You told me that you read the OP of my "Burning Bush" thread, in which case, you already know my stance regarding the ontology of the universe.
However, coming at this from the perspective of hardcore materialism, this image we've been discussing...
...is a visual representation of a bubble of reality that, at this present moment (and based on pre-James Webb telescope discoveries), is estimated to be approximately 93 billion light-years in diameter.
We're talking about a 93 billion light-year in diameter bubble of reality that, approximately 13.8 billion years ago, was allegedly (and literally) smaller than the tiny dot between these two brackets [.].
And the point is that the blackened area of the above image, along with the blackened area in the following gif that depicts the moment when the infinitesimal singularity [.] began expanding,...
...are both visual representations of whatever it is that is forever making room (relenting/giving-way/opening up, etc.) for the ever-expanding bubble of the universe.
And seeing how the proponents of hardcore materialism allege that time, space, and matter didn't even exist prior to the initial expansion of the infinitesimal singularity [.],...
...then what else other than "absolute nothingness" could those blackened areas be called?
Btw, don't get hung up on the details of those rudimentary images. Instead, use your imagination to peer-out into the farthest reaches of the actual universe, to what, logically, must be a light barrier, and try to picture what the ever-expanding light barrier (the metaphorical "film" of the bubble) is expanding into.
Indeed, if not into an infinite and "boundless" nothingness that could never be filled to capacity no matter how many universes come into existence,...
...then what else could it be?
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