- #1
DLeuPel
- 56
- 2
The understanding that I have of temperature is that it is defined as the vibration of particles. Now, does this mean that in a vacuum where there are no particles the temperature is the absolute 0 ?
DLeuPel said:Now, does this mean that in a vacuum where there are no particles
Is that true? Wasn't the CMB originated in the BB itself, where all the matter in the Universe was present when the radiation was formed? I think the 3K figure actually describes the temperature of a body that would be radiating with a spectrum of the CMB.anorlunda said:. It permeates the universe, even when there are no atoms around.
So, how does the heat from the Sun propagate trough vacuum if there are no particles in the vacuum?sophiecentaur said:Is that true? Wasn't the CMB originated in the BB itself, where all the matter in the Universe was present when the radiation was formed? I think the 3K figure actually describes the temperature of a body that would be radiating with a spectrum of the CMB.
I think the OP is suffering from (as we all were) having been told half a story and half a definition, in his/her youth. Rather than 'vibrations of particles' there is a much better definition of temperature in most cases which is 'The average Kinetic Energy of particles'. It actually has Units.
There are a number of inconsistencies or confusions of how Temperature is manifest. The 'Temperature of the Sun's Corona is measured as several million K, which really doesn't fit in with the simple model of an 'atmosphere' around a body with surface temperature of 6000K.
As light. That light has a distribution of frequencies [at least once you settle on a frame of reference to measure it from] and that distribution has a temperature which follows from the average kinetic energy per photon, ##E=h \nu##DLeuPel said:So, how does the heat from the Sun propagate trough vacuum if there are no particles in the vacuum?
sophiecentaur said:Is that true? Wasn't the CMB originated in the BB itself, where all the matter in the Universe was present when the radiation was formed? I think the 3K figure actually describes the temperature of a body that would be radiating with a spectrum of the CMB.
I get stuck on "thing". In the absence of all particles and radiation (an impossibility AFAICT) is one left with more than one possible state? I think the usual assumption is vacuum is a unique state. This would seem to imply it has no temperature.Vanadium 50 said:How would you measure such a thing?
Paul Colby said:I get stuck on "thing". In the absence of all particles and radiation (an impossibility AFAICT) is one left with more than one possible state? I think the usual assumption is vacuum is a unique state. This would seem to imply it has no temperature.
Sorry - sloppy language there. But the 'stuff' was all around the same place at one time and there were definitely 'material sources' of the radiation that we see.anorlunda said:But if you think the BB was at a point, that's wrong.
No so much "no" but "indeterminate"?Paul Colby said:This would seem to imply it has no temperature.
Vanadium 50 said:How would you measure such a thing?
And what is this low intensity radiation ?stevendaryl said:Getting back to the original question: In thermodynamics, for every extensive quantity (something that is additive) there is a corresponding intensive quantity that can roughly be thought of as characterizing how willing a system is to give up or acquire more of the extensive quantity. Some examples:
Corresponding to the extensive quantity, "volume" there is a corresponding intensive quantity, "pressure". A gas at high pressure will tend to expand (increase its volume), and a gas at lower pressure will tend to contract. Internal energy and temperature are another example: A system at high temperature tends to lose energy to systems at a lower temperature.
Roughly speaking, systems with higher energy tend to have higher temperature, as well, but that's not always true.
Getting back to empty space. If the space is truly empty, devoid of matter or radiation, then it's temperature will be zero. It has no possibility of giving any energy to any other system. When they talk about the background temperature of space being 4 degrees Kelvin, they're talking about space that isn't completely empty. It has low-intensity radiation, so it has nonzero amount of energy per unit volume.
DrStupid said:Bring it in thermal equilibrium (not just steady state!) with a temperature reference.
DLeuPel said:And what is this low intensity radiation ?
anorlunda said:I don't think vacuum as "a unique state" works. The word state must describe something, not nothing.
anorlunda said:there are other definitions.
anorlunda said:The Cosmic Microwave Background (CMB) also has a temperature (roughly 3 degrees K, -270 C, -452 F). It permeates the universe, even when there are no atoms around.
DrStupid said:Bring it in thermal equilibrium (not just steady state!) with a temperature reference.
anorlunda said:I don't think vacuum as "a unique state" works.
Vanadium 50 said:And then it's not vacuum any more.
PeterDonis said:A vacuum can't be brought into thermal equilibrium with anything, because it contains no matter, radiation, or anything else.
It depends on how precise we're being when we use the word "vacuum". In casual use, "vacuum" is understand to mean "contains no matter" or "empty space" and interstellar space is an example of a vacuum even though electromagnetic radiation is present. More rigorously, vacuum is the ground state of all fields and there is neither matter not electromagnetic radiation present; this follows from the way that quantum field theories treat everything as a field, with no distinction between those fields that manifest themselves as matterDrStupid said:Vaccum contains no radiation? Please provide a corresponding reference.
DrStupid said:why should vacuum be turned into something else by the same procedure?
Klystron said:this dictionary definition
DrStupid said:Vaccum contains no radiation? Please provide a corresponding reference.
Nugatory said:In casual use, "vacuum" is understand to mean "contains no matter" or "empty space" and interstellar space is an example of a vacuum even though electromagnetic radiation is present. More rigorously, vacuum is the ground state of all fields and there is neither matter not electromagnetic radiation present; this follows from the way that quantum field theories treat everything as a field, with no distinction between those fields that manifest themselves as matter
Nugatory said:The casual definition is remarkably unhelpful when trying to understand what temperature is when working with systems that exchange energy by radiation, and this is the source of much of the confusion in this thread. The notion that temperature is the vibration of particles is even less helpful;
I don't think that is any sort of valid argument. You could only draw that parallel if water and vacuum were the same sort of entity. There is a mathematical analogy here. The value Zero follows different rules from all other values. 1, 2 and even π behave the same but Zero is different.DrStupid said:Is water not water anymore if you bring it in thermal equilibrium with a thermometer? If not, why should vacuum be turned into something else by the same procedure?
sophiecentaur said:I don't think that is any sort of valid argument.
DrStupid said:It is valid for a classical vacuum.
PeterDonis said:A classical vacuum can't be brought into thermal equilibrium with anything either; there has to be something present that can store heat, in which case it is no longer vacuum.
DrStupid said:There can be radiation in a classical vaccuum.
PeterDonis said:Please give a specific reference.