The issue with ICBM interception as I understand it is that it’s one of those cases where the economics heavily favor the attacker. An intercept missile requires a rocket just as capable the one launching the target, if not more so. But, you can’t afford letting even a few nukes get through, even one is devasting, so given that the chance of a successful intercept isn’t 100 percent (my understanding is that it’s well below 100% currently, for likely real world conditions), you need several intercept missiles for every missile your enemy has. Any countermeasures that make taking the enemy missile out harder, like deploying decoys or such, increases the needed resources on your end far more than it increases the resources used by them.
It might be viable against countries like North Korea where the difference in resources is vast enough, but against any serious opponent like Russia or China, it’s not likely to work out.
The last bit about the big bang isn’t really how it works to my understanding. The big bang is compared to an explosion, but its actually more like a balloon inflating, if you imagine the surface of the balloon as analogous to space. The galaxies don’t all move away from some original center to the universe, new bits of space get “added” in between every bit of space, so that every object gets farther away from every other object. If you go backwards in time far enough, every point sees itself as being the center. At least, that’s how I’ve seen it explained.