Does temperature have meaning where there is no matter?

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strawman

strawman

So the recent woot shirt got me thinking about temperature in space. The shirt claims the temperature is 0 kelvin (absoulute 0) but I'm thinking that there's more to it than that.

In deep space, there's about one atom per cubic meter. In our galaxy it's significantly more dense with about one atom per cubic centimeter.

If you measure the temperature of that one atom, is it very, very high, or close to zero?

If you only measure half the cubic meter, and find no atoms within, does temperature even have any meaning or use?

Aside from atoms, are there other things in deep space "filling up" that cubic meter? Do those things have meaningful temperature?

Vacuum is a very good insulator - if a human was ejected into deep space, the only way to cool them down to the "ambient" temperature of deepspace (again, claimed to be 0 kelvin) is via black body radiation. How long would it take to bring that much mass down to near 0 kelvin (I know, there's a long tail, but zero kelvin-ish would be fine)?

Maybe I should send this to xkcd's what-if email...
 
Covar

Covar

If a tree falls in a forest and there's no one around to witness it, it still makes a sound. Science Bitches!
 
MindDetective

MindDetective

I would argue that even with a single atom present, the meaning is at best academic. The meaning of temperature is usually relative to something, such as what you are going to wear today, the meal you are preparing, and whether your car is going to function properly. The temperature of the Earth two miles below the surface doesn't have much meaning...until we can use that information (to predict...?) In the absence of that value, it is a curiosity; academic only.

stienman said:
Maybe I should send this to xkcd's what-if email...
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Definitely.[DOUBLEPOST=1373302026][/DOUBLEPOST]
Covar said:
If a tree falls in a forest and there's no one around to witness it, it still makes a sound. Science Bitches!
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That's the first thing I thought of too.
 
Chad Sexington

Chad Sexington

Covar said:
If a tree falls in a forest and there's no one around to witness it, it still makes a sound. Science Bitches!
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Well, doesn't that depend on your idea of sound? I mean, sure pressure waves moving through the air will occur, but is it sound if it isn't heard? Is hearing a necessary condition for sound?
 
MindDetective

MindDetective

Chad Sexington said:
Well, doesn't that depend on your idea of sound? I mean, sure pressure waves moving through the air will occur, but is it sound if it isn't heard? Is hearing a necessary condition for sound?
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This is exactly right. To put it in terms of vision, "redness" is interpreted by the brain and is not inherent in the light itself. An entirely different brain could perceive the same apple as you in a completely different hue, even though the wavelengths are the same when striking both of your eyes.

Sound translates in a little more of an analog manner in the brain (short compressions = high pitch, energetic compressions = loud sounds) but the "soundness" of the sound doesn't exist outside of the perceiving brain.
 
bhamv3

bhamv3

If I recall correctly, temperature is a measure of how fast molecules or atoms are moving. Without these particles, temperature becomes a meaningless concept, because there's nothing to measure. Sort of like how I can have a piece of red paper on a table. If I take the paper away, so now there is no paper on the table, and then ask "What color is the paper on the table?" It's now a meaningless question.
 
tegid

tegid

MindDetective said:
I would argue that even with a single atom present, the meaning is at best academic. The meaning of temperature is usually relative to something, such as what you are going to wear today, the meal you are preparing, and whether your car is going to function properly. The temperature of the Earth two miles below the surface doesn't have much meaning...until we can use that information (to predict...?) In the absence of that value, it is a curiosity; academic only.
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Well, temperature is definitely an absolute physical quantity, and it is useful to calculate all sorts of things that may or may not have bearing on everyday life (the dynamics inside of the Sun, movement of air currents in the atmosphere used for meteorology, etc). What I mean is that temperature has an interest beyond the purely academic.

The meaning of temperature in such an extreme case, on the other hand, may not. Classical temperature is not a well defined quantity at low densities, but it is useful to have some sort of quantity that is analog to it. That's why a temperature can be defined for a single atom or even for vacuum (it is related to energy density and therefore to the radiation in that vacuum , I think), but they are definitely different 'temperatures' than usual.
 
strawman

strawman

What I really need to know is if my ice cream will freeze faster in deep space (assuming I can contain it) than in my chest freezer.

And if so, I'll need someone that can build me a transporter that's capable of sending my ice cream to deep space and bringing it back when required.
 
figmentPez

figmentPez

Staff member
stienman said:
What I really need to know is if my ice cream will freeze faster in deep space (assuming I can contain it) than in my chest freezer.
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It'll freeze much much slower, unless you rig up some sort of evaporative cooling system, I would think. In near vacuum there would be little conduction or convection of heat, leaving only radiant loss.

If you really want quick ice cream, go liquid nitrogen.
 
PatrThom

PatrThom

stienman said:
I'll need someone that can build me a transporter that's capable of sending my ice cream to deep space and bringing it back when required.
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I'm with bhamv3 on this one. Temperature has no meaning if there's nothing to measure. Spend your time instead contemplating concepts such as negative speed.
Instantaneously teleporting your ice cream deep into the hard vacuum of space would probably result in the sublimation of said ice cream due to the total and complete vacuum present at the location. Said rapid sublimation would likely instantly foam the ice cream apart into a rapidly expanding cloud, and retrieving your ice cream at that point becomes exponentially more difficult the longer you wait to try and teleport it back.

--Patrick
 
tegid

tegid

MindDetective said:
What are you proposing is the middle ground between useful and academic?
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Well, the example of the Sun could lead (doesn't yet, I think) to predictions on when a strong solar eruption is going to happen, which would be super useful. I guess everything academic is so until it's capable of being practical, and then it may become incredibly so. The middle ground is hard to find.
 
drawn_inward

drawn_inward

I suppose dark matter could have potential effects on temperature, but do we have the ability to measure such small changes? Can we measure the temperature changes due to quarks vibrating? Probably not.

Temperature is fairly relative. We think that 95°F is hot around here, but that's chilly near the sun.

If you want cold ice cream, use liquid nitrogen as suggested. Or, dry ice is much cheaper. You could potentially use dry ice in an ethanol bath, and put this ice cream mix in a sealed cylinder and spin it in the super cold ethanol bath until frozen. That could work or just go buy a Cuisinart Ice Cream maker.
 
Eriol

Eriol

figmentPez said:
It'll freeze much much slower, unless you rig up some sort of evaporative cooling system, I would think. In near vacuum there would be little conduction or convection of heat, leaving only radiant loss.

If you really want quick ice cream, go liquid nitrogen.
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nom nom nom
 
mikerc

mikerc

stienman said:
I JUST WANT COLD ICE CREAM. IS THAT SO MUCH TO ASK?
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Well don't go to space then, it's a positively boiling 2.7 degrees Kelvin. In comparison the Low Temperature Laboratory at the Helsinki University of Technology can cool your ice cream to a mere 0.0000000001K.
 
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