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.

bump

>>16776734
>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?
they do define stuff up to a certain point. but it is true that they think notation is magic and does not need to be defined.