Why does it happen?

__________________
If we don't play god, who will?-James Watson
I never think of the future, it comes soon enough.-Albert Einstein
The large print giveth and the small print taketh away.-Tom Waits
Any sufficiently advanced technology is indistinguishable from a yo-yo.-Enoch Root, The Confusion
When I was a kid, if someone brandished a shrink gun he'd get a little bit of respect!-Myron Reducto, Harvey Birdman

what exactly do you mean by vacuum welding? Do you mean as a phenomenon or as a technique?

__________________
The More I learn, The More Ignorant I Become

Eagle Eye Observatory

A piece of solid metal stays solid because of the strong bonds between the individual atoms of the metal. If you push two blocks of metal together, normally there would be a thin layer of air or metal oxide still keeping the two apart. If, however, there is nothing at all between them, the atoms of the two blocks can bond just as easily to each other as to the atoms in the same block, and you essentially end up with a single piece. There's a little more detail here.

Wow. This makes sense, but is something that freaked me out!
=D>

__________________

Feynman
>~~~~<
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.

Religion is a culture of faith; science is a culture of doubt.