what is a half-life?
In: Physics
It’s a tool we use to describe an exponential loss of something.
For linear loss, you can just use the time it takes to reach zero because the rate of loss never changes, for example your phone’s battery life is X hours.
For exponential loss, the rate of loss actually slows down and approaches zero as the amount of whatever you’re measuring approaches zero. For example, most medicine is metabolised by your body faster at higher concentrations. In this instance, it’s not really useful to talk about how long Advil will remain in your body, because trace amounts can remain for days or weeks, so we go by half-lives instead. Aspirin has a half-life of about 3 hours. So after taking a 200mg dose, the amount left in your system after 3 hours is 100mg. 6 hours after taking it, it would be 50mg. 25mg at 9 hours, 12.5mg after 12 hours, 6.25mg after 15 hours, 3.125mg after 18 hours, etc, etc.
Edit: also it’s a common mistake people make to assume amount left is zero after two half-lives (“well if after 3 hours you lost 100mg, so you should lose another 100 after another 3” is a natural assumption to make). Don’t fall into this trap. It’s actually a quarter of the original.
[RetroAhoy has you covered!](https://youtu.be/bp5vOgz8vyI)
Originally released in 1998, Half-Life was a genre defining first person shooter. It spun off many expansion packs, “stand alone expansions”, and sequels. And soon it will be in VR.
From the Wiki.
Half-Life is a first-person shooter game developed by Valve and published by Sierra Studios for Windows in 1998. It was Valve’s debut product and the first game in the Half-Life series. Players assume the role of Gordon Freeman, a scientist who must find his way out of the Black Mesa Research Facility after an experiment with an alien material goes wrong. The core gameplay consists of fighting alien and human enemies with a variety of weapons and solving puzzles. Unlike many other games at the time, the player has almost complete uninterrupted control of Freeman, and the story is told mostly through scripted sequences seen through his eyes.
Basically, it is the time it takes for half of something to become inactive. You can use this study the movement of medication through the body, the decay of radioactive substances, and plenty of other things out there.
You usually think of it in terms of radiation. Take a substance that radiates–it’s literally shooting out particles and slowly turning into something else. How long does it take half of substance A to turn into substance B? That’s your half life.
This is useful because, in a sense, the process never ends. Substance A will never FULLY turn into substance B, at least not without a significant period of time passing. Rather, as more of A becomes B, the A that is left will appear to turn to B over a longer and longer period of time as there is less of it remaining. This half life point is useful because it tells you at what point MOST (that is, 50.000000….1%) of it will have changed.
In things that decay exponentially, half-life describes how long something takes to decay to half of what it was. This is useful in various systems, but you’re probably thinking of radioactivity. Things with a shorter half-life decay faster, and so are more radioactive but their radioactivity decreases over time.
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