I spend a lot of time on this blog explaining a
physical spacetime model and the underlying metaphysics. In this series of
posts, each entry poses a physics question for the spacetime model, along with
the answer.

**Physics Qustion #4. The Cosmological Constant Problem (Dark Energy Problem).**

Measurements of the cosmic microwave background radiation confirm that the universe is flat. There is not enough matter in it to explain this, so it is thought that there must be some "dark energy" that acts like Einstein's cosmological constant and has just the right value to make the universe flat. Supernova measurements show that the universal expansion is accelerating, and the dark energy is thought to be responsible for this effect as well. Physicists have no idea what this dark energy might be or how it gets so finely tuned as to make the universe perfectly flat. The best candidate, vacuum energy density, doesn't work, because the cosmological constant is 120 orders of magnitude smaller than the vacuum energy density calculated using the Standard Model.

**a. Why is the vacuum energy density not much larger?**The quantum spacetime of our spacetime model consists of a quantum lattice of fermionic points embedded in a sea of bosonic points. The virtual particle-antiparticle pairs that are known to populate spacetime are simply unexcited point-antipoint pairs, and contrary to conventional thinking, do not contribute any observable vacuum energy. The observable vacuum energy comes from the zero point energy or quantum fluctuations of the vacuum, which are quantum fluctuations in the positions of the points from one discrete time tick to another. These positions are independent random variables. While the energy density for a single stationary point is equal to the fourth power of the Planck energy (10

^{19}GeV), which is enormous, the energy density over any appreciable volume of space, such as the universe, is near zero because it is the average of a very large number of independent random variables, which tends towards zero. It is the discreteness of space that makes this happen in our spacetime model. The vacuum energy density is so low, in fact, that it plays no role at all in the cosmological constant, which is something else entirely.

**b. What is the dark energy responsible for the cosmological constant?**In our spacetime model, the number of spacetime points expands at an enormous rate. An initial inflationary period ends with a phase transition in which all matter is created. Elementary fermions (leptons and quarks) are excited fermionic spacetime points, that is, points that remain above their vacuum or ground state energy after the phase transition. After the phase transition and the mutual annihilation of particles and antiparticles, relatively few points are left with particles. Spacetime as a whole continues to expand, although much more slowly than during the inflationary period because the exclusion principle limits the number of new fermionic points for which there is room in the fermionic lattice. At first the rate of expansion decelerates because of the gravitational attraction of the matter, but eventually it begins to accelerate as the matter density decreases and the accelerating expansion of the point creation process dominates. In this state of accelerating expansion the universe is continually driven to flatness. Spacetime is always essentially flat regardless of the amount of matter in it. So, the cosmological constant is an exotic form of energy—the accelerating expansion of the number of fermionic points—which is limited to the current small value by geometry: spacetime as a whole is essentially flat.