The reason why it can never get colder than -273.15 degrees Celsius (often rounded to -274 degrees Celsius) on Earth is due to a fundamental physical concept known as absolute zero.
Absolute zero is the lowest possible temperature that can be theoretically achieved, corresponding to 0 Kelvin or -273.15 degrees Celsius. At this temperature, all molecular motion ceases, and substances have minimal internal energy.
The concept of absolute zero is derived from the laws of thermodynamics, which describe the behavior of energy and temperature in systems. According to the Third Law of Thermodynamics, it is impossible to reach absolute zero through a finite number of processes. As an object cools, its molecular motion slows down, but it can never completely stop at any temperature above absolute zero.
On Earth, various factors contribute to the inability to reach temperatures close to absolute zero. The primary factor is the background radiation present in the universe, known as the cosmic microwave background radiation. This radiation permeates space and has a temperature of approximately 2.7 Kelvin (-270.45 degrees Celsius). Thus, even in the absence of any other heat source, the cosmic microwave background radiation prevents temperatures from dropping below this value.
Additionally, the presence of Earth's atmosphere and heat sources such as the Sun contribute to the maintenance of higher temperatures. The processes of conduction, convection, and radiation continuously transfer heat in the environment, preventing local temperatures from reaching absolute zero.
It's worth noting that while absolute zero is an unattainable theoretical limit on Earth, scientists have been able to achieve extremely low temperatures in laboratories using specialized techniques, such as using supercooling or laser cooling methods. However, these conditions exist only in controlled laboratory environments and do not represent natural conditions on our planet.