cosmology - Why do scientists think that all the laws of physics that apply in our galaxy apply in other galaxies?

I like watching different videos about space. I keep seeing all these videos saying scientists found so and so at 200 billion light years away or this happened 13 billion years ago.

My question is why do scientists think that all the physics that apply in our galaxy apply in a galaxy say 200 billion light years away?

What if, say at 135 billion light years away, all of a sudden the time space relationship changes drastically and instead of linear time space relationships the difference becomes based on a "sliding scale" (to revert back to high school). What if a light they first see and estimate to be 200 billion light years away has actually been traveling for another 300 billion light years before we could detect it? Lets be serious, we can't predict the weather farther out than 10 days accurately, and usually not that long....