Mahesh Godavarti

Zero'th law because it was a prequel to the first law of thermodynamics and discovered after the first law was discovered and already named.

It is called the "zeroth" law because it came to light after the first and second laws of thermodynamics had already been established and named, but was considered more fundamental and thus was given a lower number — zero.


When the laws of thermodynamics were originally established, there were only three. In the early 18th century, though, scientists realized that another law was needed to complete the set. However, this new law, which presented a formal definition of temperature, actually superseded the three existing laws and should rightfully be at the head of the list. This created a dilemma: the original three laws were already well known by their assigned numbers, and renumbering them would create a conflict with the existing literature and cause considerable confusion. The alternative, calling this new law the Fourth Law and putting it last on the list, was also problematic because it superseded the other three laws. One scientist, Ralph H. Fowler, came up with a third alternative that solved the dilemma: he called the new law the “Zeroth Law.” (Interestingly, science fiction writer Isaac Asimov appropriated the idea for a Zeroth Law in his 1994 novel "Robots and Empire" when he found that needed to add a new law to the Three Laws of Robotics that superseded the First Law.)

Kamini Santhanagopalan
yup. basically a prequel. so zero'th law. above answers provides details.