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marcus

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## Main Question or Discussion Point

this is a case where it could be very helpful if someone (Pervect? Wallace? hellfire?) who has the numbers handy could tell us how far away the CEH is at present according to the usual LCDM model

I don't know the exact figure. I think it is somewhere around 16 Gly.

that is, slightly further out than the Hubble radius which is 13-14 Gly.

My feeling about dogma is that everybody gets to believe whatever they want about cosmology but that we should all UNDERSTAND the mainstream consensus model somewhat so we are all on the same page in discussions.

The mainstream LCDM may be just an effective model with parameters plugged in to fit the data but it is impressively successful as such and if there is a more fundamental model lurking in deeper mathematical waters the LCDM will help guide us to it. Much respect for LCDM.

Well, one feature of LCDM is that it has a COSMOLOGICAL EVENT HORIZON somewhere out past the Hubble radius. A galaxy at Hubble radius (13-14 Gly) from us is receding at exactly c. But light from it can still reach us by a mechanism described in another YellowTriangle! thread. It can get here because H(t) is still decreasing slightly and will continue for a while more. H(t) decreasing means reciprocal--Hubble radius---increasing, so Hubble sphere can grow so as to reach out and take in light that is struggling to reach us but not making it, and then the light is home free.

but, according to LCDM, if a galaxy is significantly farther away than that, like say 16 Gly, then its light CAN NEVER REACH US IN ALL THE HISTORY OF THE UNIVERSE no matter how long we wait even until t = infty.

This is best communicated with a picture and Lineweaver 2004 paper has a picture. It is "Figure 1" in Lineweaver's "inflation and the CMB".

I will try to get a link to just that Figure 1 diagram, and also I'll paste in an exerpt from the article where he talks about it. The basic idea is pretty simple and easy to understand.

this is a basic feature of LCDM so my attitude is Nobody is forcing you to believe it. You can disbelieve that there is a CEH out there! You can believe any model you want with or without horizons. (In fact in the old CDM before 1998, there was no cosmological event horizon and all light that was aimed at us would eventually get here if you waited long enough! The coming of Lambda changed this.)

So nobody forces anybody to believe in a CEH but please lets all share some common familiarity with the main features of the consensus model.

I'd be glad if one or more experts would explain or discuss, and say actually how far away the CEH is.

=================

EDIT: The reason I said "The coming of Lambda changed this," in case anyone didnt notice, is that you only get a Cosmological Event Horizon if you have a POSITIVE LAMBDA, positive cosmological constant, or something equivalent that gives accelerating expansion.

The article by Lineweaver explains how the discovery of accel. expansion is what put the CEH into the picture.

Maybe I should have made this more explicit that it is thanks to the Lambda in LCDM. Or maybe that was obvious, I don't know.

Anyway the old CDM didnt have that feature.

I don't know the exact figure. I think it is somewhere around 16 Gly.

that is, slightly further out than the Hubble radius which is 13-14 Gly.

My feeling about dogma is that everybody gets to believe whatever they want about cosmology but that we should all UNDERSTAND the mainstream consensus model somewhat so we are all on the same page in discussions.

The mainstream LCDM may be just an effective model with parameters plugged in to fit the data but it is impressively successful as such and if there is a more fundamental model lurking in deeper mathematical waters the LCDM will help guide us to it. Much respect for LCDM.

Well, one feature of LCDM is that it has a COSMOLOGICAL EVENT HORIZON somewhere out past the Hubble radius. A galaxy at Hubble radius (13-14 Gly) from us is receding at exactly c. But light from it can still reach us by a mechanism described in another YellowTriangle! thread. It can get here because H(t) is still decreasing slightly and will continue for a while more. H(t) decreasing means reciprocal--Hubble radius---increasing, so Hubble sphere can grow so as to reach out and take in light that is struggling to reach us but not making it, and then the light is home free.

but, according to LCDM, if a galaxy is significantly farther away than that, like say 16 Gly, then its light CAN NEVER REACH US IN ALL THE HISTORY OF THE UNIVERSE no matter how long we wait even until t = infty.

This is best communicated with a picture and Lineweaver 2004 paper has a picture. It is "Figure 1" in Lineweaver's "inflation and the CMB".

I will try to get a link to just that Figure 1 diagram, and also I'll paste in an exerpt from the article where he talks about it. The basic idea is pretty simple and easy to understand.

this is a basic feature of LCDM so my attitude is Nobody is forcing you to believe it. You can disbelieve that there is a CEH out there! You can believe any model you want with or without horizons. (In fact in the old CDM before 1998, there was no cosmological event horizon and all light that was aimed at us would eventually get here if you waited long enough! The coming of Lambda changed this.)

So nobody forces anybody to believe in a CEH but please lets all share some common familiarity with the main features of the consensus model.

I'd be glad if one or more experts would explain or discuss, and say actually how far away the CEH is.

=================

EDIT: The reason I said "The coming of Lambda changed this," in case anyone didnt notice, is that you only get a Cosmological Event Horizon if you have a POSITIVE LAMBDA, positive cosmological constant, or something equivalent that gives accelerating expansion.

The article by Lineweaver explains how the discovery of accel. expansion is what put the CEH into the picture.

Maybe I should have made this more explicit that it is thanks to the Lambda in LCDM. Or maybe that was obvious, I don't know.

Anyway the old CDM didnt have that feature.

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