What is meant by the edge of the universe where velocities reach the speed of light?
There are a number of concepts put together in this question. By edge of the universe cosmologists mean the edge of the observable universe or the horizon. Just like on Earth the fact that you cannot see past the horizon doesn’t mean there’s nothing past there! (See the next question for more details.) This edge is equivalent to the distance light can travel in a time equal to the age of the universe. In an expanding universe objects separate from other nearby objects at a rate given by the Hubble law: v=H0 r where v is the recession velocity, H0 a constant called the Hubble constant, and r is the distance between the objects. If we ask at what distance R the velocity approaches the speed of light c we can solve for R=c/H0. This is known as the Hubble distance. Now the age of the universe is also given by 1/H0 so we see that recession velocities reach the speed of light when at the distance that we had just defined to be that to the edge of the universe. It all seems very neat but in f
