[mr_mitm]

> The expansion of universe is accelerating.

We knew that before. This goes deeper than that. It accelerates in a way that cannot be explained by a constant dark energy density, which is part of our standard model. We have plenty of alternative models that can explain this, but our measurements are not precise enough yet to rule any of them out. Hopefully Euclid will provide data that is.

[JoeOfTexas]

If expansion at the big bang started with a rate of X. Could the varying densities at different points cause their expansion to deviate from the original rate?

[mr_mitm]

I'm not sure what exactly you mean, but the Hubble tension could also be explained if we live in a particularly large under dense region of the universe. Then the light we observe from the CMB basically has to climb out of a gravitational well which would influence our measurement. IIRC such a substantial under density is considered unlikely though and very hard if not impossible to measure.

The spatial inhomogeneities of matter in the very early universe, which I believe you might be talking about, were extremely tiny.

[digging]

> I'm not sure what exactly you mean, but the Hubble tension could also be explained if we live in a particularly large under dense region of the universe.

That would be the proposed Local Hole.

[1]https://en.wikipedia.org/wiki/KBC_Void

[echelon]

> We knew that before.

There was an amazing paper on this published on HN a year or three ago that explained at certain discrete points in the future, entire percentages of the known universe will be beyond our reach. It was profoundly beautiful and sad at the same time.

I'll try to dig it up.

Edit: found the post (three years ago) and some of the quotes and figures I pulled from it:

https://news.ycombinator.com/item?id=26734913

Edit 2: another commenter had made a note about the Big Rip. I was writing a response, but they unfortunately deleted their (good) comment. I'll include my response below:

> wait until you find out about the Big Rip (paraphrasing)

That one's even wilder. To think every atom of every place and loved one you ever touched would vanish infinitely far away. Every atom and then subatomic particle of your own once corporal body, regardless of its final resting place, torn and scattered.

Last Contact is a great short story if you're in the mood [1].

Then there's vacuum collapse and all the other theories.

I wonder what humans or human descendents 500 years from now will figure out about the universe's ultimate fate.

[1] https://zestfullyblog.blogspot.com/2011/02/last-contact-by-s...

[peppertree]

I can explain it with higher dimensional turbulence. Where is my Nobel.

[throwway120385]

You'll have to perform some experiment to earn that, sorry. Not even Einstein could win a Nobel just by having a good idea.

[rrix2]

It's in a box wrapped up in your peer-reviewed scientific papers