Halacha and Reality

 Michtav M'Eliyahu (4:355): When Rav Dessler was asked concerning certain halachos that the reason that had been given for them is not in accord with modern science... for example (3) This that it is permitted to kill lice because they don't reproduce sexually (Shabbos 107b. Rav Dessler stated that concerning this matter and those like them the Halacha never changes even though the reason doesn't make sense to us. We are to hold on to the Halacha with two hands whether to be strict or lenient [not like the Pachad Yitzchok]. The reason for this is that the Halacha was known to Chazal by tradition through the generations and they also knew things through experience.... The important point is that the reasoning they gave did not create the Halacha but rather the reverse was true, the Halacha created the reasoning. The reasoning given in the gemora is not the only possible explanation. If they happened to give explanations on occasion which were only true according to the science of their day, we have an obligation to search out alternative explanations that will justify the Halacha according to modern science.... Even if one cannot find a convincing explanation, we must still believe with perfect faith that the Halacha is still true and we hope that G d will enlighten us with an appropriate explanation.

 Rambam (Letter on Astrology): I know of course that it is possible to search and find isolated opinions of some sages in the Talmud and Medrashim whose views contradict what I have said. ... These statements should not trouble you because one doesn’t simply discard a clearly established halacha and revert back to the initial analysis. Similarly it is not appropriate to discard a well validated principle and simply rely on a minority opinion of the sages instead. That is because the sage is not infallible and might have erred by overlooking some important facts or hints when he stated his views.