The Sporadic Logic Seminar returns this week at a new place and time
(Fridays, 2:30, K404). This week Mushfeq Khan will speak:
Title: “The Homogeneity Conjecture”
Abstract: It is often said that the theorems and methods of recursion theory
relativize. One might go as far as to say that much of its analytical power
derives from this feature. However, this power is accompanied by definite
drawbacks: There are important examples of theorems and open questions
whose statements are non-relativizing, i.e., they have been shown to be
true relative to some oracles, and false relative to others. It follows
that these questions cannot be settled purely through relativizing methods.
A famous example of such a negative result is Baker, Gill, and Solovay’s
theorem on the P vs. NP question.
The observation that techniques based on diagonalization, effective
numbering, and simulation relativize led some recursion theorists (notably
Hartley Rogers, Jr) to formulate what became known as the “Homogeneity
Conjecture”. It said that for any Turing degree d, the partial order of
degrees that are above d is isomorphic to the entire partial order of the
Turing degrees. In 1979, Richard Shore refuted it in an elegant, one-page
article which will be the subject of this talk.