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[Lord Shonus]

Sergarr is saying that, because we can build devices that get things hotter than 6000K, Randall is wrong about it being impossible to focus sunlight to achieve that temperature, despite this being a known and accepted fact.

From a 1985 paper:

Although solar energy research, development, and systems experiments were conducted in the late 1800s and early 1900s, it was the sharp increase in the price of oil in 1974 precipitated by the Middle-Eastern oil embargo the previous year that escalated national and international investment in solar energy. In the United States and other industrial countries, the technological tools and advancements produced during World War II, the post-war rebuilding and prosperity, the U.S. nuclear power and space programs, and other technological achievements were applied to solar energy research and development. The result was that research, which had been limited to backyard tinkerers and small specialized companies, was spread to universities, national laboratories, and industry. The federal solar budget rose from less than $1 million in early 1970s to over $1 billion in the early 1980s; the budget is now about $200 million, with about $50 million for solar thermal technology.

Solar thermal technology is concerned principally with the utilization of solar energy by converting it to heat. In the concentrating type of solar collector, solar energy is collected and concentrated so that higher temperatures can be obtained; the limit is the surface temperature of the sun. However, construction materials impose a lower, more practical limit for temperature capability. Similarly, overall efficiency of energy collection, concentration, and retention, as it relates to energy cost, imposes a practical limit on temperature capability.

[FearfulJesuit]

Today a good friend of mine, who is normally a perfectly reasonable individual despite being a Dark Enlightenment contrarian, postulated that Gamergate is 21st-century America's Dreyfus Affair.

...what?

[Sergarr]

That doesn't even make sense.

behold

this is why mathematicians should not try to play physicists outside of theoretical physics and its direct applications

because then you get dumb shit like this:

Lenses and mirrors work for free; they don't take any energy to operate.[2] If you could use lenses and mirrors to make heat flow from the Sun to a spot on the ground that's hotter than the Sun, you'd be making heat flow from a colder place to a hotter place without expending energy. The second law of thermodynamics says you can't do that. If you could, you could make a perpetual motion machine.

Obviously, if you could concentrate heat from the sun to achieve temperatures higher than on the Sun, then you could make perpetual motion machine. This is why we, obviously, live in the current age of infinite energy, thanks to our laser-based perpetual motion machines, than generate temperatures higher than 6000 K. OBVIOUSLY

Well... Yeah? I think? I'm unsure because of your wording but you seem to be implying that he's saying that sunlight does violate conservation of energy when he's saying the exact opposite.

he doesn't say that

he says that you can't use sunlight to generate temperatures higher than 6000 K

which is obviously false because you can use photovoltaic cells to gather the energy and then use a laser to ignite things to millions of degrees (in fusion reactors, for example)

that post of his is actually choke-filled with falsehoods; I mean, he even aknowledges that moonlight is not black body radiation - and then he just, well, does this:

"But wait," you might say. "The Moon's light isn't like the Sun's! The Sun is a blackbody—its light output is related to its high temperature. The Moon shines with reflected sunlight, which has a "temperature" of thousands of degrees—that argument doesn't work!"

It turns out it does work, for reasons we'll get to later.

No reasons are actually given btw

And this one is just, fucking, fuck:

But first, hang on—is that rule even correct for the Sun? Sure, the thermodynamics argument seems hard to argue with,[3] but to someone with a physics background who's used to thinking of energy flow, it may seem hard to swallow. Why can't you concentrate lots of sunlight onto a point to make it hot? Lenses can concentrate light down to a tiny point, right? Why can't you just concentrate more and more of the Sun's energy down onto the same point? With over 1026 watts available, you should be able to get a point as hot as you want, right?

That [3] says "because it's correct", in a true assholish manner of a person that cannot even comprehend that he may be wrong

After this btw he uses some inane optics-based argument (that's also completely wrong):

In other words, you can't smoosh light beams together without also making them less parallel, which means you can't aim them at a faraway spot.

It's amazing that he doesn't know about such simple concept as "elliptical mirror", which TOTALLY CAN "aim smooshed-together but less parallel light beams" at a faraway spot

this thing is just a fractal of failure

EDIT:
Just because a "scientific paper" says something, it doesn't mean that it's actually true, or that it's true in all conditions. Such as, the usually assumed, and usually wrong, conditions of "things are in equilibrium", or a condition of "Solar system is a closed system".

[TheBiggerFish]

*facepalms*

[Helgoland]

he says that you can't use sunlight to generate temperatures higher than 6000 K

which is obviously false because you can use photovoltaic cells to gather the energy and then use a laser to ignite things to millions of degrees (in fusion reactors, for example)

I think it's clear from context that he meant 'using optics'. That's the reason your laser free energy counterargument doesn't work, by the way: A laser is not a blackbody source of radiation.

But yeah, re-reading that I don't see a reason why approximating the moon as a blackbody is legit.

[Orange Wizard]

It's almost as though he's presenting things in a manner that makes it easier for non-physicists to understand, huh.

[Lord Shonus]

If he's wrong, he's wrong in the exact same way as every physics and optics expert on the planet.

http://www.askamathematician.com/2013/01/qhow-do-lenses-that-concentrate-light-not-violate-the-second-law-of-thermodynamics-if-you-use-a-magnifying-glass-to-burn-ants-arent-you-making-a-point-hotter-than-the-ambient-temperature-without/

It seems as though there should be some way to bring together lots of light beams using lenses and mirrors and… optical cables or something, that would allow you to get a tiny region as hot as you want.  But as it happens: no.  This is yet another example of the universe having an obnoxious no-go law.

There is a general thermodynamic rule which says that you can never focus energy in such a way that the target is hotter than the source.  So, no matter how many mirrors and lenses you have, you can never focus sunlight in such a way that it’ll be hotter than 5800K (the surface temperature of the Sun), but you can get close.  In practice that isn’t too useful, because machines tend to break at surface-of-the-sun temperatures.

[Sergarr]

If he's wrong, he's wrong in the exact same way as every physics and optics expert on the planet.

http://www.askamathematician.com/2013/01/qhow-do-lenses-that-concentrate-light-not-violate-the-second-law-of-thermodynamics-if-you-use-a-magnifying-glass-to-burn-ants-arent-you-making-a-point-hotter-than-the-ambient-temperature-without/

It seems as though there should be some way to bring together lots of light beams using lenses and mirrors and… optical cables or something, that would allow you to get a tiny region as hot as you want.  But as it happens: no.  This is yet another example of the universe having an obnoxious no-go law.

There is a general thermodynamic rule which says that you can never focus energy in such a way that the target is hotter than the source.  So, no matter how many mirrors and lenses you have, you can never focus sunlight in such a way that it’ll be hotter than 5800K (the surface temperature of the Sun), but you can get close.  In practice that isn’t too useful, because machines tend to break at surface-of-the-sun temperatures.

"on the planet"? More like "on the Internet", and that's not even true, considering that I'm a physics expert, as well.

And, fuck, you didn't even read what you've copy-pasted:

There is a general thermodynamic rule which says that you can never focus energy in such a way that the target is hotter than the source.

Given that the only thing that photovoltaic cells and lasers do is "focus energy", and "in such a way" clearly refers to the "target is hotter than the source", this argument just fails completely. TOP KEK.

What the fuck is it with thermodynamics that makes people go dumb and ignore actual reality?

[Orange Wizard]

Given that the only thing that photovoltaic cells and lasers do is "focus energy", and "in such a way" clearly refers to the "target is hotter than the source", this argument just fails completely. TOP KEK.

THATSNOTFUCKINGOPTICS
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[TheBiggerFish]

What OW said.

[IcyTea31]

Disclaimer: I never studied optics, so chances are I'm completely wrong.

I don't see how the surface temperature of the Moon has any impact on the calculation, just as the temperatures of the mirrors and lenses used don't. The Sun is the light source here, not the Moon; the Moon is just an inefficient mirror. The question really is, is it so inefficient that what's left of the energy after it would be enough to start a fire? Conventional wisdom says no, but reaching that conclusion doesn't validate an argument on its own.

[TheBiggerFish]

The Moon being an inefficient mirror is the point.  You can't get more energy than you have.

[Sergarr]

Given that the only thing that photovoltaic cells and lasers do is "focus energy", and "in such a way" clearly refers to the "target is hotter than the source", this argument just fails completely. TOP KEK.

THATSNOTFUCKINGOPTICS
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And that makes it break the "general thermodynamic rule", how, exactly? What's the fundamental thing about lasers and photovoltaic cells that makes them so special as to make them (as according to the Randall's argument) break the Second law of thermodynamics, compared with what you call "optics"?

The Moon being an inefficient mirror is the point.  You can't get more energy than you have.

what does this even mean

like do you know how moon's black body radiation looks like

its the new moon's light

its so obviously different from the reflected sunlight (during full moon) that i can't believe we're still having this argument

[Rolan7]

The Moon being an inefficient mirror is the point.  You can't get more energy than you have.

Yeah, though...  It does seem like Randall forgot to actually finish that point, like Sergarr said.

Fakedit:  Oh, okay I guess I'm just lost.  Going back to sleep now.

[IcyTea31]

The Moon being an inefficient mirror is the point.  You can't get more energy than you have.

I think you missed my question. If the Moon were a perfect mirror, how hot would its surface be, and why does that matter? Wouldn't it have a cooler surface temperature than the real Moon (as it absorbs less energy), yet reflect more energy to Earth?