Kyle <hob### [at] gatenet> wrote:
> On 23 Jun 2008 17:50:58 -0400, Warp <war### [at] tagpovrayorg> wrote:

> I think an additional reason is that this statement ...

> >  Everybody knows that there's no sound in space

> ... is not really true.  I bet if you ask 100 people, "If we are both floating in
space, and I snap my fingers, what will it sound like?", most of them will not answer
correctly.  

  There are actually much worse misconceptions about outer space. The
quintessential and by far most widespread example is: "Space is very cold.
Anything put into outer space will freeze very fast."

  I'd say 99% of people who get *all* the other facts about outer space
right (such as people *not* exploding when they are put into vacuum, etc),
get this one wrong.

  On earth there are three methods of heat transfer: Conduction, convection
and radiation. A piece of meat put into a freezer will freeze in a few
hours because of conduction and convection. Radiation plays only a very
small role.

  In vacuum there's no conduction nor convection. Vacuum has no "temperature"
which it could somehow transfer to objects. It's vacuum. There's nothing
there. The only possible mechanism for heat transfer is radiation. Vacuum
is, in fact, a pretty good insulator.

  The only way for, for example, a human to freeze in space is to slowly
radiate its own temperature away. This does happen, but it happens very
slowly, and it requires that he doesn't receive any excess heat radiation
(for example from a nearby star). In fact, if a human was floating in space
closer to the Sun than a certain distance (I wouldn't dare to bet about
the critical distance), he would never freeze because the Sun is warming
him up by radiation heat transfer.

  Even without any star or other radiating source nearby, the human body
takes a long time to radiate its own heat away in vacuum. While it will
eventually freeze, it will take quite some time to do so.

  In spaceship designs the biggest problem is not, ironically enough,
how to keep the ship warm, but on the contrary how to keep it cool.
Motors, electric devices, etc. all produce heat, and it's very difficult
to get rid of it. Putting a big thermal sink on the outer hull of the
ship is a poor way of getting rid of the heat because it radiates the
heat away very slowly in vacuum.

  Maybe some people get confused by the so-called cosmic microwave
background radiation, which causes the entire universe to radiate
at about 3 kelvin. From this they (erroneously) deduce that everything
put in outer space will quickly freeze to 3 kelvin.

  Of course it's the exact opposite: In fact, the background radiation
*adds* to the temperature of everything. It doesn't reduce the temperature.

-- 
                                                          - Warp

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