Space Temperature: Is There a Temperature in Space?

[marsi]

i was wathing a documentary about space and i came up with a (kind of stupid...) question
since there's no air on space and no material that can get warm from the sun, is there a temperature out there? and if, then what is it?

and why is the temperature on the highest levels of the atmosphere much colder than on the ground?

 

[AppleBite]

Actually your question is well justified, yet there is also an answer to it.

The temperature of the universe is determined by microwave radiation remaining after the Big Bang. Tedious measurements have found that this radiation is the same from every direction of the Universe. So even though temperature obviously varies considerably in near proximity of stars and other objects, the average temperature of the universe due to the "back-ground radiation" (which this microwave radiation is called) is acually as low as 2.7 Kelvin (some sources use 3K)

 

[Chronos]

Welcome to PF, marsi! Spacetime, as you correctly observed, has no temperature. Temperature is strictly a property of matter. The CMB temperature is the excitation a chunk of matter [like a telescope] would experience in deep space due to CMB radiation.

 

[D H]

Space, even the space between galaxies, is not entirely void of matter. Cosmologists think of this material between stars and between galaxies as a kind of atmosphere. While this atmosphere is nothing at all like the atmosphere you breath, it still does have substance. As such, one can ascribe quantities like pressure, density, and temperature to this gas.

Surprisingly, most of interstellar space is very hot: one million Kelvins or more. For example, see http://en.wikipedia.org/wiki/Interstellar_medium#Interstellar_matter. Even more surprising, you would quickly freeze if you magically teleported to such a region of space. While this "gas" is very hot, it is also so extremely tenuous that it would not warm you in the least. Your body temperature would quickly drop to radiative cooling.

While most of intergalactic space is very cold (2.7K), the intergalactic gas can get extremely hot: 50 million Kelvins. Nearby galaxies do strange things to the intergalactic medium. Sonic booms, for example: http://www.sciencenews.org/articles/20030913/fob1.asp and http://www.spitzer.caltech.edu/features/articles/20060303.shtml . These shock waves heat the intergalactic medium up to incredible temperatures. And you would still freeze to death if you found yourself in one of these ultra-hot regions.