The Los Angeles Times has a friendly piece on the latest in multidimensional cosmology: brane theory.
It’s sorta like string theory but with easier math. So if you thought all that high school string theory was going to be as useless as trig and PE, you were only half right. Branes (word derived from membrane) are compared to layers between infinitely large spaces.
Essentially, a brane is a discontinuity in space-time, a boundary where things meet, like the surface of a pond where the water meets the sky.
“It’s a defect in the quantum fabric,” said Ruth Gregory of the University of Durham in Britain. On one side of the defect would be the vacuum of empty space. A vacuum with somewhat different properties might exist on the other side.
Imagine our brane as pond scum — a thin film that divides the air above from a deep (perhaps infinitely deep) body of water below. Most of what we experience is trapped in the scum. But beyond is a whole other world of currents swirling beneath the surface. Their motion might tug on our scum. We’d feel it as nothing but a gentle disturbance, never dreaming of what lurks below.
A brane doesn’t always divide one thing from another. It may just be a condensation of stuff, “a localized lump of energy and curvature that likes to hang together,” Stanford University physicist Steve Shenker said.
The brane world we live in would have to be 3 + 1 dimensions (three dimensions plus time), but they could have many more dimensions. Infinite pond, infinite scum. But no matter how vast the other branes are, we can’t perceive them, since none of the forces we perceive with can pass between branes.
Only gravity can’t be glued to a particular brane. Gravity, as Einstein revealed, is the curving of space-time itself, so it wanders willy-nilly where it will, leaking off our brane into what physicists call “the bulk” — the rest of space-time.
Brane scenarios offer an elegant explanation for why gravity is such a weakling: Maybe it’s not any weaker than the other forces. Maybe it’s just concentrated somewhere else in the bulk, or on another brane.
It’s interesting to consider the timing of these explanations of multidimensional universes coming out in popular newspapers. Or maybe it’s depressing.
Either way, imagining the phenomenal universe as an envelope of hyper-diemsional pond scum is strangely comforting.