The idea that some clocks run slower than others is a confusion. Talk of
clocks in general relativity always refers to ideal clocks that, by
definition, run at identical rates when compared at the same place.
"Running slow" really refers to taking a shorter path (less elapsed
proper time) thru spacetime, as reflected in the metric. As AG noted
the "running slow" relation is symmetric; so it can't be invariant.
Using the CMB is an operational way to define a global time. It is the
same as co-moving coordinates in which matter is, on average,
stationary. But it is a good/useful coordinate system because it makes
the representation of an FLRW model simple. There's an implicit
assumption that the universe is homogenous and isotropic, which implies
that it satisfies an FLRW model. With that assumption a measurement of
curvature locally can be extended to infer the whole spacetime. Space
can be flat while spacetime is curved, so as to be open or closed.
Brent
On 1/29/2020 12:57 AM, Alan Grayson wrote:
Considering the distant galaxies, they're receding at near light
speed. So according to SR, their clocks should be ticking at a much
slower rates than, say, a local clock in our galaxy. OTOH, there's a
physical clock for the entire universe; namely, the temperature of the
CMBR. If we tell time by this clock, all clock readings of all
galaxies are identical. So which is it? Are clocks in distant galaxies
running slower than a local clock in our galaxy, or are both clocks
running at the same rate? TIA, AG
--
You received this message because you are subscribed to the Google
Groups "Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to [email protected]
<mailto:[email protected]>.
To view this discussion on the web visit
https://groups.google.com/d/msgid/everything-list/5c5aa450-761d-4784-9ba3-f25085991a83%40googlegroups.com
<https://groups.google.com/d/msgid/everything-list/5c5aa450-761d-4784-9ba3-f25085991a83%40googlegroups.com?utm_medium=email&utm_source=footer>.
--
You received this message because you are subscribed to the Google Groups
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/everything-list/bef2d51e-15ac-2900-cad6-ce94f7fadd80%40verizon.net.
