Everything you're about to read here seems impossible and insane, beyond science fiction. Yet it's all true.
Scientists now believe there may really be a parallel universe - in fact, there may be an infinite number of parallel universes, and we just happen to live in one of them. These other universes contain space, time and strange forms of exotic matter. Some of them may even contain you, in a slightly different form. Astonishingly, scientists believe that these parallel universes exist less than one millimetre away from us. In fact, our gravity is just a weak signal leaking out of another universe into ours.
The same but different
For years parallel universes were a staple of the Twilight Zone. Science fiction writers loved to speculate on the possible other universes which might exist. In one, they said, Elvis Presley might still be alive or in another the British Empire might still be going strong. Serious scientists dismissed all this speculation as absurd. But now it seems the speculation wasn't absurd enough. Parallel universes really do exist and they are much stranger than even the science fiction writers dared to imagine.
It all started when superstring theory, hyperspace and dark matter made physicists realise that the three dimensions we thought described the Universe weren't enough. There are actually 11 dimensions. By the time they had finished they'd come to the conclusion that our Universe is just one bubble among an infinite number of membranous bubbles which ripple as they wobble through the eleventh dimension.
Now imagine what might happen if two such bubble universes touched. Neil Turok from Cambridge, Burt Ovrut from the University of Pennsylvania and Paul Steinhardt from Princeton believe that has happened. The result? A very big bang indeed and a new universe was born - our Universe. The idea has shocked the scientific community; it turns the conventional Big Bang theory on its head. It may well be that the Big Bang wasn't really the beginning of everything after all. Time and space all existed before it. In fact Big Bangs may happen all the time.
Of course this extraordinary story about the origin of our Universe has one alarming implication. If a collision started our Universe, could it happen again? Anything is possible in this extra-dimensional cosmos. Perhaps out there in space there is another universe heading directly towards us - it may only be a matter of time before we collide.
Michio Kaku went online to chat about parallel universes. Read his answers to your questions in the BBC Space site.
Princeton University - Prof Paul Steinhardt http://feynman.princeton.edu/~steinh/
Dr Michio Kaku www.mkaku.org
Superstring phenomenology and the brane-world
Hyperspace: a scientific odyssey through parallel universes, time warps and the tenth dimension, Michio Kaku
The Elegant Universe: superstrings, hidden dimensions and the quest for the ultimate theory, Brian Greene
Parallel Universes: the search for other worlds, Fred Alan Wolf
The Universe in a Nutshell, Stephen Hawking
Flatland: a romance of many dimensions, Edwin Abbott Abbott, Kendahl J Jubb. 19th century fiction, first published in 1884.