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Comment by ethbr1 | Hacker News Reader

And on the follow-up, "Why use 2.4(5) GHz for microwaves?"

Because it happens to be a convenient frequency that water absorbs readily, which is the easiest way of heating up what we'd want to heat with a microwave (read: food).

https://en.wikipedia.org/wiki/Electromagnetic_absorption_by_...

And once we'd polluted the frequency for any stable commercial use, why not use this weird carve-out for a little thing called WiFi?

Rabbit hole: Apparently the precise mechanics of EM heating of molecules are surprisingly complex, and offer a number of frequency options. But this would have been the 1950s(?), so I'd assume they empirically determined a balance of functionality + technical feasibility for water, called it a lunch, and went to have five martinis in a practical fashion.

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> "But this would have been the 1950s(?), so I'd assume they empirically determined a balance of functionality + technical feasibility for water, called it a lunch, and went to have five martinis in a practical fashion."

Or maybe they just wanted to revive frozen hamsters more humanely: "I promise this story about microwaves is interesting." by Tom Scott, about scientist James Lovelock - https://www.youtube.com/watch?v=2tdiKTSdE9Y

Holy shit. That at 101 I should be so blessed as to recall technical specifications from experiments performed decades earlier.

Sadly, it looks like Dr. Lovelock passed away a year after that was recorded, last year in 2022.

https://en.m.wikipedia.org/wiki/James_Lovelock

HN obit: https://news.ycombinator.com/item?id=32250694

To build off your rabbit hole, I've read about using the way microwaves selectively heat molecules in cooking. In particular, they can heat oil molecules in a way that increases flavor extraction without causing thermal breakdown of the flavors like uniform heating would.

To further build off your rabbit hole, this is also why 2.4ghz long range wifi connections (like via a yagi antenna) is also problematic. Foliage fucks with your range. Also why central air conditioners and wet walls create wifi shadows.

But the rabbit hole goes further. Higher frequencies are more susceptible to wall in the middle problems, you can see that easily with 5GHz WiFi, lower frequencies might be better but require larger antennas and might suffer from other limitations. As everything else in engineering this is a compromise.

IIRC, the precise frequency was further narrowed to _not_ be absorbed as well by water, because then all the energy would hit the surface of your food and not the inside (although I'm still not sure if that is relevant at a wavelength that is almost as large as the food you'd want to heat).

And then, again IIRC, finally pinned down slightly to the side of that because of the parts that could be sourced to build the first ovens.

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