There are a lot of numbers in science that are so big as to be mind-boggling. The number of atoms or molecules in a substance is an example of that. Physicists seem to delight in the weird and wonderful ways to convey these kinds of numbers, and one example that has been repeated for several decades (and maybe longer) is how much of Caesar’s last breath we are currently breathing in. And yes, we are sharing in that delight.
Quick history recap. On March 15, 44 BCE – the famous Ides of March – Julius Caesar was stabbed 23 times to protect the Roman Republic from his dictatorial attempt to concentrate power in his own hands. The average lung capacity of a human is around 6 liters and we will assume for ease of calculation (anyway, none of you were there) that Caesar was perfectly average.
There are about 2.5×1022 molecules in a single liter of air. That’s 25 followed by 21 zeroes. Caesar’s last breath was six times as large, so 1.5 x1023 molecules. Twenty-one centuries later, the molecules of Caesar’s last breath are now well distributed around the atmosphere, where the number of molecules is usually given to be around 1044 based on its estimated mass and surface density.
The average breath is not as big as our whole lung capacity, so let’s place it for convenience at one liter. To find the number of “Caesar” molecules in each of your breaths, you first divide the number of molecules in the atmosphere by the number of molecules in the Roman dictator’s last breath. Then you take the number of molecules in your breath and divide it by that number. We find that with each breath you inhale, you get 31 Caesar molecules.
We’re sure we hear you complain: “Well, technically those molecules were only coming out of Caesar, they were not part of his body!” That’s a fair comment, so let’s give to Caesar what belongs to Caesar. After his assassination, Caesar was cremated. During cremation, about 3.5 percent of the original bodyweight is left behind.
Again, assuming Caesar to be an average human male of 70 kilograms (154 pounds) that gives us 6.5×1027 atoms in his body. Most of that will be water, so let’s say that on average the molecules will be a bit more than triatomic and say that 1.5×1027 molecules of Caesar were freed during the cremation. That means every breath you take contains 31,000 molecules that were within the Roman ruler. The number sounds enormous, and yet it would be just 0.000000000000000124 percent of your breath!
Some of you might be saying: “Dear IFLScience, we commend the calculations and the commitment to the bit, but telling my relatives at Thanksgiving that they are breathing tens of thousands of dead dictator molecules is not nice.” Firstly, we say give it a go, although we do also have a less macabre and more fragrant alternative.
Cleopatra, the last ruler of the Ptolemaic Kingdom of Egypt whose life and eventual death were intertwined with Caesar’s, was renowned for her perfume. Its possible fragrance was recently reconstructed, smelling of resins, herbs, and spices, and it was long-lasting. Let’s assume that in the 38 years of her life, Cleopatra used one liter of that perfume – well, five molecules of that are entering your nose with this very breath!
