How long does an individual atom survive?

Factual Questions
1

I know that probably by most, if not all definitions, atoms are not “alive” as we would phrase it, but they ARE little bits of matter that cohere in a manner necessary for them to be called atoms as opposed to say, free-floating electrons or neutrons just hanging out by themselves (if that were even possible).

As you can see , I’m no physicist, but what I mean to ask is how long does a typical unit that we know as an atom – which I’m assuming is a collection of particles like electrons and neutrons and other things that we may or may not be aware of, held together by either the weak or the strong nuclear force – look, don’t jump on me because of my acute and gross ignorance of what an atom actually is (or isn’t) – but what I mean is, if you took what we’d all agree was an atom – let’s just say a hydrogen atom, just for randomness’s sake – is it the prevailing knowledge now that atoms came into existence several hundred thousand years after the so-called Big Bang? And is my understanding that there are a finite number of atoms in our as-of-now “known” universe – in other words, no new atoms “get born” or die of old age or anything like that – in other, other words that they never actually are “removed” from the universe, never to be heard from again – then do they have anything that might constitute a life span?

I mean, let’s say an atom – let’s call him Algernon, just to call him Algernon – sprang into existence several hundred thousand years after the Big Bang. Where he sprang into existence is anyone’s guess, but somehow, Algernon ended up in ME. Maybe he’s an atom in a molecule that hangs out in the minor calcyx of one of my kidneys.

Now I don’t know when Algernon got there – maybe he’s been present since my father’s sperm met my mother’s egg, maybe not – but before that, Algernon was somewhere else, was he not? He didn’t spring into being just because I did.

So, when I die, and I decay, and my atoms go their own ways – I assume that the group of atoms Algernon hung around with in my kidney molecule don’t hang out together after I die “for old times’ sake” but just randomly disperse – how long is Algernon going to be around as we know him? In other words, the same collection of the same electrons and neutrons and other subatomic particles that formed Agernon at the moment he sprang into existence and presumably are the same guys now?

Is Algernon going to just keep going, moving from structure to structure, perhaps being part of a raindrop for a while, then being part of an Arctic moss for a while, then eventually being blasted into space again when the sun explodes, or (God forbid!) be part of a nucleus for an atomic weapon and get fissioned to death?

I guess my question is, will Algernon ever just cease to exist, at least as we know him now? Not “be” under our terms of what “being” is? Will he get annihilated by an atom of anti-matter in a random act of destruction, or will he just entropize out of existence one day?

How long will Algernon, gods bless him, inhabit this area of existence we call the universe?

I’ll leave the question of how many atoms of Albert Einstein are circulating even now in my brain for another session.

2

To start with, since you’re including the same electrons in your definition, not long at all. Chemical reactions, including biochemistry for your friend Algernon, involve swapping electrons around all the time.

3

This is mostly correct. The more accurate statement is that the number of “baryons” — which, for our purposes, means the total number of protons and neutrons in the Universe — is constant. Most atoms consist of multiple protons and neutrons (along with some electrons to keep things electrically neutral), but hydrogen is an exception: most hydrogen atoms consist of just a single proton and an electron, no neutrons.

Now, every time Algernon enters into a chemical reaction with another atom or molecule, his electron is going to get shuffled around. So if you view Algernon as irrevocably changed when his electron is replaced, he’s not going to last very long at all. But the nucleus is going to persist unchanged, so if you view the Algernon in terms of his nucleus alone, and the electron as a replaceable part (as most scientists would view it), then Algernon will live on.

Under this definition, the only time when an atom can be born or die is in a nuclear reaction. (Neglecting antimatter, which is vanishingly rare outside of laboratories.) In these reactions, the total number of baryons is conserved, but they can be shuffled between nuclei, causing one element to turn into another. (Neutrons can also be turned into protons or vice versa in these reactions, which has roughly the same effect.) It’s possible that he’ll be picked by a scientist to be collided with another atom, or participate in a nuclear bomb somehow.

But the far more likely ultimate fate of Algernon is that he hangs out on Earth, shuttling from molecule to molecule, until the Sun turns into a red giant billions of years from now and swallows up the Earth. At that point, Algernon is likely to get smashed into another atom at very high speeds (since the atoms in the Sun are so hot), at which point his protons and neutrons will end up in another atom and he’ll cease to exist in any meaningful sense of the word.

Note, by the way, that if Algernon is a hydrogen atom, it’s highly likely that he’s been around since the Big Bang. If he’s a helium atom, it’s probable as well. But anything heavier on the periodic table (lithium, beryllium, boron, carbon, etc.) was most likely created out of primordial hydrogen atoms in a star, via the same kind of process in which Algernon will eventually meet his doom.

4

Protons do decay - however their half life is extremely long. Their decay hasn’t been observed, but is required by several theories. But the half life is in the 10^30+ year range, the current age of the universe is nothing compared to this. But if the universe doesn’t close in on itself first then eventually there will be no protons left and Algernon will be no more.

5

Algernon may live forever, or he might decay tommorow - it’s just probable that he will decay in a long time, and live out the rest of forever as a bunch of sparsely spread subatomic particles

6

Stellar nucleosynthesis isnt churning out protons and neutrons as we speak?

7

Stellar nucleosynthesis is putting protons and neutrons together into new nuclei, but it isn’t creating the raw materials. There’s nothing in the current Universe that protons and neutrons could be produced from.

8

Leaving aside the possibility of proton decay, isn’t the notion of “survival” of subatomic components such as protons and neutrons moot?

I say this since there is no way, even in principal, to distinguish among, say, any two protons or any two neutrons. In other words, we could never determine whether the protons in an atomic nucleus today are the same ones that were there yesterday.

9

Only if he is radioactive, surely (and many atoms are not) or is unlucky enough to suffer a direct hit by some very energetic particle.

By the same token, you could never determine that they were different, and it is definitely more parsimonious to assume they are the same.

Is it really a fact, though, that we could not distinguish one proton or neutron from anther in principle, or is it just that we do not currently know of any way, and can’t think of any way, in which we might distinguish them? It seems to me it is bad policy to rule out the possibility of further discoveries unless there are very compelling reasons to do so.

10

Isn’t the case, though, that the indistinguishabilty of subatomic particles of the same “species” (even in principle) underlies many of the properties of quantum physics? I am asking, not pontificating.

11

In statistical mechanics this comes up when counting microstates a lot. If you assume particles are distinguishable, you get too many microstates and the wrong answer. Wikipedia has an example.

So it’s not just “here are all the properties of particles we’ve found – we think that’s all of them, so any two that match on those properties must be the same”, there are actual experiments that get different results as a result of indistinguishably.

12

Great cite.

I’ll dig around Stanford Philosophy for relevant discussion

13

Not quite right. Protons are produced through beta decay. That uses up a neutron, though. Neurtons are produced through reverse beta decay, which uses up a proton. In either case, consevarion of baryon number is maintained.

Protons are also produced in some high energy situations where no neutron is used up. But there’s always an antiproton produced at the same time. Again, this conserves the number of baryons, since antiprotons count as -1 baryons.

14

Well, isn’t it also the case that for certain statistical purposes it is useful to regard people as though they were indistinguishable? I am not sure that just because it is useful to treat certain similar things as identical in order to get certain calculations to work it necessarily follows that they are identical, especially if, as might be the case, the differences are irrelevant to whatever the calculation is about.

Foe example, suppose gas molecules were all different colors, but that that had no effect on their mass, elasticity, kinetic energy or whatever. You would certainly be justified in ignoring their colors (which you might not even know about) in any calculations relating to the statistical thermodynamics of the gas, but it does not follow that the colors are not there and might affect something.

15

I know it’s just Wikipedia, but the principle (and reality) of indistinguishability of atomic particles seems pretty well established. Don’t like Wiki? Okay here’s a more erudite source.

16

There’s nothing in theory though stopping each particle having it’s own identity, for example in Bohmian mechanics particles do have trajectories and yet it recreates the predictions of quantum mechanics. What is important is that any label given to indistinguishable particle is interchangeable between them.

17

I don’t doubt that it is widely assumed. I do doubt, however, whether there is any sound basis for such assumptions, or whether science needs to make such assumptions. The Wikipedia article does not inspire confidence in me. Early on in it I find this:

This is obviously nonsense. It is not an empirical fact that every electron in the universe carries exactly the same charge. They have not measured every electron, or even a high proportion of electrons in order to ascertain this. On the contrary, it is not an empirical fact but a theoretical assumption, and one that, so far as I can see, might well be false. If the charges on each individual electron were all slightly different the empirical consequences might not be at all easy to detect. After all, most measurable phenomena in which electrons are involved involve huge numbers of the things, so that slight differences would readily average out.

This may just be a case of Wikipedia giving an inaccurate account of the argument, but I see no particular reason to think it is.

18

And, surprisingly enough, colours would actually effect some thermodynamic properties of the system. The indistinguishably is related to the thermodynamic properties through the partition function which takes a different form for distinguishable particles than it does for distinguishable particles.

To cite a different example (that is less reliant on me remembering my stats mech not get right :slight_smile: ), an electron in an atom can be in a number of states. Mostly those states are determined by the charge of the nucleus and the energy and angular momentum of the electron around the nucleus. By the Pauli exclusion principle, we might expect that would be only one electron allowed in each state, but that is wrong.

It is wrong because electrons also have an internal degree of freedom (spin) that comes in two states (up and down), so the PEP doesn’t prevent a spin up electron and a spin down electron from being in the same state otherwise. One of the many consequences of this, is that the periodic table is twice as wide as it would be otherwise, since twice as many electrons can “fit” into each energy level.

But suppose that electrons had another property, spang, that also came in two varieties (spang right and spang left). That would mean that we could fit four electrons into each state (spin up, spang left), (spin up, spang right), (spin down, spang left), (spin down, spang right) and the periodic table would look different because of it.

The fact that we don’t observe spang in the periodic table suggests that spang does not exist*, and that spin is all she wrote for electron internal degrees of freedom. It’s not just “we’ve looked at electrons for a very long time and not seen any other properties”, but an actual observation of “there are no other properties”.

(*You could certainly imagine more complicated theories that have spang, but also explain why it doesn’t show up in the periodic table, like “all particles in our part of the universe are spang left and spang is conserved so the spang right states are all unoccupied”, but those theories are all more complicated than “there is no spang”.)

19

There are so many electrons out there, how can you make general statements about? After all you couldn’t even hope to examine a significant percentage of them.

What you do is you examine a number of them, infer the general properties of electrons from your observations and form a hypothesis in that regards and then test that hypothesis by examining a number more. The larger the number of electrons you examine to test your hypothesis, assuming observation agrees with it, the more statistically likely your hypothesis is correct; even if it is not a significant percentage of the total number of electrons.

This is empiricism in a nutshell and this is why it is so useful: it’s a rigorous system for making general statements about the World around us, without having to make impossibly exhaustive observations, e.g. examine every single electron. Statements which have been tested to a very high degree of certainty can be regarded as ‘empirical facts’, even if we cannot rule out the small chance they are incorrect.

Therefore it is not incorrect to say “it is an empirical fact that every electron in the universe has the same charge”, even if that isn’t the way I would’ve chosen to state it. Now of course we can’t quite rule out that there is a very small, but in principle measurable, variance in the charges of electrons, though without any reason to believe this, it’s exactly the kind of statement that is likely to fall foul of Occam’s razor). However the success of quantum spin statistics in describing ensembles of particles could be taken as evidence against this as it’s predictions specifically rely on exchange symmetry i.e. the fact that you can swap around indistinguishable particles without altering the state of the system. If there was a difference in charge between electrons that could be measured, then exchange symmetry would be broken and quantum statistics flawed.

20

How about “according to Standard Theory and as generally accepted”? Sure the very laws may be different in different sections of the universe, we don’t really know for sure as verified fact, but we have no current reason to believe it to be so, or that electrons elsewhere behave differently than the ones measured so far.

Thinking about some of this I get confused (no surprise): quantum theory states, I think, that every elemental particle actually is at any particular moment that it is not intercting/“being observed”, both existing, in many forms, and not existing, in some statistical manner, all at the same time, yes? Coherent superimposition.

Doesn’t that imply that each indistinguishable elemental particle is actually replacing itself with every interaction it has? Is, on some quantum time scale, constantly anew?