# What is the equality theory, or equal transit time theory, and is it supported by scientific evidence? [duplicate]

Throughout flight training when learning about the mechanics of lift I read and was taught this story about two molecules that part ways at the wing tip and reach the trailing edge of a wing at the exact same time. Later on I heard this referred to as the "equality theory."

The idea is that a wing makes a molecule travel farther to end up at the trailing edge at the same time rendering a greater velocity and a lower pressure through Bernoulli's principle.

I'd like to find the best articulation of the equality theory as well as information on whether scientific research actually supports it. Whether it's scientifically supported or not, it may at least serve as a useful teaching tool. In any case, if I talk about it I'd like to be able to cite something truly scientific.