[NatureNS] Big bang, scattering and red shift

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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> 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> 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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