작성자: roberto.c.alfredo 방: physics 일시
The universe is expanding.
That sentence seems to invite an obvious follow-up question: expanding from where?
If a firework explodes, its fragments race outward from the place where it detonated. If a stain spreads across a sheet of paper, we can trace it back toward the point where the first drop landed. If the universe was once much smaller, hotter, and denser than it is today, it feels natural to imagine that somewhere in space there must be a central location from where everything began.
Perhaps there is a cosmic midpoint: one privileged coordinate at the heart of creation.
Perhaps standing there would be like standing at the North Pole, where ordinary directions begin to behave strangely. Maybe galaxies would appear to recede in perfect symmetry. Maybe expansion would look different. Maybe the universe would finally reveal where it keeps its zero.
But according to standard cosmology, there is no such geographic center.
The universe can expand without expanding outward from a place. It can have an age without having a birthplace. And although every observer can truthfully regard themselves as standing at the center of the observable universe, no one occupies the center of the universe as a whole.
To understand how all of those statements can be true, we first have to separate several ideas that sound almost identical.
The Center of the Observable Universe
There is one sense in which you really are at the center of the universe.