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Question: Is there an end to the universe. If so, what is it made of and what is on the other side of the barrier?
Is there an end (edge) to the Universe? We commonly talk about the edge of the Universe as being as far as we can see and perhaps beyond. The reality is, we cannot see the edge of the Universe. The Universe is expanding and the edge is what the Universe was at the beginning of the expansion.
Conditions in the Universe were quite different 13.7 billion years ago when this started. Understanding what the conditions were like will help in explaining why we can't see the edge of the Universe.
For about the first 300,000-400,000 years, the Universe consisted of a soup of particles like quarks, electrons, protons, neutrons, and eventually the nuclei (centers of atoms) for hydrogen, helium, and some deuterium. Also, moving around among these particles were photons, bundles of electromagnetic energy, or what we commonly call light. The high energy, high temperature conditions at the time caused the photons to continuously interact with the particles.
This interaction stopped the light from passing through the Universe because its energy was used up in breaking apart combinations of particles that came together, for example, a proton and an electron (hydrogen atom). The Universe was opaque, meaning if you were there, you would not be able to see through the Universe. And, if you were inside the Universe, you would not be able to see outside. To be able to see through anything, light must be able to pass through it.
About 380,000 years after the Universe began to expand (what is called the Big Bang), an interesting event took place. The electrons were able to remain combined with the nuclei of the hydrogen, helium, and deuterium to form stable neutral atoms, that is, atoms with a net charge of zero.
To put it more formally, a neutral atom has equal numbers of positive charges (protons) and negative charges (electrons). Once this occurred, the light no longer needed to interact with the particles and the Universe became transparent. Light could now pass through the Universe, and if you were inside, you could see in all directions all the way to the time when the neutral atoms were formed, but not beyond that time. No light ever came through the Universe from time zero to about 380,000 years after the expansion began.
So, to summarize, the farthest regions of the Universe represent the earliest times in the Universe, and we can't see past that time. We can only see the Universe at times when light was allowed to pass through. The barrier is actually the edge of the time when the Universe was opaque, just before it became transparent.
This leads to part of the answer to your second question: we don't know what the edge of the Universe looks like because we don't receive any light from that time.
What is on the other side? Since we can't see past the time when the stable neutral atoms were formed, we can't see what is on the other side. Discussing this would be the highest form of scientific speculation, or, an intelligent discussion of something we know little, if anything, about. There could be nothing beyond the edge, or there could be millions of other universes. These universes could be going through the same events taking place in our Universe.
Maybe some day with increased understanding and improved technology, scientists will be able to break the opaque barrier and we will know what the edge is like and what lies on the other side
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