Does Cristiano Ronaldo exist? Scientists have pondered this question for millennia. French philosopher Rene Descartes provided perhaps the most widely-believed theory when he posited that "I think, therefore I am." This, in essence theorizes that one can only know that one's self is real, therefore it is impossible to prove whether Cristiano Ronaldo exists.
On the other hand, if one's thoughts include Cristiano Ronaldo, that would mean Cristiano Ronaldo exists, at least in the minds of those thinking about him. It's all very confusing. German thinker Friedrich Nietzsche, for his part, introduced the concept of "Infinite Cristiano Regression", in which Cristiano Ronaldo's career is played out infinitely on a loop. That means it has no beginning and no end, and how can something with no beginning and no end exist?
Of course, this all leads to the problem of "Schrodinger's Cristiano", which posits that you can't know if something exists or not if you cannot see it. For example, if you put Cristiano in a box and left him there, you could not say definitively if Cristiano was alive or dead. You would not even be able to show if Cristiano existed in that moment.
Albert Einstein, for his part, believed in the Theory of Cristiano Relativity, which says that Cristiano Ronaldo is the same in a vacuum, regardless of the movement or position of an observer.
And don't even get us started on Steven Hawking.
For Chilean midfielder Arturo Vidal, the answer is a bit more black and white.
"Cristiano is a smart ass! For me he does not exist," Vidal said ahead of Chile's Confederations Cup semifinal against Portugal.
This answer in itself creates a new problem: if Cristiano Ronaldo does not exist, how could he be a smart-ass? The brightest minds on planet earth will likely ponder that one for generations.