‘It Is Impossible To Ascertain Exactly’
R.Yosi Hagelili rules that if a sheep gives birth for the first time to two males, both are deemed a bechor. Both, therefore, must also be given to a kohen. The Sages, however, disagree, arguing that we cannot tell if the two animals really came out at the exact same moment – “ee efshar l’tzamtzem.”
D’bei R. Yanai question whether, in general, this rule – of not being able to tell – applies only to natural occurrences or to occurrences orchestrated and controlled by man as well. Rashi (s.v. “vekal sheken…”) writes that the Sages perhaps invoke this rule only for events that generally do not occur simultaneously (like twins emerging at exactly the same moment) but agree in principle that two things can occur at exactly the same moment if man wants them to.
Tosafos (s.v. “efshar l’tzamtzem”) maintains that the issue at hand is not whether it is possible for two events to occur simultaneously. The Sages agree, Tosafos writes, that two events can occur at the exact same moment – even by chance. But they don’t believe man is able to tell with certainty that they did, in fact, occur at the same moment. That’s why we cannot label two children who were born at the same time “bechor.” Although they seemed to have been born at once, perhaps one really emerged a split second before the other.
In answering their question, D’bei R. Yanai seem to suggest that the Sages apply the rule of “ee efshar l’tzamtzem” only to events that occur suddenly and cannot be measured or clocked. The Gemara (18a) concludes that the rule applies in all situations according to the Sages – whether they are natural or the result of human design and ingenuity.
A point to ponder: Most people today believe that two timepieces can give you the exact same time. Indeed, many watchmakers boast that their products are perfectly accurate and calibrated. But should these claims be relied upon? Interestingly, when it comes to adhering to various zemanim, we generally allow for some margin of error, even if it is very slight.