[HN Gopher] Caesar's Last Breath
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Caesar's Last Breath
Author : charliesabino
Score : 118 points
Date : 2025-05-23 14:22 UTC (8 hours ago)
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| lkmill wrote:
| isnt the half life of most types of molecules in air far shorter
| than 2k years? maybe i am nitpicking, but would it not be more to
| correct to say we are breathing the same atoms as those in
| caesers last breath?
|
| edit: itchy trigger finger, think i subconsciously wanted to be
| the first to comment. it is stated quite early that molecules
| preservation is assumed. still think it would be more correct and
| just as interesting to discuss atoms, not molecules.
|
| edit 2: quick research has taught me that nitrogen gas, n2, and
| naturally occurring isotopes do not even have a half life. they
| do not radioactively decay. til.
| oatsandsugar wrote:
| I don't think so -- Nitrogen, the most common part of air, is
| stable in its most common isotope
| lkmill wrote:
| indeed it seems so, i thought all atoms (except hydrogen) had
| some kind of decay. i thought so called stable atoms still
| had half-lives of 10^{very large number} years.
| tgv wrote:
| In this scenario, you can think of a reaction as
| terminating a molecule's life. So if there's a 50% chance
| that an H2O (or CO2) molecule reacts in a certain period,
| that could be its half-life time.
| SJC_Hacker wrote:
| If you buy into the Big Rip, then all particles in the
| universe (including protons and neutrons) will eventually
| disintegrate
| jasongill wrote:
| your post made me laugh because it makes the theory sound
| like propaganda that is sponsored by Big Rip
| kjs3 wrote:
| Big Bang, Big Rip, Big Crush. Cosmologists like Big
| Things.
| cyberax wrote:
| If we're talking about these kinds of scales, N2 molecules
| are not stable because there's a non-zero probability for
| the atoms to fuse into a heavier element through tunneling.
| And this will release more than enough energy to break the
| chemical bonds, of course.
| hnuser123456 wrote:
| Maybe you saw this story recently?:
| https://phys.org/news/2025-05-universe-decay-years-sooner-
| pr...
|
| Also, bismuth was once thought to be the most massive
| "fully" stable element, but turns out does decay with a
| half life of 10^19 years, compared to the universe's age of
| ~10^10 years.
|
| Neutrons decay into a proton/electron pair after 15 minutes
| when not part of a nucleus.
|
| Protons appear to be fully stable for any practical
| considerations, however they might decay after 10^30 years.
| pvg wrote:
| What's the 'half-life' you're thinking of? Your basic gas
| molecules will last a lot longer than 2k years short of being
| involved in some reaction or another. And a lot of these
| reactions aren't that easy in atmospheric conditions- e.g.
| pulling nitrogen out of the atmosphere
| https://en.wikipedia.org/wiki/Nitrogen_cycle
| victorNicollet wrote:
| I have seen the similar assertion "some of the water molecules
| you drank today were once part of a dinosaur", which is false
| because water molecules do not last very long when in liquid
| phase (they continuously swap protons, turning into hydronium
| ions and back).
|
| The O-O and N-N bonds are much stronger than H-O bonds, but
| there are still atmospheric processes that can break them. For
| instance, O2 undergoes photodissociation under ultraviolet
| light and recombines into O3 ozone, and N2 likely also
| undergoes photodissociation. And obviously, the fact that
| living beings breathe O2...
| satvikpendem wrote:
| People should instead say atoms, not molecules. Or maybe even
| say quarks.
| BurningFrog wrote:
| Photosynthesis breaks up CO2 and H2O molecules to make O2 and
| C6H12O6 (glucose).
|
| I don't know how often the average water CO2/H2O molecule
| gets dismantled this way, but there can't be many left since
| 44 BC.
| victorNicollet wrote:
| The atmosphere is estimated to have ~830PgC worth of CO2,
| and plants are estimated to photosynthesize ~120PgC worth
| of CO2 every year, so a given molecule would have 14%
| chance to be broken down in a year. The probability to
| survive for 2000 years would be around 1e-60.
|
| Of course, CO2 contents of the atmosphere have varied over
| the last 2000 years, and not all CO2 is produced into or
| consumed from the atmosphere (it can be dissolved in
| surface water, etc).
|
| EDIT: since there's much more O2 than CO2 in the
| atmosphere, a given O2 molecule has a 8% chance to not be
| broken down by respiration over 2000 years.
| adonovan wrote:
| > would it not be more to correct to say we are breathing the
| same atoms as those in caesers last breath?
|
| You may be right, but according to quantum mechanics, you can't
| really meaningfully talk about the "same" atoms, or any
| particles, because they don't have identities. There was a
| particle here, now there's a particle there, but we can't say
| exactly where it was at all the times in between, and it may
| not have been at any particular place: its amplitudes may have
| passed through two doors at once.
| hilbert42 wrote:
| This is sn oldie but it beautifully illustrates orders of
| magnitude and how many atoms there really are.
| ninalanyon wrote:
| Estimation without any attempt to quantify the distribution of
| each of the components of the formula doesn't give me much
| confidence in the result.
| d--b wrote:
| What? There is 10^22 breaths in the atmosphere? I guess the
| atmosphere is huge.
| lkmill wrote:
| i guess this also means there are around 10^23 farts in the
| atmosphere. a quick empirical study just showed there around 10
| farts to a breath.
| dudeinjapan wrote:
| So we're also breathing Caesar's last fart.
| d--b wrote:
| Well, once every 10 breaths on average.
|
| But on the other 9 breaths, you get to breath quite a lot
| of his other farts... So... your breath is really never
| Caesar-fart-free.
|
| But as a consolation, most of humanity will breath your
| farts on every breath, so...
| shmeeed wrote:
| Empirically, my buddies' farts seem to weigh in way above 0.1
| breath.
| xixixao wrote:
| But do the molecules really disperse like that? The molecules
| were all in Caesar's mouth before he released them in his last
| breath. Is the movement of molecules such that they are now,
| roughly 2000 years later, about equally spread around the Earth?
| Is there more of them in Rome? In Italy? In the norther
| hemisphere?
| pvg wrote:
| The dispersion assumption tends to make the estimate more
| rather than less conservative.
| horsawlarway wrote:
| I think the contention is that I don't have an intuition for
| how molecules actually disperse, but I do know that general
| climate trends certainly aren't "random dispersion".
|
| Ex - we see consistent, long term, patterns in weather that
| make it unlikely that this dispersion is anything close to
| "ideal gas in a chamber" style dispersion.
|
| Further - we have all sorts of compounding effects. Ex -
| atmospheric escape is a real thing, plants do nitrogen
| fixation, hydrogen and oxygen can be bound up in the oceans,
| etc...
|
| Maybe 2000 years is enough time for real random dispersion,
| maybe it's not. But it's a huge assumption baked into this
| that doesn't feel especially reasonable to me.
|
| All we have is this:
|
| >If we assume that a breath diffuses evenly throughout the
| atmosphere and that these molecules are preserved over time
| (a reasonable assumption--nitrogen is relatively inert)
|
| Which... I challenge is likely not a particularly reasonable
| assumption to base this on.
| kortilla wrote:
| Long term climate patterns are much slower than dispersion.
| pvg wrote:
| _we have all sorts of compounding effects._
|
| It's still an atmosphere mostly made of nitrogen, on a
| scale vastly exceeding 2000 years.
|
| _I don 't have an intuition for how molecules actually
| disperse, but I do know that general climate trends
| certainly aren't "random dispersion"._
|
| Big volcano eruptions make for pretty sunsets across the
| world. Nuclear testing fallout is detectable in everything
| since atmospheric nuclear testing began. Everywhere we find
| the K-P boundary, we find iridium. The counter-assumption
| (which may well be true!) is the counter-intuitive one.
| hnuser123456 wrote:
| The jetstream moves north and south over the US in somewhat
| predictable ways each year. But the molecules in the
| jetstream never stop flowing, and the jetstream tends to
| diverge after it reaches the Atlantic ocean. Sometimes it
| does another tight lap around the artic circle, sometimes
| it veers down towards Africa, sometimes it splits and goes
| both ways:
|
| https://en.wikipedia.org/wiki/File:Aerial_Superhighway.ogv
|
| The jetstream blows at around 110 mph, and Earth's
| circumference at mid-northern latitudes is around 12500
| miles, so it takes 12500/110=114 hours or just under 5 days
| for the jets to complete a lap around the planet, assuming
| we choose a molecule that doesn't take a diverging path on
| that lap. That's 73 laps per year, so 2000 years is nearly
| 150,000 times that the faster parts of the atmosphere have
| circled the globe, twisting, breaking, and reconnecting
| paths the whole time.
| advisedwang wrote:
| It depends where you are. If you live in Italy, assuming
| dispersion makes the estimate more conservative (ie the
| assumption that it has dispersed means there is less of
| caesar's breath near you than the alternative) but if you
| live in Australia, it is less conservative (ie dispersion
| favours there being caesar breath near you).
| lkmill wrote:
| i believe so, https://en.wikipedia.org/wiki/Maxwell%E2%80%93Bol
| tzmann_dist....
|
| 2k years is a long time for gas dispersion in such a "small"
| volume as the earth's atmosphere. early weather behaviour
| probably affected the distribution unevenly, but by now it
| should be relatively evenly distributed across the globe. no
| more or less in rome or italy. this is, however, as we say in
| sweden, a "guy's guess".
| pugworthy wrote:
| Not gas dispersion, but it's crazy how fast some compounds can
| disperse in the human circulatory system when introduced by IV.
| If you've ever had IV saline flush you may know that metallic
| taste that seems to show up in your mouth almost instantly.
|
| Similarly, there is a sensation from Adenosine for chemical
| cardioversion that creates a hot flushing feeling inside your
| body as it spreads, and it's quite the sensation to feel it
| going from your chest down to your extremities in a few
| seconds.
| foobiekr wrote:
| Wait hang on. Is it possible the metallic taste after a flu
| vaccine is the saline?
| munchler wrote:
| > If we assume that a breath diffuses evenly throughout the
| atmosphere and that these molecules are preserved over time
|
| In other words, let's hand-wave away the most interesting part of
| the question, and then come up with a trivial answer to
| whatever's left.
| symmetricsaurus wrote:
| Well actually, air molecules (N2, O2) are indistinguishable. This
| means that they are fundamentally interchangeable with each other
| and it's not well defined what "same" molecules mean. You can't
| label the individual molecules.
|
| It's of course possible to track a single molecule if you really
| try hard. But this hasn't been done since Caesar's time and the
| molecules have mixed. Even if we knew the exact state of the
| universe right now and could play back time perfectly it would be
| impossible to say that some particular molecules were part of his
| last breath.
| fedeb95 wrote:
| doesn't this assume both the external layer of the atmosphere and
| all of the earth to be impermeable to breath molecules?
| jamesgill wrote:
| _" Obviously, many simplifying liberties were taken."_
|
| Yes, I would agree. Perhaps too many. But it's a fun exercise.
| cm2012 wrote:
| Super neat. Did not expect the math to work.
| seydor wrote:
| Well now every salad is Caesar's salad
| diego898 wrote:
| Purely empirical observation, in my own life, make no claim as to
| humanity/society/etc.:
|
| It's interesting how often fermi estimation problems are used as
| proxy's for "intelligence". Something like: 'let's assess how
| well "they can think" - how many golf balls fit in a baseball
| stadium?' etc.
|
| Often, doing well in these kinds of problems can more than makeup
| for a lack of specific knowledge in something someone is
| interested in assessing!
| miobrien wrote:
| This reminds me of a question from my first interview as a
| college grad: estimate the number of taxis in New York City. I
| was totally baffled by it.
| singleshot_ wrote:
| I'll simplify for manhattan and extrapolate for the four
| outer boroughs. Ten avenues, a hundred streets. A thousand
| blocks? One cab per block? One thousand cabs in manhattan?
| 5,000 total?
|
| There are about 13,500 taxi medallions.
| BubbleRings wrote:
| How many breaths do I have to take, to pull in an oxygen atom
| that used to be part of a dinosaur, and was also in Caesar's last
| breath? Could we turn this number into a unit of measure, so we
| can name it the...Caesaur? Caesarasaur?
| tempodox wrote:
| I fell for it, I thought it was _kai su, teknon_ ("you too,
| child"), to Brutus.
| dimitrios1 wrote:
| technically, the diminutive teknion would be more appropriate
| in this context. Teknon was more formal, and in its colloquial
| usage was used commonly in the stereotyped phrase "women and
| children", which in the ancient world was a symbol of low
| social status. The diminuative would indicate a different
| usage, more affectionate, friendly, etc.
| throe73848484 wrote:
| > How many molecules from Caesar's last breath do we inhale with
| each breath we take?
|
| > If we assume that ... these molecules are preserved over time
| (a reasonable assumption--nitrogen is relatively inert),
|
| But they are not inert. Single UV photon can break single N2
| molecule bond.
|
| Elemental N is highly reactive and will form new N2 molecule
| pretty fast, but that is NEW and different molecule!
|
| N2 is not stable over period of 2000 years under constant
| exposure to solar UV radiation!
| dmurray wrote:
| A really good point.
|
| So what's the rate of this photodisassociation?
|
| I found it weirdly hard to Google an answer on this. Firstly,
| rates are given in terms of decays per second instead of in
| half-life which would be more relevant for our purposes.
| Secondly, it seems to be well studied in the interstellar
| medium than in atmospheric conditions.
|
| Anyway, the most relevant measurements I could find [0] say
| photodisassociation of N2 in the interstellar medium happens at
| a rate of approximately 10^-10 s^-1 - i.e. every 10 billion
| seconds on average.
|
| Caesar died about 60 billion seconds ago [1] so at that rate,
| many of the molecules would still be alive.
|
| However, we don't live in the interstellar medium. By
| interstellar standards, we pretty much live on the surface of
| the sun. The average point in the ISM is maybe 2 light years
| from the nearest star [2] but we are only 10^-5 ly away.
| They're all the same photons, but radiation intensity
| diminishes with the square of the distance, so our nitrogen
| molecules should disassociate every 1 second instead. If that's
| true, Caesar's last breath had its last surviving molecules
| persist for only a minute or two after Caesar himself.
|
| [0]
| https://www.aanda.org/articles/aa/full_html/2013/07/aa20625-...
| https://www.aanda.org/articles/aa/full_html/2013/07/aa20625-...
|
| [1] https://math.answers.com/math-and-
| arithmetic/How_many_second...
|
| [2] https://www.livescience.com/space/how-far-apart-are-stars
| munchler wrote:
| True, but I think that only occurs in the upper atmosphere and
| at a very low rate. Atmospheric N2 is also converted by
| bacteria into ammonia, which is absorbed by plants. And
| lightning oxidizes N2, as do combustion engines. I'm not sure
| if all those different reactions add up to a significant
| fraction, though. It might be true that most of the N2
| molecules from Caesar's time still exist.
| ahazred8ta wrote:
| Air is 1% argon (9340 ppm) and those atoms remain in the
| atmosphere without being chemically removed.
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