Or up end our estimates of what happened when in our Big Bang timeline. (My "favorite" Big Bang hypothesis: 'the universe was expanding at speed X for a long time after the initial "Bang", then spontaneously slowed down. Just accept it.' Yes, I'm aware that the size discrepancies between continued maximum expansion and visible expansion now are immense. I just don't accept the magical "Suddenly, it changed [for no reason].". )
Yes, it could move (early galaxies have already moved) the timeline somewhat.
As for the rest of the comment, I'm not sure what you mean. 'Magical' is poor terminology for something that is mainstream cosmology - the Lambda Cold Dark Matter [LCDM] model in it's modern, self consistent, inflationary big bang form - and where main processes are fairly well understood and parameters are tested to within 0.1 % uncertainty. The cosmological expansion rate is understood to be described by Einstein's equations for the underlying general relativistic
Friedmann–Lemaître–Robertson–Walker [FLRW] universe. (Which, yes, suffice to approximate the mass energy content as a homogeneous "liquid" density. Until you want to describe the initially 10^-5 parts variation that shows up in the cosmic background spectra and later as cosmic filaments, where you need to switch to "gas" particles to do analysis and simulations.)
Long story short, the expansion rate in a FLRW universe with energy and pressure variables is decided by its inner state, akin to a pressure vessel. This is described in Cosmology 101 courses, which you may be interested in studying if you are amazed by the changes. (I recommend Susskind's free Stanford MOOC's, or you could watch some PBS Space & Time videos. But before you do that you may enjoy the overview video I link to later in this comment.)
During the initial era of inflation the expansion is decided by the inflation field potential energy, so being constant energy density the universe expanded exponentially, and being immense energy it expanded immensely fast. After our universe ended its slow roll inflation*, the inflation field energy was released in the hot big bang, and we see inner state change and the expansion rate change accordingly to much slower rates of expansion**.
* This ending is not by magic but natural though conceptually complicated. Essentially inflation is a process where a system - the universe - rolls down a hill of a Higgs like scalar field. The quantum fluctuations of the field kicks some volumes down the hill to end faster and some volumes up the hill to continue - but the main point is that an exponentially increasing volume is stuck in inflation while some local universe volumes enter their hot big bang era [
https://www.forbes.com/sites/starts...-was-it-like-when-the-universe-was-inflating/ ].
[The image won't insert, but look at the image titled
Inflation ends (top) when a ball rolls into the valley. But the inflationary field is a quantum one (middle), spreading out over time, and taking on different values in different regions of inflating space. While many regions of space (purple, red and cyan) will see inflation end, many more (green, blue) will see inflation continue, potentially for an eternity (bottom). ]
No magic, just process.
** If you want a quick summary of the expansion rate changes, after inflation the hot big bang starts with a radiation dominated era - no matter yet - and then a matter dominated era - radiation becomes too diluted by expansion. Both of those expands sub-exponentially somewhat like if you throw a mass (or energy) "ball" against gravity, so the expansion rates look akin to parables. But radiation becomes stretched by expansion so expands somewhat differently than matter. After a longer while both energy and matter becomes so dilute that the constant energy density dark, vacuum energy starts to dominate, and again the expansion rates becomes exponential as it was under inflation.
An overview video, which doesn't describe the expansion rate changes but the inner state changes and is a convenient orientation to grok the modern inflationary big bang universe:
View: https://www.youtube.com/watch?v=P1Q8tS-9hYo
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