# I What is the most general form of Hubble's law?

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1. Feb 13, 2017

### Tahmeed

Is the Hubble's law(recessional velocity linearly proportional to distance) valid for all cases even when the spacetime is curved? Is there a nonlinear model for Friedman models or it's always linearly proportional?

2. Feb 13, 2017

### Jorrie

Any non-static spacetime (expanding or contracting) is always curved, so yes, the linear distance-recession rate relation (Hubble's law) always holds. The distance-redshift relation is non-linear and depends on the curvature of space (the spatial curvature-density parameter).