At the Software Architect 2015 conference in London I presented "What if? Supporting decisions with software dynamics simulations".  This talk introduces the idea of performing numerical simulations of software development teams and the products they build. The value in such simulations is to inform policy decisions and guide deliberate perturbations to the software development process, such as whether and when to add or remove personnel from a project. Simulations should not be used to make hard predications about, for example, when a particular project will be finished.