On 12/29/2017 9:26 PM, [email protected] wrote:
On Friday, December 29, 2017 at 7:45:41 PM UTC-7, [email protected] 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*
Look at these spacetime diagrams and you will see that however great the expansion there will remain a part of the CMB that will be visible, but increasingly redshifted, to us.
http://www.astro.ucla.edu/~wright/cosmo_03.htm Brent -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
