Francis wrote:
This is a question out of pure human curiosity. Suppose there is a
closed box, a box that completely seals of it's contents from the
outside world. Would it be possible, according to the law's of
physics, that a mechanism inside the box, either mechanical or
chemical or something else, would cause the weight of the box to
change?

No.

(Well, you can play games with the problem specification. For example, the
box could jump around enough to knock itself off a table, which would
increase its weight a bit because it would be closer to the surface of the
earth. Also, it isn't really possible to completely seal a box. But in what
I think was the intended spirit of the question, the answer is no.)

-- Ben