Every single breath we take, we get at least one atom from Julius Caesar's last breath?

I’ve heard this touted as a fact a few times.

Is it true?

No way to know for sure but this article goes thorough the calculations.
And now we know what The Police were really singing about.

So now we have two estimations: the volume of air in the entire atmosphere and the number of molecules in a single breath. Given that your breath and Caesar’s have the same volume, all we have to so is divide them out, giving us a figure of 6.4x10ˉ⁴. However, we’re not quite there yet; as this is the number of molecules in every cubic meter, so we must now divide this by the volume of a single breath (0.5 liters), and doing so our number comes out to be… drum roll … 1.28 molecules! What does this mean?

Every time you breathe, there’s a good chance that at least one of those molecules was exhaled by Julius Caesar in the throes of death.

Thank you! That is perfect.

ETA: good joke, took me a minute

I was taught it as Galileo’s last breath. It is a favourite question to lead into the entire order of magnitude estimation techniques in science, but especially physics. When I did our equivalent of final year high school / university entrance exams, there was always a question of this nature in the physics paper. They were a lot of fun. Clearly there wasn’t an exact answer, but it was the opportunity to prove that you had a handle on the fundamentals rather than just rote learning.

The link doesn’t work for me.

Very often, the “answer” in articles like this fail to address an important point. Some do, but many don’t. Since the link is dead for me I can’t tell what this article does.

The point is this: Many of the atoms in Caesar’s last breath are no longer in the air at all. Consider the oxygen atoms. You don’t just have to count the number of oxygen atoms in the air. You also have to count the number of oxygen atoms in the oceans. Various biological processes take oxygen and turn it into water. Other processes destroy water molecules and release oxygen. So many of the atoms breathed by Caesar are now part of the Indian Ocean.

The question is sometimes phrased as “molecules” of Caesar’s last breath rather than atoms. This is almost certainly wrong. Probably none of the molecules still exist intact.

Good points. The link is still working for me, maybe try it again.

Atoms react. So any “O” or “C” or even “N” in Julius’s last breath could now be in mineral, vegetate or animal molecules and not be breathable.
But the point stands for realizing the huge numbers of atoms on Earth.

The initial question was never framed to come up with a trivial pursuit like answer. It was always about the methodology. The numerical answer is near irrelevant. But the modern world, and Internet click-bait in particular, morphs these into stupid things that really don’t have much to do with the intent.

A deeper answer that attempted to include metrics of the various metabolic and chemical cycles in the environment would make for an interesting question, but nobody would be expected to have numbers to hand without references. But the simple answer, just assuming simple mixing, should be answerable by anyone with high-school science and some scribble paper, without reference to any other source. That is the point of the question. Not that one possible answer is about 1.

I sincerely doubt it! First of all, the amount of air he exhaled compared to the total volume of air around the earth is fantastically small. Secondly, we exhale CO2, much of which ends up inside of plant life and is no longer in a gaseous state. I do agree with this, however: “Every breath you take contains a molecule of history.”

That bit is, to some extent, the point of the question when posed in a useful context. Yes the volume of air is tiny in comparison, but the number of molecules in a breath is fantastically large. So much so that to a good approximation they cancel out. Avogadro’s number is silly big. 6.02 \times 10^{23}

Mostly not. Mostly what we exhale is just the same air that we inhaled, with only a slight decrease in the oxygen and corresponding increase in the carbon dioxide (and no change at all in the nitrogen, which is most abundant).

That said, the statement in the thread title is certainly too strong. If the average number of et-tu atoms in a breath is 1.28, then it will surely be fairly common to have a breath with no such atoms at all (as well as breaths with 2, 3, 4, or more such atoms).

This is not a comparison of air inhaled vs air exhaled. It is a reference to the fate of most CO2 in the atmosphere: incorporation into a carbohydrate by a plant.

But only temporarily. The plant will eventually be eaten, or die and rot away, and the hydrocarbons will turn into CO2 again.

As I said above, not the same CO2 molecules.

We could easily ignore both oxygen and carbon dioxide in the question. 79% of the air is nitrogen, plus another 1% argon. It goes in and out unchanged each breath. Moreover nitrogen is very stable in the atmosphere, taking significant effort to make it react.

Most of the oxygen we inhale is exhaled again as well. The idea we inhale oxygen and when we exhale it is all replaced with carbon dioxide is far from true (otherwise CPR would not work). Only 3.9% of exhaled breath is carbon dioxide.

Even if all the oxygen and carbon dioxide in the exhaled breath was reworked and wiped from consideration, that 80% of stable nitrogen and argon leave the basic approximation answer correct.

I don’t think that’s correct. As far as I understand, atmospheric nitrogen is taken by bacteria in the soil, which convert it to nitrates. Plants absorb the nitrates and make proteins. This enters the food chain. It passes from plant to animal to other animal. When an organism dies it rots, and releases nitrogen back into the atmosphere. Not so stable.

This is true, but it is very slow. The rate of uptake from atmospheric nitrogen is tiny, within the scope of the question it is probably not going to be significant. Going by the cites, about 700 million tons of nitrogen a year is fixed. So 7 \times 10^{11} kg. The mass of the atmosphere is 5.15 \times 10^{18} kg. We are of the order of one ten millionth of the nitrogen being fixed in a year.

Even over say 2000 years since Caesar, we are fixing well less than a thousandth of the atmospheric nitrogen.

There’s a big difference between “there’s a good chance” and the thread title, which states “every single breath”. When someone says “every single”, unequivocally, that is clearly an exaggeration.

If I’d say, “Ten average breaths will usually contain about 13 molecules,” that would be much more accurate. Some breaths will have none, and some could have five.