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What do you share in common with everyone who ever lived? 

Albert Einstein. Adolf Hitler. Issac Newton. Lao Tzu. Joseph Stalin. Charles Darwin. Princess Diana. Karl Marx. Nikola Tesla. Confucius. Marilyn Monroe. Stephen Hawking. A hungry wolf. A huge gorilla. A majestic lion. A young elephant. 

 

What do you share in common with all of the above?
 

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I've gotten many answers over the years. The earth. The sun. The sky (this is not a good answer though - what is the sky?). A common ancestor. A love for weight-lifting. A love for neuroscience.

Well, there is something much more intimate and immediate.

We all share the same breath. Air molecules that have passed through every single one of the people and animals above have almost certainly passed through our lungs as well. In fact, there's a good chance you have breathed in the dying breath of everyone in history.

If you're interested, here's the math.

 

​For simplicity, let's just look at oxygen and hydrogen. At any given time, it is estimated that there are about:

  • 4.1 × 10^40 oxygen atoms (atmosphere),

  • 4.5 × 10^43 oxygen atoms (water), and

  • 9.0 × 10^43 hydrogen atoms (water)
     

At any given moment in time, your body contains approximately (for an average-sized human):

  • 4 × 10^27 hydrogen atoms

  • 2 × 10^27 oxygen atoms
     

Working this out:

  • One out of every 21 quadrillion hydrogen atoms (2.1 × 1016 atoms) come from your body.

  • One out of every 26 quadrillion oxygen atoms (2.6 × 1016 atoms) come from your body.
     

Every breath you take are atoms that were once inside another human being (in fact in another living organism). If you take the total number of atoms in the atmosphere divided by the total number of atoms in your body multiplied by the number of breaths you take per year (assuming fairly random distribution):

  • You arrive at quite a startling statistic - you have hundreds of billions of atoms in your body right now that must have come from someone else

  • In particular - if you take a deep breath right now, there is a good chance that one atom from your breath will wind up in the lungs of every other person on Earth at some point in their lifetime. 

  • Which also means that you have a good chance of, at some point in time in your life, to breathe in what someone else had breathed out, but to have in you an atom from his/her dying breath. 
     

We share a lot, literally, with one another.​ In this world of atoms and molecules, we have interacted with every single person who has ever lived. And writing this on the death anniversary of an old friend who is no longer around, I am slightly comforted by the shared memories and that his breath has kept me alive. 

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