How big is the Visible Universe?

Let's play with some numbers


We know that the speed of light is a constant

300,000 km/sec

and we know there are 3.26 light-years in a parsec,

so 3.26 Mly = 1 Mpc

Now suppose Hubble's constant (H₀) is 65 km/s / Mpc

This is 65 km/s / 3.26 Mly = 20 km/s / Mly

At what distance from us will the speed of recession reach the speed of light?

Hubble's Law:


v = H₀ d

or

d = v / H ₀

d = 300,000 km/s / 20 km/s / Mly

d = 15,000 Mly = 15 billion light-years

Another thought

How long does it take an object travelling at the speed of light to travel 15 billion light-years?

answer