B Difference between LQC and Causal Sets

[windy miller]

Ive read that Casual Set theory says that spacetime is made of spacetime atoms. But doesn't LQG says something similar? Or is just space atoms in LQG? A laypersons expansion fo the main difference would be very much appreciated?
Also does Cause Set theory assume spacetime is fundamental rather than emergent?
Many thanks

 

[AfonsoDeAlbuquerque]

I will try to explain main differences between Causal Set Theory (CST) and LQG. First of all, both proposals "predict" that spacetime at the fundamental (quantum) level is discrete - in other words made up from "grain", "atoms". However, from conceptually point of view these theories are different. CST essentials are partially ordered causal sets (causal posets) i.e. sets of events with some chronological order. Those posets encode causality and since they are locally finite - discreteness (finite volumes of continuum contain finite amount of elements of the causal set).
On the other hand, LQG assumes that spacetime at the fundamental level is composed from spin networks - nodes and links with assigned quantum properties - spacetime will be discrete and built from "chunks".

CST just like LQG assumes that spacetime is fundamental (but discrete), so gravity/spacetime isn't an emergent phenomena.

 

[windy miller]

thanks for this, much appreciated.

 

[Fractal matter]

thanks for this, much appreciated.

There is also Causal dynamical triangulation where spacetime is made of simplexes(higher dimensional triangles).