I'm reading this article on Dark matter and dark energy. There is a statement in the document which is as follows
What is the best bet for the nature of dark energy?
...The simplest candidate for dark energy is Einstein’s cosmological constant, which denotes a perfectly uniform fluid with negative pressure that is associated with the lowest energy (vacuum) state of the Universe. However, the observationally required value of the cosmological constant is $10^{120}$ times smaller than the theoretical expectation..
I'm not sure I understand the final sentence here. $120$ orders of magnitude difference is huge and I fail to see what the connection is here between the CC and simplicity?
Any suggestions?
Answer
The $10^{120}$ still worries physicists a lot. It came from assuming the CC is due to vacuum energy in the universe, and the most natural number when one does basic calculations of it gives you the $10^{120}$. See how to get the number, and other description of the CC at https://en.m.wikipedia.org/wiki/Cosmological_constant
So the problem is that we don't know how to calculate for sure the CC from quantum field theory, or any other theory that is completed and accepted as valid. That will remain an issue, with the corresponding uncertainty about what the CC is until we discover what are the particles or 'things' that are responsible for the dark energy, and get a way to estimate the number that would lead to for the CC, from some accepted quantum gravity theory.
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