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Why Don’t You Boil Alive In The Centre of A Cold Spherical Cave?

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posted on Mar, 13 2009 @ 01:05 PM
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Firstly here’s why you “should”: Any object above absolute zero is constantly emitting infrared light and receiving it back from it's surroundings. Because at 26C the real temperature of a body is actually 300K (given absolute zero) this infrared exchange is quite substantial.

Common sense dictates that providing two bodies are at the same temperature an infrared equilibrium should be reached.

However a dark cave is generally round, so no matter if you imagine the infrared been given of from the walls at random angles (or even perfectly straight ones) you would have thought the centre of a cave would (on average in time) always receive more infrared than any other area.

Therefore if you place a “black object” at the centre, (even if it’s just another piece of broken cave wall) you would have thought that this object would become substantially hotter than the outer cave walls. In fact the more cave wall area you have the hotter the object should be.

Furthermore oxygen and nitrogen are 100% transparent to infrared (hence why TV remotes work, and part of the reason why mountains are warmer at the bottom than top. They are also bad for conducting heat. Therefore they should be nearly as good as a vacuum.

But given that there are many substantial caves in nature this would mean that there should also be lots of very burnt-unlucky bats-insects deposited at the centre of these caves. As far as I know this is not the case, so what’s going on?

A further consideration: The Second Law of Thermal Dynamics states “energy always flows from a high concentration to a low one”. However one look at a Parabolic Trough en.wikipedia.org... or even a magnifying glass starting a fire, might convince you this isn’t always the case as infrared-light is in fact moving from a low concentration into a very high one.
But if The Second Law hasn’t stopped magnifying glasses or Parabolic Troughs working; why does it (at least appear) to stop cave bats and insects burning to death?

I am asking this question because if the only reason why bats don’t get burnt is one like “they stay away, or move too quickly” then there is huge free energy to be had, as using e.g. water pipes to collect this heat we could e.g. boil water to make electricity.
Which would blatantly be just far too good to be true!!!!
(Right?)




posted on Mar, 13 2009 @ 01:34 PM
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As a very short and sweet explanation...



... nothing reflects perfectly... especially not rock.



posted on Mar, 13 2009 @ 02:02 PM
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The walls of the cave absorb any excess heat and transfer it through the earth until an equilibrium is reached.

The deeper you go into the earth the hotter it gets though so at some point you will get cooked. But it has nothing to do with reflecting your own body heat.

[edit on 3/13/2009 by Phage]



posted on Mar, 13 2009 @ 02:52 PM
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Thanks johnsky and Phage!
So johnsky if you built a bigger object in the centre, or even a partition wall through either a cylinder or spherical shaped cave would that work? (At least up and till e.g. a degree of so in the case of partition wall).

Phage I wasn’t meaning you would get cooked by your own body heat (though I suppose that would be possible in almost perfectly round metallic surface) rather I was meaning you would get cooked by the infrared exchange of the cave walls.
It seems they should get colder (until heated by their surrounding earth) at the expense of you getting warmer-hotter.

[edit on 090705 by Liberal1984]



posted on Mar, 13 2009 @ 03:19 PM
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It would have to be a perfectly insulated and perfectly reflective hollow sphere.

Any point of heat exchange or radiation emission would sink it all out.



But no, we have nothing like that on earth, and nothing we could build such a thing with. All materials known to man are thermally conductive to some degree, and I don't know of anything that is perfectly reflective, even mirrors absorb a little.

[edit on 13-3-2009 by johnsky]



posted on Mar, 13 2009 @ 03:33 PM
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reply to post by Liberal1984
 

You and the cave walls are both absorbing and radiating infrared. If the cave walls are colder than you, they will emit less infrared than they receive from you. Ignoring the air (which does absorb infrared, BTW. Infrared is what heats the atmosphere.), you will warm the cave walls. If the cave walls are warmer than you, they will warm you in the same manner.

The earth surrounding the cave is a very large heat sink, it can contain a very large amount of heat. If the temperature of the cave walls is colder than you they will continue to transfer your heat to the surrounding earth until you stop producing body heat. The converse is true. If the walls, and the surrounding earth are warmer than you, they will transfer heat to you until you are at the same temperature they are.

Either way an equilibrium is reached where you and the cave walls are emitting and absorbing the same amount of infrared radiation and are at the same temperature.

[edit on 3/13/2009 by Phage]



posted on Mar, 13 2009 @ 03:59 PM
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Thanks Phage; everything you’ve said made great sense. Except for one thing; it doesn’t seem to take into account the concentration effect of infrared in the centre of any round shape (that at least should surely be caused) by a higher than average level of infrared particles (photons) passing through the same relatively small area of space.
Is there no concentration effect? If so how does this work out? Or is the problem merely one of the infrared concentration been too small to harvest?
I would have gone for the later if it wasn’t for the fact at 300K a lot of infrared is still being exchanged (it certainly doesn’t take very long for something warm to freeze in outer Space).



posted on Mar, 13 2009 @ 05:44 PM
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reply to post by Liberal1984
 

Sorry, I guess I did miss that point. Maybe because the scenario is very unlikely to occur naturally.

A parabolic reflector works by gathering the energy from a wide area and concentrating it on a small area. The wider the area covered and the smaller the point of focus, the more energy is transferred to that point. To produce a small focal point the reflector must be of a very particular shape. The same is true in order to gather radiated heat.

If the walls of the cave were shaped in such a way that all of the energy of a significant area were to be concentrated at a single point, I suppose an object at that point would be heated. It is unlikely in the extreme that any such scenario would occur naturally. The walls of the cave would have be be shaped such that each point on the surface radiated in the direction of that single point. In other words, the walls would have to be very smooth and have a very spherical shape, otherwise most of the radiation would be sent in random directions and not converge.

It should also be noted that CO2 does absorb somewhat at 300K and water vapor is highly absorptive of infrared so some of the energy would go into heating the air before it reached the focal point.


Correction: While water vapor does absorb infrared, it is not accurate to say it is highly absorptive.

[edit on 3/13/2009 by Phage]



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