The microwave background radiation establishes a temperature for "deep space", the temperature that will be reached in time by a grain of sand located "far" from any other object. As the universe is expanding and the background is accelerating it will become cooler yet in a long time.cyleung_2001 said:As temperature is emergent and is only describing the speed of molecules in a substance, is it meaningful to speak of temperature in an empty space? If not, can we say that the microwave background radiation is "heating" up the universe? As most of the universe is empty space
Temperature is not an imergent property (it can be defined for any system which can store energy in two or more different ways), and it is certainly much more general then the speeds of molecules in a substance (temperature can be defined for systems that do not have speed).As temperature is emergent and is only describing the speed of molecules in a substance
No one talks about the temperature of empty space. It would be possible to define this mathematically, and work on formulas, but the results would be unmeasurable and uninteresting.is it meaningful to speak of temperature in an empty space? If not, can we say that the microwave background radiation is "heating" up the universe?
That definitely qualifies as a minority opinion. It violates GR energy conservancy as well as observational evidence that empty space is virtually transparent to EM as far back as we can currently 'see' [~z=6].turbo-1 said:It may be helpful to point out that the energy received by an entity in "empty" space will be re-radiated at a LOWER energies (longer frequencies). Before quantum physicists posited (and later demonstrated) the existence of a dynamical vacuum field, empty space was assumed by many to be truly empty. With a dynamical vacuum field, impinging EM transfers energy to the field and is re-emitted at lower and lower energies.
The vast majority of physicists would say that article is a compelling refutation of Eddington's prediction on a number of grounds. But that does not rule out the possibility you have some new physics to pony up to the table.turbo-1 said:The article that Chronos cited does not falsify Eddington's estimate of the temperature of space - the estimate was made at a time when "empty" space was assumed to be transparent to EM.
Agreed, but irrelevant. It says nothing about the 'true' background temperature of deep space. You are missing the point. I think you really should reread the article and further investigate how the WMAP team made corrections for local contributions to the CMB temperature.turbo-1 said:Taking into account the effects of extra-galactic sources does not significantly effect the results predicted by Eddington.
Also agreed, but irrelevant.turbo-1 said:Since energy flux falls off as a function of the square of the separation of emittor and sensor, galactic-scale separations make the energy contribution of a star in M31 VERY insignificant relative to a star in our own galaxy, to say nothing of a star in our local neighborhood.
I don't think that very many of the CMBR photons have interacted with anything on the way to our instruments. Else the nice maps and impressive science in the field would be meaningless. There are some absorption lines in some directions here and there but for the most part we see a black body curve.Chronos said:One more time, read the literature. The CMBR interacts with all matter it encounters along the way to our observational outpost. That was the whole point of the study I cited. I think the majority would agree you are not addressing the observational evidence. If you have an alternative explanation - show the math.