
Sans les mathématiques on ne pénètre point au fond de la
philosophie.
Sans la philosophie on ne pénètre point au fond des
mathématiques.
Sans les deux on ne pénètre au fond de rien.
— Leibniz
[Without mathematics we cannot penetrate deeply into philosophy.
Without philosophy we cannot penetrate deeply into mathematics.
Without both we cannot penetrate deeply into anything.]
Tribute to Leibniz: Essay on Leibniz, Complexity and Incompleteness

NOTICE: This website is being gradually phased out. My new website is hosted by Academia.
Please visit
Gregory Chaitin Academia website.
Thanks for your interest!
However the LISP software for my three Springer books will not be moved to Academia.
We intend to freeze this website, not remove it. — GJC, 22 January 2014
METABIOLOGY:
Programming without a Programmer
Darwin's theory of evolution has been described as "design without a designer." Instead we study "programming without a programmer," that is, the evolution of randomly mutating software. We propose a toy model of evolution that can be studied mathematically: the new field of metabiology, which deals with randomly evolving artificial software (computer programs) instead of randomly evolving natural software (DNA).
[Note on George Bernard Shaw (18561950): The first use of the term metabiology
of which I am aware is in Shaw's 1921
play Back to Methuselah: A Metabiological Pentateuch.
A better play of Shaw's that is also on evolution is his 1903 Man and Superman. Shaw's ideafilled plays, which feature lengthy prefaces, were originally meant to be read rather than performed.]
Ursula Molter, Gregory Chaitin and Hernán Lombardi opening the Buenos Aires Mathematics Festival (Argentina, May 2009)
G J Chaitin Home Page
Gregory Chaitin is well known for his work on metamathematics and for the celebrated Ω number, which shows that God plays dice in pure mathematics. He has published many books on such topics, including Meta Math! The Quest for Omega. His latest book, Proving Darwin: Making Biology Mathematical, attempts to create a mathematical theory of evolution and biological creativity.
His least technical book is Conversations with a Mathematician.
Chaitin is a professor at the Federal University of Rio de Janeiro and an honorary professor at the University of Buenos Aires, and has honorary doctorates from the National University of Córdoba in Argentina and the University of Maine in the United States. He is also a member of the
Académie Internationale de Philosophie des Sciences (Brussels) and the LeibnizSozietät der Wissenschaften (Berlin).
Carnival in Rio de Janeiro, 1970. Photo by Peter Albrecht
Latest Book Covers
Selected Papers
Videos of Lectures
Books
 Algorithmic Information Theory, Cambridge University Press, 1987.
 Information, Randomness and Incompleteness: Papers on Algorithmic Information Theory, World Scientific, 1987, 2nd edition, 1990.
 InformationTheoretic Incompleteness, World Scientific, 1992.
 The Limits of Mathematics: A Course on Information Theory and the Limits of
Formal Reasoning, Springer, 1998.
Also in Japanese.
 The Unknowable, Springer, 1999.
Also in Japanese.
 Exploring Randomness, Springer, 2001.
 Conversations with a Mathematician: Math, Art, Science and the Limits of Reason, Springer, 2002.
Also in Portuguese and Japanese.
 From Philosophy to Program Size:
Key Ideas and Methods. Lecture Notes on Algorithmic Information Theory from
the 8th Estonian Winter School in Computer Science, EWSCS '03,
Tallinn Institute of Cybernetics, 2003.
 Meta Math! The Quest for Omega, Pantheon, 2005.
Also UK, French, Italian, Portuguese, Japanese and Greek editions.

With Ugo Pagallo,
Teoria algoritmica della complessità,
Giappichelli, 2006.
 Thinking about Gödel and Turing: Essays on Complexity, 19702007,
World Scientific, 2007.

Matemáticas, Complejidad y Filosofía / Mathematics, Complexity and Philosophy (bilingual Spanish/English edition), Midas, 2011.

With Newton da Costa and Francisco Antonio Doria,
Gödel's Way: Exploits into an Undecidable World, CRC Press, 2012.

Proving Darwin: Making Biology Mathematical, Pantheon, 2012. Also in Spanish, Italian, Japanese and Chinese.
Warning: the ebook version was not sent to the author for proofreading and has many errors in the formulas.
LISP Software for Springer Books
The Limits of Mathematics (1998)
LISP Code
LISP Runs
The Unknowable (1999)
LISP Code
LISP Runs
Exploring Randomness (2001)
Part I—Introduction

Historical introduction—A
century of controversy over the foundations of mathematics

What is LISP? Why do I like it?

How to program my universal Turing machine in LISP
utm2 code,
utm2 run
Part II—ProgramSize

A selfdelimiting Turing machine considered as a set of (program, output) pairs
exec code,
exec run

How to construct selfdelimiting Turing machines: the Kraft inequality
kraft code,
kraft run

The connection between programsize complexity and algorithmic probability:
$H(x) = \log_2 P(x) + O(1)$.
Occam's razor: there are few minimumsize programs
occam code,
occam run

The basic result on relative complexity: $H(yx) = H(x, y)  H(x) + O(1)$
decomp code,
decomp run,
lemma code,
lemma run
Part III—Randomness
Part IV—Future Work

Extending AIT to the size of programs for computing infinite sets and to computations
with oracles

Postscript—Letter to a daring young reader
\[
\Omega =
\sum_{\text{program $p$ halts}}
2^{(\text{size in bits of $p$})}
\]
\[
\Omega_U =
\sum_{\text{$U(p)$ halts}}
2^{p}
\]
\[
\Omega' =
\sum_{n \,=\, 1,\, 2,\, 3,\, ...}
2^{H(n)}
\]