Question

Which is larger: the number of meters across the Milky Way, or the number of cells in all humans? Explain or show your reasoning.

Some useful information: The Milky Way is about 100,000 light years across; There are about 37 trillion cells in a human body; One light year is about 10^16 meters; The world population is about 7 billion.

Answer 1

there are more cells in all humans than the number of meters across the Milky Way

Explanation:

Here we are told that 1 light year is equivalent to:

`1ly=10^(16)m`

We also know that the diameter of the Milky Way is

`d=100,000 ly`

Therefore, the diameter of the Milky Way in meters is:

`d=(100,000)\cdot (10^(16))=10^5\cdot 10^(16)=10^(21)m`

On the other hand, the world population is about 7 billion:

`p=7\cdot 10^9`

Every human body has about 37 trillion cells, which corresponds to

`n=37\cdot 10^(12)`

Therefore, the total number of cells in all humans is

`N=np=(37\cdot 10^(12))(7\cdot 10^9)=2.6\cdot 10^(23)`

The second number is larger: therefore, there are more cells in all humans than the number of meters across the Milky Way.