"dlzc" wrote in message
oups.com...
Dear Robert Karl Stonjek:

On Feb 28, 4:45 am, "Robert Karl Stonjek"
wrote:
This one is a little obvious after some thought, but I
haven't heard it mentioned before.

The frequency of light is like a clock in itself - if the
frequency is lower then the clock at the source is
slower as measured by an observer who also
measures that redshift.

The frequency of light is not something intrinsic to light, though,
Robert. It only says something about the relationship between the
emitter and the receiver... and then only if you know something about
the emitter. (Something like characteristic stellar emissions, for
example.)

If the redshifted electromagnetic radiation was a
radio carrier wave then the frequency the observer
must tune to is further down the dial, as expected,
but the sounds transmitted via that carrier wave
will also appear to be slowed down, like an audio
tape running at the wrong speed.

Yes. The analysis of type Ia supernovae provide about four different
measures of distance that are in good agreement. Comparison of clocks
(redshift) to intensity (1/r^2), and more.

This is true regardless of the cause of redshift - source
moving away from observer, source near a gravitating
body, or source at a very great distance (Hubble shift).

The Hubble redshift observed on Earth must also be
accompanied by time dilation. If the frequency of light
received is half, for instance, then the clock at the
emitting end of that electromagnetic transmission is
running at half the pace as the clock at the receiving end.

No. Please consider that proper motion can yield a "half speed clock"
in the other frame... for both frames.


There is a difference between the measured time dilation and actual time
dilation. In expanding space we expect redshift in both directions. But
time dilation is still measured at the receiver end. The frequency of light
is known for certain elements, which is how redshift is established - I
assumed this knowledge above.

Instead of a light wave, let's consider photons. The time it takes for a
photon to pass from emitter to receiver is t=d*c where d is the distance, t
is the transit interval and c is the speed of light. For two photons
transmitted 1s apart, the first photon travels distance d in dc seconds.
But space expands continually so that when the second photon is emitted d
has expanded to d' where d', the distance travelled by the second photon, is
greater than d ie d'd therefore t't

Thus a stream of photons emitted at 1s intervals arrives at a remote
receiver at intervals greater than 1s. Thus any temporal information
emitted will also be time dilated (the intervals are dilated).

But as you point out, this is true *in either direction* ie if the receiver
emits photons at 1s intervals back to the original emitter then they will be
received at intervals greater than 1s.

We know that in one's own frame, time dilation never occurs (by one's own
measure). That is not at issue. Also, when two high velocity objects pass
each other they both measure time dilation and redshift in the other.

In the case of the expansion of spacetime, redshift indicates time dilation.
Thus if the redshift halves the frequency of the emitted light, the
intervals of transmitted photons will also double by the receiver's clock -
time dilation halves the speed of the emitters clock by the receivers
measure.


--
Kind Regards
Robert Karl Stonjek