Article Why doesn’t the expanding Universe break the speed of light?

[C C]

https://bigthink.com/starts-with-a-bang/...eed-light/

KEY POINTS: It’s absolutely true that there’s an ultimate speed limit for how fast any object can travel through the cosmos: the speed of light in a vacuum, or 299,792,458 m/s. And yet, when we consider the expansion of the Universe itself, we have to reckon with the fact that today, just 13.8 billion years after the start of the hot Big Bang, we can see objects up to 46.1 billion light-years away. How does this not violate Einstein’s theory of relativity, and how does this not break the cosmic speed limit: the speed of light? You have to go deep into the science to understand it.

EXCERPT: . . . most of us understand the basic concept of special relativity — the “nothing can move faster than light” part — but fail to appreciate that the real Universe cannot accurately be described by special relativity alone. Instead, we need to take into account that the Universe has a dynamical fabric of spacetime underpinning it, and that it’s only the motion of objects through that spacetime that obey those laws of special relativity.

What isn’t encapsulated in our common conception is the way that the fabric of space departs from this idealized, flat, three-dimensional grid where each successive moment is described by a universally applicable clock. Instead, we have to recognize that our Universe obeys the rules of Einstein’s general relativity, and that those rules dictate how spacetime evolves. In particular:

• space itself can either expand or contract,
  
• space itself can be either positively or negatively curved, not only flat,
  
• and that the laws of relativity apply to objects as they move through space, not to space itself.
  

In other words, when we say “nothing can move faster than light” we mean “nothing can move faster than light through space,” but that the motion of objects through space tells us nothing about how space itself will evolve. Alternatively, we can only assert that nothing moves faster than light relative to another object at the same location, or event, in spacetime... (MORE - missing details)