On Friday, December 29, 2017 at 7:45:41 PM UTC-7, 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 jurney **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 *
>
*The CMB does "wink out" and the simplest way of seeing this is to
recognize that the rate of expansion is a purely geometric effect. It is
greater the farther away one is from our present location, consistent with
Hubble's law. So if distant galaxies "wink out" when they cross the cosmic
horizon, so must photons comprising the CMB since they're coming from an
earlier epoch, that is a more **distant **location, beyond all galaxies,
where the rate of expansion is greater than it is for all galaxies at all
distances. AG*
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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