[continued from previous message]
>>> NGT and one of his humor sidekicks talking about the effects of
>>> Special Relativity, and how General Relativity puts no constraints on
>>> the rate of cosmic expansion.
>>>
>>>
>>>>>> The claim is that the expansion of space accelerated faster than light
>>>>>> for parts of the universe that are no longer visible to us. Space
>>>>>> expanded and nothing really accelerated to faster than light, but they
>>>>>> are just too far away to observe. There was the initial inflation when
>>>>>> space expanded much faster than the speed of light creating a "flat
>>>>>> universe" with just the right amount of mass and energy to keep it from
>>>>>> collapsing. Dark energy is supposed to account for the continued
>>>>>> expansion of space within the universe. One article that I recall
>>>>>> claimed that the visible universe extends out to around 45 billion light
>>>>>> years in all directions from where we are. The visible light has to be
>>>>>> younger than the age of our universe (less than 14 billion years), but
>>>>>> space has expanded.
>>>>>
>>>>>
>>>>> An important point is, according to the evidence, there was a time
>>>>> before about 4bya when the universe was dominated by gravity, and its
>>>>> rate of expansion was actually slowing. Now the universe is dominated
>>>>> by dark energy, and so its rate of expansion has become ever faster
>>>>> since then.
>>>>
>>>> The claim in the article is that the expansion of the universe continues
>>>> to be currently accelerating, but the rate of acceleration is
>>>> decreasing, so dark energy effects seem to have limits.
>>>
>>>
>>> What you say above is contrary to what I have read:
>>>
>>> ********************************
>>> In 1998, the High-Z Supernova Search Team published observations of
>>> Type Ia ("one-A") supernovae. In 1999, the Supernova Cosmology Project
>>> followed by suggesting that the expansion of the universe is
>>> accelerating. The 2011 Nobel Prize in Physics was awarded to Saul
>>> Perlmutter, Brian P. Schmidt, and Adam G. Riess for their leadership
>>> in the discovery.
>>> ********************************
>>>
>>>
>>>> I recall an article claiming that our current visible universe extended
>>>> out to around 45 billion light years in any direction (maybe it was 45
>>>> billion light years across, the light within visible space has to be
>>>> less than 14 billion years old) but there has to be a lot of the
>>>> universe that we can no longer see. Kestrel indicated that this limit
>>>> applied to the points within our visible universe so that every location
>>>> had a different horizon and could see a different part of the existing
>>>> universe. There would have to be a lot of matter that is not in the
>>>> visible universe.
>>>
>>>
>>> Correct. This is something I pointed out to Peter Nyikos awhile ago,
>>> and I pointed out to you in my last post. Every point in the cosmos
>>> is surrounded by its own Hubble Sphere. The working assumption is
>>> that the cosmos outside our Hubble Sphere is largely similar to the
>>> space inside. The problem is there is no way to know this for
>>> certain, even in principle.
>>>
>>>
>>>> Ron Okimoto
>>>>>
>>>>>
>>>>>> It doesn't matter, what I wanted was if the mass of the universe
>>>>>> estimate includes the mass that is not observable. We have the
>>>>>> background radiation map of the universe, and estimates based on what we
>>>>>> can see (these are based on the observable universe). The estimates
>>>>>> would have included what we could not see within the visible universe
>>>>>> because we lacked the ability to detect the light from the distant
>>>>>> objects. Did this estimate also include the mass that was too far away
>>>>>> to be visible? How do we know how much mass is no longer visible and is
>>>>>> beyond the horizon of what we can see? We've been trying to estimate
>>>>>> the amount of dark matter within the visible universe, so how would we
>>>>>> measure the amount of matter further away than the visible horizon?
>>>>>> Even though we can't observe it, it is still part of our universe.
>>>>>>
>>>>>> Ron Okimoto
>>>>>
>>>
>> Good advice regarding the reliability of social media such as Facebook
>> or this forum for that matter. Best to check to primary sources. Some
>> popular outlets are reliable, some not.
>
>
> Some consider Wikipedia "social media, which I cited, and consider to
> be at least as reliable as other collections of facts. I agree the
> above case illustrates a challenge when citing rapidly-changing
> sources, in this case Facebook. I was unable to read/listen to RonO's
> original cite, so I could not determine what his source material
> actually said. I would be very surprised if any current source said
> there was evidence that the universe's expansion rate was slowing
> down.
Here's a source I found useful, as a first-pass primer:
https://newscenter.lbl.gov/2025/03/19/new-desi-results-strengthe
-hints-that-dark-energy-may-evolve/
It's still pop science, but at least it's pop science written by actual
scientists. The page is careful to state "the preference for an evolving
dark energy has not risen to '5 sigma,' the gold standard in physics
that represents the threshold for a discovery." Also it does not claim
that cosmic expansion is slowing; only that the *rate of increase* in
expansion due to dark energy may have slowed in the past (and is
presumably still slowing). In other words, the car isn't slowing down,
but dark energy is very slowly easing up on the throttle.
--
[The address listed is a spam trap. To reply, take off every zig.]
Kestrel Clayton
"Every normal woman must be tempted, at times, to stoke the fire,
host the black mass, and begin eating hearts." — Rose Bailey
--- SoupGate-DOS v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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