The Limit of Cold
Absolute zero is 0 K, or −273.15°C, or −459.67°F. At this temperature a system has the minimum possible thermal energy. It's a fundamental limit of nature: you cannot cool something below absolute zero because there is no lower energy state to reach.
Why It Can't Be Reached
The third law of thermodynamics says you can get arbitrarily close to absolute zero but never reach it exactly, because removing the last bit of heat requires more energy than it releases. Laboratories have cooled samples to within billionths of a kelvin.
Three-Scale Reference
| Scale | Absolute zero |
|---|---|
| Kelvin | 0 K |
| Celsius | −273.15°C |
| Fahrenheit | −459.67°F |