecture for semistable elliptic curves, opening a new era in number theory".

Prior to Wiles's proof, thousands of incorrect proofs were submitted to the Wolfskehl committee, amounting to roughly Шаблон:Convert of correspondence. In the first year alone (1907–1908), 621 attempted proofs were submitted, although by the 1970s, the rate of submission had decreased to roughly 3–4 attempted proofs per month. According to some claims, Edmund Landau tended to use a special preprinted form for such proofs, where the location of the first mistake was left blank to be filled by one of his graduate students. According to F. Schlichting, a Wolfskehl reviewer, most of the proofs were based on elementary methods taught in schools, and often submitted by "people with a technical education but a failed career". In the words of mathematical historian Howard Eves, "Fermat's Last Theorem has the peculiar distinction of being the mathematical problem for which the greatest number of incorrect proofs have been published."

In popular culture

Шаблон:MainThe popularity of the theorem outside science has led to it being described as achieving "that rarest of mathematical accolades: A niche role in pop culture."

Файл:Czech stamp 2000 m259.jpg

Czech postage stamp commemorating Wiles' proof

Arthur Porges' 1954 short story "The Devil and Simon Flagg" features a mathematician who bargains with the Devil that the latter cannot produce a proof of Fermat's Last Theorem within twenty-four hours.

In The Simpsons episode "The Wizard of Evergreen Terrace", Homer Simpson writes the equation <math display=inline>3987^{12} + 4365^{12} = 4472^{12}</math> on a blackboard, which appears to be a counterexample to Fermat's Last Theorem. The equation is wrong, but it appears to be correct if entered in a calculator with 10 significant figures.

In the Star Trek: The Next Generation episode "The Royale", Captain Picard states that the theorem is still unproven in the 24th century. The proof was released 5 years after the episode originally aired.

See also

• Euler's sum of powers conjecture
• Proof of impossibility
• Sums of powers, a list of related conjectures and theorems
• Wall–Sun–Sun prime

Bibliography

• Шаблон:Cite book
• Шаблон:Cite book
• Шаблон:Cite book
• Шаблон:Cite book
• Шаблон:Cite journal
• Шаблон:Cite book
• Шаблон:Cite book
• Шаблон:Cite book
• Шаблон:Cite book
• Шаблон:Cite book

Further reading

• Шаблон:Cite book
• Шаблон:Cite book
• Шаблон:Cite book
• Шаблон:Cite journal
• Шаблон:Cite book
• Шаблон:Cite book
• Шаблон:Cite book
• Шаблон:Cite journal
• Шаблон:Cite book

External links

• Шаблон:Commons category-inline
• Шаблон:Cite web
• Шаблон:Cite web
• Шаблон:Cite web Blog that covers the history of Fermat's Last Theorem from Fermat to Wiles.
• Шаблон:SpringerEOM
• Шаблон:Cite journal Discusses various material that is related to the proof of Fermat's Last Theorem: elliptic curves, modular forms, Galois representations and their deformations, Frey's construction, and the conjectures of Serre and of Taniyama–Shimura.
• Шаблон:Cite web The story, the history and the mystery.
• Шаблон:MathWorld
• Шаблон:Cite web
• Шаблон:Cite web The title of one edition of the PBS television series NOVA, discusses Andrew Wiles's effort to prove Fermat's Last Theorem.
• Шаблон:Cite web Simon Singh and John Lynch's film tells the story of Andrew Wiles.