Recent content by S Holtom

Thanks to everyone (except one) for the informative responses. My understanding so far: Space -- The CMB doesn't work so well as a reference frame over large distances, as two observers at rest relative to the CMB will be moving apart. Time -- TBH I'm still not 100% clear on this one. Sorry...

What have I said that violates the laws of physics? Everyone agrees that any arbitrary reference frame can be chosen, including the CMB. Why are you trying so hard to straw man what I've said? Not only have I not claimed that the CMB has a special status in the laws of physics, I have said...

Of course not. We frequently make a distinction in discussion between theory and practice, and rarely does doing so imply that the latter is against the law of physics. That's not what we mean by these expressions. And note that I didn't bring up the laws of physics. I was addressing the point...

This objection doesn't make a lot of sense. If something was explicitly laid out in the laws of physics then it would necessarily be true in theory. So when I suggest that X might be true only in practice, not in theory, it seems strange to point out that X is not in the laws of physics as a...

I don't know what the relevance of these questions is. My answer to both would be: "Use whatever clock you like". I'm not a lobbyist for the CMB consortium. The OP is just about how, while in theory time intervals are relative, in practice there is a universal (lower case u) reference. One that...

What? I'm asking the question as a means of trying to digest the answers given so far. Let's be clear: I have no agenda on this. I'm quite happy with the idea that the CMB cannot be used as a universal clock. What I am trying to get is an idea of why. I wouldn't have started this thread if I...

I think this is being a bit silly. Upthread I said that even if the universe had a visible grid overlaid, then that would techically-speaking also just be an arbitrary frame. However, no-one would deny that it would be special, as a single frame visible to everyone in the whole universe. You...

This is the thing I am still not getting. Let's imagine that you're put into stasis. You wake up, and discover that the CMB now has a wavelength of 5cm. You can be pretty confident that you've been asleep a hell of a long time, but the question is, can you use this observation to know roughly...

It would be the same. (well, actually galaxy scale and universe scale are two different things. But I'll assume you meant to say universe scale) But the point is, the CMB frame does exist, and no others do that we're aware of. It's like if I were to say that the Earth's magnetic field is...

The difference is though, that everyone everywhere has access to "Charlie's" POV. I mean, put it this way: if there was a literal, visible grid overlaid over the whole universe we could call that "just another" frame of reference too. We would still likely consider it "special" though. And...

I think you misparsed what I wrote. I was trying to ascertain whether you were referring to the CMB varying over time or over space. The CMB isn't perfectly uniform over space, but pretty close to it. I wasn't trying to make a claim about the clock varying over space. We might be talking past...

Ah of course

Well they can choose to. They can choose to use the Earth as the basis of a shared reference frame (as we obviously do every day). Why's that?

I said different observers though. We can look at the edge of our observable universe and see events that will never be seen by an observer on the other edge.

Do you mean it doesn't change in a linear way over time, or a uniform way across space? If it's the former, then of course we can factor that into our calculations, and still have a universal clock. If it's the latter...well, I guess that constrains the accuracy of this hypothetical clock.