Dark matter: A phenomenological existence proof
  The non-Keplerian galactic rotational curves and the gravitational lensing data strongly indicate a significant dark matter component in the universe. Moreover, these data can be combined to deduce the equation of state of dark matter. Yet, the existence of dark matter has been challenged following the tradition of critical scientific spirit. In the process, the theory of general relativity itself has been questioned and various modified theories of gravitation have been proposed. Within the framework of the Einsteinian general relativity, here I make the observation that if the universe is described by a spatially flat Friedmann-Robertson-Walker cosmology with Einsteinian cosmological constant then the resulting cosmology predicts a significant dark matter component in the universe. The phenomenologically motivated existence proof refrains from invoking the data on galactic rotational curves and gravitational lensing, but uses as input the age of the universe as deciphered from studies on globular clusters. 
D. V. Ahluwalia-Khalilova