[douglas]

Yes, the delayed decay could be caused by some unknown factor, but why postulate a new mystery when the current theory predicts not only the qualitative effect observed but also the exact quantitative effect to well within experimental measurement error? Both general and special relativity have been tested extensively many times, and the experimental results have never disagreed with the theoretical predictions without a flaw being discovered in the experiment's procedure, despite scientists striving for the smallest margins of error possible.