Hungarian solution to the CC puzzle?

Csaba Balázs from Argonne, IL, and István Szapudi from Honolulu, HI, propose their courageous solution to the cosmological constant problem.

• hep-th/0603133

It is based on holography, especially its Fischler-Susskind-Bousso cosmological version. It reminds me of the debates around 1998. My advisor Tom Banks would say that according to holography, there are no bulk degrees of freedom, and therefore there should really be no bulk contribution to the vacuum energy. I have always been excited by these ideas. Problem solved. Almost.

The new paper is philosophically similar. The authors argue that the total energy in some region can't ever get larger than the mass of the black hole of comparable radius. This principle of course implies that the vacuum energy is determined from the known value of the radius of the Universe or, if you wish, the Hubble constant - just like the observations indicate.

If the Universe gets bigger, the maximum allowed vacuum energy density goes down like "1/R^2" in the Planck units. The authors explain why their bound should hold for vacuum energy just like it holds for conventional matter. It is not hard to buy this argument, I think.

What seems much harder to me is to answer the question Why is the Universe so big then? In their picture, the vacuum energy density is pegged to the Hubble scale. They don't explain how can this link be compatible with effective field theory that is successful in all other respects. More importantly, they don't say how the vacuum energy and the pegged radius of the Universe evolve with time. Why does not the vacuum energy stay near the Planck density, keeping the Universe Planckian in size?

As you can see, I remain skeptical about the details but if you have something more positive to write, write it here!