Dear Robert Karl Stonjek:

"Robert Karl Stonjek" wrote in message
...

"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.

If all we can do is measure, then "actual" becomes some
superfluous adjective.

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.

Understood. However you are trying to draw some artificial line
between "apparent" and "actual", and measurement will not support
such a distinction.

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

Assuming the interval is expanding...

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,

It does no such thing. The emitted light is not affected by what
happens to the receiver, or the Universe the receiver is located
in. Only the receiver is affected, the emitter and light are
not.

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.

I am simply trying to drive a wedge between your assumption that
anything that happens here affects what happened then/there. You
may not mean it, but that is what your words are saying.

David A. Smith