Three Pieces of the Puzzle.

The cosmological constant problem is a major mystery in physics. The value of the constant, part of Einstein's GR equations, seems to be much smaller than theories predict it should be.

Which 'theories' are meant? The sentence is not clear.

At the heart of this puzzle are three intertwined concepts  vacuum energy (the energy of empty space), dark energy (the cause of the accelerating universe) and the constant itself.

The problem is none of these terms are physical clear.
Starting point of the evolution of the universe is, that at any instant, the total universe is expanding in size. The consequence is that the energy density is decreasing, but it does not mean that the energy density is everywhere the same. When we assume that vacuum energy is involved than it should be physical clear what it means.

Vacuum Energy
The energy in empty space, made of virtual particles  pairs of particles and antiparticles that constantly appear and disappear.

The amount of Vacuum Energy can be small

The Cosmological Constant
A term, represented by the Greek letter Lambda, that Einstein included in his general relativity equations that describe how matter and energy bend spacetime.

The issue is much more what exactly means: the bending of space time. How is this measured.

The Einsteins Field equations
This equation consists of 6 terms.
 Gij the term which describes the curvature of space time.
 gij the term which describes the structure of space time.
 Lamda the cosmological constant is a term that can describe a repulsive force throughout space.
 G the gravitational constant
 Tij the term which describes the energy and momentum of matter and radiation.
 c is the speed of light.

Specific the details of the terms Gij, gij and Tij are very important to understant the structure of the universe.
'Nothing' is mentioned of what is observed. What makes all of this complicated and almost unsolvable that all observations are a function of x,y,z and t, with t in the the range between 0 and 13.7 billion years and with r in the range of 0 and 45 billion light years.



Dark Energy
The force causing the expansion of the universe to accelerate.









