# Is the speed of light consistent through everywhere?

A lightyear is a system of measurement based off of how much distance light will travel in a year. But if light is heading away from a black hole that is close enough to be pulling it closer, isn't a lightyear in the negatives? Isn't the light travel speed slower in some places than others?

• In a curved spacetime, there are no global inertial reference frames. Dec 7, 2016 at 3:25
• Possible duplicate of How can a black hole reduce the speed of light? Dec 7, 2016 at 4:02

• I think the OP is referring to co-ordinate speed, in particular the apparent light speed near the Schwarzschild horizon from the standpoint of an observer infinitely far away from the hole (which is what the co-ordinate $t$ in the Schwarzschild metric refers to). This apparent light speed indeed is slower near the hole. You need to stress that your point 2 is the local freespace light speed, i.e. that measured by an observer in a local laboratory confined to their momentarily comoving inertial frame. I think the OP needs a clarification of the difference between local and co-ordinate $c$. Dec 7, 2016 at 4:09