[Avodah] Modifying Halachos based on scientific findings?

[Micha Berger]

On Tue, Dec 30, 2008 at 09:41:33AM -0500, Galsaba at aol.com wrote:
: Do we change Halachos based on scientific findings?
: The two I am referring to are Birchat Hachama. 
: On this one we hold by Amora Shemuel Calendar...

Which isn't bad science, simply the chosen estimation. Any value chosen
would be limited by the choice of precision. Had we chosen R' Adda's
tequfah, birkhas hachamah would only be said once every 98,496 years --
and that too is only an estimate. We also don't find anyone saying we
should say it on Elul 28 to follow R' Eliezer. It would seem the whole
idea is that the 28 yr cycle brings maaseh bereishis to mind, and no
claims are being made about actual celestial events occuring.

: On the other hands, the measure Revi'is, to those that hold the Mida Ketana 
: ... Recently, I read a few articles that shows that Harav Na'eh based his 
: measurement (86.4 cc) on the coin called Dirham. According to the
: Rambam, Reviis is 27 Dirham.
: The weight of a Dirham (according to Harav Na'eh) is 3.2 gram.  However, the 
: new articles claims that 3.2 grams was the weight of the Dirham during the 
: Ottoman regime in Eretz Israel, but in the time of the Rambam it was about 2.8
: grams, therefore Revi'is is 75 grams.

: In this case it looks like we change Halacha based on archaeologic
findings : (that claims that Dirham in the time of the Rambam was
2.8 grams.) : Can we do that?

According to the Gra and RAYKook, scientific findings can only change the
halakhah lechumerah. The reason for a pesaq usually includes motivations
beyond those documented. Therefore, if we find a flaw in the documented
reason, we do not know if we should remain with the chumrah because of
any other sevaros. However, we do know that if one reason lehaqeil is
removed, we have motivation lehachmir.

This topic has been discussed on Avodah repeatedly, particularly in
light of the gemara's belief that maggots are not the product of piryah
verivyah. My own rebbe, RDLifshitz, made a point of explaining how the
science would not impact that particular din.

You might want to check the archive. See also RGS's essay at
<http://www.aishdas.org/toratemet/science.html>, he gives a survey
of responses to the question, and how they appeared in several real
questions (bein hashemashos, tereifos, babies born in the 8th month,
and spontaneous generation of lice).

Tir'u baTov!
-Micha

-- 
Micha Berger             I slept and dreamt that life was joy.
micha at aishdas.org        I awoke and found that life was duty.
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