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The long-sought value of $q_0$, the deceleration parameter, remains elusive. One method of finding $q_0$ is to measure the distortions of large scale structure in redshift space. If the Hubble constant changes with time, then the mapping between redshift space and real space is nonlinear, even in the absence of peculiar motions. When $q_0 > -1$, structures in redshift space will be distorted along the line of sight; the distortion is proportional to $(1 + q_0 ) z$ in the limit that the redshift $z$ is small. The cosmological distortions at $z \le 0.2$ can be found by measuring the shapes of voids in redshift surveys of galaxies (such as the upcoming Sloane Digital Sky Survey). The cosmological distortions are masked to some extent by the distortions caused by small-scale peculiar velocities; it is difficult to measure the shape of a void when the fingers of God are poking into it. The cosmological distortions at $z \sim 1$ can be found by measuring the correlation function of quasars as a function of redshift and of angle relative to the line of sight. Finding $q_0$ by measuring distortions in redshift space, like the classical methods of determining $q_0$, is simple and elegant in principle but complicated and messy in practice.
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