How is redshift measured?

Light is not analogous to sound waves. Sound requires a medium through which to
pass, light does not. That having been said, however, light does travel through
different mediums at different velocities; that's how lenses work. But the
density of space is for all practical purposes as close to a vacuum as one can
get. Light does not travel at a different velocity through the solar system
than it does in interstellar space. The speed of light in a vacuum is a
constant.

"Ed and Kathy Hannig" wrote in message
m...
Okay, then considering that light travels as a wave, and waves travel at
different speeds through different mediums (speed of sound through water is
different than it's speed through air (at sea level) and different speeds at
different altitudes) wouldn't it make sense that light traveling through
intergalactic space would have a speed different than when it's traversing a
solar system or a galaxy? Once light encounters one of these 'speed traps'
you wouldn't expect it to speed up again as it re-enters intergalactic
areas, would you?
--

In GOD We Trust

9/11/2001
Lest we forget

On Sat, 17 Jan 2004 23:55:19 -0000, OG wrote:

"Bill Oertell" wrote in message
...

Now my question to the rest of the group: gravity has more effect on lower
frequencies, less on higher frequencies. A good example is radio
frequencies,
the lower ones follow the curvature of the earth while the higher ones
shoot
straight off into space.

I'm pretty certain that's not a gravitational effect. I believe it's due to
diffraction allowing the longer wavelengths of low frequency radio to follow
the curve of the Earth's surface.

I'm curious, everyone seems to attribute the red shift to Doppler effect.
What about gravity of the entire, distant galaxy we observe? Surely it,
too, must account for some of the reddening of light?


--
The butler did it.

"Ed and Kathy Hannig" wrote in message
m...
Okay, then considering that light travels as a wave, and waves travel at
different speeds through different mediums (speed of sound through water
is
different than it's speed through air (at sea level) and different speeds
at
different altitudes) wouldn't it make sense that light traveling through
intergalactic space would have a speed different than when it's traversing
a
solar system or a galaxy?

Intergalactic space, solar system space or galaxy space are all pretty much
a vacuum. Even the impressive flouresencent clouds are a better vacuum than
anything you're going to produce. So the speed change in down in the
immeasurable area. I should add, that light is different from sound in that
it does not require a medium to travel through.

Secondly, even if you put light through a Bose condensate and slow it way
down and then bring it out the other side to measure for spectral shift,
there isn't any. The shift is related to the frequency and can be affected
by the speed of the object emitting or reflecting the light or receiving the
light. But the frequency does not change even under the extreme speed
changes that can be created in a laboratory.

Once light encounters one of these 'speed traps'
you wouldn't expect it to speed up again as it re-enters intergalactic
areas, would you?

Yes, you would. The speed of light in a vacuum is a constant, no matter
where it has been before. And the speed of light in any medium will be the
same, regardless of where the light has been before. And again, it still
will not change the frequency shift that is measured.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/

************************************

"Bill Oertell" wrote in message
...
Now my question to the rest of the group: gravity has more effect on lower
frequencies, less on higher frequencies. A good example is radio
frequencies,
the lower ones follow the curvature of the earth while the higher ones
shoot
straight off into space. Wouldn't this also hold true for light,
certainly not
as pronounced but still measurable? If so, wouldn't it be possible to
determine
if a spectral shift was due to velocity or gravity?

Light does not vary in its response to gravity dependent on its frequency.
All frequencies are affected the same.

Radio frequencies do not follow the curve of the earth because of gravity.
Some frequencies are reflected back by the ionosphere. Others are scattered
more by objects. But they all react to gravity in the same degree.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/

************************************

"Ed and Kathy Hannig" wrote in message
m...
Didn't I read something within the past several years about light being
affected by the sun's gravity? And if I'm not mistaken there are instances
of galaxies being magnified due to gravitational lens in space.

Yes, this was predicted by Einstein and was first tested at a solar eclipse.
Hipparchos then measured it for stars even farther from the line of sight to
the limb of the sun. But it is not frequency dependent. And it does not
shift the frequencies.

And yes, if it did affect the frequencies like the red shifts we observe, it
would have been easy to detect in gravitational lensing. If there were the
range hypothesized by the other poster in radio wavelengths (which are the
same thing as visible light, just at a different frequency), then we would
have a range from the sun's mass barely affecting visible wavelengths to
radio waves being bent into the radius of the earth's gravity. And slightly
longer radio waves would not propagate outward at all. They would leave the
antenna and bend straight down to the earth and never make it to the horizon
at all. Radio astronomy would be impossible because the radio frequencies
would never make it here. And what little did arrive would be so distorted
that we could not image anything. Additionally, the objects which are
gravitationally lensed would appear to be elongated into a little spectrum,
like we were viewing them through a prism.

Obviously, none of this takes place.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/

************************************

"Ed and Kathy Hannig" wrote in message
m...
Didn't I read something within the past several years about light being
affected by the sun's gravity? And if I'm not mistaken there are instances
of galaxies being magnified due to gravitational lens in space.


Yup, but this is not the same as radio waves following the curvature of the
earth.

Light certainly is affected by gravity, but the effects are very small. In
1919, Eddington measured a very slight bending of light of a star as it
passed the sun during a total eclipse; this confirmed a prediction made by
Einstein's General Relativity theory. A google search for eddington
eclipse will bring a number of references.

More recently, gravitational lensing has been detected where light from a
distant galaxy is bent around a galaxy closer to us, giving multiple and
distorted images (similar to what is seen through old 'bottle' glass panes).
Do a google search for einstein's cross .

An important point to note with both of these is that the effect is very
small. The bending is measured in tiny fractions of a degree.

It is true that there is a small gravitational effect on light giving rise
to a red shift, but this is also very small. The correlation between
galactic redshift and distance has been measured and seems to be consistent
with the 'recession' model. Alternative causes have been proposed, tested
and explored, but have not been broadly accepted. So far, the expanding
universe model seems to be the best bet.

Hope this helps.

I'm curious, everyone seems to attribute the red shift to Doppler effect.
What about gravity of the entire, distant galaxy we observe? Surely it,
too, must account for some of the reddening of light?

Google for "tired light" and you will find all the problems with this idea.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/

************************************

The butler did it.

I heard it was Mrs Green in the parlor with the lead pipe!

"Ugo" wrote in message
...
On Sat, 17 Jan 2004 23:55:19 -0000, OG wrote:

"Bill Oertell" wrote in message
...

Now my question to the rest of the group: gravity has more effect on
lower
frequencies, less on higher frequencies. A good example is radio
frequencies,
the lower ones follow the curvature of the earth while the higher ones
shoot
straight off into space.

I'm pretty certain that's not a gravitational effect. I believe it's due
to
diffraction allowing the longer wavelengths of low frequency radio to
follow
the curve of the Earth's surface.

I'm curious, everyone seems to attribute the red shift to Doppler effect.
What about gravity of the entire, distant galaxy we observe? Surely it,
too, must account for some of the reddening of light?

Gravitational Red shift does exist, but it is a very minor effect. If the
effect was significant we would expect to measure similar red shifts for
nearby galaxies as for distant ones.

Some people have proposed a general loss of energy from light as it travels
further and further. This is called 'tired light'.

However I understand there are instances where a spectrum shows multiple
absorbtion bands (caused by the light passing through 1 or more clusters of
galaxies between the source and us), which is hard to explain by tired light
theories. There is also no physical model to allow light to lose energy in
this way (don't forget that according to the geodesic equation, as far as
the light is concerned it takes no time at all to pass from the distant
object to us - so there's no time for it to lose energy).

Hope this helps.

Not being an expert in physics I'm going to need an explanation of the
statement 'as far as
the light is concerned it takes no time at all to pass from the distant
object to us - so there's no time for it to lose energy' the last I heard
light traveled at 186,000 miles PER SECOND. Which to me indicates that while
very fast it still requires some measurement of time to traverse a given
distance. I do agree that light itself probably has no concept of time, but
then it more than likely has no consciousness to speak of.
Which, by the way, brings up another interesting concept which may or may
not be related, the relationship of time to gravity. From what I have heard
experiments have been conducted which show that an atomic clock in Denver,
which has a slightly lower gravitational field due to elevation, over the
span of one year will record two more seconds than a similar clock at
Greenwich, England. The point of this being, with gravitation in space being
considerably lower still - and here I have to make the assumption that the
passage of time is also relatively faster - does that mean that light would
travel further in say intergalactic space (extremely low gravity) than it
would near the center of a galaxy? How about light that passes near the
influence (but not trapped by) a black hole?

--
In GOD We Trust

9/11/2001
Lest we forget

Odysseus:

I thought that god created both the primordial pea and The Red Shift.

Isn't the psycholgical argument that you provide the proof of that fact?

Your advocacy of creationism, and your denial of any other possible
cause of the Red Shift based upon actual evidence, is showing.

The Red Shift, in as of itself, is not, however, the cause of the
Creationist's Big Bang.

Ralph Hertle





Odysseus wrote:

AngleWyrm wrote:

How do we know what the frequency should have been?


The spectral lines produced when each type of molecule emits or
absorbs radiation have distinctive patterns. These 'fingerprints' are
observed both in laboratories on earth and in the spectra of objects
in our own galaxy and its neighbours, so to all appearances they are
the same everywhere; moreover they can be predicted or 'derived from
first principles' by quantum mechanics. So once a distinctive pattern
of lines is recognized in the spectrum of a distant galaxy, it's
quite straightforward to measure its offset from the reference position.