Understanding the universe’s expansion can be quite perplexing, especially when we try to envision what it’s expanding into. Unlike everyday experiences where objects expand into surrounding space, the universe doesn’t expand into anything; it expands within itself. This concept challenges our intuition because we’re accustomed to expansions occurring within a pre-existing space.
A helpful analogy is to imagine the universe as a loaf of bread baking in the oven. As the dough rises, raisins embedded within it move farther apart. Importantly, the dough isn’t expanding into the oven; it’s expanding within its own structure.
Similarly, galaxies within the universe move away from each other as space itself expands, but there’s no external space into which the universe is growing.
This expansion traces back to the Big Bang, approximately 13.8 billion years ago, which marked the beginning of the universe’s rapid expansion from an extremely dense and hot state. Since then, space has been stretching, causing galaxies to recede from one another.
Notably, this doesn’t imply that galaxies are traveling through space away from a central point; rather, space itself is expanding, increasing the distance between galaxies.
It’s natural to wonder about the “edge” of the universe or what’s beyond it. However, current cosmological models suggest that the universe doesn’t have an edge in the conventional sense. If the universe is infinite, it doesn’t require an external space to expand into; it simply becomes less dense over time as space stretches.
If the universe is finite, it might curve back on itself, similar to the surface of a sphere, meaning you could theoretically travel infinitely without encountering a boundary.
In essence, the universe’s expansion is an intrinsic process where space itself grows, increasing the separation between galaxies without necessitating an external “outside” to expand into. This concept, while abstract, aligns with our current understanding of cosmology and the nature of space-time.
So, to put it simply, the idea that the universe is expanding but not really expanding into anything is very difficult to grasp.
Even experts in the field admit that it is a real brain teaser, but that is certainly where the evidence points.
For now, humanity will have to be content with continuing to research this topic and hopefully someday developing a fuller understanding.
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