We are trying to tell you that the universe started off from an unimaginably small, hot and dense point. There was not an explosion, but an expansion of that point. Every part of the universe was expanding. Mass was not expanding, the universe was expanding. There was no mass in the early universe, atoms formed around 370,000 years after the big bang.
The universe is still expanding. All the non-gravitationally bound galaxies are move away from each other. The are all moving away from each other because the universe is expanding. The galaxies are not moving away from some point in space.
Again the universe is not expanding away from a point in space. That would be easy to determine from the velocity of the galaxies. The galaxies are all moving away from each other. It is like, not exactly, but like a raisin bread loaf rising as it is cooked, all of the rasins move away from each other and there is no void in the middle of the loaf.
As the universe expands it cools. Since every point in the universe is expanding the entire universe is cooling not just the nonexistent center.
If there were this void that you propose, that would not support the big bang theory that would disprove it!
The poster brought up a cloud as an analogy. The universe is not a cloud and it is not a raisin loaf.