Absolute zero
Absolute zero is the lowest temperature permitted by thermodynamics, where a system has the least thermal energy available to it.
0 KTemperatureEveryday quantities
Absolute zero vs Cosmic microwave background
What are they, and what does the difference actually look like?
Two things. One honest scale.
Meet the pair
What these two things are
Cosmic microwave background
The cosmic microwave background is faint thermal radiation filling the universe, left over from the early stages after the Big Bang.
2.725 KTemperatureAbsolute zero is 2.725 K cooler than Cosmic microwave background.
01
Absolute zero0 KTemperature
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Cosmic microwave background2.725 KTemperature
Celsius and Fahrenheit zero points are offsets. Compare temperature differences, not ratios in °C or °F. The kelvin axis starts at absolute zero.
Measurements, assumptions & sources +
Absolute zero
The zero of the thermodynamic kelvin scale. It is approached in experiments, not reached by ordinary finite cooling.
NIST — 2022 CODATA fundamental constants
The marked temperature is calibrated. Unmeasured illustration details are representative.
Cosmic microwave background
The temperature of the nearly blackbody relic radiation. It is not the temperature of every object in space.
The marked temperature is calibrated. Unmeasured illustration details are representative.
Change the comparison
Put something else beside it.
Measurement details
Why these numbers?
The visual compares temperature with temperature. The records below preserve each value’s basis and caveats.
Absolute zero
0 KTemperature · approximate
The zero of the thermodynamic kelvin scale. It is approached in experiments, not reached by ordinary finite cooling.
Cosmic microwave background
2.725 KTemperature · approximate
The temperature of the nearly blackbody relic radiation. It is not the temperature of every object in space.
- Comparing
- Temperature ↔ Temperature
- Relative size
- Temperature comparisons use an absolute difference in kelvins rather than a multiplicative ratio.
How to read the visual
The labelled spans and stored measurements determine the scale; unmeasured illustration details do not.
- Absolute zero is labelled approximate; treat the displayed value as a comparison anchor rather than false precision.
- Cosmic microwave background is labelled approximate; treat the displayed value as a comparison anchor rather than false precision.
There’s always another scale
Follow your curiosity.
TemperatureAbsolute zero0 KAbsolute zero is the lowest temperature permitted by thermodynamics, where a system has the least thermal energy available to it.TemperatureCosmic microwave background2.725 KThe cosmic microwave background is faint thermal radiation filling the universe, left over from the early stages after the Big Bang.TemperatureRoom temperature20 °CRoom temperature describes indoor air conditions generally considered comfortable for people and suitable for ordinary activities.
SpaceSun1,391,000 kmThe Sun is the star at the centre of the Solar System.
Fundamental physicsPlanck temperature1.417 × 10³² KThe Planck temperature is a theoretical temperature scale at which quantum gravitational effects are expected to become important.Side by side
Another point of view.
