An identical copy necessarily cannot be measured in a way that distinguishes itself from the original. So "scientifically" because we're restricting the space to measurements of the physical world, and "of course" because the conclusion falls almost tautologously out of the definitions, no experiment needed. How can the thing scientifically not be you if it is not materially different from you?

To your example- I am not sure which of two points are being made, so I'll address both. I'm not saying that everything that happens to entity 1 also happens to entity 2, just that both are you. Two things can both be apples, even though biting one leaves the other intact. And if something happening to you makes you not 'you' anymore, 'you' isn't really a coherent concept across even a fraction of a second; you'd cease to exist and be replaced multiple times in that time.