Loop quantum gravity (LQG) is a leading approach to quantum gravity that attempts to reconcile general relativity with quantum mechanics by proposing that spacetime itself is quantized. Unlike string theory, which introduces additional dimensions and particles, LQG keeps the framework of general relativity but applies quantum principles directly to the geometry of space.
At the heart of LQG are spin networks—mathematical graphs whose nodes and links represent quantized units of space. These networks describe the geometry of space at the Planck scale (about 10−3510^{-35} meters), where:
- Area and volume are not continuous but come in discrete “chunks”.
- Spacetime is not smooth but has a granular, atom-like structure.
- The fabric of the universe is formed by constantly evolving quantum loops of gravitational fields.
As these spin networks evolve over time, they create spin foams, which describe the quantum history of spacetime—essentially a path-integral approach for geometry.
Loop quantum gravity has made important predictions, such as:
- The resolution of black hole singularities
- A quantum-corrected version of the Big Bang, leading to a possible “Big Bounce”
- Discrete spectra for geometric quantities like area and volume
Though still under development and lacking direct experimental verification, LQG offers a compelling vision of a universe where space and time are fundamentally made of quantized building blocks, governed by the rules of both gravity and quantum mechanics.