“Yes, after all…

• **M. P. Hobson & A. N. Lasenby**: “How an we calculate the energy density of the vacuum? … The simplest calculation involves summing up the quantum mechanical zero-point energies of all the fields known in Nature. This gives an answer about 120 orders of magnitude higher than the upper limits on Λ set by cosmological observations. This is probably the worst theoretical prediction in the history of physics! Nobody knows how to make sense of this result. Some physical mechanism must exist that makes the cosmological constant very small. Some physicist have thought that A mechanism must exist that makes Λ exactly equal to zero. But in the last few years there has been increasing evidence that the cosmological constant is small but non-zero. The strongest evidence comes from observations of distant Type Ia supernovae that indicate that the expansion of the universe is actually accelerating rather than decelerating. … the theoretical problem of explaining the value of the cosmological constant is one of the greatest challenges of theoretical physics.” [General Relativity: An Introduction for Physicists (Cambridge, 2006), 187.]

• **Eli Michael**: “Such high theoretical calculations of are a real limit to the plausibility of a non-zero cosmological constant. The above was only an example for a single field, and it is possible that the the contributions of all the different fields associated with the particles of the standard model conspire to produce a cosmological constant that is small. This argument, however, leads to the belief that the cosmological constant is exactly zero, for how could the fields conspire to cancel out all but 1 part in 10^{120}?” [“*How physically plausible is the cosmological constant?*” from the University of Colorado, Boulder, (1999): online]

• **Robin Collins**: “Theoretically, however, the local minimum of the inflaton field could be anything from zero to ρi (see Sahni & Starobinsky 1999, sec. 7.0; Rees 2000, p. 154). The fact that the effective cosmological constant after inflation is less than ρmax requires an enormous degree of fine-tuning, for the same reason as the Higgs field mentioned –for example, neglecting other contributions to the cosmological constant, the local minimum of energy into which the inflaton field fell must be between zero and ρmax, a tiny portion of the its possible range, zero to ρi… If the cosmological constant were not fine-tuned to within one part in 10^{53} or even 10^{120} of its natural range of values, the universe would expand so rapidly that all matter would quickly disperse, and thus galaxies, stars, and even small aggregates of matter could never form.” [*The Rationality of Theism* (Routledge, 2003), 135.]

• **Alejandro Jenkins **(Center for Th. Physics, MIT) & **Gilad Perez** (Yang Inst. for Th. Physics): “one quantity still seems to be finely tuned to an extraordinary degree: the cosmological constant, which represents the amount of energy embodied in empty space. Quantum physics predicts that even otherwise empty space must contain energy. Einstein’s general theory of relativity requires that all forms of energy exert gravity. If this energy is positive, it causes spacetime to expand at an exponentially accelerating rate. If it is negative, the universe would recollapse in a “big crunch.” Quantum theory seems to imply that the cosmological constant should be so large—in the positive or negative direction—that space would expand too quickly for structures such as galaxies to have a chance to form or else that the universe would exist for a fraction of a second before recollapsing. One way to explain why our universe avoided such disasters could be that some other term in the equations canceled out the effects of the cosmological constant. The trouble is that this term would have to be fine-tuned with exquisite precision. A deviation in even the 100th decimal place would lead to a universe without any significant structure.” [“Looking for Life in the Multiverse”, Scientific American (Dec. 2009): Online]