Is the red shift discrepancy the same at all distances?

[ianke]

Having a beer over it as we speek. Misplaced the modifier<img src="/images/icons/blush.gif" /> <div class="Discussion_UserSignature"> </div>

 

[ianke]

Irm harvink a thrid one nwo<img src="/images/icons/crazy.gif" /> <div class="Discussion_UserSignature"> </div>

 

[ianke]

Every body sing along. "93 Bottles of Beer On The Wall" <br /><br />Yay I'm a rock!<img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[brellis]

hey Ianke<br />Congrats on rockley-hood. <br /><br />I'm very much enjoying the ongoing process here! Once again, speedfreek is elucidating what can easily become chaotic. Everybody's input is great -- this thread is a very entertaining and illuminating read. The rate of expansion of our collective understanding is accelerating! <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>

 

[ianke]

Thanks <br />I thought the original question would bring out the best in the expansion issue.<br /><br />I love being able to stretch the old neurons on issues like this. There are some very good questions coming out of it. Also, it has sent me on other quests to help with this one. Most definately "expanding knowledge"<br /><br />Note; while perplexing at first, what speedfreek says in his last post is pretty much how I understand it. General Relativity is amazing and I still find myself freaking at the implications. The real trouble is in the waiting for our technology to catch up and yeild answers. <br /> <div class="Discussion_UserSignature"> </div>

 

[unclefred]

speedfreek - I agree with your conclusion but not your thought process. You said "When the light leaves its source, it is not redshifted at all". That statement make no sense. A red shift is caused by the relative velocities of the source and the observer. You statement has only a source thus the concept of red shift cannot apply. The question is "When the light leaves its source, it is not redshifted" as viewed by whom? Somebody near the original object? And what speed, direction, etc. is he traveling at?<br /><br />The rest of your post describes the intervening space. Your concept is that light is permanently affected by the expansion properties of the space it travels through. I am unfamiliar with this theory. Light routinely travels through lots of things but is never permanently affected. Light slows down, changes direction, is reflected, is refracted, bent, dispersed, calumniated, focused, and other things by all sorts of media but is never permanently affected. Light always returns to its exact original properties when it is returned to a medium that is identical to the original medium, perhaps vacuum in this case. <br /><br /> If the space between you and the source is expanding then you and the source are getting farther apart and thus a red shift. If, as in your example, the intervening space is expanding at various rates, the net result is the combination of all the intervening space. How that space is expanding, in zones as in your example or linearly or log or x-squared or whatever, does not matter. For redshift, all that matters is the relative velocity between the source and the observer. Thus I agree with your conclusion, but not your logic.<br /><br />

 

[SpeedFreek]

I was talking about <i> cosmological </i> redshift (also called Hubble redshift), which is the wavelength of light being increased by the expansion of spacetime.<br /><br />The redshift you describe as caused by relative velocities is <i> relativistic </i> redshift, which is due to classical momentum and energy transfer, and is independent of the orientation of the source movement.<br /><br />There is also gravitational redshift, caused by light being stretched by gravity.<br /><br />But an objects light can have redshift caused by any or all of these different factors.<br /><br />So, I think relativistic redshift is caused by the relative velocities of objects that are receding from each other and will look different depending on your frame of reference, but cosmological redshift is caused by the actual stretching of the light by the expansion of space.<br /><br />Our relative velocities will impart a relative amount of redshift to the light from all objects receding from us, but that light will already have a definite amount of redshift caused by the expansion of space.<br /><br />If I am mistaken in this, would someone explain why light that has been stretched by the expansion of space only has relative redshift, with links if possible. I am always learning and acutely aware I could be wrong! <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[R1]

confused again. they were talking about it in the Ask the Astronomers forum too, <br /><br /><br />In my example a few posts ago I was asking how can it be accelerating, when<br />the greatest redshift was observed a long time ago around 10 billion years ago,<br /><br />then around 2 to 4 billion yrs ago it was abserved that the red shift was little(if any)<br /><br /><br />But guess what, recently around 2.5 million yrs ago there was a 'negative' 300 redshift value observed! (a blueshift as I call it)<br /><br />With the same logic that time flows from the past towards the present, a<br />universe looking the way I described is actually losing speed since a long time ago!<br /><br />I'm not even sure if it's expanding<br /><br /><br />Andromeda is not only approaching us at 120 km/sec, it's on a collision course with The Milky Way!<br /><br />Andromeda is the closest big neighbor, meaning that it's giving us the most recent speed and values and direction.<br /><br />so it can't be expanding, I think a more accurate description is that:<br />sure,<br /><br /> around 10 billion years ago stuff was flying away, but more recently 2 to 4<br />billion years ago stuff was hardly flying away from us, and<br />then the most recent measurements of the universe, about 2.5 million yrs ago<br />stuff is flying towards us!<br /><br /> <br /> <div class="Discussion_UserSignature"> </div>

 

[R1]

I know, maybe I'm not considering enough variables.<br /><br /><br />what's the name of some galaxies in the range of 2 to 4 billion years ago?<br />so I can look them up and get intermediately aged readings?<br /><br />really I need a lot of galaxies and I'll look up their redshift values and how old<br />and long ago the measurements are.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[SpeedFreek]

Yes, Andromeda is heading towards the Milky Way, due to gravitation or inertia. At the local level, objects are interacting inertially. But that doesn't mean space is metrically contracting between us and them!<br /><br />We may see negative redshift (blueshift) for close objects, as their relativisitic doppler effect puts them more in the blue due to relative velocity, than the space is expanding between us at this close range. At close range, the expansion of space is very small, and it's miniscule amount of redshift is easily cancelled out by our relative velocities due to the local inertial movements of our galaxies.<br /><br />But at large distances, the redshift added by the metric expansion of all the space in between us and them is far more than any blueshift caused by their local inertial movement.<br /><br />...I think! <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[control_group]

Now that I (sort of) have my head around the difference between cosmological expansion and relativistic expansion, I'm in complete agreement with your last post, speedfreek.<br /><br />Everything I've read indicates that we see a fairly uniform rate of expansion in all directions at sufficient distances. So, as you said, once you get past the bounds of local interaction, expansion takes over.