Time and Space
I've always been a bit challenged when it comes to visualising the size of stuff. When we were buying our first home in Bristol I couldn't imagine the size of rooms, so a friend advised me to imagine that her husband (who is over 6 foot tall) was lying down in the space. Since then I have bought a further 2 properties by the simple 'two Adrians by two and a half Adrians...sounds about right' method.
So I was delighted by this little nugget of astounding information, from last Saturday's Guardian: there is so little matter inside an atom (the only matter, the sub-atomic particles, only fill a teeny-tiny fraction of the space) that if you could extract all the empty space inside all the atoms of every human being then the whole of the human race could fit into a space the size of a sugar cube. Though I'm unsure whether that still applies if all the human beings were Adrians.
This reminds me (vaguely) of another favourite nugget of astounding information, that Richard regularly uses in his classes: first stretch out your arms as wide as they will go (I think this works even better for Adrian). Let this span represent the length of time that the earth has existed. Now take a nail file, and lightly rub it across the nail of your middle finger. You have just shaved off the whole of human history.
Of course all of this is a bit mind-boggling, and a long way from being able to reduce the space I live in to a simple Adrian equation. For Douglas Adams fans out there, this may remind you of his advice: that the one thing that you cannot afford to have when living in a Universe this size is a sense of perspective.