Layman's question: When determining the time it takes for a chemical element to decay, why do we document it by half the time it takes(ie. half life)?

[ModerationNow!]

When you ask the distance to a destination, do you ask the "half distance"? When a doctor takes your blood pressure, do they document it in "half pressure"? When you step on a scale to measure your own weight, does the scale indicate your "half weight"?

No.... Nobody does that! We make whole measurements, not half measurements. But for some reason, when you look to see how long it'll take for an element like plutonium to FULLY decay, they don't provide you with the whole measurement. Instead, they inexplicably tell you it's "half life", which is only half the time it'll take to fully decay. Why??

 

[AmNat]

When you ask the distance to a destination, do you ask the "half distance"? When a doctor takes your blood pressure, do they document it in "half pressure"? When you step on a scale to measure your own weight, do you look down and see the scale's display, and it reads 170lbs, do you think to yourself, "ahh, my half weight is 85lbs".

No.... Nobody does that! No one makes "half measurements"! We make whole measurements, not half measurements. But for some reason, when you look to see how long it'll take for an element like plutonium to FULLY decay, they don't provide you with that measurement. Instead, they inexplicably tell you it's "half life", which is only half the time it'll take to fully decay. Why??

Decay is exponential, not linear. After two half-lives, 1/4 of the sample will be left. After three, 1/8. And so on. The “full” decay time is infinite.

 

[Redress]

When you ask the distance to a destination, do you ask the "half distance"? When a doctor takes your blood pressure, do they document it in "half pressure"? When you step on a scale to measure your own weight, does the scale indicate your "half weight"?

No.... Nobody does that! We make whole measurements, not half measurements. But for some reason, when you look to see how long it'll take for an element like plutonium to FULLY decay, they don't provide you with the whole measurement. Instead, they inexplicably tell you it's "half life", which is only half the time it'll take to fully decay. Why??

1: "chemical element" is kinda redundant. Just say element.
2: Not all elements have half lifes, just radioactive ones...ie ones that decay.
3: As mentioned above, it is because radioactive decay is exponential. If a half life is X units of time, and you have 100 atoms of that element, then after X, you will have 50 atoms. After 2X, you will have 25, and so on.

 

[RabidAlpaca]

When you ask the distance to a destination, do you ask the "half distance"? When a doctor takes your blood pressure, do they document it in "half pressure"? When you step on a scale to measure your own weight, does the scale indicate your "half weight"?

No.... Nobody does that! We make whole measurements, not half measurements. But for some reason, when you look to see how long it'll take for an element like plutonium to FULLY decay, they don't provide you with the whole measurement. Instead, they inexplicably tell you it's "half life", which is only half the time it'll take to fully decay. Why??

I feel like this is something you could've easily googled if you don't remember it from middle school science class. Did you really think this was just some wacky thing someone cooked up?

 

[bluesmoke]

I feel like this is something you could've easily googled if you don't remember it from middle school science class. Did you really think this was just some wacky thing someone cooked up?

Maybe he hasn't taken that class yet. Or is naturally suspicious of anything scientific. Like climate science and epidemiology.

 

[AConcernedCitizen]

When you ask the distance to a destination, do you ask the "half distance"? When a doctor takes your blood pressure, do they document it in "half pressure"? When you step on a scale to measure your own weight, does the scale indicate your "half weight"?

No.... Nobody does that! We make whole measurements, not half measurements. But for some reason, when you look to see how long it'll take for an element like plutonium to FULLY decay, they don't provide you with the whole measurement. Instead, they inexplicably tell you it's "half life", which is only half the time it'll take to fully decay. Why??

The "half life" is not half the time it takes to fully decay. Rather, it is the time it takes for half of the element to decay.

 

[Loulit01]

Maybe he hasn't taken that class yet. Or is naturally suspicious of anything scientific. Like climate science and epidemiology.

And evolution and they're not quite sure the earth is round.

 

[ModerationNow!]

Maybe he hasn't taken that class yet. Or is naturally suspicious of anything scientific. Like climate science and epidemiology.

So, you're insinuating that I don't believe in science just because I asked a question about science? Not that I owe you an explanation(or that I'd want to deal with you in any capacity, now that you've outed yourself as a angry conspiracy theorist), but it was just a question, which is literally what science is! You're the one jumping to irrational conclusions about other people, simply for asking a question, which is a completely UN-scientific mindset btw!

 

[ModerationNow!]

Decay is exponential, not linear. After two half-lives, 1/4 of the sample will be left. After three, 1/8. And so on. The “full” decay time is infinite.

Thank you for a logical answer to my question. Thanks for not automatically inferring that, by asking a scientific question, I'm a "science denier".

 

[ModerationNow!]

And evolution and they're not quite sure the earth is round.

Seriously dude? I asked a question about chemistry, and included a little bit of humor to it, but you take that innocent, humorous scientific question, and jump all the way to the conclusion that I'm denying that the Earth is round? That's an incredibly paranoid leap! Science is literally about asking questions and being skeptical. It's NOT about being blindly and uncritically dogmatic, and it's not a paranoid leap to assume that you personally prefer option B.

 

[Loulit01]

Seriously dude? I asked a question about chemistry, and included a little bit of humor to it, but you take that innocent, humorous scientific question, and jump all the way to the conclusion that I'm denying that the Earth is round? That's an incredibly paranoid leap! Science is literally about asking questions and being skeptical. It's NOT about being blindly and uncritically dogmatic, and it's not a paranoid leap to assume that you personally prefer option B.

My post was meant to be humorous as well. My intent was not to offend. I apologize.

 

[ModerationNow!]

The "half life" is not half the time it takes to fully decay. Rather, it is the time it takes for half of the element to decay.

Thanks.

1: "chemical element" is kinda redundant. Just say element.
2: Not all elements have half lifes, just radioactive ones...ie ones that decay.
3: As mentioned above, it is because radioactive decay is exponential. If a half life is X units of time, and you have 100 atoms of that element, then after X, you will have 50 atoms. After 2X, you will have 25, and so on.

1). I used "chemical element" because I wasn't sure everyone in an off topic political forum would know what I was talking about if I just said "element".
2). I am aware of that. I was going to use the most stable, unstable element as my example, but there are just too many zeros to bismuth's half life.
3). Thanks for answering the thread question.

 

[ModerationNow!]

I feel like this is something you could've easily googled if you don't remember it from middle school science class. Did you really think this was just some wacky thing someone cooked up?

In the first days of my 9th grade science course, the teacher(Mrs Gordon) decided to bump me up to an 11th grade chemistry course, because she thought I could handle it. Little did she know that was the beginning of my rebellious phase, where I completely lost interest in school work, because I hated that new school. So I returned to the 9th grade science course, where the justification for the use of half life was never explained.

We were transferred from NC to southeast PA, where my strong southern accent made me an instant target for ridicule and bullying, which took a toll on my self esteem. So my primary daily goal was to get the hell out of there! I ended up signing up for a work release program in 11th and 12 grade, and we only needed 2 years of science and math to graduate.

So that's all I took.

 

[bluesmoke]

And evolution and they're not quite sure the earth is round.

They'll make their own decision after reviewing the facts.