Question

How many miles is the universe across?

Answer 1

After centuries we finally have an estimate of the size of the universe. The size of the universe is usually given in units used in astronomy because they are very large numbers and it would be impractical to use common units. We can convert the astronomical unit to metres and then convert metres to miles to calculate size of the universe in miles
Formulas used:
$1\,light\,year=9.46\times {{10}^{15}}m$
$1mile=1609.3m$

Complete answer:
The system of planets revolving around a star is called a solar system. A galaxy is a collection of solar systems. In our galaxy, The Milky Way, there are billions of solar systems. The collection of galaxies is contained within the universe. Billions and billions of galaxies exist in the universe. So the universe spreads far and beyond.
It is estimated that the universe has a diameter of $93\times {{10}^{9}}light\,years$. We know that,
$1\,light\,year=9.46\times {{10}^{15}}m$
Diameter of universe in light years will be-
$\begin{aligned} & 93\times {{10}^{9}}light\,years=93\times {{10}^{9}}\times 9.46\times {{10}^{15}}m \\\ & \Rightarrow 93\times {{10}^{9}}light\,years=8.79\times {{10}^{26}}m \\\ \end{aligned}$
Therefore, the diameter of the universe in metres is $8.79\times {{10}^{26}}m$.
To convert metres into miles-
$1mile=1609.3m$
The diameter of the universe in miles will be-
$\begin{aligned} & 8.79\times {{10}^{26}}m=\dfrac{8.79\times {{10}^{26}}}{1609.3} \\\ & \Rightarrow 8.79\times {{10}^{26}}m=5.4\times {{10}^{23}}miles \\\ \end{aligned}$
The diameter of the universe in miles is $5.4\times {{10}^{23}}miles$.
Therefore, the size of the universe in terms of its diameter in miles is $5.4\times {{10}^{23}}miles$.

Note:
The main observable universe is much larger and is still expanding every second. Light years is an astronomical unit which is the distance travelled by light in a year. Other astronomical units are AU, light second etc. When we convert from a smaller unit to a larger unit, we divide the quantity by number of parts.