Before I post my question, I'd first like to remind everyone (who don't already know) that Hawking's new book, "The Grand Design", is available through Amazon, and may also already be in the the bookstores. If it's as good as his last 2, it should be a beauty! Now for my question: A recent post in this forum on "Planck Length" got me thinking. In Hawking's prior book, "The Universe in a Nutshell", he mentioned the possibilty of other universes (Branes) that could exist outside of our own. We would never be able to observe such Universes, since light is confined to 'our' Brane Universe (although he noted that short wave gravity waves might be able to penetrate through the Brane into our Universe). Anyway, he noted that if such universes exist, they could be as close as a "few millimeters" away from ours. Now I was wondering, why a few millimeters? Wouldn't a "Planck's Length" away from ours be more 'logical'? What's the significance of a ' silly few millimeters"? The Planck length is very significant..a few millimeters is not, in my opinion. Agree?