  We describe a new class of models of quantum space-time based on energetic
causal sets and show that under natural conditions space-time emerges from
them. These are causal sets whose causal links are labelled by energy and
momentum and conservation laws are applied at events. The models are motivated
by principles we propose govern microscopic physics which posit a fundamental
irreversibility of time. One consequence is that each event in the history of
the universe has a distinct causal relationship to the rest; this requires a
novel form of dynamics which an be applied to uniquely distinctive events. We
hence introduce a new kind of deterministic dynamics for a causal set in which
new events are generated from pairs of progenitor events by a rule which is
based on extremizing the distinctions between causal past sets of events. This
dynamics is asymmetric in time, but we find evidence from numerical simulations
of a 1+1 dimensional model, that an effective dynamics emerges which restores
approximate time reversal symmetry. Energetic causal set models differ from
other spacetime-free causal set approaches, e.g. Ref. [1] proposed causal sets
based on quantum information processing systems, and Ref. [2] proposed causal
sets constructed out of standard model particles. Finally we also present a
natural twistorial representation of energetic causal sets.

General Relativity and Quantum Cosmology