On Saturday, December 30, 2017 at 2:28:52 PM UTC-6, agrays...@gmail.com
wrote:
>
>
>
> On Saturday, December 30, 2017 at 1:03:58 PM UTC-7, Lawrence Crowell wrote:
>>
>> On Friday, December 29, 2017 at 8:45:41 PM UTC-6, agrays...@gmail.com
>> wrote:
>>>
>>>
>>>
>>> On Friday, December 29, 2017 at 6:59:22 AM UTC-7, Lawrence Crowell wrote:
>>>>
>>>> The cosmological constant is Λ ~ 10^{-52}cm^{-2} and the scale factor
>>>> evolves as
>>>>
>>>> a(t) = a_0 exp(t sqrt{Λc^2/3}).
>>>>
>>>> The factor sqrt{Λc^2/3} ~ 10^{-18}sec^{-1}. For a billion years this is
>>>> t ~ 3x10^{16} sec and so sqrt{Λc^2/3}t ~ .03 and the scale factor
>>>> increases
>>>> by 1.03. The CMB microwave background will be expanded by a small change.
>>>> In 10 billion years this is t ~ 3x10^{17}sec and so sqrt{Λc^2/3}t ~ .3 and
>>>> the scale factor expands by 1.4. At 100 billion and a trillion the scale
>>>> factor expands by 20 and in a trillion years by 10^{13}. This means the
>>>> CMB
>>>> peak wavelength will be about 10^{10}m. That is not quite the length of
>>>> the
>>>> cosmos, but in 10 trillion years the expansion factor is close to ~
>>>> 10^{800} which means the wavelength at this point is larger than the
>>>> cosmological horizon scale. At that point the CMB will be removed from the
>>>> view of any observer. The time where wavelength becomes longer than the
>>>> cosmological horizon occurs in about 2 trillion years.
>>>>
>>>> LC
>>>>
>>>
>>> *Does the CMB just keep getting progressively redder as the cosmos
>>> expands, or does it actually "wink out", meaning CMB photons which we might
>>> eventually observe, begin their journey beyond our horizon? Since no new
>>> ones are being created, and the original ones are within our immediate
>>> neighborhood, like Andromeda, I don't see how they can wink out. AG *
>>>
>>
>> Think of a cube with sides length L. This is a region that permits
>> wavelengths of λ = L/2, L, 3L/2, ...as standing waves. By this as one
>> photon of those wavelength leaves another enters. So we can think of space
>> as having properties similar to a resonance cavity. As space expands this
>> box expands, which means the permitted standing waves have longer
>> wavelength. So as space expands electromagnetic waves within it also
>> becomes stretched. This is the red shifting of light.
>>
>> Local clusters of galaxies that are gravitationally bound will not have
>> this issue. These galaxies will remain in relative close proximity. If it
>> were not for the fact Andromeda and the Milky Way are going to coalesce in
>> about 4 billion years Andromeda would be observable from this galaxy far
>> into the future in wavelengths of light emitted by stars. The other galaxy,
>> M33 or Triangulum, the smaller of the three large galaxies in the local
>> group, may orbit around this newly formed Androway or Milkomeda galaxy for
>> a nearly indefinite time into the future.
>>
>> LC
>>
>
> *So you agree with Brent that the CMB will grow redder as the universe
> expands, but will never "wink out" as will be the case for galaxies not
> gravitationally bound to the MW? The key difference is contained in the
> concept of photons entering the box as others leave, and I suppose this
> follows from the omnidirectional nature of the CMB. Correct? AG*
>
Once the wavelength of CMB radiation has expanded beyond any possible
quarter wave stack size it it no longer detectable. Once it has expanded to
a scale larger than the cosmological horizon it is absolutely impossible to
detect. In that case we can say the CMB has winked out. This will happen in
a finite time in the future, though two trillion years is 144 times the age
of the universe now and almost eternity compared to our lifetimes. In the
extreme time frame beyond from 10^{30} to 10^{110} years there will only be
supermassive black holes. The cosmological horizon does emit Hawking-Gibbon
radiation that is analogous to Hawking radiation. This radiation will
perturb black holes, and potentially a civilization or collective of
intelligent life that lives around such a SMBH using its angular momentum
as energy might be able to detect this perturbation. The SMBH might not
decay quite as it would in a pure vacuum. This might be the detection of
the cosmological horizon. I will refrain from much comment on the
plausibility of such civilizations.
The box argument in part works because of the isotropy of the CMB radiation.
LC
>
>>
>>>
>>>> On Thursday, December 28, 2017 at 10:38:29 PM UTC-6, John Clark wrote:
>>>>>
>>>>>
>>>>>
>>>>> On Wed, Dec 27, 2017 at 3:17 PM, <agrays...@gmail.com> wrote:
>>>>>
>>>>> >
>>>>>> Since galaxies were formed after the CMB came into existence about
>>>>>> 380,000 years after the BB, and those far away will wink out as they
>>>>>> cross
>>>>>> the cosmic horizon, why doesn't the CMB also wink out?
>>>>>>
>>>>>
>>>>>
>>>>> The CMB will wink out, its only a matter of time. The CMB came from
>>>>> when the universe was at a temperature of about 4000K and glowing
>>>>>
>>>>> by black body radiation mostly in visible red light, but because of
>>>>> the huge Doppler shift we see it as microwaves
>>>>>
>>>>> and it appears to us as if its only at 2.8K. In a few billion years we
>>>>> won't be able to see that part of the universe anymore
>>>>> ,
>>>>> we'll see a cooler part and it will no longer be microwaves it will be
>>>>> in longer
>>>>>
>>>>> and
>>>>>
>>>>> weaker radio waves. A few trillion years after that the wavelength of
>>>>> light from the BIG Bang will become shifted so much it will be larger
>>>>> than
>>>>> the observable universe and
>>>>>
>>>>> thus
>>>>>
>>>>> it will become impossible even in theory to detect; if there are any
>>>>> astronomers around in that era they will
>>>>>
>>>>> know nothing about the CMB and
>>>>>
>>>>> have no evidence the Big Bang ever happened and no evidence the
>>>>> universe is accelerating or even expanding, for them the entire universe
>>>>> will consist of the Milky Way and the
>>>>>
>>>>> Andromeda
>>>>>
>>>>> Galaxy
>>>>>
>>>>> and thats it.
>>>>>
>>>>> We're lucky to be living when we are, we have access to information the
>>>>>
>>>>> far
>>>>>
>>>>> future will not have.
>>>>>
>>>>> John K Clark
>>>>>
>>>>>
>>>>>
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