Present Simple vs Present Perfect

I have a question about verb tense in the following passage: "Partially digested food starts to arrive in the small intestine as semi-liquid chyme, one hour after it is eaten. After two hours the stomach HAS EMPTIED." Could I use a verb in the simple presente instead of perfect? For example, "the stomach IS empty", or "the stomach EMPTIES".

Grammatically both are correct, but scientifically you can't say "after two hours the stomach empties" because that would imply that the emptying only starts after 2 hours; it's actually an ongoing process that is completed in 2 hours or less.