The CMB is everywhere, and anywhere in the universe it’s the same distance from a hypothetical observer. I fail to see how you can use it as an absolute reference frame.
Not only that, it’s not even a single object. It’s just the name given to a group of radiation, which is ultimately just light going randomly here and there.
It isn’t a single “thing” you are some distance away from. It’s photons remaining from the early universe that can be found everywhere without direction. Pick “one” of them and you can track your speed relative to it. It’s the closest thing we have to a universal reference frame.
Then there’s you who forgot that we actually do have a universal reference frame with the cosmic microwave background.
The CMB is everywhere, and anywhere in the universe it’s the same distance from a hypothetical observer. I fail to see how you can use it as an absolute reference frame.
I think they’re trying to say, it can be considered to be a non-accelerated reference frame, where stuff like planets and stars would be accelerated.
Though I have a problem in understanding how it could be taken as a reference frame in the first place.
Indeed, it can’t be a reference frame, as even if it’s not accelerated, it’s everywhere, so it doesn’t have a position or orientation.
Not only that, it’s not even a single object. It’s just the name given to a group of radiation, which is ultimately just light going randomly here and there.
It isn’t a single “thing” you are some distance away from. It’s photons remaining from the early universe that can be found everywhere without direction. Pick “one” of them and you can track your speed relative to it. It’s the closest thing we have to a universal reference frame.
Also see the later questions on https://www.astro.ubc.ca/people/scott/faq_basic.html
Edit: I’m stupid, photons move at light speed of course. But you can detect a colder and hotter side of the CMB and use that as a reference frame.