Can the implications of dark energy be used to bridge the gap between Quantum Mechanics and General Relativity?

Question

Can the findings of the Physics Nobel Laureates of 2011, namely the overpowering existence of dark energy (vacuum energy) have any implications in the quest the combine Quantum Mechanics and General Relativity? Maybe toward a theory of Quantum Gravitation?

Answer 1

YES. The cosmological constant is extremely fine tuned. In a nonsupersymmetric world, bosons contribute enormous zero-point energies to the cosmological constant while fermions contribute an enormous negative amount. For both contributions to cancel in one part in 10 to the 123 is nothing short of miraculous. No other mechanism than unbroken symmetry appears to explain such fine-tuning needed for the evolution of life. Increase the cosmological constant by a few orders of magnitude and sufficient structure formation of galaxies and stars won't happen.

This points to the anthropic principle giving a special role to consciousness and needs a multiverse of pocket universes with different laws of physics. This fits in very nicely with the landscape of compactifications in string theory, and the theory of eternal inflation.

In string theory, any vacuum with a positive cosmological constant has to be metastable, and if so, our phase will have to decay to a more stable vacuum in the future.

As long as we remain in our current phase, the maximum entropy of our causal patch of the universe is bounded by the holographic bound of 10 to the 123.

Answer 2

Dark energy certainly can have implications for unifying QM and GR, in the sense that if we do develop a proper theory of quantum gravity, it should (probably) explain dark energy along with everything else. So any candidate theory that does give the correct density for dark energy becomes much more appealing than one that does not. So in this sense we can use dark energy as a "filter" for candidate QG theories.

However, I doubt that the knowledge of dark energy can lead directly to a quantum theory of gravity. If that were possible without being too difficult, someone would probably have done it already, and as Peter Shor posted in a comment, we probably would have heard about it.