OK so we've all heard of this from Carl Sagan, Lawrence Krauss and others and we know the argumentation, I don't refute that. There are other examples, for instance I once calculated (this was before I had taken any QM-course) that since there are more particles in a glass of water than there are glasses of water in the world, eventually, (given enough time, could be millions of years?) you will have a particle (atom/molecule) from each individual every lived on Earth (since we all drink water etc.)

But like I said this was before I had heard of indistinguishable particles etc. So later on, I wasn't so sure if I wanted to tell everyone I met about this amazing revelation, because quantum mechanically, every proton (say) is indistinguishable from every other proton, so this whole story breaks down right?

Similarly with the "we're all star dust"-thing. Is it not wrong to state that the protons in my right hand might come from this, and my left from that?

Or, am I overcomplicating things?

To make things clear:

My question is; if it is right to say that "This atom is from that supernova and that atom is from the other etc." At what level is it right to speak of distinguishable particles. For instance, I breath in, breath out...then someone else in the same room takes a breath, swallowing my atoms/particles. Is it right to say that we've shared the same atoms/protons?


You're overcomplicating things. The point is that all elements heavier than helium (and most of helium, too) were created only in stars as elements undergo fusion, and later in bursts of nuclear reactions associated with supernovae. Stars are the universe's transmutators.


You're right that atoms don't carry any sort of identity of where they came from (beyond isotope percentages). Whether the hydrogen atoms in your body were made in the big bang or were made in nuclear decay doesn't matter at all.

The term you want is Nucleosynthesis and there are several processes that produce elements and isotopes but the bulk of the atomic material heavier than iron is the result of the R-process and S-process.

It's certainly tempting for us humans to feel like where something came from or has been is somehow special. For example touching a meteorite may seem like you're touching something unique but the elements in these items don't retain any source identity that would make them special atomically.

  • $\begingroup$ With regard to isotopes, there are things like Carbon-14 in your body that you can say with certainty was made recently in a high-energy interaction such as from cosmic rays in the atmosphere. In a sense Carbon-14 is "star dust" mixed in with some atmospheric cosmic ray reactions and nuclear bomb explosions. $\endgroup$ – Brandon Enright Apr 15 '13 at 15:45

Your edit asking about the distinguishably of particles changes the question enough that another answer is warranted.

At the subatomic level, absolutely nothing distinguishes particles. Every electron is the same as every other. The same is true of protons and neutrons.

Almost all of the heavy elements we (our bodies, the Earth, our solar system) were made in supernova explosions which is why the phrase "we're all star dust" gets said.

What supernova actually make though are just the nucleus of heavy elements. The explosion is so energetic that all the electrons are stripped away and everything is a plasma. It isn't later after the explosion when everything cools and condenses into non-ionized atoms and can form molecules.

There are some distinguishing features of some atoms (isotopes) based on the number of neutrons in the nucleus so it can be said that even at the atomic level there are some distinguishing features. Even with isotopes though, it isn't possible to say "this atom was made in a supernova" and "this other atom was made in a cosmic ray shower in the atmosphere". It's really a statistical distinguisher. If you have a group of a bunch of the same atom of different isotopes you can sometimes say something about those atoms. This is how radiometric dating works.

At the molecular level the diversity is huge. Even within a particular molecular formula you can have different molecules called isomers and even within identical molecules you can have chirality. Molecules are really the smallest compounds where its possible in some cases to identify the origin of a substance or distinguish between substances.

In your example of breathing in the same room as someone else, the distinguishing thing that identifies particles from you versus them is at the molecular level. All of your protons and electrons are the same. You both will have essentially the same balance of atomic isotopes, and most of your molecules will be the same. There will be some complex molecules like proteins or even whole cells that are unique to you. The difference is not in the building blocks but in the macro objects those building blocks make.

  • $\begingroup$ Yeah my question or comment is really that I think on strict technical level it's wrong to state "we're from the stars" (even though I understand the metaphor) etc. simply because of the indistinguishable etc... $\endgroup$ – Faraday Apr 18 '13 at 17:51

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