THE PROBLEM OF CRITICAL DENSITY
"Imagine the Universe, beautiful, just and perfect.
Then, ensure you of one thing: The ‘One’, imagined it a little better than you did."
- Richard Bach -
Another issue currently open is a paradox raised by cosmology, also much too difficult to understand and very peculiar. It is the problem of the average density of matter in the Universe, or more simply, the problem of Critical Density.
The fate of the Universe is dependent on its density. To understand this problem we must consider that the destiny of the Universe is dependent of a precious number omega: Ω. This number represents the overall average density of all the matter / energy in the Universe.
If the density is high, the influence generated by the gravitational forces are stronger and they will stop the expansion, forcing the Universe to close and collapse, getting back to a Big Crunch; otherwise if the average density of matter is low, nothing will be able to stop the process of expansion, and our Universe will expand forever, becoming in to an open Universe, dispersed, empty and cold.
What occurs in practice is that the density of our Universe has got a very delicate value, very close to the critical density, which means Ω0 = 1. This number puts us exactly between an Open Universe and a Closed Universe, which makes our Universe with a radius of curvature practically plane, flat and null.
These data report that the density of matter/energy existing in the Universe is not substantially higher or lower than the critical density and therefore the space is not substantially curved, positively or negatively.
A real puzzle that points to the fact that our Universe is neither open nor closed, but somewhere between the middle of these two states.
Within an infinite number of possibilities that could have led to an open or closed Universe, how come our Universe seems to have exactly the critical density Ω0?!
This issue is very delicate and it’s often associated to another 'cosmic tuning'!
Currently, it is assumed this incredibly precise number of matter/energy and density of the Universe as a fact, however, still waiting for an explanation.
The density and the fate of the Universe are closely related according to this variable omega:
Ω0 = 1 => Plane Universe
Ω ≥ 1 => Closed Universe
Ω ≤ 1 => Open Universe
The observed abundance of Hydrogen, and also Helium indicates that the baryonic density of normal matter cannot be greater than 0,1 of critical density. However, to this value we must add the dark matter, which in total will not exceed an overall density much higher than 0,2. This implies that the density of our Universe is very close to the critical density.
Why is omega so close to 1? Is it really equal to 1?
Given that the Universe has been expanding and in a continuous process of creation since the period of inflation, we could consider the fact that the current density is very near to the critical density implies that this constant would have the exact value equal to 1 at a time closer to the beginning of Universe.
This leads us to suspect that the initial critical density of the Universe would be exactly equal to the critical density. Which means that at sometime in the past Ω0 = 1!
With the new model of inflation presented, with absence of gravitational forces, this issue could be easily resolved and this cosmological problem of the critical density would no longer be a problem!
After this period of huge inflation expansion occurs, whatever it was the geometry of the Universe before this period, the new geometry would be necessarily flat after the expansion; and the value of its density would be necessarily 1.
Track number 4: The Universe could arise with any density it desires ... The period of inflation ends precisely when the Universe reaches the critical density! As soon as the energy of the false vacuum enters and restores the positive density, just above the value zero!
There is a specific process and a scientific principle that explains why the density of the Universe has the value it has. This number of this mysterious constant did not need any ‘cosmic tuning’!
Thus, by changing only one variable, we can solve three major cosmological problems! In the hypothesis used it was sufficient to remove from our equation one single variable: the Gravitational Force!