What Are Lapse Functions in 3+1 General Relativity?

[Mazulu]

I have this very interesting article,
http://xxx.lanl.gov/abs/gr-qc/0107097
that found a way to reduce the energy requirements of the Alcubierre drive. The article mentions "lapse functions". Does anybody know what those are?

I'm looking at their definition at http://en.wikipedia.org/wiki/Canonical_quantum_gravity
By the way, I'm still new to tensors.

 

[atyy]

GR as a 4D geometrical theory involves equations that relate the 4D spacetime metric and matter.

GR can be reformulated as a 3D theory with time evolution, provided spacetime topology isn't weird. The lapse is a function that appears in the 3+1 version. http://arxiv.org/abs/gr-qc/0703035