This paper extends interplanetary trade theory to an interstellar setting. It is chiefly concerned with the following question: how should interest rates on goods in transit be computed when the goods travel at close to the speed of light? This is a problem because the time taken in transit will appear less to an observer traveling with the goods than to a stationary observer. A solution is derived from economic theory, and two useless but true theorems are proved.


From an abstract to “The theory of interstellar trade” by Paul Krugman, Nobel prize in economics 2008 winner.

I started talking with Post regularly. He gave me a batch of his reprints. John Stachel and I asked Post if we could do a reading course with him in mathematical logic. That was in my junior year. We didn’t get very far in the course, because Post had one of his breakdowns after a few weeks. He had just made an important discovery regarding incomparable degrees of unsolvability, and the excitement was too much for him and pitched him over into the manic phase. We didn’t see him again for some months.

Particularly logicians seem to be prone to it! In fact, I had a joke with John Stachel. Post had lost an arm in a childhood accident. Hans Reichenbach, who was sort of a logician and a philosopher, came to City College for a semester to give some courses, and he was essentially stone deaf. Church had vision problems—he had bad cataracts, which in those days was much more of a problem than it is today. So the joke was that, if I’m going to be a logician, maybe I should give up a finger now, instead of something worse!


From the AMS Notices interview with Martin Davis.

Better late

April 16, 2008

Grothenieck with hair

Mai 1988 in Südfrankreich.


From “In höheren Dimensionen” article by Winfried Scharlau (check out this awesome materials!).

Kolmogorov complexity

March 24, 2008

… Я чувствую себя очень виноватым перед Вами за столь неудачное руководство – мне следовало, конечно, кое-что знать о работах Gödel’я. Правда, они оставались незамеченными в Москве, а я сам не занимался математической логикой с лета 1930 года, но берясь руководить Вами, я был бы должен находиться в курсе хотя бы основных работ…

… Ваш курс по теории алгоритмов конечно необходимо поскорее издать, а 45 страниц на построение универсальной функции в самом деле очень мешают распространению соответствующей необходимой грамотности среди наших молодых математиков…

… а то, моя Бальзановская премия все–таки составляет 46 000 рублей, а не 7 000. Пока министерство финансов разрешило истратить из них 20 000 на покупку иностранных книг МГУ. Кажется, позволят истратить в валюте и на более личные потребности тысячи две. Боюсь, что теперь решат любую мою заграничную поездку уже не субсидировать из казенного кармана …


Фрагменты переписки А.Н. Колмогорова и А.И. Мальцева, “Сибирские Электронные Математические Известия”.

Unlike wine

March 16, 2008

Unlike wine, the paper has failed to mature during the several years that it has been stored on the hard drive of my computer; nevertheless, I have decided to make it available, since it is in my opinion a nice application of idempotent ultrafilters to recurrence results.


In “Idempotent ultrafilters and polynomial recurrence” by Christian Schnell.

Por la liberacion de Alf Onshuus, Ana Aldana y secuestrados en Colombia

Thorny Forkings – Thorny Days (Alf’s blog)

Una oración y muchas velas por Alf,Ana y todos los secuestrasdos

Tarski Symposium

February 5, 2008

He lamented C. C. Chang’s move from mathematics to mysticism after Chang found his Hindu guru during the 1971 Tarski Symposium. On returning from Poland three years earlier (followed then by a week in India), I had became devoted to the Indian spiritual master Meher Baba, but Alfred later said he felt I would continue to do science, unlike Chang who declared himself to be finished with research.


Benjamin Wells, “Alfred Tarski, Friend and Daemon