The Hubble constant, expressed as v = Hd, indicates that the recessional velocity of galaxies is directly proportional to their distance from Earth. This relationship implies that observations of galaxies reflect their velocities at various points in time, raising questions about the interpretation of an expanding universe. The equation is valid only under the assumption of a constant expansion rate; when this rate varies, an integral approach must be employed to accurately describe the dynamics of cosmic expansion.
PREREQUISITESAstronomers, astrophysicists, and students of cosmology who seek to deepen their understanding of the Hubble constant and the dynamics of the universe's expansion.
The above equation only holds when you have a constant expansion rate. When the expansion rate changes with time, you have to use an integral.madness said:The Hubble constant v = Hd tells us recessional velocity of galaxies is proportional to distance. But distance is equivalent to looking back in time. So what we are seeing is the recessional velocities of galaxies at different times in the universe? This surely can't be right, because for an expanding universe, recessional velocity should be proportional to physical distance, not time.