P-man is saying another universe provided the background for this universe to work in, like, we are standing on the other universe. But what if you have to provide your own background from one concept? That concept is "what exists". We try to start with nothing, but nothing is two concepts. What exists is one concept. Outside of what exists is nothing, so nothing requires existence. Existence doesn't require nothing.
The idea "it is" defines inertia. It is, therefore it takes energy to become something else; or, it can't become something else. It has inertia. Existence has inertia. Inertia is what caused repelling forces. A particle of matter hits something and knocks it away because of inertia. It takes time for the particle to reach the thing, and then it knocks it away. But a particle cannot take time to reach something, then draw it to it. Gravity doesn’t take time but acts instantaneously all over the universe. So maybe all attractive forces are different. It is not a repulsive force caused by inertia or existence. It is an attractive force, caused by what?
If the repulsive force comes from inertia, and inertia comes from the definition of existence, the best candidate for the attractive force is the opposite of existence: nothing.
We can't agree that particles make up and define all of space, as I think, but we can agree that particles make up and define all molecules and atoms. We have the idea that the strong force is some attractive force inherent to particles, like a charge. But charges get weaker with distance. I believe the strong force is really a particle trying to separate into nothing, like pushing against the walls of something that doesn't have any more space. That analogy makes sense when you know the further they try to separate, the harder it becomes, like they are trying to get out of an inner tube.
And strings, which have attractive tension are defined as tubes. A string is two particles trying to separate. Particles are existence. When they separate within the world of an atom, they are separating into nothingness, and the fact that nothingness has no space to separate into is the strong force.
There is no such thing as empty space. Having the concept of empty space would mean that something else, another universe had to create the empty space, as you said. Since it didn't, we have a space made of point particles, which has six underlying spatial dimensions since you can't arrange real points in any 3D pattern that has more than 12 directions total, six directions back and forth, six dimensions. This idea that space is made of strings under tension allows attractive forces to happen. Magnetism is a complex set of spatial strings that form in loops, creating an attractive force. Snowflakes form on the strings of space itself.
If you take literal strings or short sticks, like toothpicks, and glue them together to create a real 3D space, the toothpicks line up in six directions, with every angle 60 degrees. Every angle in a snowflake is 60 degrees.