Current eff. universe limited to redshift 1.73

In summary, the figure 1.73 is approximate, given uncertainties, somewhere around 1.7. Galaxies can be seen beyond z = 7, and the ancient background light has a redshift of 1090, allowing us to see ancient matter emitting light before it even formed stars and galaxies. However, according to the standard model, nothing more than 15.7 billion lightyears away can affect us from now on, which corresponds to a redshift of 1.73. This means that our causally effective universe only extends to the cosmic event horizon at z = 1.73. All photons from outside this horizon are already on their way to us and will never reach us. While we can still see millions
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marcus
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the figure 1.73 is approximate...given uncertainties, somewhere around 1.7.

We see galaxies out beyond z = 7, of course, and the ancient background light has redshift 1090, so we see ancient matter emitting light, before it even formed stars and galaxies.

But as of now, the standard model says, nothing that happens more than 15.7 billion lightyears away can affect us, from now on.
And that 15.7 distance corresponds to redshift z = 1.73

In a curious way our "from now on" causally effective universe only extends to the socalled "cosmic event horizon" at z = 1.73.

All the photons that will ever reach us from OUTSIDE that horizon are already on their way to us and already inside that range. If they were not, they would be destined to not ever reach us.

Most of the galaxies we can see are outside the z = 1.73 range. And we can look forward to admiring these millions of beautiful galaxies for a great many more years. But if something happens today in one of them--like a supernova--we will never see it. Nothing that happens to them or in them from now on can affect us.

There is a good article about the cosmic event horizon by Charles Lineweaver here
http://arxiv.org/abs/0909.3983
also a new article by Nobelist George Smoot et al.
http://arxiv.org/abs/1002.4278
==================

This leads to a curious question. Our model of the cosmos is the pair of Friedman equations. These run on "universe time" a universal time parameter t, and govern the evolution of the scalefactor a(t). What the model predicts will happen with a(t), what it says about future expansion, depends only on the present. That's just as we expect with any system of ordinary differential equations.

Normally one thinks of the Friedman model as treating the whole boundless universe as an organic whole. But maybe we should modify the Friedman equations by introducing a boundary term representing the cosmic event horizon.

This seems to be what the co-authors Smoot, Easson and Frampton are doing. I suppose it could be thought of as primarily a formal change: a change of interpretation or in how we think about the model. But right now I find it a bit puzzling. If other cosmologists go along with this, it will take some getting used to.
 
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Ok, I've been just skimming the Smoot paper. Not that I really understand much of this information/entropy thing, but their logic sounds extremely circular to me. As i understand it, they use the horizon (which is due to acceleration) as a cause of acceleration. That's fine, and circulary, IMHO. But when they use the Hubble scale to predict acceleration, independent of a horizon, as they do in eq. 12, that's ...weird.
I know that I'm near to obnoxious with my constant use of non-cosmological coordinates, but in this case you see that (12) gives us arbitrary acceleration (measurable) in an empty universe, depending on how we choose H (not measurable).
Either I haven't understood at all what they're proposing, or there is something really wrong with it. Maybe someone can enlighten me.
 
  • #3
Relax, Ich. It is early days. This is a potential paradigm shift which will either catch on or not catch on. We just have to wait and see. Smoot might get a second Nobel, or he might not.

It might help to get an idea of the personality of the man. Here is a 16 minute video lecture by him with some interesting slides including computer-simulation movies of the early universe. Google "Smoot TED"
and you get


It is a popular wide-audience lecture. You might not like it because it is so wide-audience. But it gives some glimpse of a real person instead of just an author's name.
 
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1. What is the significance of the redshift 1.73 in the current effective universe?

The redshift 1.73 is significant because it marks the furthest observable distance in the current effective universe, also known as the maximum observable redshift. This means that the light from objects beyond this redshift is so redshifted that it is beyond our current ability to detect.

2. How does redshift affect our understanding of the universe?

Redshift is a measure of the expansion of the universe, and it allows us to determine the distance and age of objects. By studying the redshift of objects, we can better understand the structure and evolution of the universe.

3. What objects can we observe at a redshift of 1.73?

At a redshift of 1.73, we can observe distant galaxies, quasars, and other astronomical objects. These objects are extremely far away and provide us with valuable information about the early universe.

4. How does the redshift limit of 1.73 impact our ability to study the universe?

The redshift limit of 1.73 sets a boundary for our current understanding and observations of the universe. It means that we are unable to see beyond this point, and therefore, our knowledge of the universe is limited to a certain extent.

5. What does the redshift of 1.73 tell us about the age of the universe?

The redshift of 1.73 is equivalent to a time when the universe was approximately 6.7 billion years old. This means that anything beyond this redshift is from an even earlier time in the universe's history. By studying objects at this redshift, we can gain insights into the early stages of the universe's development.

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