Coldness of space - Explain please

[Kyanzes]

Why would you freeze in space without protection (forget about the other deadly effects for a sec)? What I don't understand is that there is no matter around you in vacuum to conduct the heat of your body so what makes you freeze? I'm sure it has to be something obvious but it seems I'm not aware of it. First I thoguht that your body heat would simply radiate away but how could it happen so rapidly? I mean in movies ppl/stuff freeze immediately when exposed to vacuum. Then I thought it had to do something with pressure, but, if I know correctly, spacesuits are heated even though they are pressurized. Also, in movies ppl. are always worried when the heating on a space station/spaceship starts to malfunction. Vacuum, at first glance, seems to be a perfect insulator. Help me clear this up pls.

 

[f95toli]

Well, this is just another example of why you should not trust movies. You do NOT freeze "instantly", in fact you would probably survive for quite some time.

But you are right that the primary reason why you would eventually freeze is probably radiation.
Heat transfer can happen in 3 different ways: Convection (transport of particles, e.g. air), conduction (via another material) and radiation.
A good vacuum takes care of the first point (which is why vacuum IS used to insulate, that is how a thermos bottle works) and as long as you do not touch anything the second point is not a problem. That leaves radiation.

However, note that I wrote "probably". Space, especially near earth in orbit, is far from a perfect (or even good) vacuum which means you DO loose a lot of energy via convection (stricly speaking you are probably in the Knudsen limit because of the low pressure, so it is not really convection but never mind).

A "good" vacuum would be something like 10^-6 mBar (1/1 000 000 000 of one atmosphere) which is a typical pressure used to insulate equipment in low temperature physics (which is what I work with). If the pressure ishigher than that you are still lossing much of the energy via convection. AFAIK the pressure in near-orbit is much higher than that.

 

[Special K]

I thought the average temperature of the universe was like 3.7 K or something? Wouldn't you pretty much freeze instantly in those temps?

 

[Mark R]

Originally posted by: Special K
I thought the average temperature of the universe was like 3.7 K or something? Wouldn't you pretty much freeze instantly in those temps?

Not instantly. A typical human shaped object, at body temperature, only radiates about 600 W of heat. In a normal room temperature environment, about 500 W of heat is radiated by the environment and absorbed by the object - a net 100 W loss (apporoximately).

In space, there would be very little heat reabsorbed - so rate of heat loss would be about 600 W. It would certainly feel very cold, but this would not cause immediate freezing - in fact, given the body's ability to generate heat (e.g. by shivering, etc) it would almost be possible to keep up with heat loss and not even develop hypothermia for a short period, at least.

 

[f95toli]

I dip things into liquid helium (4.2K) at a daily basis. If the mass is large it can take quite some time to cool things down from room temperature. Note also that liquid helium as is much more efficent than a near vacuum in transporting heat from a body (being a liquid).

If you dip something with a good insulation vacuum around it in liquid helium (e.g equipment surrounded by a vacuum pumped cylinder) and rely only on radiation cooling it can take hours to cool down even just a few kg of copper down to 4.2K.

 

[silverpig]

Originally posted by: Special K
I thought the average temperature of the universe was like 3.7 K or something? Wouldn't you pretty much freeze instantly in those temps?

2.73 K actually. If you were put in a vat of some new material that was liquid at 2.73 K then yeah, you'd freeze pretty quickly, but there is very little matter in space to take the heat away from you.

 

[Gibsons]

Originally posted by: f95toli
I dip things into liquid helium (4.2K) at a daily basis. If the mass is large it can take quite some time to cool things down from room temperature. Note also that liquid helium as is much more efficent than a near vacuum in transporting heat from a body (being a liquid). .

Dang, I only get to play with liquid nitrogen and dry ice.

I'm a little jealous, but then again, I might've lost a finger by now. (yes, I'll stick my ungloved hand into liquid N2 and throw it on the ground to watch people jump )

 

[Genx87]

Wouldnt you die from the vacuum before the coldness set in?
I would imagine the difference in pressures would cause your lungs to delfate rather quickly?

 

[Gibsons]

Originally posted by: Genx87
Wouldnt you die from the vacuum before the coldness set in?
I would imagine the difference in pressures would cause your lungs to delfate rather quickly?

The change in pressure would be fatal. Your lungs would expand due to the expansion of air within them, air would be forced out through the throat very rapidly. Maybe even through other orifices... Soon after that, dissolved gasses in the bloodstream would start to boil out - basically a case of decompression sickness (aka the bends, what careless scuba divers can get), but very fast and much much worse.

 

[iwantanewcomputer]

Originally posted by: Gibsons

Originally posted by: Genx87
Wouldnt you die from the vacuum before the coldness set in?
I would imagine the difference in pressures would cause your lungs to delfate rather quickly?

The change in pressure would be fatal. Your lungs would expand due to the expansion of air within them, air would be forced out through the throat very rapidly. Maybe even through other orifices... Soon after that, dissolved gasses in the bloodstream would start to boil out - basically a case of decompression sickness (aka the bends, what careless scuba divers can get), but very fast and much much worse.

not just dissolved gasses. basically all the liquids in your body would immediately boil off in a 0 pressure environment...you would explode

and vacuums only transmit heat by radiation emminating from your body. pretty slow for a room temperature human body

 

[Special K]

Originally posted by: Mark R

Originally posted by: Special K
I thought the average temperature of the universe was like 3.7 K or something? Wouldn't you pretty much freeze instantly in those temps?

Not instantly. A typical human shaped object, at body temperature, only radiates about 600 W of heat. In a normal room temperature environment, about 500 W of heat is radiated by the environment and absorbed by the object - a net 100 W loss (apporoximately).

In space, there would be very little heat reabsorbed - so rate of heat loss would be about 600 W. It would certainly feel very cold, but this would not cause immediate freezing - in fact, given the body's ability to generate heat (e.g. by shivering, etc) it would almost be possible to keep up with heat loss and not even develop hypothermia for a short period, at least.

People who die from hypothermia are subjected to much higher temps than 3.7 K though. How long does it take them to die?

 

[MrDudeMan]

Originally posted by: Special K

Originally posted by: Mark R

Originally posted by: Special K
I thought the average temperature of the universe was like 3.7 K or something? Wouldn't you pretty much freeze instantly in those temps?

Not instantly. A typical human shaped object, at body temperature, only radiates about 600 W of heat. In a normal room temperature environment, about 500 W of heat is radiated by the environment and absorbed by the object - a net 100 W loss (apporoximately).

In space, there would be very little heat reabsorbed - so rate of heat loss would be about 600 W. It would certainly feel very cold, but this would not cause immediate freezing - in fact, given the body's ability to generate heat (e.g. by shivering, etc) it would almost be possible to keep up with heat loss and not even develop hypothermia for a short period, at least.

People who die from hypothermia are subjected to much higher temps than 3.7 K though. How long does it take them to die?

the difference is the person who died of hypothermia was exposed to a medium which would permit conduction, effectively pulling heat away from the person much more rapidly than radiation alone. if you didnt die from the lack of pressure in space, you would probably last longer than if you fell in an almost frozen pond in winter. the water would suck every bit of heat from your body in a much shorter amount of time than you would be able to radiate it off into space.

 

[sao123]

Without regard to heat radiation.... would not the pressure laws dictate that (assuming that skin was strong enough to withstand 0 pressure without bursting) due to the drop in pressure create a proportional change in temperature?

PV = nRT

obviously thats the gas law, but i believe similar results happen in liquids and solids...so temperature is a measure of kinetic energy, and pressure is a measure of inter molecular static forces... would not a change in one, require a proportional change in the other, without violating conservation of energy laws?

So a drop in pressure could freeze you instantaniously?

 

[Calin]

This is how I see the issue:
If you have ice a bit under freezing, and subject it to pressure, it will become liquid (i.e. water). However, the temperature and pressure range where this happens is limited, and near the body temperature, the body won't freeze even in zero pressure.
However, if you decrease the pressure, water will evaporate (in order to maintain a pressure of water vapors). The higher the temperature, the higher the water vapors pressure is (the "relative humidity" you hear of is the ratio of existing water vapors compared to the maximum theoretical possible. If you try to get more than the "100%" you will have condensation (on walls, or in volume - see clouds).
The vaporisation of water (in order to keep the partial pressure of vapors) will cool the volume of remaining water, and after enough cooling, water is freezing.
Now, the ice will vaporise too (going from solid to gas has a different name), and the cooling goes on.

If you throw a bucket of water in space, assuming it won't "explode" (transform to droplets), the vaporisation will be quite violent, so the cooling will be quite violent too. This could make it a bucket of ice in a very short period of time, so you would think space is cool.
Space is not cold - if you repeat this with other liquids, your experience will vary. If you put a piece of aluminium, it will stay (if light by sun) at a good temperature - in fact, surfaces hit by sunlight will be warm. Remember the temperature of the Earth - most of it come from sunlight

 

[f95toli]

Originally posted by: sao123
Without regard to heat radiation.... would not the pressure laws dictate that (assuming that skin was strong enough to withstand 0 pressure without bursting) due to the drop in pressure create a proportional change in temperature?

PV = nRT

obviously thats the gas law, but i believe similar results happen in liquids and solids...so temperature is a measure of kinetic energy, and pressure is a measure of inter molecular static forces... would not a change in one, require a proportional change in the other, without violating conservation of energy laws?

So a drop in pressure could freeze you instantaniously?

There are a few problems here. First of all the gas law does not hold at very low pressures (it breaks down when the mean free path of the particles becomes very long) so you have to be carefull about when you use.

The second problem is that there is no such simple law for liquids, as Calin points out a liquid will probably vaporize pretty quickly if you lower the pressure, alternatively will freeze into a solid. It all depends on the phase diagram of that substance.

I used to demonstrate this to my students my pumping on liquid nitrogen (77K). When you start pumping the nitrogen starts to boil and most of it vaporizes but since lowering the pressure also lowers the temperature the nitrogen freezes into ice (which as as far as I remember happens at 64K or so), once this has happened you reach a "stable" condition; the temperature won't drop any further since I can not remove any more energy by pumping (all the particles are frozen).

The point here is that the temperature of a solids is more or less insensitive to the surrounding pressure (unless you change it so much that if affects the crystal structure) since all the particles are "stuck", once the particles are frozen into place it does not matter if the pressure is 10^-3 or 10^-6 mBar.

You can easily verify this by touching a thermos bottle, there is an insulation vacuum inbetween the two walls but that does not mean that the bottle is cold.

 

[icarus4586]

Haven't you read the Hitchhiker's Guide to the Galaxy? You can survive for about 30 seconds in the void of space if you hold your breath. So says the book anyway.

 

[MrDudeMan]

Originally posted by: icarus4586
Haven't you read the Hitchhiker's Guide to the Galaxy? You can survive for about 30 seconds in the void of space if you hold your breath. So says the book anyway.

i think holding your breathe is a terrible idea. i remember reading in a physics book a while back (i have no idea why this was addressed in this book) that the best way to prolong your life, assuming you will be rescued by a nearby (ha!) friend, is to blow out all of your air, cover your eyes with your hands and get in the fetal position (probably just for comfort...lol) and you may have a shot at surviving.

 

[everman]

Originally posted by: MrDudeMan

Originally posted by: icarus4586
Haven't you read the Hitchhiker's Guide to the Galaxy? You can survive for about 30 seconds in the void of space if you hold your breath. So says the book anyway.

i think holding your breathe is a terrible idea. i remember reading in a physics book a while back (i have no idea why this was addressed in this book) that the best way to prolong your life, assuming you will be rescued by a nearby (ha!) friend, is to blow out all of your air, cover your eyes with your hands and get in the fetal position (probably just for comfort...lol) and you may have a shot at surviving.

Don't forget your towel!

 

[spikespiegal]

The vaporisation of water (in order to keep the partial pressure of vapors) will cool the volume of remaining water, and after enough cooling, water is freezing.

Hence the problems with the toilets freezing up in the space shuttle if they don't rotate the craft towards the sun once in awhile.

 

[Capitalizt]

God I love this forum. Thanks to all of you who answer (and ask) these weird questions.

 

[mrd31486]

ok. first of all, the way I see it: space isn't cold. there is just no matter to conduct the energy from the sun (or whatever heat source) true?
therefore average temperature in space would have to be determined by all the chunks of matter floating around in the vacuum.
so wouldn't the vacuum itself not technically have a temperature? I would guess this is what makes it such a good insulator.

 

[Sc4freak]

No, I don't think you understand how heat transfer works. Heat can be transferred in 3 ways - Conduction, Convection and Radiation. Conduction is the moving of heat from substances through direct contact. Convection is movement of heat through moving particles. In a vacuum, these obviously aren't possible, and heat is moved as radiation. Its how we get light and heat from the sun.

In deep space, there is little to no heat because there is no heat source. The only heat you'd be recieving would be from the distant stars, that's why in deep space an object would be close to absolute zero.

Vacuum only makes a good insulator because we're comparing heat transfer via. radiation (which is the only form of heat transfer in a vacuum) against convection and conduction. In an atmosphere, conduction and convection can take away huge amounts of heat. Radiation is not so effective. And since you can only have heat transfer via. radiation in a vacuum, it insulates well compared to conduction and convection.

 

[KF]

The last time I read a thread like this the consensus went more the other way. Since I didn't quite follow the explanation, I should probably shut up. But...

The claim then was that heat sinks in the vacuum of space are much more effective, and rather than having trouble getting rid of heat, spacecraft have trouble holding it. Basically, although heat transfer by conduction and convection are nil, radiation into nothing is far more effective than radiation into air. I would have thought that air was nearly as tranparent to radiation as a vaccuum and there would be little difference in transfer by radiation. However, air is warm and therefore radiates into a heatsink too, which does not happen with a vacuum. So the temperature of the air also matters for radiation as well as conduction.

A thermos bottle has a mirror coating to reflect radiation, so you can't conclude much from the comparison.

That 2.73 Kelvin is the what the temperature of the blackbody radiation of the big bang fireball has been red-shifted to by the expansion of space itself since matter condensed out and allowed radiation to pass through. Whatever molecules might be in the vacinity of stars or planets could be a different temperature.

I recall the early days before any astronaut had been put in space. There were pictures in such as LIFE magazine showing volunteers that had been put through "explosive decompression" at the very instant the pressure dropped. There was no suggestion it would be deadly. They looked weird and bloated, but they didn't explode and die.

 

[sao123]

Originally posted by: KF
The last time I read a thread like this the consensus went more the other way. Since I didn't quite follow the explanation, I should probably shut up. But...

The claim then was that heat sinks in the vacuum of space are much more effective, and rather than having trouble getting rid of heat, spacecraft have trouble holding it. Basically, although heat transfer by conduction and convection are nil, radiation into nothing is far more effective than radiation into air. I would have thought that air was nearly as tranparent to radiation as a vaccuum and there would be little difference in transfer by radiation. However, air is warm and therefore radiates into a heatsink too, which does not happen with a vacuum. So the temperature of the air also matters for radiation as well as conduction.

A thermos bottle has a mirror coating to reflect radiation, so you can't conclude much from the comparison.

That 2.73 Kelvin is the what the temperature of the blackbody radiation of the big bang fireball has been red-shifted to by the expansion of space itself since matter condensed out and allowed radiation to pass through. Whatever molecules might be in the vacinity of stars or planets could be a different temperature.

I recall the early days before any astronaut had been put in space. There were pictures in such as LIFE magazine showing volunteers that had been put through "explosive decompression" at the very instant the pressure dropped. There was no suggestion it would be deadly. They looked weird and bloated, but they didn't explode and die.

Let me give you a familiar explanation to prove you wrong from the start...

how do you cool down a computer better?
A plain Heatsync. (pure radiation)

or

A Heatsync with attached fan. (radiation + convection)


Now which would cool better in a complete vacuum?
Neither... they would both cool at the same rate... (radiation only, since convection cannot happen without a medium)


Air has nothing to do with radiative cooling, using air requires convective cooling.

 

[BladeVenom]

Convection works in space since it isn't a complete vacuum. It's about 1 atom per cubic centimeter.