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

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

• If temperature refers to mean energy of particles (as it does in everyday use), it would no energy at all or absolute 0. On the Kelvin scale, there are no negative temperatures, unless you find a way to define negative energy. As far as I know, particles can't exist without energy, so even absolute 0 is unattainable. – user21 Apr 2 '15 at 16:40
• so the answer is -273.15 Celsius or thereabouts. – Rob Jeffries Apr 2 '15 at 17:26
• @barrycarter Aren't there places in the universe where there are no particles? – Scottie Apr 2 '15 at 21:08
• @Scottie, temperature is a property of particles. If there are no particles, then the concept of temperature is meaningless. – Mark Apr 2 '15 at 22:25
• 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 Apr 3 '15 at 14:16

## 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 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 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, 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 in the Kelvin scale. 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 fluctuates around 2.8 K.
• The Boomerang Nebula, the coolest natural place currently known in the universe, measures 1 K.
• Absolute zero is 0 K.
• 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 Apr 3 '15 at 14:53
• 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 Apr 3 '15 at 14:55
• @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 Apr 4 '15 at 0:13

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.

• Motion does not stop at absolute zero. – BowlOfRed Sep 23 '16 at 18:37