# Hubble parameter

When we observe a distant galaxy we must see that as it is moving from us its speed regarding Earth increases according hubble constant.But as seems it is not a constant but an increasing function of time we have to take in account that for a distant galaxy hubble time function was different in the past as we see far objects as they were in the past.So we have to add a functiion to hubble function to get its actual value for different distances as the speed of light is finite.That function depend how time needed for a photon to reach a distant point in an inflating space depend on time.My question is does the time needed for a photon to reach a point depends only lineary to distance or it also depends of space inflation?

• a distant galaxy [...] speed regarding Earth increases according hubble constant” - While this is model dependent, it is incorrect in the general sense. The Hubble law implies that all speeds remain the same (again, with model specific adjustments). You seem to be misinterpreting the Hubble law by incorrectly assuming that the Hubble parameter is constant in time (so speeds must increase). This is incorrect. The Hubble parameter is generally a reciprocal of the age of the universe (with model specific adjustments) or the Hubble Time. So all speeds remain the same (disregarding repulsion). – safesphere Feb 14 at 3:03
• Hubble law can be interpreted in two ways.1)Every object from big bang has different velocity and it is same till now, distances change but velocities remain the same.....2)space is inflating so every point at a greater distance will move with different speed regard another one but as distance change the velocity also changes like for points on a inflating baloon.... – jbradvi9 Feb 16 at 22:16
• If you are addressing to me (no @ sign), then what you are saying has nothing to do with my comment. In both of your cases, 1 and 2, the Hubble parameter is (at least approximately) a reciprocal of the age of the universe. Also, these two interpretations are not fully equivalent. For example, in the velocity interpretation (1), the entire universe is observable, but in the space expansion interpretation (2), it depends on the cosmological model. – safesphere Feb 16 at 23:09