Is our cosmos just a membrane on the edge of a far stranger reality?

String theory is the best candidate we have for a theory of everything. Bend to its rule and the various tangled theories of conventional physics emerge as part of a sublime, higher-dimensional tapestry. It can unify all four of nature’s forces, including the most troublesome of all, gravity. With any luck, it can also tame big bangs and black holes without losing the thread.

There’s just one catch: string theory can’t explain a universe like ours. Its maths can describe gazillions of different possible universes, just not one expanding at an accelerating rate, which is precisely what we see ours doing. To be sure, no one knows what is driving this acceleration – a mysterious “dark energy” is the usual placeholder. According to theory, though, it probably shouldn’t be happening at all.

For 25 years, this has been a big problem, but now we may have found a way past it. Superficially, the answer won’t shock anyone used to the extravagance of modern physics: we just have to rethink our universe as part of a much grander enterprise. Do this, and it can balloon to its heart’s content – indeed, accelerated expansion seems to come naturally. But this new scheme may be the wildest yet, one in which our familiar space is delicately poised between high-dimensional hyperspace and complete nothingness. “In our proposal, our existence is like a shadow – a projection onto a wall at the end of the world,” says Antonio Padilla, a physicist at the University of Nottingham in the UK.

For all its present-day grandeur, string…