Absolute zero is the theoretical lowest temperature, where a substance has no thermal energy and particle motion ceases, marking 0 Kelvin (K) or -273.15 degrees Celsius (°C). The Kelvin scale starts at absolute zero, making it an absolute temperature scale crucial for scientific measurements, while the Celsius scale, a relative scale, defines 0°C as water's freezing point and 100°C as its boiling point. The relationship between the two scales is T(K) = T(°C) 273.15. #physics #science #temperatur