Transcendental number explained
In mathematics, a transcendental number is a real or complex number that is not algebraic – that is, not the root of a non-zero polynomial with integer (or, equivalently, rational) coefficients. The best-known transcendental numbers are and .[1] [2] The quality of a number being transcendental is called transcendence.
Though only a few classes of transcendental numbers are known – partly because it can be extremely difficult to show that a given number is transcendental – transcendental numbers are not rare: indeed, almost all real and complex numbers are transcendental, since the algebraic numbers form a countable set, while the set of real numbers and the set of complex numbers are both uncountable sets, and therefore larger than any countable set.
All transcendental real numbers (also known as real transcendental numbers or transcendental irrational numbers) are irrational numbers, since all rational numbers are algebraic.[3] [4] [5] [6] The converse is not true: Not all irrational numbers are transcendental. Hence, the set of real numbers consists of non-overlapping sets of rational, algebraic non-rational, and transcendental real numbers.[3] For example, the square root of 2 is an irrational number, but it is not a transcendental number as it is a root of the polynomial equation . The golden ratio (denoted
or
) is another irrational number that is not transcendental, as it is a root of the polynomial equation .
History
The name "transcendental" comes,[7] and was first used for the mathematical concept in Leibniz's 1682 paper in which he proved that is not an algebraic function of . Euler, in the 18th century, was probably the first person to define transcendental numbers in the modern sense.
Johann Heinrich Lambert conjectured that and were both transcendental numbers in his 1768 paper proving the number is irrational, and proposed a tentative sketch proof that is transcendental.
in which the th digit after the decimal point is if is equal to (factorial) for some and otherwise.[8] In other words, the th digit of this number is 1 only if is one of the numbers, etc. Liouville showed that this number belongs to a class of transcendental numbers that can be more closely approximated by rational numbers than can any irrational algebraic number, and this class of numbers are called Liouville numbers, named in his honour. Liouville showed that all Liouville numbers are transcendental.
The first number to be proven transcendental without having been specifically constructed for the purpose of proving transcendental numbers' existence was, by Charles Hermite in 1873.
In 1874, Georg Cantor proved that the algebraic numbers are countable and the real numbers are uncountable. He also gave a new method for constructing transcendental numbers. Although this was already implied by his proof of the countability of the algebraic numbers, Cantor also published a construction that proves there are as many transcendental numbers as there are real numbers.Cantor's work established the ubiquity of transcendental numbers.
In 1882, Ferdinand von Lindemann published the first complete proof that is transcendental. He first proved that is transcendental if is a non-zero algebraic number. Then, since is algebraic (see Euler's identity), must be transcendental. But since is algebraic, must therefore be transcendental. This approach was generalized by Karl Weierstrass to what is now known as the Lindemann–Weierstrass theorem. The transcendence of implies that geometric constructions involving compass and straightedge only cannot produce certain results, for example squaring the circle.
In 1900, David Hilbert posed a question about transcendental numbers, Hilbert's seventh problem: If is an algebraic number that is not zero or one, and is an irrational algebraic number, is necessarily transcendental? The affirmative answer was provided in 1934 by the Gelfond–Schneider theorem. This work was extended by Alan Baker in the 1960s in his work on lower bounds for linear forms in any number of logarithms (of algebraic numbers).[9]
Properties
A transcendental number is a (possibly complex) number that is not the root of any integer polynomial. Every real transcendental number must also be irrational, since a rational number is the root of an integer polynomial of degree one. The set of transcendental numbers is uncountably infinite. Since the polynomials with rational coefficients are countable, and since each such polynomial has a finite number of zeroes, the algebraic numbers must also be countable. However, Cantor's diagonal argument proves that the real numbers (and therefore also the complex numbers) are uncountable. Since the real numbers are the union of algebraic and transcendental numbers, it is impossible for both subsets to be countable. This makes the transcendental numbers uncountable.
No rational number is transcendental and all real transcendental numbers are irrational. The irrational numbers contain all the real transcendental numbers and a subset of the algebraic numbers, including the quadratic irrationals and other forms of algebraic irrationals.
Applying any non-constant single-variable algebraic function to a transcendental argument yields a transcendental value. For example, from knowing that is transcendental, it can be immediately deduced that numbers such as
,
,
, and
are transcendental as well.
However, an algebraic function of several variables may yield an algebraic number when applied to transcendental numbers if these numbers are not algebraically independent. For example, and are both transcendental, but is obviously not. It is unknown whether, for example, is transcendental, though at least one of and must be transcendental. More generally, for any two transcendental numbers and, at least one of and must be transcendental. To see this, consider the polynomial . If and were both algebraic, then this would be a polynomial with algebraic coefficients. Because algebraic numbers form an algebraically closed field, this would imply that the roots of the polynomial, and, must be algebraic. But this is a contradiction, and thus it must be the case that at least one of the coefficients is transcendental.
The non-computable numbers are a strict subset of the transcendental numbers.
All Liouville numbers are transcendental, but not vice versa. Any Liouville number must have unbounded partial quotients in its continued fraction expansion. Using a counting argument one can show that there exist transcendental numbers which have bounded partial quotients and hence are not Liouville numbers.
Using the explicit continued fraction expansion of, one can show that is not a Liouville number (although the partial quotients in its continued fraction expansion are unbounded). Kurt Mahler showed in 1953 that is also not a Liouville number. It is conjectured that all infinite continued fractions with bounded terms, that have a "simple" structure, and that are not eventually periodic are transcendental (in other words, algebraic irrational roots of at least third degree polynomials do not have apparent pattern in their continued fraction expansions, since eventually periodic continued fractions correspond to quadratic irrationals, see Hermite's problem).
Numbers proven to be transcendental
Numbers proven to be transcendental:
} (by the Gelfond–Schneider theorem).
- The natural logarithm if is algebraic and not equal to 0 or 1, for any branch of the logarithm function (by the Lindemann–Weierstrass theorem).
- if and are positive integers not both powers of the same integer, and is not equal to 1 (by the Gelfond–Schneider theorem).
- All numbers of the form
\pi+\beta1ln(a1)+ … +\betanln(an)
are transcendental, where
are algebraic for all
and
are non-zero algebraic for all
(by
Baker's theorem).
, for rational such that
.
[11] - The fixed point of the cosine function (also referred to as the Dottie number) – the unique real solution to the equation, where is in radians (by the Lindemann–Weierstrass theorem).[12]
- if is algebraic and nonzero, for any branch of the Lambert W Function (by the Lindemann–Weierstrass theorem), in particular the omega constant .
- if both and the order are algebraic such that
, for any branch of the generalized Lambert W function.
[13] - , the square super-root of any natural number is either an integer or transcendental (by the Gelfond–Schneider theorem).
- Particular rational values of the gamma function, namely:
\Gamma\left(\tfrac16\right),\Gamma\left(\tfrac14\right),\Gamma\left(\tfrac13\right),\Gamma\left(\tfrac23\right),\Gamma\left(\tfrac34\right)
and
\Gamma\left(\tfrac56\right)
.
[14]
(following from their respective algebraic independences).
(in which
and
are non-integer rational numbers).
[15]
\tfrac{J'\nu(x)}{J\nu(x)}
are transcendental when
is rational and
is algebraic and nonzero,
[16] and all nonzero roots of and are transcendental when
is rational.
[17]
\tfrac{\pi}{2}\tfrac{Y0(2)}{J0(2)}-\gamma
, where and are Bessel functions and is the
Euler–Mascheroni constant.
[18] [19]
.
.
[23] - The so-called Fredholm constants, such as
=0.bf{1}bf{1}0bf{1}000bf{1}0000000bf{1}\ldots
which also holds by replacing 10 with any algebraic number .
| -\left\lfloor\betak\right\rfloor |
10 | |
;
where
\beta\mapsto\lfloor\beta\rfloor
is the
floor function.
[24]
(where
,
are polynomials in variables
and
,
is algebraic and
,
is any integer greater than 1).
[25]
and
with only two different decimal digits whose nonzero digit positions are given by the
Moser–de Bruijn sequence and its double.
where
is algebraic and
.
[26] The lemniscatic values of
theta function
(under the same conditions for
) are also transcendental.
[27]
is algebraic but not imaginary quadratic (i.e, the
exceptional set of this function is the number field whose degree of
extension over
is 2).
and
in the formula for first index of occurence of
Gijswijt's sequence, where k is any integer greater than 1.
[28] Possible transcendental numbers
Numbers which have yet to be proven to be either transcendental or algebraic:
- Most nontrivial combinations of two or more transcendental numbers are themselves not known to be transcendental:,,,, ,,,, are not known to be rational, algebraically irrational or transcendental. At least one of the numbers and is transcendental, according to W. D. Brownawell (1974).[29] It has been shown that both and do not satisfy any polynomial equation of degree and integer coefficients of average size 109.[30]
- The Euler–Mascheroni constant : In 2010 M. Ram Murty and N. Saradha found an infinite list of numbers containing such that all but at most one of them are transcendental.[31] [32] In 2012 it was shown that at least one of and the Euler–Gompertz constant is transcendental.[33]
- The values of the Riemann zeta function at odd positive integers
; in particular
Apéry's constant, which is known to be irrational. For the other numbers even this is not known.
; in particular
Catalan's Constant . (none of them are known to be irrational).
[34]
and
are not known to be irrational, let alone transcendental.
[35] It is however known that for
at least one the numbers and is transcendental.
Related conjectures:
Proofs for specific numbers
A proof that is transcendental
The first proof that the base of the natural logarithms, , is transcendental dates from 1873. We will now follow the strategy of David Hilbert (1862–1943) who gave a simplification of the original proof of Charles Hermite. The idea is the following:
Assume, for purpose of finding a contradiction, that is algebraic. Then there exists a finite set of integer coefficients satisfying the equation:It is difficult to make use of the integer status of these coefficients when multiplied by a power of the irrational, but we can absorb those powers into an integral which “mostly” will assume integer values. For a positive integer, define the polynomialand multiply both sides of the above equation byto arrive at the equation:
By splitting respective domains of integration, this equation can be written in the formwhereHere will turn out to be an integer, but more importantly it grows quickly with .
Lemma 1
There are arbitrarily large such that
is a non-zero integer.
. More generally,
if
then
.
This would allow us to compute
exactly, because any term of
can be rewritten as
through a
change of variables. Hence
That latter sum is a polynomial in
with integer coefficients, i.e., it is a linear combination of powers
with integer coefficients. Hence the number
is a linear combination (with those same integer coefficients) of factorials
; in particular
is an integer.
Smaller factorials divide larger factorials, so the smallest
occurring in that linear combination will also divide the whole of
. We get that
from the lowest power
term appearing with a nonzero coefficient in
, but this smallest exponent
is also the multiplicity of
as a root of this polynomial.
is chosen to have multiplicity
of the root
and multiplicity
of the roots
for
, so that smallest exponent is
for
and
for
with
. Therefore
divides
.
To establish the last claim in the lemma, that
is nonzero, it is sufficient to prove that
does not divide
. To that end, let
be any
prime larger than
and
. We know from the above that
divides each of
for
, so in particular all of those
are divisible by
. It comes down to the first term
. We have (see
falling and rising factorials)
and those higher degree terms all give rise to factorials
or larger. Hence
That right hand side is a product of nonzero integer factors less than the prime
, therefore that product is not divisible by
, and the same holds for
; in particular
cannot be zero.
Lemma 2
For sufficiently large,
\left|\tfrac{Q}{k!}\right|<1
.
Proof. Note that
where are continuous functions of for all, so are bounded on the interval . That is, there are constants such that
So each of those integrals composing is bounded, the worst case being
It is now possible to bound the sum as well:
where is a constant not depending on . It follows that
finishing the proof of this lemma.
Conclusion
Choosing a value of that satisfies both lemmas leads to a non-zero integer
\left(\tfrac{P}{k!}\right)
added to a vanishingly small quantity
\left(\tfrac{Q}{k!}\right)
being equal to zero: an impossibility. It follows that the original assumption, that can satisfy a polynomial equation with integer coefficients, is also impossible; that is, is transcendental.
The transcendence of
A similar strategy, different from Lindemann's original approach, can be used to show that the number is transcendental. Besides the gamma-function and some estimates as in the proof for, facts about symmetric polynomials play a vital role in the proof.
For detailed information concerning the proofs of the transcendence of and, see the references and external links.
See also
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-
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- Fritsch, R. . 2003 . Hilberts Beweis der Transzendenz der Ludolphschen Zahl . de . Дифференциальная геометрия многообразий фигур . 34 . 144–148 . University of Munich (mathematik.uni-muenchen.de/~fritsch) . https://web.archive.org/web/20110716060726/http://www.mathematik.uni-muenchen.de/~fritsch/pi.pdf . 2011-07-16.
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