eli5 / How do we know the half life of (or even that it is radioactive) Bismuth-209 when it is literally longer than the age of the universe by several orders of magnitude
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Some good answers here. But it’s worth noting two things—
1. We don’t KNOW (like we do with shorter life things and can see the entire decay curve). We measure a small part of that curve and make the (reasonable) assumption that it will curve like everything we DO know about.
2. The two most cited articles in Metrologie (the premiere measurement journal) are both about the high level of uncertainty in the very rare times we’ve measured them. We do make a lot of assumptions and have little data for these age-of-universe decays. As opposed to, say, carbon dating which is much better demonstrated.
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