> I think the point that Einstein was making that you should be able to explain it to a 6 year old but not necessarily expect him to understand your explanation.

Perhaps, but (a) I don't think so and (b) we'll never know for sure. :)

I'm pretty sure the point he was making is that most scientific ideas are accessible to concise explanation with no loss of comprehension. Of course, he said this before the time of quantum theories, to which he strenuously objected for the remainder of his life.

> I would love to hear him explain why e=mc^2 to a 6 year old and then quiz the 6 year old.

e = mc^2 is actually pretty easy to explain, if one accepts the premise of energy conservation. But I agree that the read-back from the average six-year-old would at best be mildly entertaining. From a truly bright six-year-old, I would hope to hear something like, "Because all energy has to be somewhere, potential energy makes things heavier."

e=mc^2 is the sort form of an equation that includes velocity. Getting a 6 year old to understand energy takes a sloped hill and tossing balls up it. The harder you throw the ball the farther up the hill it goes and the faster it is when it rolls back. To talk about mass take a heaver ball and get the idea that how far up the hill something is * how heavy it is gives some idea how much energy it has at the end. Say knocking stuff over or hitting a wall of sand.

Then describe mass as having energy like a being on top of a vary big hill. If you converted a little bit of mass into energy you have a really fast ball. Like a big ball that's 1/2 way down the really big hill.

This of course assumes an intelligent 6 year old. But, the expression is talking about some six year old not, all of them. You may need to talk about wind resistance as well, but there are some vary good demonstrations for that: http://www.youtube.com/watch?v=ndFXXasM6ZE

PS: Honestly, I think after that discussion your intelligent six year old would probably understand it better than your average high-school or even collage student who has no clue there is more than just e=mc^2.