9. The computer system of claim 8 , wherein the program instructions to identify comprise: program instructions to identify the particular experts as ones that have activity relating to the topic within a period of time from a current time at which an identification is made, wherein, for each one of the particular experts, the amount of activity of the particular expert is used to determine the likelihood of participation of the particular expert.
8. A computer system for managing collaborations, the computer system comprising: one or more processors, one or more computer-readable memories and one or more computer-readable storage devices, and program instructions, stored on at least one of the one or more storage devices for execution by at least one of the one or more processors via at least one of the one or more memories, the program instructions comprising: program instructions to receive a request for collaboration on a topic; program instructions to identify, for a collaboration, a plurality of experts that have expertise in the topic, wherein at least two of the plurality of experts have a different one of a plurality of different threshold levels of a likelihood of participation in the collaboration, wherein the likelihood of participation in the collaboration is the percentage based estimation that the expert will participate in the collaboration based on a relative location of the expert to a collaboration site and whether the expert belongs to an organization hosting the collaboration, and wherein the plurality of experts are identified using a number of collections of information; program instructions to set the plurality of different threshold levels according to a level of expertise of the plurality of experts; and program instructions to identify particular experts of the plurality of experts that have a respective particular likelihood of participation that exceeds one of the plurality of different threshold levels.