I have been thinking about how length contraction should work between two identical objects. Suppose object 1 is stationary relative to object 2, and as measured by object 1, object 2 is a distance of l away. Then, 2 starts moving towards 1 with relativistic velocity v. Because the length l is relative to 1, it does not contract in length in the reference frame of 1, only object 2 itself contracts. However, 2 is moving relative to the length l, so it sees the length itself contracted, as well as object 1. This makes sense to me, and after reading through this post: Special Relativity: Length Contraction Confusion it agrees with what I was thinking.
But then I wondered, why does one of them experience the contraction of the length between them and not the other? What would happen if these were the only two objects in space and had always been moving towards each other at relative velocity v, with no information about which one accelerated; how do you know which one is which? Where and how is the information itself stored which says 'Object 2 should experience the length between them to be contracted whereas object 1 shouldn't', when this seems like such a symmetrical situation? Or am I interpreting this incorrectly?