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Well, a million years is a long time for chemicals to change into other chemicals, too. Do you have citations that show chemicals that take longer to convert in

by pflanze 11y ago

Well, a million years is a long time for chemicals to change into other chemicals, too. Do you have citations that show chemicals that take longer to convert into harmless chemicals in environmental conditions than the atoms in radioactive waste take to convert into harmless atoms?

mikeash 11y ago
The substances listed in the comment I replied to are stable elements. The timeframe for their eventual decay is speculative. If proton decay is real, then these elements will decay with a half-life related to that. There's a rough lower limit on proton decay from available experimental evidence in the neighborhood of 10^34 years. That would give a half life for these elements of something like 10^32 years. All very rough, but it's something along those lines. If protons don't decay (proton decay is predicted by some theories but has never been observed), then it's even more speculative. Wikipedia's "timeline of the far future" (a fun article to read for many reasons) gives an estimate of 10^46 to 10^200 years for all atoms in the observable universe to decay through other means. I'll leave converting that to a half life up to the reader. Incidentally, this means that the popular "launch it into the sun" disposal process actually kicks in automatically, before any appreciable decay occurs. Some billions of years in the future, the sun will expand into a red giant and swallow the Earth, and everything on it. Wikipedia says this happens at 7.59 billion years from now, which is a suspiciously accurate number, but I think for the purposes of this discussion, "billions" is sufficiently precise.
- pflanze 11y ago
  > The substances listed in the comment I replied to are stable elements. The comment you replied to said "more mundane sorts of toxic waste". That would usually be molecules, i.e. built from multiple atoms, probably multiple elements. And every chemical transformation works both ways, and while the probability for a molecule to fall apart or recombine with other molecules might be low, it will never be zero. So to the best of my understanding there's no such thing as a completely stable molecule, the question is simply how long of a time that you consider. Which leads me back to the question what references you have for (toxic, nonetheless, thus probably somewhat reactive) molecules that have a molecular (not radioactive) half life longer than those for the radioactive decay you compare them to. To restate my point: molecules may be less stable than the atoms they are made of, and less stable than the radioactive elements you compare them to.

by pflanze 11y ago

mikeash 11y ago

The substances listed in the comment I replied to are stable elements. The timeframe for their eventual decay is speculative. If proton decay is real, then these elements will decay with a half-life related to that. There's a rough lower limit on proton decay from available experimental evidence in the neighborhood of 10^34 years. That would give a half life for these elements of something like 10^32 years. All very rough, but it's something along those lines. If protons don't decay (proton decay is predicted by some theories but has never been observed), then it's even more speculative. Wikipedia's "timeline of the far future" (a fun article to read for many reasons) gives an estimate of 10^46 to 10^200 years for all atoms in the observable universe to decay through other means. I'll leave converting that to a half life up to the reader. Incidentally, this means that the popular "launch it into the sun" disposal process actually kicks in automatically, before any appreciable decay occurs. Some billions of years in the future, the sun will expand into a red giant and swallow the Earth, and everything on it. Wikipedia says this happens at 7.59 billion years from now, which is a suspiciously accurate number, but I think for the purposes of this discussion, "billions" is sufficiently precise.

pflanze 11y ago
> The substances listed in the comment I replied to are stable elements. The comment you replied to said "more mundane sorts of toxic waste". That would usually be molecules, i.e. built from multiple atoms, probably multiple elements. And every chemical transformation works both ways, and while the probability for a molecule to fall apart or recombine with other molecules might be low, it will never be zero. So to the best of my understanding there's no such thing as a completely stable molecule, the question is simply how long of a time that you consider. Which leads me back to the question what references you have for (toxic, nonetheless, thus probably somewhat reactive) molecules that have a molecular (not radioactive) half life longer than those for the radioactive decay you compare them to. To restate my point: molecules may be less stable than the atoms they are made of, and less stable than the radioactive elements you compare them to.