The “theory of everything” is one of the most cherished dreams of science. If it is ever discovered, it will describe the workings of the universe at the most fundamental level and thus encompass our entire understanding of nature. It would also answer such enduring puzzles as what dark matter is, the reason time flows in only one direction and how gravity works. Small wonder that Stephen Hawking famously said that such a theory would be “the ultimate triumph of human reason – for then we should know the mind of God”.

But theologians needn’t lose too much sleep just yet. Despite decades of effort, progress has been slow. Rather than one or two rival theories whose merits can be judged against the evidence, there is a profusion of candidates and precious few clues as to which (if any) might turn out to be correct.

Here’s a brief guide to some of the front runners.

The theories they summarize:

-String theory
-Loop quantum gravity
-CDT
-Quantum Einstein gravity
-Quantum graphity
-Internal relativity
-E8

New Scientist: Seven theories of everything

(via Wade)