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1 hour ago, Jacke said:

Proper motion

Does look that way. I was expecting something precise based on the fact that everyone's pretty confident that collision will happen, and that parallax methods have garbage precision at intergalactic distances, even for close neighbors, and indeed, best figure I found is 80km/s ± 40km/s from this ref. And with the outside result of 120km/s transverse, -300km/s radial, it's a lot less "straight on collision" than I was picturing, but I guess, it's close enough for gravity to do the rest.

I'm disappointed, though. I was hoping for something like second-order red shift measurements, based on periodic changes as Earth moves around its orbit for some very precise numbers... Measuring proper motion from parallax was exciting two centuries ago.

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@K^2Thanks for the explanation!

Okay - I think I understand my confusion.  I was trying analogize 'background' to a visual background rather than 'background noise'.  Background noise makes sense - especially given how Penzias and Wilson discovered it. 

 

So the CMB photons are everywhere - and, effectively, always have been. 

 

On to the thing I'm curious about:

Given the vast distances, and that the greater the distance the higher the chances of admittedly rare photon-photon scattering... Is it possible that our current measure of the redshift of distant galaxies might be less due to expansion (and/or rate) and possibly due to photon scattering

b/c from what I can tell, the more scattering you have, the redder light appears.  https://www.optics4kids.org/what-is-optics/scattering/why-is-the-sky-blue-why-are-sunsets-red#:~:text=Within the visible range of,red and yellow light remaining.

(note: this mathematically challenged jarhead is not discounting some tenured physisists' conclusions - but rather asking whether photon scatter is accounted for in the explanation of expansion rate / redshift - or a gentle explanation of why it would not, could not contribute to redshift) 

Edited by JoeSchmuckatelli
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5 hours ago, K^2 said:

Does look that way. I was expecting something precise based on the fact that everyone's pretty confident that collision will happen, and that parallax methods have garbage precision at intergalactic distances, even for close neighbors, and indeed, best figure I found is 80km/s ± 40km/s from this ref. And with the outside result of 120km/s transverse, -300km/s radial, it's a lot less "straight on collision" than I was picturing, but I guess, it's close enough for gravity to do the rest.

I'm disappointed, though. I was hoping for something like second-order red shift measurements, based on periodic changes as Earth moves around its orbit for some very precise numbers... Measuring proper motion from parallax was exciting two centuries ago.

There is a minuscule relativistic transverse red-shift effect, but I'd think it's impossible to see in practice.

This isn't parallax, which is back-and-forth, but to reduce data for that is challenging at any range, especially as aberration of light has to be accounted for first.  (Fun fact: if "aberration of gravitation" existed, there'd be no stable orbits.  Because it doesn't exist, Newtonian Gravitation had to assume its speed of propagation was instantaneous.  General Relativity solved this issue.)

Anyhoo, proper motion has to be measured against more distant objects that can be safely assumed to be near static.  It can be tricky to confirm this and properly reduce the data, but it has been done in some cases out to the Local Group of Galaxies, as discussed here.

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9 hours ago, JoeSchmuckatelli said:

Given the vast distances, and that the greater the distance the higher the chances of admittedly rare photon-photon scattering... Is it possible that our current measure of the redshift of distant galaxies might be less due to expansion (and/or rate) and possibly due to photon scattering?

Scattering can create smooth attenuation in spectrum. To a human eye, yes, this can cause the light color to change, but when we measure the red shift, we aren't looking at spectrum overall. We are looking at spectral lines, which are rather narrow gaps in spectrum due to absorption by various atoms in the star's atmosphere. Since it's a sharp gap, even if the overall spectrum is distorted, the gaps will still be quite identifiable, and their position cannot change due to scattering or absorption in interstellar medium.

sun_spectrum_lines_noao_900x600.jpg

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9 minutes ago, JoeSchmuckatelli said:

Okay - so all the breaks shift together?

The light at a given frequency is effectively transformed by the expansion of space as if it had a red shift.  I can't at the moment remember how the frequency changes (because I can't recall the exact formulae), but the frequencies of the light in the original rest frame of emission become transformed down in frequency and up in wavelength as the formulae specify.  This means the dark lines (which are the light absorbed by cold elements and compounds), the lack of frequencies, are also transformed.

Edited by Jacke
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Physics is fascinating - partly because the specificity of meanings used defy the common understanding of the use of the same words.  I wonder if it is the same with German.  Are, perhaps, Einstein's ideas better expressed in German?  Certainly, the maths are universal (you have to learn that language to converse in it)... but my Internetting without the language of maths tends to leave me with a remarkably incomplete understanding.

 

Again - thanks for 'splaining.

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Does a cartoonish cone-shaped drill actually makes sense or practical to be used to dig through earth? Because as far as I know, no drill in real life looks like that, it's either long, spiralling drill or a massive flat-headed tunneling cylinder with crushing teeth lining up the front part

Edited by ARS
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1 hour ago, ARS said:

Does a cartoonish cone-shaped drill actually makes sense or practical to be used to dig through earth? Because as far as I know, no drill in real life looks like that, it's either long, spiralling drill or a massive flat-headed tunneling cylinder with crushing teeth lining up the front part

The long spiraling part of an drill is to push the material out of the hole, standard for handheld tools but not so much for large diameter wood ones. 

I don't think the cone makes sense, if you drill deep you drill trough rock, rock drills  5-15 cm tend to have an rounded head and they use compressed air to blow the dust out. 
Drilling for oil you drill so deep you don't rotate the entire pipe, you use hydraulic to rotate the head and more so spin 2-4 cutting heads, the hydraulic removes the dust, again the head is rounded but more like an first.
Last the flat full profile rigs for drilling 2 meter and larger tunnels. 
 

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1 hour ago, magnemoe said:

The long spiraling part of an drill is to push the material out of the hole, standard for handheld tools but not so much for large diameter wood ones. 

I don't think the cone makes sense, if you drill deep you drill trough rock, rock drills  5-15 cm tend to have an rounded head and they use compressed air to blow the dust out. 
Drilling for oil you drill so deep you don't rotate the entire pipe, you use hydraulic to rotate the head and more so spin 2-4 cutting heads, the hydraulic removes the dust, again the head is rounded but more like an first.
Last the flat full profile rigs for drilling 2 meter and larger tunnels. 
 

Deep sea, they pump mud into the drill pipe sleeve to push out the rock and other material they don't want.

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