wolram said:
To date AFAIK Dark matter and Dark energy are mathematical anomalies, What is the evidence for their existence and what is the latest thoughts as to what these hypothetical enteritis are?
The evidence for dark matter today is quite solid. Here's a pretty good blog post on the subject:
http://www.preposterousuniverse.com/blog/2006/08/21/dark-matter-exists/
There are lots of other pieces of evidence, but the Bullet Cluster is a nice, visual demonstration of dark matter. Though personally I feel that the CMB evidence is much stronger and harder to explain with any alternative model.
As for dark energy, that's a bit more uncertain at the current time. Back in the late 90's/early 00's, there was a flurry of work involving attempts to find alternative explanations for the observations. Currently there are only three main explanations that still fit with the evidence:
1. Dark energy.
2. Modified gravity.
3. Cosmological constant (which is largely considered a subset of option 1).
Modified gravity is largely only still in the running simply because it's a wide-open possibility. There haven't actually been any specific proposals that work well theoretically and also fit the evidence. But the theoretical work that has been done has managed to show that it's really, really hard to modify General Relativity in a self-consistent way that explains the acceleration but doesn't cause other observational problems.
Dark energy is also there because it's wide-open: there aren't any well-motivated theoretical models where some kind of dark energy is derived. There are nothing but ad-hoc models whose specific purpose is to produce dark energy. There are probably many hundreds of such models that fit with the evidence, because nearly all dark energy models are indistinguishable from a cosmological constant with certain parameter choices. Dark energy, at this point, is largely a placeholder for, "Maybe there's a cause we don't yet know?"
The only (somewhat) well-motivated theoretical model around is the cosmological constant, as it is an unavoidable component of General Relativity, one that people had for a long time assumed must be set to zero by some as-yet-undiscovered fundamental symmetry. This was largely assumed to be zero because it has to have a magnitude less than about [itex]10^{-120}[/itex] for the universe to not either immediately recollapse or expand so quickly that no structure forms, and theorists generally feel that such an absurdly small number is highly unlikely to occur. No such symmetry has yet been found.
Largely the theories around the cosmological constant fall into two groups:
1. The cosmological constant is dynamically determined by some physical processes, and has a tendency to relax to very small values (here's one example among many:
http://arxiv.org/abs/hep-th/0311011)
2. The cosmological constant takes on more-or-less random values in different regions of the universe and the one we observe is so small because there would be nobody here to observe it otherwise. This is the case under the string theory landscape, for example.