Lie-to-children
A lie-to-children is an expression that describes a form of simplification of material. The universe, so far as we can observe, is extremely complicated. The first time one explains something to a person (especially a child), one might give an explanation that is simple, concise, or simply "wrong" — but in a way that attempts to make the truth more understandable. (Sometimes, an explanation can accompany it, such as "This isn't technically true, but it's easier to understand.")
Later on, one can admit that the first explanation was a lie, and replace it with the truth, or a more sophisticated lie-to-children, which is nearer to the truth.
Later on you end up having to admit you were wrong, and you can replace your explanation by a more sophisticated lie-to-children, which also happens to be nearer to the truth. You can continue this process all through a persons education.
A lie-to-children in physics
(From [1])
- Weight is constant.
- Children in primary school learn that the weight of something doesn't change if you just change its shape.
- Weight is not a constant. What's actually constant is mass.
- In secondary school, children often learn that on the moon or on mars, an objects' weight will be different, because gravity in those places is different, but the mass will stay the same.
- Mass is not a constant, but depends on the velocity of the object, relative to the speed of light, which is a constant.
- Later on, we find out that relativity says that the mass of an object can vary depending on velocity.
- The speed of light is not, in fact, a constant, but may have been significantly larger than its current value during the early life of the universe.
- This is a theory that may or may not be true. But even if it is "true", it may still be a lie-to-children, for which we don't know the truth.
The term appeared either in one of the few serious books co-authored by Terry Pratchett, The Science of Discworld, or in Collapse in Chaos or Figments of Reality, both by the other two co-authors of The Science of Discworld, Ian Stewart and Jack Cohen.