> Quasar 'clocks' show the universe was five times slower soon after the Big Bang ... By observing quasars, this time horizon has been rolled back to just a tenth the age of the universe, confirming that the universe appears to speed up as it ages.

This seems like an incorrect summation of both the research and one of the researcher's quotes.

I believe this is the paper: https://arxiv.org/pdf/2306.04053.pdf

The researcher quote I presume inspired the article headline was: "Looking back to a time when the universe was just over a billion years old, we see time appearing to flow five times slower ... If you were there, in this infant universe, one second would seem like one second—but from our position, more than 12 billion years into the future, that early time appears to drag.

From what I gather, the researchers have applied a novel measurement of 190 quasars monitored over two decades, and have formed the view that the photons received on Earth have experienced time dilation on their journey to us due to consistent redshifting of wavelengths. It appears there has been some debate in previous research about whether quasar photons were consistently redshifting as expected and/or whether redshifts were caused by time dilation or other causes. This has in turn placed some doubt on cosmological expansion theories. The researchers feel their analysis confirms mainstream theories.

This relies on the argument that:

1) Time has run at the same local speed for the universe's history (for all physics equations, t today is the same as t billions of years ago) - this is the opposite of what the phys.org article implies to me as a reader

2) Light has run at the same velocity for the universe's history (aka c has been constant)

3) Quasars act today as they did billions of years ago

4) The light from more distant quasars is redshifted consistent with expansion and relativity theories

As a bit of an aside thinking about this, I'm wondering if anyone can help me understand an erroneous interpretation I have.

If the observable universe is estimated at around 93 million light years in diameter, or around 28,500 megaparsecs, and the expansion of the universe is estimated at around 73.24 ± 1.74 (km/s)/Mpc, then the most distant objects are moving apart from each other at something like 2,087,340 km/s. Surely that should mean that any light emitted from those two objects never reaches the other as this is well above the speed of light. Or to frame it another way, surely that means we should only be able to see in our light cone around 4,096 megaparsecs of universe, with anything further than that expanding away from us faster than the light emitted from it can travel. Which should mean the most distant objects are constantly disappearing from view.

This article tries to explore the issue: https://bigthink.com/starts-with-a-bang/dark-energy-myth-dis...

It reasons, due to dark energy:

1) There are parts of the observable universe that we are still yet to see (that as the universe expands new objects will enter our light cone for the first time)

2) That there are objects we will never see (that never will enter our light cone, and because of expansion will be prevented from doing so)

3) That any object we see we will continue to see indefinitely.

However I feel like #1 and #2 goes against my understanding of the Big Bang where all objects were once upon a time really close together (so share a common light cone), and I feel like #3 is hard to understand for the reasons I've outlined above.

How do I patch my understanding here?