Is dark energy lurking in hidden spatial dimensions?

The mysterious cosmic presence called dark energy, which is accelerating the expansion of the universe, might be lurking in hidden dimensions of space. The idea would explain how these dimensions remain stable – a big problem for the unified scheme of physics called string theory.

Ever since astronomers discovered in the mid-1990s that other galaxies are accelerating away from us, physicists have struggled to explain why. Their favourite suggestion is quantum vibrations in the vacuum of space (called vacuum energy or the cosmological constant) that could produce repulsive gravity.