Why "space" is not cold (this week question?)

[Aepervius]

I might be wrong (or maybe not) but space isn't cold because temperature is an (indirect) measurement of the speed of the molecule in a gas. The higher the temperature the wider the speed distribution (boltzman ?). Since in true space there would not be many/any molecule per cubic meter and thus no "temperature" per see as people define it or measure it. Although i might be wrong at that...

Now on the other hand direct exposure to the whole radiation spectrum can in empty space rise temperature of a "body" very high. Thus for exactly the same pressure of air, a body at a certain point in space (near a solar system) would experience wildy different in the dark side or bright side. And so space might indeed hot. Fiery Hot melting death hot.

Feel free to correct me I would glady check whether my memory is fooling me on the above or not.

[MRC_Hans]

In space, heat is conveyed only by radiation. A body suddenly placed in space will radiate away heat till it's outgoing radiation equals the ingoing. In deep space, this happens around 2K, which is pretty damn cold :eek:.

Of course, if you are near to a star, e.g. the Sun, that equilibrium is elsewhere, in fact, if you are close to the Sun, it might be pretty damn hot. If course, if the body in question is not a good heat conductor, it might be PD cold on one side and PD hot on the other, as you say.

The short story is that the temperature of space is defined by the level of radiation, and this puts the temperature of interstellar space at around 2K.

Hans

[geni]

From what I have read the particles that are in interstella space are at thousands of degrees kelvin. The reason is that they only lose energy through collisions and since spce is basic empty there are very few collisions. This means that is they start off at high energies they are going to take a long time to lose this energy

[BillyJoe]

From this week's commentary....

The real kicker, I have found, is trying to convince people that space itself isn't actually cold. The writer is saying that "space itself" isn't actually cold.

Is he saying "space itself" as opposed to

- the (widely spaced) molecules within space
- the radiation travelling through space

But this sort of space still feels cold doesn't it? (because, as Hans said, we radiate our heat into space). So, does he mean that although "space" feels cold, "space itself" is not cold.

If so, isn't what he says sort of meaningless?

BillyJoe

[geni]

Well technicaly there is no such thing as cold.

[Skeptical Greg]

Originally posted by geni
Well technicaly there is no such thing as cold.

You beat me to it... I was going to point out that ' cold ' is actually the absence of heat...


Ever since I came to realize this, I have been irritated by statements like " Close the reefer, you are letting the cold out ", or people refering to ' a blast of cold air '...

[Hamish]

Originally posted by MRC_Hans
In space, heat is conveyed only by radiation.

I'm going to be pedantic and say that evaporative cooling works extremely quickly in vacuum.

[bjornart]

Originally posted by BillyJoe
But this sort of space still feels cold doesn't it? (because, as Hans said, we radiate our heat into space). So, does he mean that although "space" feels cold, "space itself" is not cold.


Actually space, or vacuum, doesn't feel cold. The only heat you lose will be through radiation, unlike in an atmosphere where you'll lose heat warming up the surrounding air as well.

Except if you're wet, then you'll have to deal with evaporation as someone pointed out.

[BillyJoe]

Originally posted by bjornart
Actually space, or vacuum, doesn't feel cold. The only heat you lose will be through radiation, unlike in an atmosphere where you'll lose heat warming up the surrounding air as well. But if you lose heat (through whatever mechanism) you will feel cold won't you?

So, if you walk out into the night air, you will lose heat and start to feel cold and you will say "It's cold out here". And, unless you are a pedant like geni and Diogenes, you will have made a correct statement. So why is this also not correct in relation to space. You walk out into space, you lose heat, you feel cold and you say "It's friggin' cold out here"

What's good for the goose is good for the gander

BillyJoe
(Or am I missing something?)

[bjornart]

Originally posted by BillyJoe
But if you lose heat (through whatever mechanism) you will feel cold won't you?

So, if you walk out into the night air, you will lose heat and start to feel cold and you will say "It's cold out here". And, unless you are a pedant like geni and Diogenes, you will have made a correct statement. So why is this also not correct in relation to space. You walk out into space, you lose heat, you feel cold and you say "It's friggin' cold out here"

What's good for the goose is good for the gander

BillyJoe
(Or am I missing something?)

Sure. But if you walk out into a nice summer day you will also be loosing heat (as long as the temperature is below that of the body), but you wont feel cold. And heat loss through radiation is magnitudes smaller than heat loss through contact, which is why a thermos works. Heat can only escape (or enter) the thermos through radiation across the vacuum, or ... whatever it's called ... conduction? ... through the bits where the outer and inner bottle touches. When you're in outer space you are in fact in a frigging huge thermos.

Does that make it any clearer? ;)

[BillyJoe]

Originally posted by bjornart
Does that make it any clearer? ;) Are you saying I am going to get cold very slowly in space because the only way to lose heat in space is by radiation and this process is very slow?

In other words, it'll be a very long time before I'll be saying "It's friggin' cold out here".

[bjornart]

Originally posted by BillyJoe
Are you saying I am going to get cold very slowly in space because the only way to lose heat in space is by radiation and this process is very slow?

In other words, it'll be a very long time before I'll be saying "It's friggin' cold out here".

Yup.

[Interesting Ian]

Originally posted by BillyJoe
From this week's commentary....

The writer is saying that "space itself" isn't actually cold.

Is he saying "space itself" as opposed to

- the (widely spaced) molecules within space
- the radiation travelling through space

But this sort of space still feels cold doesn't it? (because, as Hans said, we radiate our heat into space). So, does he mean that although "space" feels cold, "space itself" is not cold.

If so, isn't what he says sort of meaningless?

BillyJoe

No no, not at all! There are 2 types of temperature. Scientific temperature, and felt temperature. Just like there is "colour" as measured ie a certain length of electromagnetic radiation, and colour as experienced ie a particular qualia.

Now for a given scientific temperature eg 10C it might feel cold for one person on a particular occasion, but feel warm for another person, or even feel warm for the same person on a different occasion. Lots of things can affect felt temperature eg wind chill factor etc.

[Interesting Ian]

Originally posted by Diogenes


You beat me to it... I was going to point out that ' cold ' is actually the absence of heat...


Ever since I came to realize this, I have been irritated by statements like " Close the reefer, you are letting the cold out ", or people refering to ' a blast of cold air '...

:rolleyes: You become irritated because other people haven't been "brainwashed" by the scientific story? ;)

[MRC_Hans]

Bill: You would loose heat from radiation rather quickly. And your sensation of cold is very much a feeling of radiation, even before you were actually being cooled off, you would sense the immense cold of the universe.

If you were actually in space unprotected, you would also be cooled by a violent evaporation of skin moisture, but in that situation, I suspect feeling cold would be rather one of your lesser worries ;).

Hans

[BillyJoe]

Okay, there are three ways to lose heat

- Convection
- Evaporation
- Radiation

Convection doesn't apply because there are no molecules out there. Radiation certainly does and, according to Hans, this happens rather quickly (but bjornart diasgrees). And evaporation is rather violent. Therefore space is going to feel cold pretty damn quickly.

So, what does the author mean when he said that "space itself isn't actually cold"?
Is this what Ian refers to as "scientific temperature"? (or is he just trying to work his "qualia" in here :cool: )

BillyJoe
(I'm assuming here, of course, that "cold" means "cold relative to us humans")

[MRC_Hans]

Since space is (reasonably) devoid of matter, you could farly well claim that it does not have a temperature itself, and is thus not cold. An object left in space, OTOH, will soon become very cold.

Whether heat loss from radiation is slow or fast, is a matter of definition, but when exposed to cold, that is, lack of heat radiation, the feeling of cold is almost instant. Try to stick your hand into a freezer; within seconds you sense that it is a cold place.

Hans

[Skeptical Greg]

Originally posted by BillyJoe

So, what does the author mean when he said that "space itself isn't actually cold"?
Is this what Ian refers to as "scientific temperature"? (or is he just trying to work his "qualia" in here :cool: )

BillyJoe
(I'm assuming here, of course, that "cold" means "cold relative to us humans")

I believe the pedants, such as myself, are being catered to..


I notice no one has brought up that ol' scientific instrument the ' thermometer ' yet....


What would it read, if you hung it outside the shady side of your space ship? ( not touching anything, of course )

Got a feeling the reading will translate as ' cold ' .....

[Skeptical Greg]

A google turned up this...

Is Space Hot or Cold? (http://spider.ipac.caltech.edu/staff/waw/mad/mad5.html)

It really explains it pretty well, and answers may question above, about the thermometer...

[bjornart]

So how fast would heat loss through radiation be? Anyone got the formulae at hand?

[Interesting Ian]

Originally posted by BillyJoe
Okay, there are three ways to lose heat

- Convection
- Evaporation
- Radiation

Convection doesn't apply because there are no molecules out there. Radiation certainly does and, according to Hans, this happens rather quickly (but bjornart diasgrees). And evaporation is rather violent. Therefore space is going to feel cold pretty damn quickly.

So, what does the author mean when he said that "space itself isn't actually cold"?
Is this what Ian refers to as "scientific temperature"? (or is he just trying to work his "qualia" in here :cool: )

BillyJoe
(I'm assuming here, of course, that "cold" means "cold relative to us humans")

No, it will mean what they would call the "real temperature" (measured or scientific temperature). Anyway, it's very easy to determine the temperature of deep space. Just place a thermometer there.

[Interesting Ian]

Originally posted by Diogenes


I believe the pedants, such as myself, are being catered to..


I notice no one has brought up that ol' scientific instrument the ' thermometer ' yet....


What would it read, if you hung it outside the shady side of your space ship? ( not touching anything, of course )

Got a feeling the reading will translate as ' cold ' .....

Oh well, someone mentioned a thermometer already LOL

[bjornart]

Seeing as a rough calculation, based on science I'll have to keep secret for reasons of national security, indicates that a naked human in space will radiate energy at a rate three times higher than the produced by the body (340W compared to 100W) you will indeed feel cold when exposed to vacuum. Someone else will have to do the calculations to see how fast you get hypothermia though.

And a good jacket will help a lot.

[BillyJoe]

A SUMMARY?


The original question.....

"Why is space itself not actually cold"

Answer 1: SPACE HAS NO TEMPERATURE
Space is devoid of matter and therefore does not have a temperature. (courtesy Hans)

Answer 2: PRETTY DAMN COLD (2.73K)
The temperature of space is defined by the level of radiation, and this puts the temperature of interstellar space at around 2K. (courtesy Hans)
Presumably an approprately calibrated and sensitive thermometer would register this temperature (?)

------------------------------------------------------------------------------------

the secondary question.......

"Does space feel cold"

Answer: IT FEELS PRETTY DAMN COLD
An exposed body would lose heat relatively rapidly due to radiation and extremely rapidly due to evaporation (and not at all due to conduction/convection)


BillyJoe

edit: Diogenes link (http://spider.ipac.caltech.edu/staff/waw/mad/mad5.html) explains it pretty well

[Brian the Snail]

Originally posted by bjornart
Seeing as a rough calculation, based on science I'll have to keep secret for reasons of national security, indicates that a naked human in space will radiate energy at a rate three times higher than the produced by the body (340W compared to 100W) you will indeed feel cold when exposed to vacuum. Someone else will have to do the calculations to see how fast you get hypothermia though.


Although I realise that it's national security, could you tell me where you get 340W from, please? I'm using as an estimate the Stefan-Boltzmann law for a blackbody, assuming a temperature of 310 K and a surface area of the human body of 2m^2. If I plug in the number I get a radiation loss rate of 1000W. Though, of course, if you have to kill me after telling me, then I'd rather not know...

As for how quickly the body will cool, you can get an upper bound by taking the value above and assuming no sources of heating (internal or external). If you then approximate the specifc heat capacity of the body as that of water (c=4200 J kg^-1 K^-1), then for a 80 kg body it takes 336000 J to cool it down by a degree celsius, or about 5 minutes using the value for the heat loss above. Though this is just for radiation- it says nothing about evaporative cooling, which could well be much faster.

[Jeff Corey]

You are neglecting the fact that a human body exposed to a vacuum will rapidly explode into little bits and become all messy, making the determination of the temperature very, very messy.
And it's hard to find volunteers for this kind of research and your institution's IRB would surely object.

[epepke]

Originally posted by Diogenes
What would it read, if you hung it outside the shady side of your space ship? ( not touching anything, of course )

Well, if it's a mercury thermometer, and it's in the sunlight, it would probably pop its wad pretty quickly.

The trick for getting a spaceship cool near the Earth is the right color of paint. Bare aluminum, like an Airfoil trailer, you could probably roast a turkey in. Nice white paint, and it's pretty comfy.

Which makes me wonder about Soyuz green...

[Hamish]

To kill all argument, let's use a decent thermocouple thermometer, of which the measuring junction only is outside your spacecraft. To be fair, lets put this junction inside a chunk of something - lets encase it in a small ball of metal (iron say) which should have a somewhat greater heat capacity and give us a fairer reading. Now let's assume we reomve all moisture from the iron ball and paint it uniformly in the colour of your choice.

What will the reading be taken in:

a) Earth orbit, day side (our thermometer is exposed to sunlight)?
b) Earth orbit, night side (sun on the other side of the earth)?
c) Deep space?

[BillyJoe]

Would (b) = (c) = 2.73k ?

[bjornart]

Originally posted by Jeff Corey
You are neglecting the fact that a human body exposed to a vacuum will rapidly explode into little bits and become all messy, making the determination of the temperature very, very messy.
And it's hard to find volunteers for this kind of research and your institution's IRB would surely object.

No it wouldn't. Bad, evil, naughty you for perpetuating such myths. :D The straight dope on: If you were thrown into the vacuum of space with no space suit, would you explode? (http://www.straightdope.com/classics/a3_147.html)

[Jeff Corey]

Sorry, but I refuse to believe any research based on chimps and monkeys. The good lard gave them only 96 to 98 percent of our DNA and a rib or two, with BBQ sauce.
And why do they call it "explosive decompression"?
What explodes?
Or do you just become extremely flatulent and go zooming around like a released toy baloon?

[bjornart]

Originally posted by Jeff Corey
Sorry, but I refuse to believe any research based on chimps and monkeys. The good lard gave them only 96 to 98 percent of our DNA and a rib or two, with BBQ sauce.
And why do they call it "explosive decompression"?
What explodes?
Or do you just become extremely flatulent and go zooming around like a released toy baloon?

You dare to mock me! Explosive decompression is just the antonym (or would be the antonym if it were one word instead of two) of slow leak.
If you keep your mouth open, your eyes shut, your skin thick and don't hold your farts you'll survive in space until you die of asphyxia. Or so I believe the laws of physics indicate. They should toss some mice out of the ISS to test the hypothesis. :D

[Skeptical Greg]

Originally posted by bjornart


They should toss some mice out of the ISS to test the hypothesis. :D

Hmm.. I wonder if they have...

Surely they would keep such an experiment under wraps...

[Hamish]

Originally posted by BillyJoe
Would (b) = (c) = 2.73k ?

I reckon (c) would be but (b) would be a little higher since the earth does radiate somewhat.

Now, for (a), a quick back-of-the-envelope calculation tells me that I'd expect a black body, perfectly conductive sphere to achieve an equilibrium temperature of about 277K if in direct sunlight in Earth orbit. That's about 4 degrees centigrade. I'd call that cold in human terms. Of course most things aren't black body and have less than perfect thermal conductance so in reality we'd expect one side to be hot and the other to be cold.

So, is space cold? Define cold. Define what you mean by temperature in the context of the question (radiation temperature, mean energy of gas molecules, ability to transfer heat etc) . Define what you mean by space (deep space, Earth orbit day/night, next to a star etc).

[BillyJoe]

Originally posted by bjornart
They should toss some mice out of the ISS to test the hypothesis. :D I say we sacrifice the cats....

Darat
edthedoc
richardm
Rolfe
sparklecat
Wyvern
wayrad
Ravenwood
BillyTK
WildCat
Keziah Meson

and Ceptimus (but , hurry, he ias changing back soon)


Your little mouse,
BillyJoe

[BillyJoe]

Originally posted by Hamish
So, is space cold? Define cold. Define what you mean by temperature in the context of the question (radiation temperature, mean energy of gas molecules, ability to transfer heat etc) . Define what you mean by space (deep space, Earth orbit day/night, next to a star etc).

So the person who said the following......

The real kicker, I have found, is trying to convince people that space itself isn't actually cold......is blowing off

With the right definition, space IS cold

But he says "space itself", so I think he is talking about space devoid of matter and radiation which, I think, doesn't actually exist does it? (there is the odd molecule in space and at least the cosmic background radiation). He's defining something that doesn't exist so that he can get a kick out of other people's "ignorance"?

BillyJoe

[Skeptical Greg]

Originally posted by BillyJoe


He's defining something that doesn't exist so that he can get a kick out of other people's "ignorance"?


BillyJoe

That's the way I see it.. I feel the same about the ' moon ' question..

However, both questions kicked up a lot of interesting discussion, and I definitely learned something....

[Wyvern]

Originally posted by BillyJoe
I say we sacrifice the cats....

Darat
edthedoc
richardm
Rolfe
sparklecat
Wyvern
wayrad
Ravenwood
BillyTK
WildCat
Keziah Meson

and Ceptimus (but , hurry, he ias changing back soon)


Your little mouse,
BillyJoe
I heard that. Better be more careful, little mousie . . .

[BillyJoe]

Hmmm....I'd better wear a disguise -> :cool: