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When we think of expansion, we usually imagine something getting bigger or moving outward into an already existing space. However, how can something that already consists of everything there is still get bigger?
We know from observations that galaxies that are already far away from us are seemingly moving farther. This phenomenon is thought to have been happening since the Big Bang. Yet, this leads to one of the strangest questions in cosmology: if the universe is believed to have no edge or outer boundary, how could it expand, and what exactly is it expanding into?
The Universe May Not Need an Outer Edge to Expand
One of the reasons this idea is confusing is that we often think of expansion as an object in a room moving outward from its center toward an outer boundary. Like, from that boundary, it is getting bigger and taking up more space in the room. However, researchers believe that the universe may not actually behave like an object expanding into a larger room.
One possible reason is that the universe may be infinite or curved in a way that would make it not have any edge that could expand. In other words, there may not be an “outside” to expand into. Instead, the expansion could be happening internally.
Think of this example for a second. If you marked some dots in a balloon, and imagine each dot as a galaxy, those dots will move farther from each other when you inflate that balloon. However, these dots are not moving across the surface themselves, but rather the space between them is increasing. This could be how our universe is expanding.
Read more: BBC Sky at Night
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Space Itself May Be Stretching
According to modern cosmology, the stars, planets, and galaxies are not simply existing or travelling through a static space. Instead, researchers believe that the space around them is actually expanding over a long period of time.
Today, studies suggest that this could be happening all throughout the universe, and not just in a particular location. In other words, it is not just in our galaxy, even for others, the galaxies around them would seem like it is moving away in every direction.
This phenomenon doesn’t mean that the galaxies themselves are physically growing larger, but instead, the expansion could be happening on a large-scale fabric of space between these galaxies over a long period of time.
Read more: Forbes
Author's Final Thoughts
Although scientists have created a mathematical model that describes the expansion of the universe very accurately, there are still so many questions that need to be answered. Researchers still do not know what could have caused the Big Bang, how dark energy could have influenced the universe’s expansion, or whether the universe itself is truly infinite without any edges.
However, studies still suggest that for the universe to expand, it does not need any outer edges because the expansion is likely happening internally, where the space itself between the galaxies is the one stretching.
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