It’s a little humbling to think that everything we can experience, everything that makes us who we are, is a cosmic afterthought made possible by infinitesimal imbalances of energy from the greatest of all natural events. No imbalances, no us.
If the number of matter-antimatter particles created by the vacuum energy that pushed the universe outward had been identical, the universe would be completely empty.
If anti-matter particles has outnumbered normal matter, we would be living in a completely different house.
So any universal boundary that exists (an edge to the universe), is between place and time, and nothing. Of existence and non-existence. Of laws of nature and no laws of nature.
It is that boundary which is expanding and has no center. It is the “when” and “where” that things can occur that is getting bigger all the time.
Imagine pulling a large rubber sheet with white dots on it from every direction. All of the dots are spreading apart from each other everywhere, not from some central point. From the perspective of each dot, all the other dots are moving away from it.
Outside of the sheet, nothing can happen, you can’t put stuff in there because there is no ‘in there’ to put it.
If everything in the universe is flying apart from everything else, this begs the question, Why aren’t the galaxies, stars, planets, the atoms in my body, also flying apart? Shouldn’t we all be slowly disintegrating as space and time expands?
After all, there is space and time in between protons and electrons, isn’t that space increasing all the time as well?
The answer is yes, but there are other forces at work at closer distances that fight against the expansion of the cosmos. If those forces didn’t exist (things like gravity and the strong and weak nuclear forces), then nothing could form to begin with. It is those forces that create structure and beauty, and us.
For example, gravity keep atoms in a star together so they can shine, it also keeps stars clumped together in galaxies. On a local level, other forces can counteract the expansion of the universe. Chemical bonding and gravity keeps us alive.
These forces can’t hold out forever though. Eventually the universe will win. But for now, we have the upper hand.