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The cosmic horizon.



 
 
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  #1  
Old October 24th 13, 10:08 PM posted to sci.physics,sci.astro,sci.physics.relativity
Tom Roberts
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Posts: 344
Default The cosmic horizon.

On 10/24/13 10/24/13 9:32 AM, Jeff-Relf.Me wrote:
The "cosmic horizon" is 47 gigaâ‹…lightâ‹…years away
( and growing exponentially ) and 13.8 gigaâ‹…years ago.


No. It is indeed 13.8GY ago, and is therefore 13.8GLY away. Its distance and age
are growing linearly, not exponentially.


The Cosmic Horizon is an event horizon, where clocks slow to a stop,
due to the nearâ‹…infinite "gravitational eXergy" there-then.


No. The cosmic horizon is merely the boundary beyond which we on earth cannot
observe anything. It is merely a surface, with no physical characteristics
distinguishing it other than distance from earth at a given time. No observer
located there can identify it via any observations other than measuring distance
to earth [#]; clocks behave normally there. Note this is the conventional
wisdom, and implicitly assumes there is no physical feature there (e.g. an
actual boundary of the universe) -- IOW it assumes the universe is (much) larger
than the cosmic horizon; we really have no information on this (we can have none).

[#] which would take them at least 13.8GY.

I have no idea what you mean by "eXergy". When you make up words you cannot
expect other to understand them.


<Here http://en.wikipedia.org/wiki/Black_hole#Alternatives> WikiPedia says: <<

A much anticipated feature of a theory of quantum gravity
is that it will not feature singularities or event horizons
( and, thus, no black holes ).


This is wrong, or at best disingenuous.

The current best guess is that a theory of quantum gravity will explain or
eliminate singularities. Event horizons are expected to remain essentially
unchanged, because they are in a (low-to-modest-curvature) region where GR is
expected to be valid. There are currently some conjectures that event horizons
might be quite different from GR, but those are not well-vetted yet.


Tom Roberts

  #2  
Old October 26th 13, 03:03 AM posted to sci.physics,sci.astro,sci.physics.relativity
Tom Roberts
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Posts: 344
Default The cosmic horizon.

On 10/24/13 10/24/13 9:49 PM, Jeff-Relf.Me wrote:
<Here http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN>
Ned Wright says: <<

The current best fit model which has an ACCELERATING expansion
gives a maximum distance we can see of 47 billion light years. >>


Yes. There are several different ways to measure distance over cosmological
scales, and his claim and mine use different ones. I am not expert on this.


[...]
From here, on earth, we see clocks slow to a hault At:
A.) The event horizon of a black hole.
B.) The cosmic horizon ( the start of the big bang ).


But our cosmic horizon is not necessarily at the big bang. Indeed the
expectation is that the universe is considerably larger than our cosmic horizon.
In that case, things at the cosmic horizon are as I said.


Get a dictionary, look it up, <eXergy https://www.google.com/search?q=define:eXergy&num=50&newwindow=1&complete =0&hl=en>;


OK, you didn't make it up.


A TRUE black hole is a singularity.


The term "black hole" refers to the region inside its event horizon, not just
the singularity inside.


An APPARENT black hole, i.e. a black hole CANDIDATE, isn't a black hole.


Astrophysicists today generally accept that the compact objects at the center of
most (if not all) galaxies are indeed black holes. The "candidate" has been
removed over the past decade or so.


For example, a supermassive black hole could be modelled by
a large cluster of very dark objects. >>


Except that their size is too small by orders of magnitude to be ordinary matter.


Tom Roberts

 




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