If any of you discover a material that absorbs heat faster than it radiates it,
please let me know. We
can become millionaires together. Conservation of energy in the universe -
materials absorb and radiate
energy at the same rate.
Jim, I like your analogy, except that at some temperature the outer layers of
the carbon would begin
to ablate off and the box would slowly vaporize. Now, if the box was a perfect
sphere, and you
instantly heated the outer surface of that sphere super hot, the ablation of
the outer surface would
cause an equal and opposite reaction, the sphere would implode and fusion would
occur.
This is the concept of Inertial Confinement Fusion, or Laser Fusion as it
sometimes called. It's what
we are trying to do at my place of employment. We have the largest laser in the
world - it's over a
football field long and three stories high. Google NIF Laser, NIF short for
National Ignition Facility.
Mike K6MDS
One final comment, for those wonder how something that absorbs radiation can
also emit radiation. Imagine what would happen if that didn't happen.
Suppose, for example, we take a graphite box and set it in outer space so
that the sun shines on it. In outer space, there's no convective heating or
cooling (let's ignore the solar wind, meteor dust, and other minor
complications), so the only way heat can enter or leave the graphite box is
by radiation. If the graphite didn't emit radiation, then it would keep
absorbing sunlight and get hotter and hotter. Its temperature would keep
rising, until it became white hot and then blue hot, and then finally so hot
the carbon atoms would fuse and it would explode like a hydrogen bomb (in
this case a carbon bomb). Of course, that doesn't happen and the reason is
that the graphite box eventually reaches thermal equilibrium; the energy it
absorbs exactly equals the energy that it emits. If we replace the graphite
with, say, a block of wood, then the same thing will happen. But because
wood isn't as good an absorber of radiation as graphite, it won't get as hot
when it reaches equilibrium. In other words its equilibrium temperature will
be lower. And, if we put a glass mirror in outer space, it won't heat up
much at all, because it will absorb only tiny bit of energy. However, even
that tiny bit gets reradiated, and if one measures the spectrum of the
radiated energy, it will look very much like a blackbody spectrum. So the
bottom line is that all things absorb radiation to some degree, thermalize
it, and reradiate it back out. A theoretical blackbody does this perfectly,
everything else less so, to varying degrees, but the basic concept is the
same. And it's a good thing Mother Nature works this way, because if she
didn't the universe as we know it wouldn't exist and we wouldn't be having
this conversation.
End of lecture. Tnx for the bandwidth!
73.
Jim W8ZR
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