On those stepping into the same river, ever different waters flow.
— Heraclitus of Ephesus
Taking a photograph of flowing water, so that it can be recognized as such, is not as simple as it may seem. A good rule of thumb that photographers use is that the exposure time should be somewhere between 1/100 and 1/20, to depict movement convincingly in the resulting image. A patient photographer will try several test shots with different exposure times, in order to achieve the wanted effect.
When the exposure time is too long, half a minute or more, instead of water the photograph will show heavy, oily fog creeping over the landscape. If the exposure is too short, in millisecond range and under, individual droplets float crisply in mid-air, and the viewer cannot tell where they came or where they are going.Only in the middle exposures, here at 1/100, we immediately see that the water is flowing from right to left.
Come to think of it, why should any still image be interpreted by the viewer’s brain as depicting motion? Is 1/20-1/100 the most natural exposure range because it corresponds well with the gamma wave frequency of the human brain?
In the real world, as revealed by modern physics, solidity is the illusion, not flowing movement.
In the real world, as revealed by modern physics, solidity is the illusion, not flowing movement. Every part of the world is in constant motion. What we sense as solid objects are in reality a hypermassive clouds of electrons and ions orbiting each other at ridiculously high speeds. Human cognition happens millions of times slower than electrons flow, giving plenty of time for random opposing fluctuations in their movements to cancel out, like individual droplets of water that disappear in the long exposure photograph. Because we experience time at a rate that is massively slower than the speed of elementary particles, we see only the stable overall shape of the object.
Movement is relative, we can measure the movement of individual droplets or particles only against a “solid” object. “The same river” is just the pattern of moving water that is stable enough for us to draw it on maps, even though it is formed from ever new water, rained down from ever new clouds. Raindrops and clouds are not drawn on maps, they are not solid enough at human perceptual timescale.