...there is no precise time point dividing gametes from zygote.
I'm saying that there's an extremely brief time interval (not moment or instant) during which conception occurs; before that interval begins, one may say with confidence that conception has not occurred and after it one may with confidence say that conception has occurred. There is a well-defined chemical change in the membrane of an ovum after a single spermatozoon has penetrated it, which change prevents other spermatozoa from penetrating the membrane. Before that change occurs, sperm and egg are distinct, after it occurs, the single fertilizing sperm and egg begin their fusion dance.
Naturally, this interval of time, while extremely brief, is not an 'instant' (i.e., a mathematical point of time). But it's not clear that 'nature at an instant' has any actual meaning anyway. No physical measurement of which we're aware is capable of recording an interval of time shorter than the Planck time, which is approximately 10-43 seconds, and, of course, we're nowhere near being able to measure so short an interval. But the chemical interactions which take place in biological cells are of much longer duration, anyway.
But we're probably not disagreeing. It's probably just this 'precise moment' terminology that's getting in the way.
Yes, the conclusion that: therefore you can't know when life begins is quite false.
Yes, that is right. Sorry I doubted you, but there are people on this forum willing to chop off your left foot in defense of the "scientific fact" that a precise dividing time exists. In fact, you are quite a rarity in my experience.
But it's not clear that 'nature at an instant' has any actual meaning anyway. No physical measurement of which we're aware is capable of recording an interval of time shorter than the Planck time, which is approximately 10-43 seconds, and, of course, we're nowhere near being able to measure so short an interval.
Maybe, but the continuum doesn't require real-number-line kind of smoothness. The fallacy of the beard (when describerd as plucking hairs one by one) is a good example of a continuum of discrete intervals. Our current technology is resolute enough to see that there is no sharp division in the life cycle, because we can see short enough intervals to know that no two adjacent time points at our best resolution are significantly different.
Yes, this is key. We are in agreement.