Comoving Visibility Limit & other questions...

[stevebi]

Hello. Sorry if this question comes off as silly but why can we not see what is after the comoving visibility limit? I keep hearing about the "event horizon" but it's related to black holes. What exactly is at the limit and what could possibly be after it?<br /><br />I took a look at the logarithmic map and I'm confused after z />20. What comes next? ..Since the visibility limit is a bit further.<br /><br />One other question: the map shows only north correct? But it extends to every possible angle? I mean what about z<0. (Ex: z=-5 (what came after us.)) I hope I'm grasping the directions and "layout" of space correctly.<br /><br />Sorry if I came off as confusing.. space is blowing my mind. It makes me wonder so much.<br /><br />Thank you,<br /><br />Steve

 

[elzzie]

The way I understand it is that z>20 is it. We can't see any further back than the Big Bang. If you consider that the big bang was the actual begging of time itself. We will actually never be able to see further back than the Quark-Gluon Plasma. Due to the fact that photons couldn't escape the plasma barrier. So the only <i> visible </i> light we can see is as far back as 400,000 years after the big bang (at the end of the Quark-Gluon Plasma). The only radiation we can see ( from the big bang ) is the <i> cosmic microwave background. </i> <br /><br />The only thing that could be after z />20 is the False Vacuum of space. Which we will never be able to observe directly. ( possibly with quantum physics but not any time soon )<br /><br />Thats how I understand it anyways. I'm sure I will be corrected and soon figure out I'm all wrong! <img src="/images/icons/tongue.gif" />

 

[elzzie]

<blockquote><font class="small">In reply to:</font><hr /><p> One other question: the map shows only north correct? But it extends to every possible angle? I mean what about z<0. <p><hr /></p></p></blockquote><br /><br />The map starts off at the center of the earth. So for all logistic purposes you really can't ( and don't need to) go to <i>z<-x</i>.

 

[SpeedFreek]

Actually, we need to consider the Cosmic Microwave Background Radiation here, which has a redshift of around z=1089!<br /><br />The CMB was emitted around 380,000 years <i>after</i> the big-bang and shows a redshift of z=1089, whereas the most distant objects we have seen (probably the earliest objects that formed) don't have redshifts over z=20, and they formed something around 100-500 <b>million</b> years after the big bang (the highest redshift galaxies we have seen have redshifts of around z=10, and there are some quasars at z=15).<br /><br />So what does this all mean?<br /><br />Well, the redshifts in all these cases represent how much space has expanded since the light/radiation was emitted. So we have the CMB redshift of z=1089 at 380,000 years in, versus the earliest objects that formed at something over 100 million years in and have redshifts around z=15.<br /><br />What we end up with is a picture where the big bang happened, and space was expanding really fast but decelerating. The primordial quark-gluon plasma then went through many transitions as the universe expanded and cooled, culminating with the recombination after 380,000 years where atoms finally formed and photons split off and evolved independently (when the CMB was emitted).<br /><br />At this time the expansion was a lot slower than it was at the beginning, but was still incredibly fast (equating to z=1089). As time went on, structure started to form as the expansion continued (still slowing) and finally after over 100 million years, the first objects in the universe formed. By the time that the galaxies finally formed the expansion had slowed an incredible amount since the CMB (from z=1089 down to z=10 or so during a period of around 500 million years). You can see from this that the high rates of expansion in our early universe give us a view of space-time which is highly curved at the furthest distances.<br /><br />So z />20 represents the epoch before any objects formed. We cannot see any objects <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>