[Avodah] electronics on shabbat

[Micha Berger via Avodah]

: 
: I agree that this ability did not exist until recent times, and that is
: exactly why they never asked the question: How do we define fire for
: Hilchos Shabbos? Is the glowing metal considered fire because of the heat,
: or because of the light, or because of some combination of the two? ...

Or neither, and heating metal until it glows is bishul, not havarah.

Rambam (Shabbos 12:2) - Heating metal kedei letzarfo bemayim is a tolsadah
    of mav'ir and he is chayav (ie it is deOraisa)

Raavad (sham) -- why wouldn't it be bishul?

The gemara discusses gacheles shel matches twice, and both times it's
about kibui.

Shabbos 42a - Shemu'el permits extinguishing a gacheles shel mateches
    in a reshus harabim to avoid hezeq of the rabim, but not a real
    coal (gacheles shel eitz).

Rashi says this is because the GSM would only be kibui derabbanan.

Rashba quote R' Hai Gaon that it's because the coal glows red and
    provides its own warning, but hot metal can be an invisible danger.

Implied from the Rashba -- a GSM isn't even necessarily glowing.

Ritva: the GSM is a sakanas nefashos

To the Raavad, this lack of mechabeh shows that the problem of heating
metal is bishul, not hav'arah.

Yuma 34b - R Yehudah says that they would heat up asasios shel barzel from
    erev Yom Kippur to drop in the kohein gadol's miqvah to take the
    chill out of the water. Abayei says that even if they were heated
    higia letziruf, it's mutar as a davar she'ein miskavein that even
    intentionally would have only been derabbanan.

Magid Mishnah Shabbos 12:2 - we can derive from Yuma that in had the metal
    been put on the fire on YK itself, heating the metal would be assur
    deOraisa.

: According to Rav Moshe Heinemann (of the Star-K; in "Guide to Halachos" by
: Nachman Schachter, published by Feldheim, pg 29):
...
: Unfortunately, he does not offer any explanation or sources for his choice
: of words "heat OR light". Does anyone know of other poskim who offer
: opinions about technologies that make light without heat, or heat without
: light?

Since it is (AFAIK) impossible to have a maqor for answering this
question, and it's a safeiq deOraisa, I think RMH's pesaq is the only
possible one.

Tir'u baTov!
-Micha

-- 
Micha Berger             What we do for ourselves dies with us.
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