I filled out the Personal Disproof of Time Travel a number of years ago, for fun, and I have yet to go back to meet up with myself at that time. This proves that I will never of had a time machine, right?
If you've ever done anything with collaborative software projects, you would have most likely come across something that uses "git".
When you clone a git repo, make a change, and commit that change, you effectively add a new "branch" to the git tree. So, how do we know that when we do things, it doesn't change in the same way for the timeline?
Pretend each action "commits" a new change to our shared timeline. Each "general improvements and bugfixes" commit we put in changes things for everyone else on this timeline. Why haven't we seen the time traveling happening? Because you aren't on the right timeline. You are on the one where you don't time travel, since the other version(s) of you who will time travel are on different branches already.
In this theory, the other timeline branches are not observable on their own, much like how viewing one git fork does not let you see multiple other people's forks, hence we won't know about the time traveling happening in those timelines. We cannot, however, observe the "main" line when someone does something that deviates our line off from the main one, since we were not the version of ourselves that stayed in the unchanged line. That version of us is out there, but we cannot access it at the moment.
A key part to traveling through time would be accessing these other timelines. Once we do that, we should be able to figure out the secret to going back to past times, whether individually, or as a group.
There, however, are more theories than the "Git model" theory. Before the use of version control software, many people could of had access to an entire web/ftp site's files along with write access to do anything, including adding and deleting whatever.
The "shared read/write" model to our timeline explains why changes are almost always going to be out of our control, as well as why we can't go back to revert things we don't like -- as one can do with Git -- because a backup simply will not exist to go back to.
There is just no way to make a backup of reality, and maybe, it is for good reason that it cannot happen.
Whether we like it or not, many things happen for a reason, regardless of if it is a good reason or not. If we were to change what happened, the good things would never happen either. Sometimes, the overall good can outweigh the overall bad. This, however, is our timeline. Other timelines may have gained time traveling, but ours won't
In conclusion, our timeline is like a shared directory
chmod perpetually set to 777, hence why we cannot
travel to past versions of things and why people are constantly
ruining things for others.
In other words, you, in another universe/multiverse may have time traveled by now. You, here will never have a time machine let alone the ability to do so though.
For more information, please see the Metaverse's (real world's) /info/README.html file. (You must be logged in locally to the metaverse to view it.