I mean if I drop a rock into a lake, its makes circles and the outermost circles are the oldest. Or if I blow something up, the furthest debris is the oldest.
In: Physics
Imagine a number line. The number line extends infinitely in both directions, but imagine you are looking at the portion of it that goes from -10 to 10. Each integer has a tick mark.
Now squish the tick marks closer together. Now the portion of the number line you are looking at goes from -100 to 100.
Squish them closer together again. Now the portion of the number line you are looking at goes from -1000 to 1000.
Keep squishing them.
This is like working backwards towards the Big Bang (if our universe were 1D).
The moment of the Big Bang would have been when all the tick marks are squished as close together as they can possibly be. The number line is still infinite in extent, though, so there is no center of it.
After the Big Bang, all the tick marks start expanding away from each other at the same time. So the Big Bang didn’t happen at one spot — it happened everywhere.
You can imagine that all the tick marks start expanding away from 0. Or you can imagine that they all start expanding away from 5. Or you can imagine that they all start expanding away from 100.
Every single point on the number line can be thought of as the center of expansion.
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