[js1138]

You can't extrapolate and assume that it will work outside them.

So you are saying that if oxygen and hydrogen are mixed under controlled laboratory conditions and a spark is introduced, that the results can't be extrapolated?

I agree that there are limits to extrapolation. Artificial life is a long way away. My question is the same one I always ask. Which is the more productive assumption in science: the assumption that knowledge can be gained incrementally through observation, conjecture, hypothesis and experiment, or the assumption that things are just too darned complicated to understand?

[metmom]

Useful experiments are always carefully designed to limit or eliminate uncontrolled causes and effects. Does this imply that the cause and effect relationship will not work outside the controlled environment?

So you are saying that if oxygen and hydrogen are mixed under controlled laboratory conditions and a spark is introduced, that the results can't be extrapolated?

Yeah. We know that O2 and H2 outside the lab would produce the same result as inside the lab from real life experience. Not because we extrapolated it and assumed it for no reason.

Just because something can be done in a carefully designed experiment to eliminate uncontrolled causes and effects, means that it can happen in *nature* where those causes and effects are not designed out.

If those causes and effects did not exist in nature either, then it would be safer to assume that the same reaction is likely to occur. But they're there so you can't presume that the reaction could have happened in nature.