Cosmological Redshift and Expansion of Space

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Thomas</i>
<br />
For the 'photon', space <i>would</i> effectively contract when going from expanded into unexpanded space.

As an analogy, consider for instance the change of wavelength of light in a refracting medium: whether the refractive index is changed by lets say continuously changing the density of the medium by a certain amount, or simply by the photon going from a region with one density in one with another, doesn't make any difference. The wavelength will always adjust to the present refractive index (i.e. after the light leaves a refractive medium, its wavelength is the same again as before entering it).

Thomas

<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">I think you have a fundamental misunderstanding of what expanded space is and isn't. Expanded space is exactly the same as unexpanded space. Light propagating through expanded space will neither redshift or blueshift. Expanded and or even expanding space does not have a different density or refractive index than unexpanded space, it is <u>exactly</u> the same. The redshift is theorized to be the result of the <i>expanding</i> of space. It is a side-effect of the <i>expansion process</i>, not as a result of some property of the space itself.

JR

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by jrich</i>

I think you have a fundamental misunderstanding of what expanded space is and isn't. Expanded space is exactly the same as unexpanded space. Light propagating through expanded space will neither redshift or blueshift. Expanded and or even expanding space does not have a different density or refractive index than unexpanded space, it is <u>exactly</u> the same. The redshift is theorized to be the result of the <i>expanding</i> of space. It is a side-effect of the <i>expansion process</i>, not as a result of some property of the space itself.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

This is clearly not so:

the redshift is theorized to be given by the equation

1+z=a(t_o)/a(t_e) ,

where a(t_o) is the scale factor of the space metric when the light is observed, and a(t_e) when it was emitted. So it does not depend on the expand<i>ing</i> space, but on the expand<i>ed</i> space. If space has locally not expanded in our solar system since the light was emitted, we have therefore effectively a(t_o)=a(t_e) and thus 1+z=1 or z=0 (i.e. no redshift at all should be observed).

Thomas

In the equation a(t_e) and a(t_o) are not the scale factors for the solar system. They correspond to the scale factors for the entire expanding Universe (or at least the portion encompassing the emmitter and the observer) at times t_o and t_e. No wonder you are confused.

JR

quote:

---

Stars are closer than they appear

No chance of that. The distances to relatively nearby stars are measured directly by triangulation, using the Earth's orbital diameter as a baseline.

---

Didn't realize this thread was so active, else I would have come back sooner. In any case, I do realize the distance to stars is measured by triangulation, probably in comparisons every six months after 186 million miles of travel around the sun, with one angular degree of motion (wobble) over that year representing one parsec, or just over 3 light years in distance. Clearly all stars have less than one degree of wobble, so we know distances are very great. However, what I meant was, if space is not expanding, stars are closer than the mainstream theorizes. Because let's face it, if they are all moving away, this many eons "after" we've detected their light, then many are already beyond the boundaries of our current universe. And are more alone than we think we are.

As for simplicity, math theories, that can never be proven by scientific means, are just that. Just theory. In relative terms, ask yourself this basic question. Would any maker of such a wonderous collection of nebula's and quasars design such a universe that could never be admired up close? (Or at least close enough not to be destroyed by it). Or are we just temporarily fooled into thinking it is what it isn't, like a sea urchin pretending to be a predator? And so ... is this just a grand puzzle to solve? But not possible to ever visit? I think not.

I would like to think light from a Star traveling to us over a billion years in no way represents the state it was in when it originated. All things age and change. Likely, light coming from the most remote places in the universe represent stars that have long since died, so light observations only tell us how things used to be, not how they are now. So I believe using expanding space to make a theory of red shift more plausible to explain seems so contrary to simplicity, which generally all things are, once understood. People once thought clouds were spirits and stars the eyes of gods. Silly only when we look back on it with what we know now. Clouds are simple.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by jrich</i>
<br />In the equation a(t_e) and a(t_o) are not the scale factors for the solar system. They correspond to the scale factors for the entire expanding Universe (or at least the portion encompassing the emmitter and the observer) at times t_o and t_e. No wonder you are confused.

JR
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
I am not confused. I am just pointing out an inconsisteny in the 'expanding space' assumption here.


In the usual formulation, the universe is assumed as homogeneous, so you wouldn't be able to cover the case of locally different metrics due to inhomogeneities with this. You obviously would have to make the scale factor dependent on the location as well in this case, so you would have

1+z=a(r_o,t_o)/a(r_e,t_e) .

where r_e is the location of emission and r_o the location of observation.
And if space has locally not expanded with the Hubble expansion since the light was emitted, then we would have a(r_o,t_o)=a(r_e,t_e), i.e. z=0.


I also quote from the Wikipedia article en.wikipedia.org/wiki/Metric_expansion_of_space :
<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">
In the metric expansion of space, rather than objects in a fixed "space" moving apart into "emptiness", it is the space that contains the objects which is itself changing.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

So it should be quite clear from this that the wavelength of light is directly determined by the metric at the point where it is being measured. And if it is claimed that our local space has not expanded together with the overall expansion of the universe, we thus shouldn't see any redshifts at all.

Thomas

I'm going to try this one last time and then I'll be generous and just assume willful ignorance.

Expansion only occurs where space is gravitationally unbound. This would include space between distant galaxies, but not space within our solar system or our galaxy. The expansion is believed to occur at the same rate everywhere in the universe <i>where it occurs at all</i>. That is what is meant when one says that the universe is homogenous with respect to metric expansion. If you want to take the position (and I don't know that you are because your statements are imprecise) that because gravitationally bound space does not expand then the expansion is not homogenous then you are simply changing the meaning as defined in the theory and you can't then use your revised definition to poke holes in it.

Since according to theory the redshift of the light is caused by the increase in the metric of the space through which it is propagating the only metrics that matter are the metric of the space <i>that the light propagated through</i> at the time the light was emitted and the metric of the space <i>that the light propagated through</i> at the time the light was observed. More simply, it is the change in the metric of the transitted space over the transit time of the light that is responsible for the redshift (or blueshift) and that relationship is what the equation represents. The only questionable assumption is that the cosmological redshift is not caused by some other mechanism.

Unexpanded space has no effect on the wavelength of light. The transition from expanded space to unexpanded space does not change the wavelength of light in any way other than the normal gravitationally induced ways. Expanded space is not stretched like a rubber sheet, there is no change in "density". Expansion is more like growing, like my waistline. It's expanded over the years, but the fat that its composed of has the same density as it did a few years ago, there's just more of it. And like the wavelength of redshifted light gets longer, I have to keep fastening my belt further to the ends.

JR