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To point at first my question has a part of trying to make a concept and is not about was there a Big Bang or not. We accept expansion so it is right to think about a starting point of expansion and I am not concerned about that. I doubt about time elapsed between the Big Bang and the present time! Please consider this before You read my question. My question is partially a try to answer. Now the question...

If we think about all the most distant objects from Earth we get a spherical area of radius 13.8 billion light years. Now if we have such a group of objects present like a composite object due to measurements it must be old like every single part of it, at least time for light to travel to Earth: 13 billion years. So from this sphere to 'now': 13.8 billion years.

Now we must add time between Big Bang and the '13.8 billion light years sphere'. If we presume speed of light from central point to area of that sphere that is 13.8 billion light years to add. But massive objects have not that speed so let presume a factor between 0.5 and 0.8.

There is the space inflation also to take in account so the factor rises. The whole inflating observable universe has a growth of speed slightly less than c and thanks to that the objects can be seen from Earth but very close to c because we see the red shift of these objects, so time does not change much from 13.8 billion light years.

Finally adding time between Big Bang and the '13.8 bly sphere' to the time from '13.8 bly sphere' to 'now' gives 13.8 by + 13.8 by = 27.6 by.

Is this concept right?

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  • $\begingroup$ I can't write a complete answer right now, but rest assured that cosmologists know what they're doing, they haven't forgotten anything in their calculations. The math accounts perfectly for the expansion and everything. $\endgroup$
    – Javier
    Commented Jan 31, 2020 at 15:20
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    $\begingroup$ Your intuition is correct, but you are not accounting for the optical effects of the expansion. The old sphere you are describing as “large”, is large in the sky due to the optical magnification of the expanding space. If you see two objects of the very early universe in the opposite sides of the sky each 14 billion light years away from you, it doesn’t mean they were 28 billion light years from each other. They were very close back then, but their image is hugely magnified by the expanded space between you and them, as explained here: physics.stackexchange.com/questions/422644 $\endgroup$
    – safesphere
    Commented Jan 31, 2020 at 19:22
  • $\begingroup$ @safesphere Can the ADD effect be caused by a partial difraction of radial beams so part of them bend and hit the target at a larger angle so the picture is enlarged?Are enlargements of blue objects smaller than red objects (let say for galaxy that has relativistic rotation) ? $\endgroup$
    – jbradvi9
    Commented Feb 5, 2020 at 18:46
  • $\begingroup$ I am not sure what “ADD” stands for, but here is my take. First, the magnification I described above has not been observed. We don’t see any magnified objects of any color despite this theoretical result of the modern cosmology. Second, spacetime geodesic (trajectories) are the same for light of any color. So the curved spacetime has no observable dispersion. $\endgroup$
    – safesphere
    Commented Feb 6, 2020 at 3:34

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Nope. I think u are mistaken the age of the Universe with the particle horizon which settles the limit of the observable Universe. The $\Lambda$CDM model gives us a value of $d=45 \text{ }\mathrm{by}$. With time, as the Universe expansion is faster than light for certain distince (Hubble radius), the observable Universe will change, galaxies which are in this radius tomorrow won't be.

But the age of the Universe is $13.8 \text{ }\mathrm{by}$ for any observer.

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