Boltzmann sought to integrate physics with the philosophy of science, opposing both the a priori, uninformed speculations of philosophers, and the philosophically indifferent approaches of many physicists. His emphasis on the open-ended hypothetical nature of theorizing strikingly anticipates the falsificationism of Popper, whilst his connection between the direction of time and the increasing entropy of a universe in which some states can be achieved in more ways than others, is still one of the major contributions to the problem of time's arrow.

http://www-history.mcs.st-andrews.ac.uk/Biographies/Boltzmann.html A biography of Boltzmann, with a bibliography

http://scienceworld.wolfram.com/biography/Boltzmann.html A summary of Boltzmann's scientific contributions, with links to related issues