Poincare, in the early twentieth century, found that even the slightest error in the measurement resulted in enormous unpredictability in the behavior of astronomical system (Poincare, internet). Repeated experiments by him reaffirmed his earlier results that changes in the measurement did not follow Newtonian laws of producing identical behavior but produced outcomes that were vastly different and unpredictable.
In 1963, Edwards Lorenz, a meteorologist, discovered that while predicting weather forecast, slight changes in the values in the equations for the theoretical model of prediction of the weather, produced hugely different outcomes. When he used .506 instead of .506127, a slightly lesser precise measurement, the results were radically different as opposed to very little variation that should have happened as per Newton’s laws. The continued erratic outcomes of the computerized model of prediction, with slight variation in the values, emphatically disproved the earlier Newtonian theory. Lorenz became the first scientist to prove it wrong. In 1972, while talking in a seminar on "Predictability: Does the Flap of a Butterflies Wings in Brazil set off a Tornado in Texas?" (AAAS, 1972), he successfully illustrated that the behavior of a complex system is impossible to predict even when the conditions or factors influencing its outcomes are known mainly because of the fact that those precise conditions cannot be foretold or predicted and therefore the unpredictability of the outcome. Therefore it is impossible to predict the weather accurately.
The unpredictable behavior of a physical system came to be known as the ‘butterfly effect’ because of the slight difference in the starting point of the curves which can be compared to the flapping of a butterfly’s wings. As Stewart says ‘The flapping of a single butterfly’s .wing today produces a tiny change in the state of the atmosphere. .