Every now and then I look at a certain actor or actress and marvel that he or she still manages to find steady work. When will this person's career finally end? I ask myself.

The question has always been rhetorical, until now. Through the marvel of science and mathematics, researchers have developed formulas for determining exactly when a performer's 15 minutes will expire. I offer some examples so that you, too, can be awestruck by their scientific accuracy.

Dane Cook

Given: The material he does that isn't lifted from other comedians tends to consist solely of making a face or bouncing around the stage like a monkey. In movies, he strongly resembles Ryan Reynolds -- and since we already have a Ryan Reynolds, this makes him redundant.

Formula: (current date) + 12 (minutes of stage time in which no actual jokes are told) ÷ (anger from other comics) - Ryan Reynolds2

Career expiration date: Oct. 14, 2009

Jessica Alba

Given: Her most popular assets will begin to sag unappealingly in the future. Her insistence on playing the Invisible Girl even though her physical appearance is her primary selling point will also be a factor.

Formula: (current date) ÷ 4(hit movies) x 3(bad choices) - (current age) + 2(.)(.)

Career expiration date: June 3, 2012

Jon Voight

Given: Has three Oscar nominations plus one win, yet has recently appeared in such garbage as Anaconda, Baby Geniuses 2, Transformers, Bratz, Pearl Harbor, and Karate Dog. He is the father of Angelina Jolie -- the world's most selfless, sainted, humanitarian woman -- yet is on bad terms with her.

Formula: (current date) + 4(Oscar nods) x (box office success) ÷ (Bratz) - (Karate Dog) + (number of films in which he wears prosthetics on his face)

Career expiration date: July 28, 2003 (Whoops! This one's already gone bad!)

Jon Heder

Given: He gave the world Napoleon Dynamite, and then continued to give the world the same character in every subsequent film. In Blades of Glory, he almost succeeded at making Will Ferrell unfunny.

Formula: (current date) + (breakout role) - 6(novelty factor) ÷ 23(irritating catch phrases)

Career expiration date: Jan. 30, 2010

Keira Knightley

Given: Her peculiar eating habits (i.e., she doesn't have any) have made her resemble a science class skeleton that someone has tried to stretch skin over. Her big meal ticket, Pirates of the Caribbean, is over now.

Formula: (current date) + (current weight [in ounces]) ÷ 3(hit films) - 42(teeth)

Career expiration date: March 15, 2009

Martin Lawrence

Given: Has never starred in a movie that was better than mediocre; most have been quite bad. Is known to be a little crazy in real life. Used to have that sitcom on Fox where he would sometimes dress up like Sheneneh.

Formula: (current date) + (number of inexplicably popular movies) - (number of undeniably bad ones) ÷ (number of times per film he says "Day-umn!")

Career expiration date: Aug. 20, 2022 (We're in for the long haul with this one.)

Editor's Note: Just so we're all on the same page here, there is no magic formula. This was all done in good fun and we'd prefer not to be sued, ha-ha!

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Eric D. Snider (website) is just jealous of famous people, that's all.