"Half Life", vad menas?

You see the funny upside down Y symbol. The greek Letter Lambda. Well the symbol for Half Life in physics equations. I think thats why the called it Half Life

I thought using "Half-life" was a clever way to both convey the science-fiction premise and a peculiar set of relevant artistic ideas.

The term "half-life" is a cultural currency: say half-life and people think of one thing first (in the population): nuclear disaster - half-life being the measurement of how long it takes for half a given mass of a radioactive isotope to decay into a stable form. That ominous overtone offsets other present uses for half-life neatly, including understanding lost histories through radioactive decay (usually carbon dating), medical cures that kill only slightly less than they heal, and so on. Everything to do with half-life - in our culture - is a mixed message, a dilemma, and usually it opposes science and technology against "humanities". That cultural background really speaks rather well to the state of affairs at Black Mesa, even if it wasn't precisely nuclear experimentation that went awry. It's a title that means a lot to people, and communciates a lot about the moral and ethical tensions of the game as a work of art in its own right, while consuming only eight letters (or just the one in Greek...).