[Awtem]

Good encryption should still hold, even if you know the algorithm. The same reasoning should be applied to search engines.

[Spivak]

Oh there's no way such a thing is possible. Unless you have an omniscient oracle your search engine will be based on some metric correlated with quality and relevancy. The moment those are known people will produce low quality content with high scores on those metrics.

Can you think of even a single metric that can't be gamed?