Can we stand one.

Light can be shifted by cosmological redshift, proper motion, or
gravitational redshift.

Is it possible to examine just the light and tell which cause results
in the effect.

Say I have a good telescope and send the collected light through a
hole into a room with clever people and all kinds of equipment. they
can only look at the light, they can't see where the scope is pointed
nor examine other objects in the vicinity of the source. Does the
light carry a signature?

"Charles" wrote in message
...
Can we stand one.

Light can be shifted by cosmological redshift, proper motion, or
gravitational redshift.

Is it possible to examine just the light and tell which cause results
in the effect.

Say I have a good telescope and send the collected light through a
hole into a room with clever people and all kinds of equipment. they
can only look at the light, they can't see where the scope is pointed
nor examine other objects in the vicinity of the source. Does the
light carry a signature?

ya, that is what they do. Read up on it.
Chemicals have light spectra that are shifted, to the red.
Sodium. etc.......

On Wed, 28 Sep 2005 21:11:29 -0500, "mini haha"
wrote:


"Charles" wrote in message
.. .
Can we stand one.

Light can be shifted by cosmological redshift, proper motion, or
gravitational redshift.

Is it possible to examine just the light and tell which cause results
in the effect.

Say I have a good telescope and send the collected light through a
hole into a room with clever people and all kinds of equipment. they
can only look at the light, they can't see where the scope is pointed
nor examine other objects in the vicinity of the source. Does the
light carry a signature?

ya, that is what they do. Read up on it.
Chemicals have light spectra that are shifted, to the red.
Sodium. etc.......


Maybe I didn't make my question clear. Can they look at the light and
say that this redshift was caused by proper motion and not gravity
redshift? Can they differentate the cause?

"Charles" wrote in message
...
On Wed, 28 Sep 2005 21:11:29 -0500, "mini haha"
wrote:


"Charles" wrote in message
. ..
Can we stand one.

Light can be shifted by cosmological redshift, proper motion, or
gravitational redshift.

Is it possible to examine just the light and tell which cause results
in the effect.

Say I have a good telescope and send the collected light through a
hole into a room with clever people and all kinds of equipment. they
can only look at the light, they can't see where the scope is pointed
nor examine other objects in the vicinity of the source. Does the
light carry a signature?

ya, that is what they do. Read up on it.
Chemicals have light spectra that are shifted, to the red.
Sodium. etc.......


Maybe I didn't make my question clear. Can they look at the light and
say that this redshift was caused by proper motion and not gravity
redshift? Can they differentate the cause?



It is a delta velocity, a difference in velocity that is measured. The
cause is theoretical.

Charles wrote in
:

Light can be shifted by cosmological redshift, proper motion, or
gravitational redshift.

Is it possible to examine just the light and tell which cause results
in the effect.

Interesting question. I'm not an expert on this, but here are my thoughts.
It's pretty clear that if you're just examining single photons there is no
way to determine that they've even been shifted, much less by what cause.
If, on the other hand, you're examining something like a stellar spectrum,
where the patterns of spectral components can tell you what the "original"
frequencies of the individual components were, you can determine how much
each frequency has been shifted.

As it turns out, both doppler shift and gravitational red shift are
proportional to the original frequency. The constants of proportionality
don't have any additional dependence on frequency, so I don't see any way,
even by looking at a spectrum with many components, of distinguishing
between doppler and gravitational red shift. I believe, but I'm not sure,
that cosmological frequency shift is also proportional to frequency, so I
think that the answer to your question is no.

--
Steve Gray

"Steven Gray" wrote in message
...
Charles wrote in
:

Light can be shifted by cosmological redshift, proper motion, or
gravitational redshift.

Is it possible to examine just the light and tell which cause results
in the effect.

Interesting question. I'm not an expert on this, but here are my thoughts.
It's pretty clear that if you're just examining single photons there is no
way to determine that they've even been shifted, much less by what cause.
If, on the other hand, you're examining something like a stellar spectrum,
where the patterns of spectral components can tell you what the "original"
frequencies of the individual components were, you can determine how much
each frequency has been shifted.

As it turns out, both doppler shift and gravitational red shift are
proportional to the original frequency. The constants of proportionality
don't have any additional dependence on frequency, so I don't see any way,
even by looking at a spectrum with many components, of distinguishing
between doppler and gravitational red shift. I believe, but I'm not sure,
that cosmological frequency shift is also proportional to frequency, so I
think that the answer to your question is no.

The spectrum received from very distant objects is never
pristine -- it suffers from passage through regions of
the interstellar medium which contains varying amounts of
matter of different sorts, which leaves its own "fingerprints"
on the spectrum. Passage through such debris at several
different red-shifts' distance leaves mark in the spectrum
(particularly absorption lines) that can reveal a history
of travel. This is one way to tell if a spectrum red-shift
is due only to velocity or gravity versus distance/expansion.

Presumably, a gravitationally shifted spectrum would have its
own characteristics as the light passed through the local
medium (bound to be pretty dense near a very massive object)
with a steep change in time rates for the local environs.

Steven Gray wrote:
As it turns out, both doppler shift and gravitational red shift are
proportional to the original frequency. The constants of proportionality
don't have any additional dependence on frequency, so I don't see any way,
even by looking at a spectrum with many components, of distinguishing
between doppler and gravitational red shift. I believe, but I'm not sure,
that cosmological frequency shift is also proportional to frequency, so I
think that the answer to your question is no.

Yes, there's no way of distinguishing these three kinds of Doppler shift,
and not even any clear demarcation line between them. They're all different
aspects of the same thing in general relativity -- a side effect of a
particular geometrical relationship between emitter and absorber.

Of course, there are other effects that can make light look redder or bluer
that are easily distinguished from Doppler shift.

-- Ben