Re: Mass of everything
The clue's in the name. Since WIMPS interact with ordinary matter only weakly you can't weigh them. (They'd pass right through any scale). Indeed so far we can't measure them in any way. Ergo they can't affect any measurements of mass. The only way we know of their existence is through their contribution to gravitational effects at very large scales. As to why their gravitational effect is not apparent at smaller scales - well you have to remember that that matter in the universe is near to non-existent. O.K. maybe not non-existent, but on average the universe approximates a pretty good vacuum. Assuming dark matter is not clumpy like ordinary matter (i.e. that WIMPS don't strongly interact with anything including themselves) space with WIMPS in it is effectively just space but very slightly less tenuous. It's net effect on anything on a human scale is going to be zero.
Of course, anything that anyone says about dark matter is ,of necessity, highly speculative but the basic idea is actually pretty straightforward.