system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: what is a half life, and what is it’s significance in science?
gpt
A half-life is the amount of time it takes 50% of any material to decay. Most often this term is used when talking about radioactive materials.

If Chemical X has a half life of 5 years, and you start with 1 gram, then:

* In 5 years, you'll have only 500 mg of usable Chemical X left

* In 10 years, you'll have 250 mg

* In 15 years, you'll have 125 mg

* In 20 years, you'll have 62.5 mg

* etc. You'll never theoretically reach 0 mg because you half the previous amount, not half the original amount.