Paper of the year goes to Irit Dinur's PCP
Theorem by Gap Amplification. We will never teach the PCP theorem
the same way again. Concept of the year goes to the Unique Games
Conjecture, with its applications to hardness of approximation and
metric embeddings. We've also seen the settling of the complexity of
Nash Equilibrium in matrix games, list decoding better than we had
hoped for and much more.
A good year for math in the media. The year started with a series about
a crime-solving mathematician and ended with a game show about
probability, with both shows continuing into 2006. Walk into any
bookstore and you'll see a number of popular books on mathematics like
Mario Livio's
The
Equation That Couldn't be Solved and Stephen Hawking's
God Created the Integers.
Perhaps the biggest disappointment came
from the movie Proof which never had
enough traction to get a wide release in the US.
Did I mention the White Sox won the world series?
Thanks to guest bloggers Rahul Santhanam and Ryan O'Donnell, guest
posters Boaz Barak, Ron Fagin, Bill Gasarch, Michael Mitzenmacher,
Rocco Servedio, Rakesh Vohra and my first two podcast
guests Bill Gasarch and Scott Aaronson. Thanks to all of your for your
comments, emails, support and just reading my rambling thoughts.
Why do we call the original PCP proof nonelementary and the new proof elementary? If I understand correctly, non elementary means involving complexity analysis, like the first proof of prime number theorem. Elementary does not use complex analysis, like Erdos-Selberg proof of PNT. If this is true, then both proofs of PCP are elementary, right?
True, mathematicians distinguish proofs on the basis you describe, which makes almost all of computer science 'elementary'. Obviously this is not a useful criterion for practitioners of complexity, nor do they use it this way.
The most obvious use of the term 'elementary proof' is to mean 'short proof', or, more strictly and recursively, 'short proof that doesn't have to invoke any results that don't yet have elementary proofs'.
I think the term also indicates that the techniques used in the proof are relatively familiar to most researchers. Thus, the most elementary proofs are those that are based on simulation techniques (and relativize). Somewhat less so are probabilistic arguments, then comes algebraic techniques.. if you've proved something that crucially uses topology or complex analysis towards answering questions basic to computational complexity (as opposed to showing NP-completeness of a topological problem, say), give yourself a cookie--that's probably a non-elementary proof.
Lance, many thanks for the so many pleasant hours i spent in front of your blog. Let me make a wish for 2006: I think our community deserves its own forum. Maybe you can add such a forum to your blog?