<h2>What temperature means...</h2>

<p>Temperature is the measure of the energy of particles. The higher the temperature, the more energized the particles. The more energy particles have the faster they move around. This is the particles' <a href="http://en.wikipedia.org/wiki/Kinetic_energy" rel="nofollow"><em>kinetic energy</em></a> that is rising. As it rises, the particles will begin using up more space. Moving particles need more space. In a vacuum this can be measured as pressure which is the stress of <a href="http://en.wikipedia.org/wiki/Thermal_expansion" rel="nofollow"><em>thermal expansion</em></a> on the closed system. In an open system the matter will expand freely. As the particles increase their speed they also move more erratically so the <a href="http://en.wikipedia.org/wiki/Entropy" rel="nofollow"><em>entropy</em></a>, or measure of disorder, will also increase. </p>

<h2>The coldest...</h2>

<p>Now understanding all that, what would the lowest temperature, or energy state, be in the universe? The answer is a state of no energy, 0 K, or <a href="http://en.wikipedia.org/wiki/Absolute_zero" rel="nofollow"><strong><em>absolute zero</em></strong></a> in the <a href="http://en.wikipedia.org/wiki/Kelvin" rel="nofollow"><em>Kelvin scale</em></a>. It is −273.15° on the Celsius scale and −459.67° on the Fahrenheit scale. At this temperature, which is impossible to occur by only thermodynamic means, the particles are completely still and entropy drops to 0.</p>

<h2>Temperature reference points...</h2>

<ul>
<li>The surface temperature of the sun is 5,778 K.</li>
<li>Water boils at 373 K.</li>
<li>Water freezes at 273.15 K.</li>
<li>The moon’s darkest craters that never receive sunlight are 33 K.</li>
<li>The <a href="http://en.wikipedia.org/wiki/Cosmic_microwave_background" rel="nofollow"><em>cosmic microwave background</em></a> fluctuates around 2.8 K.</li>
<li>The <a href="http://en.wikipedia.org/wiki/Boomerang_Nebula" rel="nofollow"><em>Boomerang Nebula</em></a>, the coolest natural place currently
known in the universe, measures 1 K.</li>
<li>Absolute zero is 0 K.</li>
</ul>

CC BY-SA 3.0
2015-04-03T14:53:54.463Z
Negative temperatures are not colder than absolute zero. They are instead **hotter** than any finite temperature. Negative temperatures arise in some quantum mechanical systems with a maximum energy. Here it makes much more sense to use the thermodynamic beta, $\beta = 1/(kT)$ in lieu of temperature. The number of available states starts decreasing at some point as the energy of the system approaches the maximum. At this point, $\beta$ goes through zero and becomes negative. When interpreted as temperature (not a good thing to do for these systems), that translates to a negative temperature.
David Hammen
CC BY-SA 3.0
2015-04-03T14:55:29.063Z
I'd suggest deleting the last paragraph because those negative temperatures don't mean what you think they do, and because they are specialized to specially-prepared quantum mechanical systems that are far removed from what one could find in space.
David Hammen
CC BY-SA 3.0
2015-04-04T00:13:49.917Z
@DavidHammen I have removed my last paragraph about negative temperature since it is not what it seems by it's name and is certainly not a feature of astronomy/nature.
PJS1987
CC BY-SA 3.0
2015-04-03T05:48:45.743Z
2015-04-04T00:08:50.897Z
2015-04-04T00:08:50.897Z
PJS1987
<p>0 K,"absolute zero" (-273.15°C) is the theorized measurement of energy at which all motion stops. Electrons, atoms, and particles stop all movement and it would likely be the lowest possible temperature possible anywhere in the universe. Now that temperature may or may not actually exist in the universe because of all of the radiation and energy from various stars, however it may be possible in the middle of a supervoid or other places.</p>

CC BY-SA 3.0
2016-09-23T18:37:05.293Z
Motion does not stop at absolute zero.
BowlOfRed
CC BY-SA 3.0
2016-09-23T03:27:50.270Z
2016-09-23T06:24:01.907Z
2016-09-23T06:24:01.907Z
CS2016
<p>What could be the utmost <strong>lowest</strong> temperature in the universe/multiverse?</p>

CC BY-SA 3.0
2015-04-02T17:26:45.580Z
so the answer is -273.15 Celsius or thereabouts.
ProfRob
CC BY-SA 3.0
2015-04-02T21:08:01.727Z
@barrycarter Aren't there places in the universe where there are no particles?
Scottie
CC BY-SA 3.0
2015-04-02T22:25:51.600Z
@Scottie, temperature is a property of particles.  If there are no particles, then the concept of temperature is meaningless.
Mark
CC BY-SA 3.0
2015-04-03T11:54:09.723Z
There's probably some weird tiny effect from the continual production of virtual particle pairs in the vacuum. If one in 10^93 particle pairs fails to recoalesce, it might raise background temp from 0°K to 10^-67°K. No one has ever measured such an effect, and I doubt anyone ever will.
Wayfaring Stranger
CC BY-SA 3.0
2015-04-03T14:16:18.070Z
Do you mean the current observable universe, then ladies and gentlemen please allows me to introduce you to the utmost lowest temperature in the universe and that is... ... ...in the Wolfgang Ketterle's lab at the MIT in Cambridge whereby some nerds are playing with sodium molecules trapped using magnets. They created BEC with a temperature of 810 trillionth of a degree above absolute zero. In case you're wondering outer space is no where near this feats there human 1 known observable universe 0.
user6760
CC BY-SA 3.0
2016-09-23T07:44:45.267Z
@user6760 They are now at 500nK at MIT.
cphyc
<universe><temperature><multiverse>
What could be the utmost lowest temperature in the universe/multiverse?
AmitG
# What could be the utmost lowest temperature in the universe/multiverse?

(Asked by: username_0 on 2015-04-02)

What could be the utmost **lowest** temperature in the universe/multiverse?

**Tags:** universe, temperature, multiverse

> **Comments:**
> **username_1**: so the answer is -273.15 Celsius or thereabouts.  
> **username_2**: @barrycarter Aren't there places in the universe where there are no particles?  
> **username_3**: @username_2, temperature is a property of particles.  If there are no particles, then the concept of temperature is meaningless.  
> **username_4**: There's probably some weird tiny effect from the continual production of virtual particle pairs in the vacuum. If one in 10^93 particle pairs fails to recoalesce, it might raise background temp from 0°K to 10^-67°K. No one has ever measured such an effect, and I doubt anyone ever will.  
> **username_5**: Do you mean the current observable universe, then ladies and gentlemen please allows me to introduce you to the utmost lowest temperature in the universe and that is... ... ...in the Wolfgang Ketterle's lab at the MIT in Cambridge whereby some nerds are playing with sodium molecules trapped using magnets. They created BEC with a temperature of 810 trillionth of a degree above absolute zero. In case you're wondering outer space is no where near this feats there human 1 known observable universe 0.  
> **username_6**: @username_5 They are now at 500nK at MIT.  

---

## 2 answers

### Answer by username_7 on 2015-04-03. Score: 4

## What temperature means...

Temperature is the measure of the energy of particles. The higher the temperature, the more energized the particles. The more energy particles have the faster they move around. This is the particles' [*kinetic energy*](http://en.wikipedia.org/wiki/Kinetic_energy) that is rising. As it rises, the particles will begin using up more space. Moving particles need more space. In a vacuum this can be measured as pressure which is the stress of [*thermal expansion*](http://en.wikipedia.org/wiki/Thermal_expansion) on the closed system. In an open system the matter will expand freely. As the particles increase their speed they also move more erratically so the [*entropy*](http://en.wikipedia.org/wiki/Entropy), or measure of disorder, will also increase.

## The coldest...

Now understanding all that, what would the lowest temperature, or energy state, be in the universe? The answer is a state of no energy, 0 K, or [***absolute zero***](http://en.wikipedia.org/wiki/Absolute_zero) in the [*Kelvin scale*](http://en.wikipedia.org/wiki/Kelvin). It is −273.15° on the Celsius scale and −459.67° on the Fahrenheit scale. At this temperature, which is impossible to occur by only thermodynamic means, the particles are completely still and entropy drops to 0.

## Temperature reference points...

* The surface temperature of the sun is 5,778 K.
* Water boils at 373 K.
* Water freezes at 273.15 K.
* The moon’s darkest craters that never receive sunlight are 33 K.
* The [*cosmic microwave background*](http://en.wikipedia.org/wiki/Cosmic_microwave_background) fluctuates around 2.8 K.
* The [*Boomerang Nebula*](http://en.wikipedia.org/wiki/Boomerang_Nebula), the coolest natural place currently
  known in the universe, measures 1 K.
* Absolute zero is 0 K.

> **Comments:**
> **username_8**: Negative temperatures are not colder than absolute zero. They are instead **hotter** than any finite temperature. Negative temperatures arise in some quantum mechanical systems with a maximum energy. Here it makes much more sense to use the thermodynamic beta, $\beta = 1/(kT)$ in lieu of temperature. The number of available states starts decreasing at some point as the energy of the system approaches the maximum. At this point, $\beta$ goes through zero and becomes negative. When interpreted as temperature (not a good thing to do for these systems), that translates to a negative temperature.  
> **username_8**: I'd suggest deleting the last paragraph because those negative temperatures don't mean what you think they do, and because they are specialized to specially-prepared quantum mechanical systems that are far removed from what one could find in space.  
> **username_7**: @username_8 I have removed my last paragraph about negative temperature since it is not what it seems by it's name and is certainly not a feature of astronomy/nature.  

---

### Answer by username_9 on 2016-09-23. Score: 0

0 K,"absolute zero" (-273.15°C) is the theorized measurement of energy at which all motion stops. Electrons, atoms, and particles stop all movement and it would likely be the lowest possible temperature possible anywhere in the universe. Now that temperature may or may not actually exist in the universe because of all of the radiation and energy from various stars, however it may be possible in the middle of a supervoid or other places.

> **Comments:**
> **username_10**: Motion does not stop at absolute zero.  

---

