It’s all in the wrist, right?

i like this phrase very much.

want to ask physics questions. Mostly about light.

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Tom

Albrecht says that inflation is *part* of the solution, though as he says it really only passes the buck back to even earlier times! By the way, I found your “battleship” argument very clear indeed, thanks!!

First, you didn’t take index of refraction (and further subtleties like coatings, variable index, and even the latest “inverted” materials”) into account. That still doesn’t say why the principles would conspire, and remember that if “energy” is like a stuff, then it just can’t be concentrated more than there was. OTOH, having more heat in one spot doesn’t make more of something there can’t be more of (as opposed to mathematical concepts like entropy, but I know the distinction is blurry.) As for the re-radiation from the surface: That isn’t really the point, it’s the energy density. The same energy is being put into various size spots, as we fiddle with focal length and thus f/ratio. Imagine that we have a black body surface. Then, the total power re-radiated will soon be equal to the input. A tiny image spot will emit the same energy as a larger one, to send back onto the source. But it will be hotter because its energy is concentrated into such a small area.

Anyway, that’s my quick take, but if anyone knows better let me know. I do remember, in articles about concentration of sunlight in solar ovens (one I recall in Sci Am.), they have said: the image intensity can’t be made more than the emitting surface or it would violate Thermo 2, not that success in doing so wouldn’t matter anyway.

I don’t think optics is “conspiring” to support the second law, any more than mechanics conspires to support the second law because perpetual motion machines all have flaws. There is a theoretical minimum f-number for lenses in part because a fast lens has to be highly curved, and you can’t make a curved lens surface with an arbitrarily large aperture; it can’t be any bigger than a hemisphere. I’ve read a claim that the theoretical fastest lens would be f/0.5, but don’t know the derivation.

That is not why you can’t use an optical system as a one-way heat conduit. In fact, I could make a big but not terribly fast lens and use it to concentrate light on a small image, like burning paper with a magnifying glass. However, if I succeeded in making the image hotter than the original light source, the image would simply reradiate back through the magnifying glass onto the source.

In this paper I show how the second law of thermodynamics, generalized to include event horizon area, places interesting constraints on the value of the fine structure constant. A simple analysis leads to the conclusion that classical Dirac and point-like magnetic monopoles could be used to violate the second law, and that GUT monopoles are inconsistent with minicharged particles.