In this artwork, the viewer enters a 16-meter-long hallway, which measures at the entrance 90 cm wide, opens up in the last third, and then opens the view freely to a large 2.4×3.2 meter rear-projected canvas, on which the picture of a tree can be seen. As the viewer enters the hallway, the tree is still a shoot. If the viewer moves forward, the tree begins to grow, and keeps growing until the viewer stops; then also the tree stops growing. The viewer notices that her/his position is coupled on the way with the picture of the tree in the video sequence. If he/she reaches the end of the hallway, the tree loses its leaves, becomes old and dies.
Bill Viola, who became known through his many video installations, works in
his art on the phenomenon of time in all of its experienced aspects: the absolute ^ artworks about time
and the mental time, the time during sleep, in hectic activity, and during rest. He relates the experiencing of time to the birth and death of humans. In the installation “Tree of Knowledge” (1997), the tree runs through different types of time: the lifetime of the tree itself, its youth, its strength, and its death. While the viewer walks down the hallway, the tree experiences spring and the growth of leaves; it blossoms in the early summer, bears fruit that fall in late summer, and in the fall the tree sheds its leaves. It runs through the cycle of one year.
The lighting simulates the direction and color of the sun during one day, and the wind moves the leaves, and affects the falling fruit. All this is experienced in real time. Different time experiences are here overlaid and blended together, and are in their course and time sequence dependent upon the temporal movement of the viewer.
The position of the viewer on the way is determined using an infrared laser scanner, which is installed on a hip-high platform near the entrance to the hallway. Its data are read by a PC, which calls a picture from the prerendered animation sequence. The individual pictures of a total of 600 images are sufficient for animation, and are virtually distributed over a distance of 15.5 meters. Each point in the hallway is assigned a picture from the video sequence, thus each space point is assigned one point of time. While the viewer walks along the hallway, he crosses different time levels. He can go backwards, stop, or move at a different speed. If he reaches the end of the hallway, by then the tree has shed its leaves and is covered with gray moss. Here there is no return, the tree has died.
Bill Viola, according to his own statement, for over 15 years carried with him the idea of a tree growing through the influence of the viewer. He experimented with extreme memomotion studies of a real tree, but the prospect of having to wait several decades to complete the project seemed unattractive. With the possibilities offered by plant modeling via the computer, the idea appeared for the first time realizable.
In contrast to real photography, additionally the different levels of the time experience could be worked into the sequence, and could be adapted to the appearance of the tree, which became more like the mental picture we have of a typical tree, by omitting details and oversubscribing certain characteristics of the tree shape. The color, for example, follows more the style of the Old Masters, such as Memling and Van Eyck, than a photograph of a real tree. The curvature of the trunk, which begins only during aging, is not found in nature. The duration of the youth, the period of growing up, and the age were measured using human life stages.
At the end of the sequence, the roots bury themselves into the ground: like an old man the tree finds its place. The tree becomes in such a way our projection and a mirror. For the animation of the growth, the budding, and the ripening of the fruits, the embedded keyframing described in Chap. 6 was utilized. The sequence was rendered using an integrated raycasting algorithm. The animation sequence was realized at the ZKM Institut fur Bildmedien using the Xfrog modeling system.
The basis was 20 photographs of different trees taken by Bill Viola in Huntington Gardens, out of which the idealtypical tree was chosen. The total time for modeling, timing, adjustment of the temporally variable textures etc., amounted to approximately three months. Tree of Knowledge was shown in 1997 at the ZKM in Karlsruhe and in 1999 at the Whitney Museum in New York.