  In the 2002 AMS summer conference on ``Advances in Quantum Dynamics'' in
Mount Holyoke Robert Powers proposed a sum operation for spatial E0-semigroups.
Still during the conference Skeide showed that the Arveson system of that sum
is the product of spatial Arveson systems. This product may but need not
coincide with the tensor product of Arveson systems. The Powers sum of two
spatial E0-semigroups is, therefore, up to cocycle conjugacy Skeide's product
of spatial noises.
