Due to lack of understanding of precise underlying mechanisms, turbulent flow in liquids, gases and powders (etc) can't be exactly described.

This can be very significant when attempting to predict the behaviour of complex natural phenomena - weather systems for example. Or when making predictions about dynamic forces and frictions in turbulence around man-made tech such as aircraft, ships, turbines etc. etc..

In addition, there is, as yet, no solid theorem relating Reynolds Numbers (a measure used to assess and predict fluid flow patterns in different situations) to turbulence.

Quote from: Prof. Richard Feynman - "Turbulence is the most important unsolved problem of classical physics." _{(Feynman R., Leighton R. B., Sands M. (1964) The Feynman lectures on physics)}

Quote from: Sir Horace Lamb - “I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.” _{(in a speech to the British Association for the Advancement of Science in 1932)}

Source : Transactions of the Royal Society A

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