Dark matter may consist of weakly interacting elementary particles or of
macroscopic compact objects. We show that the statistics of the gravitational
lensing of high redshift supernovae strongly discriminate between these two
classes of dark matter candidates. We develop a method of calculating the
magnification distribution of supernovae, which can be interpreted in terms of
the properties of the lensing objects. With simulated data we show that >~ 50
well measured type Ia supernovae (\Delta m ~ 0.2 mag) at redshifts ~1 can
clearly distinguish macroscopic from microscopic dark matter if \Omega_o
\simgt 0.2 and all dark matter is in one form or the other.Comment: 8 pages, 2 figures, AASTeX, replaced to conform to the version to be
published in ApJL. It is now more clearly written and addresses some possible
systematic uncertaintie