"Structural limits of the materials?" please explain.

[gordon stelter]

> Ron replied:
> >Yes, I have also heard (or heard of) all sorts of
> folks saying all 
> >sorts of things. The physical fact is that this
> doesn't work. The 
> >physical structural limits of the materials just
> don't make it 
> >possible.
> 

Please explain.
     Thump

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