Is there any way to explain how atomic decay actually works. Does this mean the atomic chart actually started with the big bang or whatever the beginning actually was? Does this decay process make it certain that at some point the universe will stop existing?
What is the atomic chart?
Dmitri Mendeleev invented the Periodic Table in 1869.
There were atoms shortly after the big bang, but there was nobody to chart them, and hence no charts, until much later.
I should have said did the time clock on decay start ticking at the big bang or before?
I’m not sure what your question actually is, so I’ll give as much background as I can, and see if we can refine from there.
Every element comes in multiple isotopes. Some isotopes of some elements are stable, meaning they’ll never break down on their own, while others are unstable, meaning that after some amount of time (which can be anywhere from milliseconds to quintillions of years) they’ll decay into some other element. Even the elements that are stable can change into other elements under extreme conditions like the interior of a star: If this takes the element closer to iron, it’ll release energy, and if it takes it further away from iron, it’ll require net energy input.
In the beginning, there were no elements. Go early enough, and the Universe consisted entirely of a sort of soup of indistinct “stuff”, that couldn’t even form protons or neutrons, and after that, there was a time when you had individual protons and neutrons, but not combined into anything.
Eventually, though, they did start fusing into other elements for a while, until the Universe expanded enough that this fusion couldn’t occur in most places. Only the lightest elements were produced this way: Hydrogen, helium, lithium, and maybe beryllium (I’m not certain about that last). Almost all of the hydrogen and lithium in the Universe, and a decent chunk of the helium, dates back to these early days of the Big Bang: It’s what we call primordial. Studying the relative abundances of these isotopes actually tells us a great deal of useful information about conditions at those times.
For anything heavier than that, you need stars. All stars can fuse hydrogen into helium; the more massive stars can also produce heavier elements by fusing helium, once their hydrogen starts running low. The most massive stars can burn all the way up to iron, though the latter stages don’t last nearly as long as the former: The time during which a star is actually producing iron can be measured in hours.
What then of the elements heavier than iron? Well, you can’t get energy out of making them, but you can still make them if there’s energy available. And there is energy available in a supernova, which is where they’re mostly made. A supernova also serves to scatter all of the other elements a star has made across space, where they can eventually find their way into other stars, planets, people, longbows, and so on.
Now, right from the start of the Universe, the laws of physics were such as to allow for some isotopes and not others, and for some to be stable but not others, and for them to gather electrons around them in particular arrangements, and so on (this last is what’s responsible for most of what we think of as the properties of an element, how the electrons tend to be arranged around it). An atom of any of those elements could have been produced at any time in the Universe’s history, given the right conditions. It’s just that, for much of the Universe’s history, those conditions were simply not to be found.
That answered the part of my question I wasn’t sure how to ask. Takes some of the mystery out of it.
Chronos didn’t make this explicit, so let me add that most of the elements are stable. To overgeneralize: A few elements high on the periodic table have no stable isotopes. Some lower down have some stable and some unstable isotopes, but the most common ones are stable. The ones at the bottom of the table have only stable isotopes (except under very unusual conditions.) The vast bulk of the visible universe is hydrogen and helium, otherwise known as stars. Those elements are stable. (Unless it turns out that protons themselves decay, and there is not any evidence of that yet.) So the universe may stop existing for any number of reasons, but radioactive decay isn’t one of them.
All that background, and I managed to miss this point. It doesn’t work by a clock. If you have a bunch of alarm clocks set to random times, and wait until half of them go off and throw them away, the alarm clocks you have left won’t be like the ones you had originally: They’ll have less time left, on average. But that’s not how atomic decays work. If you have 10^24 uranium atoms, those atoms have, on average, just as much time left as any other uranium atoms, no matter how old they are.
A useful analogy is dice. Suppose you have a whole huge pile of dice. Let’s say that they’re many-sided dice, like say 120 sides (this isn’t actually necessary to the thought experiment, but it makes the data a bit smoother). Every second, you roll each and every one of those dice, and if any of them come up 120, you throw that one away. Any given second, most of them won’t get thrown away, but a few will. After a while (in this example, about 83 seconds), half of them will be gone. But the ones that remain will be just as fresh as they were originally. So another 83 seconds, half of those will be left (1/4 of the original number). And 83 seconds after that, half of those, and so on. If you start off with millions, then even after 830 seconds, you’ll still have thousands left. And those thousands won’t know that they’re the lucky ones: They’ll still have a 1 in 120 chance each to die on the very next roll.
I gotta say, post #4 was beautiful. Thank you Chronos. It was almost poetic. A massive simplification, but still valid for all that. And in small words with the big ideas standing right up front.
It’s always neat to see a good explanation by a good explainer totally at home in their field.
Exactly my thoughts after I read his response!
It should be noted that there is a theory that says that no element is really “stable.” It is possible that Protons themselves decay on an immense time scale - half-lives many orders of magnitude larger than the Universe has been in existence.
Chronos’s answer is probably best, but I have a bit to add, if you are interested in the history of nuclear decay and the early universe.
After the big bang, as Chronos says, you have a soup of sub atomic particles, that would not be called protons or nutrons. After a very brief moment, though, those protons and nutrons would freeze out of the soup, mostly solo, but with some small clumps.
So, right after the nucleons condense out of the soup, you are going to have quite a number of isotopes, but really only 3 elements in any meaningful amounts, hydrogen, helium, and lithium. But that does not mean that all you have is these threee stable elements.
The very first things to decay are going to be your really odd elements that have no busienss being together, and really can’t stay together for any measurable period of time. Lithium-3, or hydrogen-9 for instance. These will decay instantly as soon as the pressures lower enough that they are no longer forced together.
The first things to burn off are probably going to be all the odd isotopes of lithium. Other than 6,7,8 and 9, the half lives are on the orders of nanoseconds, and 8 and 9 are on the orders of milisconds. 6 and 7 are stable.
After that, all your excess nutrons that couldn’t find a home with a prton will decay into protons themselves, in half lives of 10 minutes. After a couple hours, there shouldn’t be any free nutrons about anymore. They can’t even cheat and extend their life relatvistically, as they will be bumping into other particles and losing speed, and never get any sort of appricaible time dilation.
Finally, for nuclear decay from the big bang nucleaosynthisis, there will have actually been quite a bit of tritium produced, which will decay to helium 3 with a half life of around a dozen years. So, a century or so after the big band, there will no longer be any tritium about. And that will pretty much end the radioactive decay from the big bang.
It will be another epoch that stars are made and explode, littering the universe with its first dose of heavier elements, some of which will decay, if they are so inclined. This will “restart” the age of nuclear decay in the universe, but any “clock” on a particle would begin when it is made in a star or supernova. (very minor nitpick on chronos’s explanation is that many heavy elements ar produced in stars during their main sequence in the s-process [named so becuase s is for "slow], rather than the r-process found in supernova[named becuase r is for rapid]. This chart gives a bit of a breakdown there, though I saw a better one a few years back that I am not locating now.)
Also, dice are a better way of looking at it than a clock. If you have multiple sided die, then you can say that a particle decays when the die reads a “1”. Some elements do not have a “1” on them, and so are stable forever (at least as long as we know). The elements that do have a “1” on them are different sizes. The longer the half life, the larger the die size. If you are flipping every 10 minutes, then a neutron would be a 2 sided coin, with a 1 on one side, and something else on the other, while an atom of uranium 238 would be a die with trillions of sides.
Now, as to what is actually happening inside of the nucleus when radioactive decay happens, that’s a bit complicated, but isn’t really all that, if you just think of it as the elements seeking their lowest energy state.
There are only a few major ways that most element can decay.
It can convert a neutron to a proton, giving off an electron in the process (as well as a neutrino). This is complicated, but it is essentially because of the weak force. You have W bosons bumping around in the nucleus, never actually existing, as they mass too much to exist for any measurable period of time, but they transfer a few properties of nucleons between them, including the electric charge. They are constantly turning neutrons into protons, but then they run into a proton in the same atom, and turn it into a neutron, so nothing special happens. Except in the rare case that the w manages to get far enough away (usually through quantum tunnelling) from the nucleus before it decays, then it gives off that electron and neutrino, rather than depositing them on a proton, raising the atomic number of the element. This results in beta emission.
The other major way that an atom can decay is through alpha emission. This is when a whole helium atom (two protons and two neutrons) all leave the atom together. This happens to the big elements that have a hard time holding onto all their nucleons, and the outer ones are not as attached by the strong force as they would be in a smaller element, and they are repelled more by the electromagnetic force than they would be. This usually involves quantum tunneling again, as the strong force is in fact rather strong, but only at very short ranges. Once a part of the nucleus is beyond that range, the repulsive electromagnetic forces take over, and expel the alpha particle.
There are other modes of decay, including fission, fusion, electron capture, and double electron capture, but these two cover the vast majority of decays, and the others are more or less a derivative of these.