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.
The Hubble Constant is a measurement of the rate at which the universe is expanding. It is named after astronomer Edwin Hubble, who first discovered this expansion in the 1920s. The constant is used to calculate the distances between galaxies and determine the age of the universe.
The Hubble Constant is calculated by measuring the apparent brightness and redshift of distant galaxies. Redshift is a phenomenon where light from an object appears to be shifted to longer, redder wavelengths due to the expansion of the universe. By measuring the redshift and apparent brightness of galaxies, scientists can determine the rate of expansion and therefore the Hubble Constant.
No, the Hubble Constant has not always been the same. It was first calculated to be around 500 km/s/Mpc (kilometers per second per megaparsec) but has since been refined to be around 70 km/s/Mpc. This means that for every megaparsec (3.26 million light years) of distance, the universe is expanding by 70 kilometers per second.
A changing Hubble Constant could mean that the expansion of the universe is not constant, and may have been accelerating or decelerating at different points in time. This could also challenge our current understanding of the structure and evolution of the universe.
The current measurement of the Hubble Constant has an uncertainty of around 10%, meaning that it could range from 63 to 77 km/s/Mpc. Scientists are continually refining their methods and measurements to decrease this uncertainty and get a more accurate value for the Hubble Constant.