APOD: A Flight through the Hubble Ultra... (2020 Jul 26)

Comments and questions about the APOD on the main view screen.
sillyworm 2

Re: APOD: A Flight through the Hubble Ultra... (2020 Jul 26)

Post by sillyworm 2 » Mon Jul 27, 2020 5:12 pm

One gigantic tease.We may never reach the nearest star! What a majestic twisted trick we have been played.

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neufer
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Re: APOD: A Flight through the Hubble Ultra... (2020 Jul 26)

Post by neufer » Mon Jul 27, 2020 5:15 pm

johnnydeep wrote:
Mon Jul 27, 2020 3:46 pm
neufer wrote:
Mon Jul 27, 2020 3:11 am
rwlott wrote:
Mon Jul 27, 2020 1:36 am

Ahead! Warp factor 9 gazillion, Mr. Sulu!
  • The warp factor : 250,000
I think that's too fast. Warp 250000 would be 15.625e15 (15.625 quadrillion) times the speed light. That's a light year in about 2.02 nanoseconds, or a Gly in 2 seconds, or 27 secs to cover 13.8 Gly. Since the length of the video is 58 seconds, we'd only need to go about half the effective speed of warp 250000, which, by the magic of cubes is "only" about warp 198000 :D
The z=8 galaxies have a comoving radial distance of ~30 Gly:
http://www.astro.ucla.edu/%7Ewright/CosmoCalc.html
https://en.wikipedia.org/wiki/Observable_universe wrote:

<<The observable universe is a spherical region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time. According to calculations, the current comoving—proper distance, which takes into account that the universe has expanded since the light was emitted—to particles from which the cosmic microwave background radiation (CMBR) was emitted, which represents the radius of the visible universe, is about 45.7 billion light-years, while the comoving distance to the edge of the observable universe is about 46.6 billion light-years, about 2% larger. The radius of the observable universe is therefore estimated to be about 46.5 billion light-years.

As the universe's expansion is accelerating, all currently observable objects will eventually appear to freeze in time, while emitting progressively redder and fainter light. For instance, objects with the current redshift z from 5 to 10 will remain observable for no more than 4–6 billion years. In addition, light emitted by objects currently situated beyond a certain comoving distance (currently about 19 billion parsecs) will never reach Earth.>>
Art Neuendorffer

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neufer
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Re: APOD: A Flight through the Hubble Ultra... (2020 Jul 26)

Post by neufer » Tue Jul 28, 2020 3:40 pm

Click to play embedded YouTube video.
Art Neuendorffer

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Re: APOD: A Flight through the Hubble Ultra... (2020 Jul 26)

Post by alter-ego » Mon Aug 03, 2020 1:57 am

https://en.wikipedia.org/wiki/Observable_universe wrote: ...
As the universe's expansion is accelerating, all currently observable objects will eventually appear to freeze in time, while emitting progressively redder and fainter light. For instance, objects with the current redshift z from 5 to 10 will remain observable for no more than 4–6 billion years. In addition, light emitted by objects currently situated beyond a certain comoving distance (currently about 19 billion parsecs) will never reach
Earth.[17]
Poorly written at best, just plain wrong at worst.
For instance, objects with the current redshift z from 5 to 10 will remain observable for no more than 4–6 billion years.
  • Per the referenced paper: Objects with the current redshift z from 5 to 10 "will be only visible up to an age of 4-6 billion years" (entirely different meaning). It takes an infinite amount of time to reach the observable limiting age of these objects. After 45Gyr to 50Gyr from now the observed ages will be within 5% of their asymptote limits.
    → For present ΛCDM expansion parameters, these objects will theoretically be visible forever, although progressively getting fainter and redshifted. Presently, the objects' ages range from 0.5 - 1Gy. It's ironic that as slow as cosmic evolution is, one could say these objects will evolve in slow motion 🐌👉 until apparently nearly frozen in time 50Gyr from now.
In addition, light emitted by objects currently situated beyond a certain comoving distance (currently about 19 billion parsecs) will never reach Earth.
  • This statement is not from the paper and looks plain wrong. What comoving distance (i.e. event horizon or particle horizon) is being referred to? Without more context, 19Gpc makes no sense - it is ~36% larger than the observable universe (aka particle horizon). Correctly stated in Wiki's first paragraph (quoted by Art), the particle horizon currently has a fundamental, limiting radius ~47Gly ( or ~14Gpc).
    → Per the current ΛCDM model, NOTHING beyond this radius has been or will ever be observable. It's a hard-wall boundary to anything observable beyond it. Of course, as time progresses, the particle horizon grows as space expands without new energy/objects added to the system.
  • Regarding the Even Horizon, for any object with z ≥ ~1.8, the light emitted today will never reach the Earth. Those higher-z objects are beyond our Event Horizon (comoving distance ≈ 16Gly) - Also not 19Gpc.
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