Is the Universe really Everything?
The edge of reality has been redefined several times in the past. Perhaps "The Universe" is just the next chapter in that story.
However you believe our Universe came into being, whether it was a naturally occurring explosion of matter, or the creation of an intelligent being, you probably believe that it contains all that exists—roughly 10^80 atoms, if the latest estimates are accurate.
I would like to challenge that notion.
Heliocentrism
In 1543, humanity's top scientists knew the Earth was at the centre of everything. Then, Nicolaus Copernicus published his idea of a "Heliocentric" model, positing that it was in fact the Sun at the centre, and the Earth moved around it, making our planet no more special than Venus or Jupiter. He was of course ridiculed for his ideas, and it took a while for the heliocentric model to become accepted, largely because the existing geocentric model was endorsed by the Church. In those days, any ideas that challenged the views set out by The Bible faced significant resistance.
But, today, we accept that the Earth goes around the Sun.
The Milky Way Nebula
In 1610, Galileo Galilei used his telescope to observe that the Milky Way was composed of countless individual stars. Unfortunately for him, his findings and subsequent defence of the heliocentric model caused him to be found guilty of heresy and placed under house arrest for the rest of his life.
But, today, we accept that there are star systems beyond our own.
Sagittarius
In 1918, Harlow Shapley studied the distribution of clusters of stars and found that they were not centered around the Sun, but around a point in the direction of the constellation Sagittarius, indicating that the centre of the Milky Way lies in that direction.
Today, we accept that there is a Supermassive Black Hole, Sagittarius A*, at the centre of our galaxy, and that all the stars in the Milky Way orbit around it.
The Milky Way Galaxy
In 1923, Edwin Hubble observed stars in the Andromeda Nebula, and was able to use them to calculate the distance between Andromeda and the Milky Way, proving that it is a separate galaxy with its own collection of stars, and that other distant galaxies were much the same.
Today, we accept that there are hundreds of billions of galaxies in our universe, each containing hundreds of billions of stars.
An Expanding Universe
In 1929, Hubble analyzed the redshift of light from the galaxies he now knew were separate from our own, discovering that they were moving away from us, and that the speed at which they were moving away from us was increasing, which was formalised as "Hubble's Law".
Today, we accept that the universe is not static, but expanding uniformly in all directions at increasing speed.
The Observable Universe
In 1965, Arno Penzias and Robert Wilson decided to look as far away into deep space as they possibly could, and found that approximately 13.8 Billion lightyears away, in all directions, there was what was effectively a kind of barrier that prevented them from looking any further.
Today, we call this the Cosmic Microwave Background (CMB), a kind of "horizon" that marks the edge of the observable universe. It’s one of the key reasons we believe the universe is around 13.8 billion years old, and why the Big Bang remains our leading theory for its origin.
Observable Universes, Plural?
There are many theories as to the nature of reality. I am a fan of one of the simpler one. There could just be other universes.
Think about just how long it takes light to get anywhere in the cosmos. It takes about 8 minutes for light to reach Earth from our own Sun, and in the grand scheme of things, that's no distance at all. Our nearest stellar neighbour, Proxima Centauri, is about 4 lightyears away, meaning the light emitted from that star takes 4 years to reach Earth. The calculation made by Hubble revealed the Andromeda galaxy to be 2.5 Million lightyears away from Earth, and that's just the galaxy nearest to our own Milky Way.
Point is, these distances are already massive, and we're still talking about our own universe. Somewhere out there, in the cosmic void, there could be trillions of universes that all exploded into existence at the same time, or maybe even at different times. But if the next nearest universe were 14 Billion lightyears away, it would still be another 200 Million years before the light from its formation reaches our telescopes.
There could be a vast cosmos filled with infinite stuff, but we limit ourselves only to what we can perceive in the present moment. Arguably a fine way to live one's life, but not an ideal method for exposing the truth of reality.
Everything, For Now
Each time we thought we had found the edge of everything, we were proven wrong.
We went from one Earth to many planets. From one Sun to many stars. From one Milky Way to many galaxies. Who's to say that, some day, we won't go from one universe... to many?