# Precision of Temperature of Universe **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [August 3, 2004, 4:13pm UTC](https://boards.straightdope.com/t/precision-of-temperature-of-universe/258153 "2004-08-03T16:13:57Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [August 3, 2004, 4:13pm UTC](https://boards.straightdope.com/t/precision-of-temperature-of-universe/258153/1 "2004-08-03T16:13:57Z")
In **Karen** ’s latest Staff Report "[What’s the temperature of space?](http://www.straightdope.com/mailbag/mspacetemp.html), she states > [@](#): > > The temperature of the universe is 2.725 +/- 0.002 degrees Kelvin. The Kelvin scale, for those who slept through high school physics, is the same as the Celsius scale, only it starts at absolute zero. In short, the universe is pretty cold. Fortunately, our Milky Way galaxy is about 0.0001 K toastier. So, the Universe is 2.7250(20) and the Milky Way is 2.7251(20)? Notice that the difference is only 5% of the error bars. Can we really measure the temperature difference of the Milky Way vs the Universe that much more precisely than the absolute temperature of either? I guess it’s possible, but I’d like some confirmation. Oh, and good report. 🙂 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 3, 2004, 5:56pm UTC](https://boards.straightdope.com/t/precision-of-temperature-of-universe/258153/2 "2004-08-03T17:56:40Z")
In this case, yes. You have to pay attention to what the measurements/calculations actually are. In this case, it’s not a matter of measuring the temperature of the Universe at large, and then measuring the temperature of the Galaxy, and subtracting. Rather, what we’re doing is measuring the temperature of the Galaxy, where we are, after all, stuck for the forseeable future, and then calculating how much ambient starlight from the rest of the Galaxy is contributing to that temperature. Subtract that off from the measured “temperature of space”, and you have the temperature far away from any galaxy. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [August 3, 2004, 6:49pm UTC](https://boards.straightdope.com/t/precision-of-temperature-of-universe/258153/3 "2004-08-03T18:49:17Z")
> [@](#): > > Rather, what we’re doing is measuring the temperature of the Galaxy, … and then calculating how much ambient starlight from the rest of the Galaxy is contributing to that temperature. Umm, can you clarify this? Or do you mean the rest of the Universe? Why can’t we measure the temperature of the Universe by simply pointing a narrowbeam microwave receiver at a point in the sky with no sources (other than the CMB)? ---
**Author:** ![RiverRunner](https://avatars.discourse-cdn.com/v4/letter/r/977dab/32.png) [@RiverRunner](https://boards.straightdope.com/u/RiverRunner)\ **Post date:** [August 3, 2004, 7:13pm UTC](https://boards.straightdope.com/t/precision-of-temperature-of-universe/258153/4 "2004-08-03T19:13:37Z")
> [@](#): > > But COBE scientists didn’t stop there . . . > > COBE didn’t stop there either . . . > > Still more: . . . The COBE discovery revolutionized cosmology. I thought COBE was on trial for sexual assault. Musta probed too far. RR ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [August 4, 2004, 5:46pm UTC](https://boards.straightdope.com/t/precision-of-temperature-of-universe/258153/5 "2004-08-04T17:46:57Z")
I’d like to see the cite for the 0.0001 K number, that seems a bit small. And it seems a tad misleading to quote 2.725 K as the “temperature of the Universe” when there isn’t a place in the universe where you can leave an object and have it cool down to that temperature. (Well, except in some laboratories.) Even in inter-galactic space, you will have visible light from galaxies as well as high-energy cosmic rays that contribue to heating. ---
**Author:** ![Karen\_Lingel](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karen_lingel/32/18649_2.png) [@Karen\_Lingel](https://boards.straightdope.com/u/Karen_Lingel)\ **Post date:** [August 6, 2004, 10:10pm UTC](https://boards.straightdope.com/t/precision-of-temperature-of-universe/258153/6 "2004-08-06T22:10:46Z")
The WMAP fact sheet, which you can find [here](http://map.gsfc.nasa.gov/m_or/mr_media3.html) says: > [@](#): > > The sensitivity of the cosmic background radiation map will be better than 20 microkelvins (0.000020 kelvins) per 0.3 degree square pixel. These guys are not slackers!