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Hi Steve,
I am familiar with the raisin bread model and I am wondering if in
addition there is a fair amount of cosmic fudge so it all sticks together.
Dave
On 2019-04-07 5:44 p.m., Stephen Shaw wrote:
>
> Hi Dave, news to me too --I thought I understood this as a simple
> Doppler shift phenomenon, but as the two replies indicate, not so.
> This useful (?), seemingly appropriate raisin bread analogy comes from:
>
> www.esa.int/Our_Activities/Space_Science/What_is_red_shift
> <http://www.esa.int/Our_Activities/Space_Science/What_is_red_shift>
>
> "However, to be accurate, the red shifts observed in distant objects
> are not exactly due to the Doppler phenomenon, but are rather a result
> of the expansion of the Universe.
>
> Doppler shifts arise from the relative motion of source and observer
> through space, whereas astronomical redshifts are 'expansion
> redshifts' due to the expansion of space itself.
>
> Two objects can actually be stationary in space and still experience a
> red shift if the intervening space itself is expanding.
>
> A convenient analogy for the expansion of the Universe is a loaf of
> unbaked raisin bread. The raisins are at rest relative to one another
> in the dough before it is placed in the oven. As the bread rises, it
> also expands, making the space between the raisins increase.
>
> If the raisins could see, they would observe that all the other
> raisins were moving away from them although they themselves were
> stationary within the loaf. Only the dough - their 'Universe' - is
> expanding."
>
> Steve
> ---------------------------------------------
>
> On Apr 7, 2019, at 4:13 PM, David Webster <dwebster@glinx.com
> <mailto:dwebster@glinx.com>> wrote:
>
>> Hi Burkhard & All,
>>
>> Thanks Burkhard. You have answered my question. Not really an
>> argument; just need for clarification.
>>
>> The red shift I now understand is measured not by their being
>> less light of shorter wavelength but by displacement of spectral
>> lines, presumably to a longer than normal wavelength. So the
>> spectral lines of e.g. hydrogen in some state would all be shifted to
>> a somewhat longer wavelength.
>>
>> But I do have problems with the concept of everything having
>> started with an explosive expansion of some kernel of infinite
>> density; just after God said "Let there be light"; aka big bang.
>>
>> Dave
>>
>>
>> On 2019-04-07 12:13 p.m., Burkhard Plache wrote:
>>> Hi Dave,
>>> your last question makes the correct observation that of all the light
>>> emitted by a distant object, the shorter wavelength light will be
>>> preferentially scattered away, leaving more of the original red light
>>> than blue light arriving at our doorsteps. Your implied, though not
>>> stated, assumption seems to be that redshift is measured by 'relative
>>> amounts of light' or 'the light looking more red'. - However, redshift
>>> is measured by looking at spectral lines, which are not modified by
>>> Rayleigh scattering. - Could you clearly state what your argument is?
>>> Thanks,
>>> Burkhard
>>>
>>> On Sun, Apr 7, 2019 at 10:53 AM David Webster <dwebster@glinx.com
>>> <mailto:dwebster@glinx.com>> wrote:
>>>>
>>>> On 2019-04-07 8:45 a.m., Burkhard Plache wrote:
>>>>> Hi David,
>>>>> to correct a common misrepresentation: The cosmological red shift of
>>>>> light is not due to the source moving away but due to the space
>>>>> expanding. Two very different phenomena.
>>>>> Also, Rayleigh scattering is not changing the wavelength of the
>>>>> scattered light, hence is not contributing to redshift.
>>>>> Burkhard
>>>>>
>>>>> On Sun, Apr 7, 2019 at 8:17 AM David Webster <dwebster@glinx.com
>>>>> <mailto:dwebster@glinx.com>> wrote:
>>>>>> Hi Burkhard,
>>>> Thanks. It seems to me that we are getting tangled up in semantics.
>>>>
>>>> If space expands then it makes objects appear to be moving away.
>>>>
>>>> And, indeed, scattering does not destroy shorter wavelengths
>>>> but it
>>>> does deflect them so they are partially or entirely culled from those
>>>> waves which are moving from source to observer. Thus, at the local
>>>> level; blue skies, white clouds, red sunsets and that green flash which
>>>> one sometimes sees from the cockpit when landing and facing west near
>>>> sunset.
>>>>
>>>> The above are all effects of our atmosphere. But there is ample
>>>> evidence of cosmic dust, ranging from particles to atoms, so one would
>>>> expect scattering of shorter wavelengths throughout space to increase
>>>> with distance between observer and source; greater opportunity for
>>>> scattering.
>>>>
>>>> So rephrasing my question in current jargon, are red shifts of
>>>> light due to expansion of space, distinct from red shifts which
>>>> might be
>>>> due to Rayleigh scattering whereby shorter wavelengths from a
>>>> source are
>>>> less likely to reach an observer ?
>>>>
>>>> Or more directly, why is the observed increase in red shift with
>>>> distance between source and observer attributed to an expansion of
>>>> space as opposed to greater opportunity for scattering of shorter
>>>> wavelengths of light as this distance increases ?
>>>>
>>>> Dave
>>>>
>>>>
>>>>
>>>>
>>>>>> Dear All, but especially astrophysics experts,
>>>>>>
>>>>>> Is the red shift of light, which would be due to the source
>>>>>> moving
>>>>>> away at great speed, intrinsically unlike the red shift due to
>>>>>> Rayleigh
>>>>>> scattering (which selectively scatters shorter wavelengths;
>>>>>> 1/[length to
>>>>>> the fourth power]) ?
>>>>>>
>>>>>> With ample dust in space, ranging from particles to atoms, one
>>>>>> would expect the red shift due to scattering to also be a function of
>>>>>> distance to source.
>>>>>>
>>>>>> Dave Webster, Kentville
>>>>>>
>
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<p>Hi Steve,</p>
<p> I am familiar with the raisin bread model and I am wondering
if in addition there is a fair amount of cosmic fudge so it all
sticks together. <br>
</p>
<p>Dave<br>
</p>
<div class="moz-cite-prefix">On 2019-04-07 5:44 p.m., Stephen Shaw
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:6612FDD1-A35D-4C56-B000-EEA89382A74A@dal.ca">
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
<div class="section" id="s_5">
<p><font color="#4d22b3">Hi Dave, news to me too --I thought I
understood this as a simple Doppler shift phenomenon, but as
the two replies indicate, not so. This useful (?),
seemingly appropriate raisin bread analogy comes from:</font></p>
<p><a
href="http://www.esa.int/Our_Activities/Space_Science/What_is_red_shift"
moz-do-not-send="true">www.esa.int/Our_Activities/Space_Science/What_is_red_shift</a></p>
<p>"However, to be accurate, the red shifts observed in distant
objects are not exactly due to the Doppler phenomenon, but are
rather a result of the expansion of the Universe.
</p>
<p>Doppler shifts arise from the relative motion of source and
observer through space, whereas astronomical redshifts are
'expansion redshifts' due to the expansion of space itself.
</p>
<p>Two objects can actually be stationary in space and still
experience a red shift if the intervening space itself is
expanding.
</p>
</div>
<div class="section" id="s_6">
<p>A convenient analogy for the expansion of the Universe is a
loaf of unbaked raisin bread. The raisins are at rest relative
to one another in the dough before it is placed in the oven.
As the bread rises, it also expands, making the space between
the raisins increase. </p>
<p>If the raisins could see, they would observe that all the
other raisins were moving away from them although they
themselves were stationary within the loaf. Only the dough -
their 'Universe' - is expanding." </p>
<div><font color="#4d22b3">Steve</font></div>
<div>---------------------------------------------</div>
</div>
<br>
<div>
<div>On Apr 7, 2019, at 4:13 PM, David Webster <<a
href="mailto:dwebster@glinx.com" moz-do-not-send="true">dwebster@glinx.com</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite">Hi Burkhard & All,<br>
<br>
Thanks Burkhard. You have answered my question. Not really
an argument; just need for clarification.<br>
<br>
The red shift I now understand is measured not by their
being less light of shorter wavelength but by displacement of
spectral lines, presumably to a longer than normal
wavelength. So the spectral lines of e.g. hydrogen in some
state would all be shifted to a somewhat longer wavelength.<br>
<br>
But I do have problems with the concept of everything
having started with an explosive expansion of some kernel of
infinite density; just after God said "Let there be light";
aka big bang.<br>
<br>
Dave<br>
<br>
<br>
On 2019-04-07 12:13 p.m., Burkhard Plache wrote:<br>
<blockquote type="cite">Hi Dave,<br>
your last question makes the correct observation that of all
the light<br>
emitted by a distant object, the shorter wavelength light
will be<br>
preferentially scattered away, leaving more of the original
red light<br>
than blue light arriving at our doorsteps. Your implied,
though not<br>
stated, assumption seems to be that redshift is measured by
'relative<br>
amounts of light' or 'the light looking more red'. -
However, redshift<br>
is measured by looking at spectral lines, which are not
modified by<br>
Rayleigh scattering. - Could you clearly state what your
argument is?<br>
Thanks,<br>
Burkhard<br>
<br>
On Sun, Apr 7, 2019 at 10:53 AM David Webster <<a
href="mailto:dwebster@glinx.com" moz-do-not-send="true">dwebster@glinx.com</a>>
wrote:<br>
<blockquote type="cite"><br>
On 2019-04-07 8:45 a.m., Burkhard Plache wrote:<br>
<blockquote type="cite">Hi David,<br>
to correct a common misrepresentation: The cosmological
red shift of<br>
light is not due to the source moving away but due to
the space<br>
expanding. Two very different phenomena.<br>
Also, Rayleigh scattering is not changing the wavelength
of the<br>
scattered light, hence is not contributing to redshift.<br>
Burkhard<br>
<br>
On Sun, Apr 7, 2019 at 8:17 AM David Webster <<a
href="mailto:dwebster@glinx.com"
moz-do-not-send="true">dwebster@glinx.com</a>>
wrote:<br>
<blockquote type="cite">Hi Burkhard,<br>
</blockquote>
</blockquote>
Thanks. It seems to me that we are getting tangled up in
semantics.<br>
<br>
If space expands then it makes objects appear to be
moving away.<br>
<br>
And, indeed, scattering does not destroy shorter
wavelengths but it<br>
does deflect them so they are partially or entirely culled
from those<br>
waves which are moving from source to observer. Thus, at
the local<br>
level; blue skies, white clouds, red sunsets and that
green flash which<br>
one sometimes sees from the cockpit when landing and
facing west near<br>
sunset.<br>
<br>
The above are all effects of our atmosphere. But
there is ample<br>
evidence of cosmic dust, ranging from particles to atoms,
so one would<br>
expect scattering of shorter wavelengths throughout space
to increase<br>
with distance between observer and source; greater
opportunity for<br>
scattering.<br>
<br>
So rephrasing my question in current jargon, are red
shifts of<br>
light due to expansion of space, distinct from red shifts
which might be<br>
due to Rayleigh scattering whereby shorter wavelengths
from a source are<br>
less likely to reach an observer ?<br>
<br>
Or more directly, why is the observed increase in red
shift with<br>
distance between source and observer attributed to an
expansion of<br>
space as opposed to greater opportunity for scattering of
shorter<br>
wavelengths of light as this distance increases ?<br>
<br>
Dave<br>
<br>
<br>
<br>
<br>
<blockquote type="cite">
<blockquote type="cite">Dear All, but especially
astrophysics experts,<br>
<br>
Is the red shift of light, which would be due to
the source moving<br>
away at great speed, intrinsically unlike the red
shift due to Rayleigh<br>
scattering (which selectively scatters shorter
wavelengths; 1/[length to<br>
the fourth power]) ?<br>
<br>
With ample dust in space, ranging from particles
to atoms, one<br>
would expect the red shift due to scattering to also
be a function of<br>
distance to source.<br>
<br>
Dave Webster, Kentville<br>
<br>
</blockquote>
</blockquote>
</blockquote>
</blockquote>
</blockquote>
</div>
<br>
</blockquote>
</body>
</html>
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