[One Armed Scissor]

I dunno why, and I asked my teacher, and my entire class doesn't have an answer. Maybe you guys have one  .
Since heat is the transfer of heat from hot matter to cold matter, then why is it that in the absence of matter, it is still possible to lose heat? How is this heat lost? Infrared radiation? Or is something else? Thanks, hopefully you have an answer.

[gregpawin]

There you go... radiation.  That's why we can feel heat/energy from the sun instead of being a totally closed system.

[Mitch]

radiation is just a type of light, and it has no problem traveling in a vacuum

[One Armed Scissor]

Well if we do indeed lose heat through black body radiation in space, then how come I can't become incredibly cold (absolute zero) when I'm on Earth, standing around naked?
In addition, the space shuttle gets cold on the side not facing the Sun... it doesn't emit much heat, how does it lose all its heat all of a sudden if it isn't even transferring its heat anywhere?

[Donaldson Tan]

heat can be loss through infra-red radiation. It is part of the electromagnetic spectrum. such radiation dont need a medium to travel through.

[gregpawin]

Well, you don't lose all that much heat here on earth because you're standing in a bath of a generally warm fluid, air.  Our planet is covered with around 200 miles of atmosphere that is constantly mixing and being warmed by the sun.  It is being helped by the fact that there's carbon dioxide and other greenhouse gases in the atmosphere that prevent blackbody radiation from escaping.

Mars has an atmosphere that might only reach up to your knees and surely all the heat coming off your body would go straight off into space.

The shuttle, though its doesn't seem like its emitting heat or trying to transfer it, doesn't need to be actively trying to transfer or heat itself up to lose a lot of heat.  Everything is giving off heat all the time and there's an equilibrium between heat being absorbed, produced, and given off by all objects; its just that in space, its a lot easier to give it off and harder to absorb it if you're behind the earth.

[One Armed Scissor]

That makes a lot of sense. Thanks guys these forums rock!

[Scratch-]

In some movies you see that as soon as the astronaut takes his helmet off he freezes. While space won’t freeze you instantly, it bursts your veins, arteries, lungs etc. This is caused by the low pressure around you that boils the liquids in your body. Since boiling is a cooling process the liquids also freeze while they boil, hence the surprised expression frozen on the astronaut's face. I wouldn’t want to die that way, lol.

(Note: I’m pretty sure this is true but correct me if I’m wrong)

[Donaldson Tan]

Just wondering.. heat is dependent on the average KE of the particles in the system. A vacuum system would have virtually no particles, hence no KE to speak of. What temperature would it have?

[Mitch]

You can never get a true vacuum, so you can assign a temperature.

[Corvettaholic]

Theoretically speaking, if you had no particles, and no kinetic energy, you would have absolute zero. Introduce a particle, and voila, you got some sort of temperature.

[Mitch]

You can't assign a temperature without a particle, since temperature is defined as the average kinetic energy of an ansemble of particles. In fact most of thermodynamics woun't work for individual atoms, it is a bulk effect. Temperature would be undefined in such a situation.

[Corvettaholic]

Well isn't absolute zero mean the lowest possible temperature, and if nothing is moving (cause there isn't anything), wouldn't it be absolute zero by default?

[Mitch]

things still move The belief that they don't is common Physics dogma.

[Corvettaholic]

I'm saying lets pretend that at atom is perfectly still. no movement. Ignore the liklihood that it will fall to pieces then you'll have movement again, lets say its all perfectly still. Then it would be absolute zero. But in all reality, absolute zero is not possible cause as you say, everything moves.