# If the speed of light is 2.9972 x 10^8 m/s what is the maximum possible radius of the observable universe?

You would calculate it as approximately $1.3 \times {10}^{26}$ m, but it is actually closer to $4.4 \times {10}^{26}$ m
Since the universe began about $13.8$ billion years ago, you would think that the maximum radius is the distance light travels in $13.8$ billion years, i.e. $13.8$ Gly, but that is not so. Using the speed of light given and the time interval, you would calculate the equivalent distance in meters as approximately $1.3 \times {10}^{26}$ m
The light we see from the most distant observable galaxies has been travelling for nearly $13.8$ billion years, during which time the universe has been expanding significantly. The light from those galaxies is strongly red shifted, and the point from which the light came is now significantly more than $13.8$ Gly away from Earth. It is closer to $46.5$ Gly or about $4.4 \times {10}^{26} m$