If the universe is only 13.8 billion years old, and nothing can travel faster than the speed of light (1 lightyear per year), how can the observable universe possibly be nearly 100 billion lightyears across? How do we reconcile the sheer size of the universe with the understanding that it all emerged from an infinitely dense point not so long ago?
In: Physics
Nothing can move *through* space faster than the speed of light, but the space *between* sufficiently distant objects can increase rapidly enough that light emitted from them *right now* will never be able to traverse the distance, and the farther apart they are the more rapidly the space will grow. The overall rate of expansion has also been accelerating over the past few billion years, and this is expected to continue forever.
The entire universe also did not emerge from one infinitely dense point. The observable universe was contained with a very tiny volume, but it wasn’t infinitely small, and entire universe was still far larger than this, and may possibly be infinite. At some point shortly after the big bang, the universe entered a brief “inflationary” period where its size increased drastically before returning to normal expansion.
All of these factors lead to the universe being much larger than one would think based on the speed of light alone.
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