The lowest temperature achieved in the known universe is known as absolute zero, which is equivalent to 0 Kelvin (K) or approximately -273.15 degrees Celsius (-459.67 degrees Fahrenheit). At this temperature, the motion of particles ceases, and no further cooling is possible according to classical thermodynamics.
However, it's important to note that scientists have achieved extremely low temperatures very close to absolute zero in laboratory settings. These ultra-low temperatures are typically achieved using techniques such as laser cooling and evaporative cooling applied to atoms or molecules. In these experiments, temperatures on the order of a few billionths of a Kelvin (nanokelvins) or even lower have been reached.
The achievement and study of such extremely low temperatures have led to significant advancements in the field of physics, particularly in areas such as quantum mechanics and Bose-Einstein condensation.