Thread 16776718

a(t) = 1/(1+z)
Key Physics:

Scale factor relation: 1 + z = 1/a, so a(t) = 1/(1+z)
Scale factor is set to 1.0 at present time, smaller values in the past
Size at any time = scale factor × current size
1 MWD = 100,000 light-years
Calculations based on Planck 2018 cosmological parameters via astropy.cosmology (current universe age ≈13.79 billion years; observable diameter ≈93 billion light-years)
Post-inflation size corrected based on standard inflationary models (assuming ≈60 e-folds of expansion), yielding a physical diameter for the observable universe of ≈0.88 mm (≈0.035 inches), close to the size of a grain of sand.

Does this sound correct?

https://astronuclphysics.info/Gravitace5-5.htm

https://physics.stackexchange.com/questions/32917/size-of-universe-after-inflation

physicsforums.com/threads/big-bang-size-of-the-universe-at-different-epochs.1010248/

>>16776718 (OP)
Why do physicists refuse to define anything, and just expect you to somehow telepathically know what they're talking about and what each variable refers to?

>>16776734
Table shows the universe's observable diameter every billion years since post-inflation, based on standard scale factor physics (a(t) = 1/(1+z))

Columns:

age (billion years)

diameter (billion light-years), Milky Way Diameters (MWDs, where 1 MWD = 100,000 light-years)

redshift (z), scale factor (a)

% increase from the prior increment.

Small post-inflation size (~0.035 inches) reflects early expansion, growing to 93 billion light-years today.

these variables are used to model expansion; z measures how light stretches, and a scales the size. It's intoned to be a concise way to display the universe’s growth

adjusting the baseline to where universe is 10 inches in diameter at 1.0 billion years ago we get the following:

The % increases remain consistent with the original physics, adjusted for the new baseline.

This analogy simplifies the vast scale (93 billion light-years) into a manageable 10-inch diameter at 1.0 billion years, growing to ~66.5 inches (or ~5.5 feet) today, which is more intuitive for visualization.

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