Asklemmy

Typically people propose switching everything to UTC.

The read this doesn't work is because humans are still bound by a diurnal cycle and you won't have everyone wake up at 0800, since for some people that's the time in the middle of when the sun sets and rises.
So you still need to communicate to people across space where the sun is or will be for you at a time in the future, or otherwise relate where in your wake cycle you'll be.
Tied to this is legal jurisdictions. Within a legal jurisdiction it's important for regulatory events to be synchronized. For things like bank hours, school hours, government office hours, things like "no loud noises when people tend to be sleeping", "teenagers old enough to have a job aren't allowed to work late on school nights", and what specifically constitutes "after hours or weekend labor" for the purposes of overtime and labor regulation you need your definition to be consistent across the jurisdiction. Depending on where you are in relation to Greenwich a typical workday can start at 1900 Friday night/morning, and extend until 0300 Saturday morning/afternoon. Your "weekend" would start when you woke up around 1800 Saturday evening/morning.

Right now we solve this problem by deciding on a consistent set of numbers for where the sun is across some area that inevitably lines up with legal jurisdiction. Then we use a lookup table to translate our conception of where the sun is to where it is elsewhere.

Without timezones you instead need to use the same type of lookup table to find the position of the sun at the time and place of interest, and then try to infer what the situation would be.

We have UTC now, and people inevitably already use it where it makes sense. It's just usually easier to have many clocks that follow similar rules than it is to have one clock that's interpreted many different ways.

We could use UTC.