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  1. #1 vacuum 
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    what's the temperature inside a perfect vacuum? i'm guessing maybe it doesn't have one, that's why i'm asking...


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    I think its -273C. Or what ever the absolute zero temperature is.


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  4. #3  
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    It is not something you can measure....

    Heat is merely atoms jostling about, if there are no atoms then there can be no temperature. Any attempt to measure the temp of a vacuum requires a probe made of atoms so it will only record it's own temperature - I think.
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    Quote Originally Posted by Megabrain
    It is not something you can measure....

    Heat is merely atoms jostling about, if there are no atoms then there can be no temperature. Any attempt to measure the temp of a vacuum requires a probe made of atoms so it will only record it's own temperature - I think.
    yeah, that's what i was thinking. but if something were (theoretically) instantly teleported into the perfect vacuum, what would happen to its temperature? Would it be preserved? Because heat flows from high temp to lower temp, but if there's no temperature, what happens...? there's nothing to transfer any heat to...
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    Exactly, nothing happens. There is nowhere for energy to go so the object remains at its inherent temperature
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    It's heat would simply radiate away until the rate at which it lost heat was the same as the rate at which it gained heat (like from a star etc) - thermal equilibrium.
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    zero degree kelvin, absolute zero is defined by the absence of any heat energy. since this can only happen in a vacuum, i would think the temperature is then 0k in such a place. likewise in the reducing of a temperature, not a vacuum, all motion or activity of matter ceases, no energy produced and 0k or below temperature achieved.

    space itself is said to be 3k for x-ray energy emissions from distance space which is part of BBT. its said no matter where in space you are, this energy will generate this degree of heat. this same heat or reflective value is leading to exotic definitions of dark matter.

    way i read it...
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  9. #8  
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    Sorry jackson, as I understand it space has no temperature since it has no matter. Only matter can attain a temperature.
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    Quote Originally Posted by Megabrain
    Sorry jackson, as I understand it space has no temperature since it has no matter. Only matter can attain a temperature.
    and the warmest known anything is said to be 3k or the given temperature for space. since this is called heating from energy, i assume some one else thinks space itself is 0k. lots of things are unknown but given a value by language, if for no other reason than a comparative value. even that 3k of little bitty particles could never be known as the approach of anything would raise its temperature.
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  11. #10  
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    I don't mean to nitpick, Megabrain, but this is actually an important point:

    Any attempt to measure the temp of a vacuum requires a probe made of atoms so it will only record it's own temperature - I think.
    Doesn't every thermometer measure its own temperature? Measurement of temperature relies on the 0-th law of thermodynamics.
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  12. #11  
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    Quote Originally Posted by M
    I don't mean to nitpick, Megabrain, but this is actually an important point:

    Any attempt to measure the temp of a vacuum requires a probe made of atoms so it will only record it's own temperature - I think.
    Doesn't every thermometer measure its own temperature? Measurement of temperature relies on the 0-th law of thermodynamics.
    yeah, i actually thought of that, but didn't comment on it. Because the temp of the thermometer, to be accurate, must be allowed to reach the temperature of its surroundings before you read it. if you have a thermometer in the freezer and move it outside where it's 80 degrees, it won't change instantly. it has to reach that 80 degree temperature.
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    Right, but i think what megabrain was implying is that the thermometer would have it's own temp when it was insert and since there isn't anyway for it to transfer its heat, it would continue to read that temp.
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  14. #13  
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    Right, but i think what megabrain was implying is that the thermometer would have it's own temp when it was insert and since there isn't anyway for it to transfer its heat, it would continue to read that temp.
    No, it wouldn't. There is a way for the thermometer to lose whatever initial temperature it may have: through radiation. If there is no radiation coming in from outside through the vaccuum (or if the vacuum is infinite), it seems to me that the thermometer will ultimately lose all it's thermal energy.

    Obviously, this is a thought experiment, and not one that will ever be achieved in a lab, but even so... finish your thought.
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    THat's very good M but in practice your thermometer in it's vacuum must be contained by something, what ever temperature that container is, it will radiate to the thermometer and thus it will not be the temp of the vacuum that is measured. I am convinced 'space' does not intrinsically have a temperature, since it contains no matter, temerature is a property of matter indeed it is defined as atomic motion.
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    Sure, sure,... I agree that definition of temperature as the random kinetic energy of atoms breaks down for a vacuum, and we could end the discussion right there. But step away from the definition for one second. Would not any material object sourrounded by infinite vacuum eventually radiate out all it's internal energy? The fact that the energy (and temperature) of objects typically is bounded and varies smoothly, is because they tend toward a thermodynamic equilibrium with their surroundings. That doesn't work in a vacuum. Putting an object of some initial energy into a vacuum, it might simply maintain all it's energy. That's one possibility that was suggested. I just don't think it's the right one, because it completely disregards radiation, i.e. the form of energy transfer that does not require material contact. If all energy is radiated away from our object, this object would then have absolute zero temperature. You might then infer that in this equilibrium state the surrounding has the same temperature, namely zero Kelvin. And in some way this actually makes sense to me, even considering the definition of temperature: If temperature is defined by the sum of kinetic energies of all atoms, then 0 atoms amount to an energy of 0 Nm and a temperature of 0 K. It's not a singular problem, but seems rather like a very natural limit to me.
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    In other words... in the process of writing my latest post I changed my mind: I do not agree that the definition of temperature breaks down for a vacuum. It simply approaches it's absolute minimum, in a trivial way.
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    Well I don't have a car, cars have 4 wheels, how many does the the car that I do not own have?

    So from my point of view space has no temperature. It's like asking how many legs does an orange have, when legs are not a property of real oranges.
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    How many legs does an orange have? Zero. Perfectly valid question and answer.
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  20. #19  
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    rite what ur question was what is the tempreture of a vacuum. a vacuum is a space in which there is nothing no atoms jst empty space. tempreture is the average kinetic energy of a sample of atoms. if a vacuum has no atoms therefore it can have no tempreture as there is nothing to measure it is not 0K as that suggests there is a body of matter which is completely devoid of kinetic energy which there is not. that is what megabrain is trying to say there is nothing to be measured therefore you cannot assign it ANY position on any tempreture scale. It is like asking what is the colour of sound.
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    Well that's two uf us that know that space has no temperature, and before you ask it has no colour and no mass either...
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    Quote Originally Posted by Megabrain
    Well I don't have a car, cars have 4 wheels, how many does the the car that I do not own have?

    So from my point of view space has no temperature. It's like asking how many legs does an orange have, when legs are not a property of real oranges.
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    Quote Originally Posted by Megabrain
    Well that's two uf us that know that space has no temperature, and before you ask it has no colour and no mass either...
    I thought that the temp of space was something in the region of 2.4Kelvin. ?

    I could be wrong ?
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  23. #22  
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    Leo,

    Temperature is a property of matter, space has no matter and therefore cannot have a temperature... - think about it..
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  24. #23  
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    Quote Originally Posted by leohopkins
    I thought that the temp of space was something in the region of 2.4Kelvin. ?

    I could be wrong ?
    Perhaps that's the temperature of outer space, but the "space" we're talking about here is "space" as in empty space.
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  25. #24  
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    Quote Originally Posted by Megabrain
    Well that's two uf us that know that space has no temperature, and before you ask it has no colour and no mass either...
    you can make that three. i have to side with you. sorry M. that's really what i figured from the beginning, it just gives me more confidence in my answer to hear someone else say it.
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    I say a vacuum is 0K, here's why: Absolute zero is not a temperature because, according to definition, temperature requires energy, and at 0k all atomic energy through movement ceases thus matter ceases to exist (matter requires energy), creating...a vacuum! Of course, matter has never been lowered to 0K because bc there is also a theory stating energy cannot be destroyed (making 0K completely theoretical and unattainable). However, a naturally occurring vacuum such a the vast of outer space may be described as 0k bc of the lack of thermodynamic activity (or anything else for that matter, no pun intended).
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    yes requires energy but kinetic energy it is not a measure of anything else at 0K matter would not cease to exist it would simply stop moving its energy would not dissapear just because it is not moving the strong nuclear forces holding the nuclide together would remain and so matter would remain and so a sample of 0K matter does have matter in it and is NOT a vacuum therefore a vacuum is NOT Ok as there is no matter in it to measure.
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    Yes I know temperature solely measures atomic kinetic energy (thermodynamic) but there is a basic scientific law stating "energy can neither be created or destroyed". lowering matter to kelvin would go against that law which is why it is purely hypothetical. Also, matter and energy are inseparably tied. Theory states (I got this from a text book) if an object has no energy it cannot exist (think about that). Anyway, since a vacuum has no thermonuclear energy and Kelvin measures just that it seems logical it would be 0k. No energy...No anything! (stationary atoms don't denote 0k bc they cease existence at that point).
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    lowering matter to 0K would not go angainst this law it is just a matter of moving the energy elsewhere the same as in any refridgertion process. I have thought about that and a completely stationary object has energy known as its stationary mass i.e the equivalent amount of energy which is tied up in its mass ny taking all the thermodynamic energy from a substance still remain both the nuclear energy and the enegy contained in the very mass itself therefore it would still exist even if it had no thermodynamic energy present. kelvin measures the kinetic energy of a sample of mass therefore it cannot measure to any degree a sample of as you say "no anything" Besides there is no proof either way of what happens when an atom loses all its kinetic energy but i see no reason why it would then lose its nuclear and mass energies just as it is no longer moving
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    An atom's mass is tied to it's energy but is also dependent upon it as far as I understand. You say stationary mass still retains energy at his point but it seems non-sequitur to me as if this were true there would be no problem with lowering matter to 0k but all attempts thus far are asymptotic. What keeps us from attaining absolute 0, I assumed it existed only as a theory bc it broke the laws of physics.
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    As far as i know 0K is theoretically possable while retaining mass and the only reason it has not been proved is that the forcewhich causes energy to istribute evenly i.e heat energy moves to colder areas (cant remember its proper name) is so string that there is not technology capable of insulating it from heat. The lowest tempreture achieved was aroung 3K (thats pretty close) and was only achieved under a vacuum which would stop the heat getting to it through convection and conduction but the only problem is heat travelling as e.m waves which are impossable to stop them all. I doubt it would be able to be achieved but for technological problems rather than what you suggest
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  33. #32  
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    Quote Originally Posted by Red
    As far as i know 0K is theoretically possable while retaining mass and the only reason it has not been proved is that the forcewhich causes energy to istribute evenly i.e heat energy moves to colder areas (cant remember its proper name) is so string that there is not technology capable of insulating it from heat. The lowest tempreture achieved was aroung 3K (thats pretty close) and was only achieved under a vacuum which would stop the heat getting to it through convection and conduction but the only problem is heat travelling as e.m waves which are impossable to stop them all. I doubt it would be able to be achieved but for technological problems rather than what you suggest
    that's how i always saw that situation too.
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  34. #33  
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    red wrote:
    rite what ur question was what is the tempreture of a vacuum. a vacuum is a space in which there is nothing no atoms jst empty space. tempreture is the average kinetic energy of a sample of atoms. if a vacuum has no atoms therefore it can have no tempreture as there is nothing to measure it is not 0K as that suggests there is a body of matter which is completely devoid of kinetic energy which there is not. that is what megabrain is trying to say there is nothing to be measured therefore you cannot assign it ANY position on any tempreture scale. It is like asking what is the colour of sound.
    Not really. Asking what the color of sound is would make no sense (unless you associate color with frequency). On the other hand, asking what the temperature of a vacuum is, is simply a matter of a mathematical limit. Even zero divided by zero is not necessarily undefined. In this particular case it makes a lot of physical sense to define it as equal to zero.

    Stating that a vacuum has zero temperature is equivalent of saying it has zero energy. Don't you think that makes sense? Or would you also reject the notion that a vacuum has zero energy, applying your argument that energy has to be possessed by matter and is otherwise undefined? Or would you say it has "no" energy? And that's different from zero??

    It almost seems to me that the fact that temperature is something we "feel" tempts us to express our gut-feelings about what temperature is, rather than sticking to rational and logical scientific definitions. It may not "feel" right that a vacuum should have a temperature as a well-defined limit (0), but it's not meaningless scientifically.
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  35. #34  
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    Of course asking what the colour of sound is makes no sense sound is not an e.m wave so therefore can never have a colour but so is asking the average kinetic energy of a nin-existant source. Yes i agree a non existant source had 0K of kinetic energy true but thats because the absence of a source you cannot measure something which does not exist and say it is the same as something which does exist but has no kinetic energy. Saying a vacuum is 0K is going by as you say "gut instincts" but i am the one trying to stick to scientific fact. The definition of kelvin is the average kinetic energy of a source of atoms a vacuum does not satisfy that "source of atom" requirement and therefore cannot be put on the scale. Doing so would be scientific shorthand and would only lead to confusion and misunderstanding in those who do not know that that is what it is. What you wish to do is assign a value that "feels" right as you say as it is true a vaccum has no thermodynamic energy but its is not due to the absense of kinetic energy in a sample of atoms but the absence of atoms which therefore does not allow it to be judged under the kelvin scale if you truly wish to stick to as you say "rational and logical scientific definitions"
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  36. #35 Re: vacuum 
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    Quote Originally Posted by Chemboy
    what's the temperature inside a perfect vacuum? i'm guessing maybe it doesn't have one, that's why i'm asking...
    It's not so simple to answer this question, because we don't know what void exactly is; in particular, we don't know which is its (average) energy density.

    1. You could say void is simply a region of space without matter. But there could be energy, however (electromagnetic radiation, for example).

    Indeed, far from any star or planet or gas or powder cloud, the space's temperature is 2.7125 °K, because of cbr = cosmic background radiation (it's the light "flash" of big bang explosion who has cooled down), as some has said in this thread.

    2. You could ask: "but I want to know which could be the void's temperature even in the absence of this radiation".

    The problem is that there would be some residual energy too, because of quantum energy density's fluctuations. It's like a "faint residual noise". The Casimir Effect seems to prove that it's possible to create region of space with an average energy density even less than that, but we don't know exactly how much we can take away.

    Actually, in some theorethical computations (only heard about it) it seems that the residual void's energy density comes out infinite!

    It's a real conundrum.

    3. Would space (actually, we should say "spacetime") really exist without matter And without any energy at all?
    General Relativity relates every spacetime property to all matter and energy (any kind) in it, so I wonder if it would still exist, physically, without them.
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    This is a somewhat tricky subject, because measuring the temperature of a vacuum doesn't really have a well defined meaning. if you went to outer space and brought a thermometer what would it read? a thermometer works by becoming in thermal equilibrium with the environment its measuring. Then by the statement of the the 0th law of thermodynamics we consider the temperature it reads to be the temperature of the surroundings (which is an merely an empirical statement).

    so what is the temperature of space? if you took a thermometer just outside of the earth's atmosphere (say 300-700 nautical miles up) you would recieve energy from the sun and the earth in the form of radiation and dump heat to open space, the sun, and the earth in the form of radiation, the net exchange would result in an equilibrium temperature reading (which would depend on factors of orientation and materials of the thermometer). In an Ideal vacuum with nothing around for energy exchange (doesn't really exist and is inherently untestable) our mathematical theories of heat transfer would predict that temperature to be - 273.15 °C (or 0 °K). However, in real life, it makes more sense to talk about a sink temperature to space. What does that mean? well, in the previously mentioned example of the thermometer just outside the earth's atmosphere, we get a temperature based on net radiation exchange; as you will recall, the engergy transfer in radiation exchange is based on the temperature difference of the exhanging entities. In order to correctly predict the temperature using our mathematical model, Space (when used in radiation exchange) should be about -270 °C (or 3 °K) (which is its sink temperature: a temperature that sufficiently characterizes the heat exchange). and indeed when you look at deep space and remove the effects local solar and planet heat exchange, that is the temp you measure. although for most calculations you can be sufficiently accurate using 0 °K as your space sink temperature.
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    Quote Originally Posted by lance
    [...]
    Ok.
    In order to correctly predict the temperature using our mathematical model, Space (when used in radiation exchange) should be about -270 °C (or 3 °K) (which is its sink temperature: a temperature that sufficiently characterizes the heat exchange). and indeed when you look at deep space and remove the effects local solar and planet heat exchange, that is the temp you measure. although for most calculations you can be sufficiently accurate using 0 °K as your space sink temperature.
    It depends on what kind of calculations. If you want to study cbr properties, dark matter, dark energy...cosmology in general ecc., clearly using 0°K it's not accurate at all.
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