Where the books aren't licensed?! I didn't know there was such a thing.

Too bad on the subscriptions. :( I'd be happy to give you a page view--if it were possible--for you to never use, and thus enjoy the subscription.

It's also neat that you just let them have the address. Let's hope they remember you when they become world famous. :)

I also have a few names that i want to use but am too lazy to. Maybe we can get another site: LDNHA (Lazy Domain Name Holders Anonymous). Um, and is HTM really a tag?

I know the feeling, so I'm taking the edx Thermodynamics MOOC to try to learn more about the subject.

Something I learned in the first week: the assumptions of Thermodynamics are astonishingly limited. According to Professor Gaitonde, the science of Thermodynamics is macroscopic (so it doesn't say anything about microscopic phenomena). The assumptions are:

1) No quantum effects

2) No relativistic effects

3) No scale effects.

So any limits derived by Thermodynamics only apply to a small range of phenomena, when you consider the universe. Dark Energy, Dark Matter, Quantum Physics, and Computer Science (since scale effects are very important) are not limited by the assumptions Thermodynamics makes. The laws of thermodynamics, based on these assumptions, don't apply as broadly as people commonly assert.

What about information entropy? The entropy is lowered when the file is zipped, then raised when the file is unzipped. According to the "rule of thumb" cited above, if a process is reversible, the entropy remains constant. Zipping is reversible, but the information entropy is not constant; it lowers and increases.

What cost does the absorption and re-emission extract from me, every time I use the lens to do the work I want it to do? What am I losing, what am I giving up to get heat of ignition from sunlight?

I had to buy the glass, and there was an energy cost in producing it. But those are one-time expenditures. Once it's made, the cost to light a fire is nothing.

Also, the first law of thermodynamics seems to be violated, as outlined above. U = Q - W. U (internal energy of the system, in this case the magnifying glass) should be negative, since Q (heat added to the system) is very small, and W (work done by the system) is relatively large. But the internal energy of the magnifying glass doesn't go down, if anything it increases slightly because of a temperature increase?

Sorry, I may have spoken too soon there. Certain features of hangouts look like they still require plus, if you are not on an Apps (business) account. But they seem to have almost completely phased this out. In general they seem to have halted the major push for plus. I'd like to think they fired* the head of plus partly because of the failure of the push and the backlash of the real name, and youtube stuff...but I don't know why he "left" ( http://recode.net/2014/04/24/e... ). Anyways, here's what i could find on how to use hangouts:

https://productforums.google.c...
https://support.google.com/plu...
https://support.google.com/a/a...

Here's how to use it without plus:
https://support.google.com/han...

No, it can be used with or without plus.

"If you were trying to imply that Q is the energy added to the system that the light is being focused upon,"

No, I'm guessing Q would be the heat added to the magnifying glass on the sun side, which is very small compared to the heat produced on the side where the light is focused; the latter heat does the work you want (lighting a fire or whatever). Since Q is small, and W is large, U should be negative. But it's not.

"The process of compressing your data costs more than decompressing it. Rule of thumb holds."

Costs more in what sense? Energy cost? Lines of code cost? Time cost? In any event, it is not something that I consider when zipping a file. Zip and unzip are treated as equivalent from the user's standpoint.

"A magnifying glass, simply put, directs the energy that hits its outside lens surface to a much smaller area, at the cost of the loss due to diffraction of light."

The point that confuses me is: the energy on the outside lens surface can't light a fire, but the energy produced by the glass can. What work was done on the outside energy? It was redirected inside the lens, but how is that work? Doesn't work in thermodynamics reduce to the lifting of a mass in a gravitational field? How is the lens doing any work, in that sense?

All models are flawed, by definition. These holy "Theories" you have such emotional attachments to simply use models. In a 100 years, they will be superseded and allow us to do things we can't think of today. Like GPS wouldn't work if we relied on Newton's theory of gravity.

Where is the waste heat, or change in internal energy, in a magnifying glass system, used to focus the sun's rays to produce a concentrated, high-temperature Airy disk?

U = Q - W

The U (internal energy) of a magnifying glass does not change appreciably during use. Q is heat added to the system; it is much less than the W, or heat produced by the focused rays, which do the work of lighting a fire.

U is small, Q is small, W is large. In theory, U should be large and negative. But it's not...

http://www.askamathematician.c... says: 'A good rule of thumb for entropy is, "if you can reverse it, then the entropy is constant".'

But a zipped file has lower (information) entropy than the same file uncompressed, and the process is reversible. So that rule of thumb doesn't hold for information entropy?

The other question I have about the "ask a mathematician" response is: it assumes the energy input to the magnifying glass system is the temperature of the sun. That is not true: the atmosphere, at least, reduces the sun's irradiance. The input to the system should be the temperature on the sun's side of the glass, which can be less than zero since you can light fires on cold or windy days when the sun is out.