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 Post subject: Superconductors
PostPosted: Mon Jan 18, 2016 8:35 pm 
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This is either a reference to Larry Niven, or the same mistake Niven made.

Superconductors in the real world are perfect conductors of electric charge, not heat. Most are actually pretty terrible at conducting heat, as they're basically very exotic ceramics.


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 Post subject: Re: Superconductors
PostPosted: Mon Jan 18, 2016 9:02 pm 
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JohnSmith wrote:
Superconductors in the real world are perfect conductors of electric charge, not heat.

Superconducting liquid helium* does — although this might be connected to superfluidity, which needs even lower temperatures. I suppose we'll find out if it turns out to be possible to make a superconductor that doesn't rely on lots of cooling.

* Yes, helium stays liquid at atmospheric pressure no matter how cold it gets. Helium is weird.

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 Post subject: Re: Superconductors
PostPosted: Mon Jan 18, 2016 9:30 pm 
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JohnSmith wrote:
This is either a reference to Larry Niven, or the same mistake Niven made.

Superconductors in the real world are perfect conductors of electric charge, not heat. Most are actually pretty terrible at conducting heat, as they're basically very exotic ceramics.


he didn't specify superconductor of electricity. building a superconductor of heat would be weird, but might be possible.


maybe some sort of metamaterial, which is actually made up of nanoscopic scale heat machines? anytime the wall goes above 72 fahrenheit, it causes the nanomachines to start 'tapping' the adjacent machine edges, effectively broadcasting heat across the entire surface in the form of mechanical pressure waves?


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 Post subject: Re: Superconductors
PostPosted: Mon Jan 18, 2016 9:51 pm 
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JohnSmith wrote:
This is either a reference to Larry Niven, or the same mistake Niven made.

Superconductors in the real world are perfect conductors of electric charge, not heat. Most are actually pretty terrible at conducting heat, as they're basically very exotic ceramics.

The intuitive connection is clear enough. In most conductors you have electrons in a conduction band that can move fairly freely through the material, and those same electrons can carry thermal energy/entropy. Thus a good conductor of electricity is usually also a good conductor of heat and people get used to the idea that good at one means good at the other.

But in a superconductor the Cooper pairs that superconduct electricity allow conduction electrons to move without transferring any energy (hence the whole superconductivity thing), this means that the material is an effectively perfect electrical conductor, but that some of the conduction electrons pretty much might as well not exist for thermal conduction. So as stated above, electrical superconductors tend to be poor thermal conductors, but this is true even for metallic based superconductors, not just for ceramic superconductors. Super-conductors are worse conductors of heat than the same material is under circumstances where it can't super-conduct.

Ceramics and semi-conductors and the like also tend to conduct heat worse when cold than when warm, as fewer electrons are pushed into higher energy conduction bands; and super-conductors need to be cold enough that this sort of effect is unlikely even for electrons not involved in Cooper-pairs.

I tend to assume this mistake is due to Niven when I see it. The (incorrect) but intuitive idea that a superconductor should be a good thermal conductor is quite different from thinking it's a perfect thermal conductor, which is what Niven did.

IIRC from back when I was taking lots of physics courses there's an argument that a Niven style superconductor of heat is actually impossible; but I'm not remembering the argument and a Bose Einstein condensate would seem superficially to be a counter-example.


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 Post subject: Re: Superconductors
PostPosted: Tue Jan 19, 2016 3:05 am 
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Second sound.

May be a factor found in non-superconductors of heat, but if it were a true heat superconductor, Schlock might have a different complaint.

Heat management is very important, and such conductors may let you more easily manage heat efficiently when you need to keep large areas equally heard/cooled. For me, it's 'close enough' to call it a superconductor, if second sound moves at meters per secon. For you, you may think 'that's got nothing on a true heat superconductor'. For a soldier in the field, unless it's important to blowing stuff up its not really relevant whether it's a true superconductor.

Pi? Pi would care, but he's not rational.


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 Post subject: Re: Superconductors
PostPosted: Tue Jan 19, 2016 11:09 am 
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Karfston wrote:
Pi? Pi would care, but he's not rational.


Holy crima nut nitley! I can't believe I never noticed that joke before.


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 Post subject: Re: Superconductors
PostPosted: Tue Jan 19, 2016 11:57 am 
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Amaranthine wrote:
Karfston wrote:
Pi? Pi would care, but he's not rational.


Holy crima nut nitley! I can't believe I never noticed that joke before.

Seriously?


I remember it being mentioned a few times back when Pi was first introduced...


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 Post subject: Re: Superconductors
PostPosted: Tue Jan 19, 2016 12:05 pm 
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Aye, sooner or later that joke just comes around and around again.

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 Post subject: Re: Superconductors
PostPosted: Tue Jan 19, 2016 1:27 pm 
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Amaranthine wrote:
Karfston wrote:
Pi? Pi would care, but he's not rational.


Holy crima nut nitley! I can't believe I never noticed that joke before.


It was the entire conversation of a strip.
http://www.schlockmercenary.com/2008-06-26


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 Post subject: Re: Superconductors
PostPosted: Tue Jan 19, 2016 3:40 pm 
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Well, apparently the floor became warmer than Schlock expected, so the wall and the floor are better thermal conductors than he thought they were. On the other hand it looks like he did manage to melt a part of the wall without melting the entire habitat, so they aren't thermal superconductors. They don't have the same temperature in every point like Niven described it. And Schlock obviously thinks the floor will be cooler farther from the hole he made, which wouldn't be the case with thermal superconductors.

I don't see why it would take a superconductor to prevent a thermal search either. Any ordinary metal should be as impenetrable to infrared radiation as it is to visible light. If a wall is sturdy enough to be called a bulkhead, then it shouldn't surprise anyone to find sheets of metal in it.

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 Post subject: Re: Superconductors
PostPosted: Tue Jan 19, 2016 4:51 pm 
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Rombobjörn wrote:
Well, apparently the floor became warmer than Schlock expected, so the wall and the floor are better thermal conductors than he thought they were. On the other hand it looks like he did manage to melt a part of the wall without melting the entire habitat, so they aren't thermal superconductors. They don't have the same temperature in every point like Niven described it. And Schlock obviously thinks the floor will be cooler farther from the hole he made, which wouldn't be the case with thermal superconductors.

The walls are laced with, what we must assume are thermal, super conductors. So just because you can burn a hole in outer bit doesn't mean you can keep burning once you reach super the conductive parts. Concrete walls are laced with iron but don't perfectly match the properties there of, correct?


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 Post subject: Re: Superconductors
PostPosted: Tue Jan 19, 2016 5:45 pm 
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Rombobjörn wrote:
Well, apparently the floor became warmer than Schlock expected, so the wall and the floor are better thermal conductors than he thought they were. On the other hand it looks like he did manage to melt a part of the wall without melting the entire habitat, so they aren't thermal superconductors. They don't have the same temperature in every point like Niven described it. And Schlock obviously thinks the floor will be cooler farther from the hole he made, which wouldn't be the case with thermal superconductors.

I don't see why it would take a superconductor to prevent a thermal search either. Any ordinary metal should be as impenetrable to infrared radiation as it is to visible light. If a wall is sturdy enough to be called a bulkhead, then it shouldn't surprise anyone to find sheets of metal in it.



I've been pondering this a bit. Positing a heat equivalent of superconductor (I'm not sure such a material could exist, but hey! Science Fiction.), could you burn through it?

Niven is doubly wrong. A thermal superconductor can't have the same temperature at all points - speed of light limits kill that straight off. Instead you'll have a propagation wave through the material, like EM fields propagate through a superconductor. It isn't necessarily at the speed of light, it just has to be lossless. So if energy is added to the material faster than it propagates away, it should eventually melt just fine.


Actually, that pretty much describes normal matter. Heat doesn't decay into other forms of energy. So... I'm not sure where that leaves us after all.


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 Post subject: Re: Superconductors
PostPosted: Tue Jan 19, 2016 6:16 pm 
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Rombobjörn wrote:
I don't see why it would take a superconductor to prevent a thermal search either. Any ordinary metal should be as impenetrable to infrared radiation as it is to visible light. If a wall is sturdy enough to be called a bulkhead, then it shouldn't surprise anyone to find sheets of metal in it.

When performing a thermal search (or any search and using thermal sensors as a part of it) you aren;t simply looking for thermal signatures, you are also following thermal residue.

If the hab material redistributes thermal energy at a high efficiency... it would leave little to no trace to follow.


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 Post subject: Re: Superconductors
PostPosted: Wed Jan 20, 2016 3:53 am 
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If thermal energy propagates like a wavefront...

That wavefront can be reflected or focused. You don't need to melt the whole thing. You just need to create a hot spot that Melts.

That I recall, superconductors are not infinite conductors. They have limits that can be reached. If thermal superconductors are the same, you may be able to saturate their ability to move heat around, directly melting them.


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 Post subject: Re: Superconductors
PostPosted: Wed Jan 20, 2016 4:04 am 
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Jindra34 wrote:
So just because you can burn a hole in outer bit doesn't mean you can keep burning once you reach super the conductive parts.

What do you see in the third panel? To me it looks like we're looking through a hole in a wall. A wall that has been melted. Melted all the way through, because otherwise there wouldn't be a hole to look through.

evileeyore wrote:
Rombobjörn wrote:
I don't see why it would take a superconductor to prevent a thermal search either. Any ordinary metal should be as impenetrable to infrared radiation as it is to visible light. If a wall is sturdy enough to be called a bulkhead, then it shouldn't surprise anyone to find sheets of metal in it.

When performing a thermal search (or any search and using thermal sensors as a part of it) you aren;t simply looking for thermal signatures, you are also following thermal residue.

If the hab material redistributes thermal energy at a high efficiency... it would leave little to no trace to follow.

That may be but they haven't mentioned that as a problem. The stated problem was that they can't see through walls because of superconductors. My point was that plain old tinfoil would have the same effect.

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 Post subject: Re: Superconductors
PostPosted: Wed Jan 20, 2016 9:37 am 
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aroduc wrote:
Amaranthine wrote:
Karfston wrote:
Pi? Pi would care, but he's not rational.


Holy crima nut nitley! I can't believe I never noticed that joke before.


It was the entire conversation of a strip.
http://www.schlockmercenary.com/2008-06-26

I suppose a better statement would be that I can't believe the deliberateness of his naming is not front and center in my mind when his name comes up.

Especially since his name was the joke before he even showed up in the strip: http://www.schlockmercenary.com/2002-07-03


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 Post subject: Re: Superconductors
PostPosted: Fri Jan 22, 2016 9:32 pm 
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JohnSmith wrote:
This is either a reference to Larry Niven, or the same mistake Niven made.

Superconductors in the real world are perfect conductors of electric charge, not heat. Most are actually pretty terrible at conducting heat, as they're basically very exotic ceramics.


In one of Isaac Asimov's articles on superconductivity, he stated that all parts of a superconductor are always at the same temperature. He said that when the only known superconductors were metals based on lead, mercury, and gallium. I don't know it that's true, but he generally only quoted established science. He also said that when a superconductor lost superconductivity, it lost it everywhere simultaneously; it did not progress at lightspeed. That may be wrong, but apparently, it was accepted fact at one time. Also, there are two different kinds of superconductors, Type I and Type II. Maybe the metallic types which require temperatures in the low Kelvins behave differently from ceramic types.

These are not to be confused with zero-resistance conductors, which do not block magnetic fields.

Let's assume a superconductor really is also at the same temperature throughout. At some point, you'll force it over the temperature at which it loses superconductivity, at which point it will no longer be a superconductor. At this point, yes--you can burn through it. The rest of the superconductor will, if it drops below the superconducting point, regain its superconductivity. Thus, even if a superconductor of electricity is also a superconductor of heat, enough heat will be able to burn through it. Superconductors also exclude magnetic fields, but sufficiently-strong magnetic fields will destroy superconductivity. If the temperature stays below the critical temperature, the loss of the magnetic field will allow restoration of superconductivity.

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 Post subject: Re: Superconductors
PostPosted: Fri Jan 22, 2016 10:43 pm 
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Amaranthine wrote:
Especially since his name was the joke before he even showed up in the strip: http://www.schlockmercenary.com/2002-07-03


Which is hardly surprising, since Pi (founder of the Completely Pointless Thread) went by the title "Irrational Number" on the Schlock Boards even before Howard wrote the character into the story.


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 Post subject: Re: Superconductors
PostPosted: Wed Jan 27, 2016 9:21 pm 
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ChowGuy wrote:
Amaranthine wrote:
Especially since his name was the joke before he even showed up in the strip: http://www.schlockmercenary.com/2002-07-03


Which is hardly surprising, since Pi (founder of the Completely Pointless Thread) went by the title "Irrational Number" on the Schlock Boards even before Howard wrote the character into the story.



Note that Pi should actually be called iπ, since he's irrational and imaginary.

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"Magic is just another way of saying 'I don't know how it works.'"
Larry Niven
"Any technology, no matter how primitive, is magic to those who don't understand it."
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