I've read it; it's pretty good.

If I am at a different time in the past how could I see myself in the future  and still the most popular question. if I go to the past where I am not born yet and kill my parents what will happen to my future version. If I kill my parents then who am I really. So I go to the past kill my parents and now I shouldn't be exist neither in the past or the future

@5, there are many, many theories on what happens when a paradox is created. No one knows, obviously, and I really hope we never do discover time travel because that's just far, far too dangerous for me to be comfortable. One theory though is that if you go back and change the past and it results in an alteration of the future in such a way that you no longer exist within that future, you cease to exist. I've read theories that if two or more of an individual exist in the same time frame then all of them get wiped out because only one version of you can exist at any given moment. Don't get too hung up on thinking about time travel though; its a mental trap if there ever was one, and the human mind was never constructed to be able to comprehend time travel -- or, even, time itself. Time, and time travel by extension, is a logic minefield.

@7
I have yet to hear of a reputable scientific theory that allows for violating causality.  People aren't even on theories as to what might happen if you did because they aren't even onto theories that might let you do it.

Entanglement is strange but not many worlds parallel universes strange.  That's effectively just a way to make the trade-off "I know what this particle is doing" for "These two particles will act the same way".

You can understand things like Grover's algorithm with a hell of a lot of thought and math that's barely beyond high school honors level. Unfortunately I don't still have the accessible blog post and it's been too long since I cared to look for me to be able to explain it.

In general, in terms of physicists knowing the limits of the universe, they do.  There's not an extra layer of mystery.  You can stack a bunch of stuff up on current physics and just keep going without evidence forever, but you can also do that with religion among other things, and I promise you can find a theoretical physicist somewhere who will say whatever you want to hear.  that's not to say that theoretical physics is valueless or not science, but in general it's a branch of science that is very much the kind of thing where you can run away with it and sound smart and no one will question, so you have to be careful who you listen to.

Time being a human construct has always made the most sense to me. But then the one thing that I don't get is how does gravity influence time? Why does time pass more slowly the closer you get to a more massive object? That doesn't seem to fit with it just being entirely something that we made up. I've also never really been able to understand what gravity itself actually is. Something about mass bending the fabric of space around it, and I guess I can understand if that does happen that if you were moving how space being changed would effect your movement, but why would you still move towards the object if you are at rest.

OK, what's happening in this situation?
- I have a low-mass wormhole to another universe. Assume that the physics of this universe do not break anything that the physics of our universe wouldn't.
- I place this portal in orbit around Neptune (4.5billion km ... that'd be terameters, wouldn't it?) from the sun.
- I have a fusion-powered spaceship that I use to fly to Uranus (2.88tm from the sun, but there's no telling where the planets are relative to each other at this time, so let's round to 2tm). I have onboard what is necessary to open another portal to the same universe.
- A very rough attempt at calculating tells me that using the constant-acceleration method, the ship would lose somewhere between 0 and 120s to time dilation, to put it in horribly imprecise terms. Since we're accelerating the whole time, it's confusing and I haven't had to do time dilation problems since 2006, hence the huge range. Let's just go with a pessimistic "the ship is 60s younger than the portal at Neptune" and move on, even though I'm pretty sure there's way, way less dilation because I didn't accurately deal with the acceleration.
- I open a new portal in orbit around Uranus.
- The Far sides of the portals, in the other universe, are co-orbiting a brown dwarf, close enough that a signal can travel between them in well under 60s (aka, they're within 1 light-minute of each other).
- Exactly what steps would result in Neptune sending Uranus information from Uranus's future, given this setup? Does that change if we adjust the amount of time dilation, or the distance between the far portals?
- What if the far universe is in an apparently faster frame, such that time appears to pass twice as fast there from our perspective?

@14 I've heard the analogy of a heavy ball creating a dent in a sheet causing everything else close enough to roll towards it. That doesn't really make sense to me though, isn't that because of gravity that that happens in the first place? I doubt that would still happen in a 0 gravity environment. So I feel like it's explaining gravity by saying it's like gravity. Or am I missing something? But I guess the actual explanation is probably too technical, if there is even a generally excepted explanation at all.

@18
Everyone here is missing the point. As soon as you say "and now another universe", or "and now a wormhole" you are so far into theoretical physics that you get to pick your theory.  The authors pick the theories that are fun.  I'm not sure why you're confused, you're trying to understand literally impossible pop physics that people adopt for the sake of good stories.

Wormhole time travel is a thought experiment, an interesting consequence of choosing a particular set of equations and saying "huh, if I decide the universe works this way then...".  In that particular case the underlying assumption is that the two ends of the wormhole are always as oldest as the youngest end.  In that particular case, we have:

1. A wormhole at Earth that's 1 hour old.
2. A wormhole on a spaceship traveling at the speed of light that's also 1 hour old.
3. The universe outside the spaceship that just returned to Earth 10000 years in the future.

All of these are valid time frames.  The impossible part is that the wormhole entirely disregards 3 like it doesn't exist.  Poke our head outside, come back in, shout down your hour-old wormhole, and it's gone 9999 years, 364 days, and 23 hours back in time.  Done.  There is nothing more to it than that.

Except that it's impossible to actually do ever because doing it requires negative mass and negative energy which don't exist, and the entire thing can be used to violate the conservation of energy just by charging a battery and sending it through the time loop over and over, and in general this is just some interesting theoretical physics that some people did and then disregarded because that's how theoretical physics works.  You generate some equations over and over, some of them eventually align with experimental evidence, the rest sit on a giant bookshelf gathering dust.

For your "and now there's 2 universes" complicated topology case, other than the fact that it's impossible, if you want to posit what happens go get a PHD in Physics, talk to 10 theoretical physicists, and you'll get 10 different answers.

But the real answer, as far as you're concerned is "because the author said it works, yay".  You're not getting answers that satisfy you because there literally is no answer that doesn't boil down to authors deciding for the sake of a story.

@17
The rubber sheet isn't gravity. It's just a metaphor.  The actual math for this uses tensors, which are like the big brother of a matrix that went out and got a life, and I don't pretend to understand it in the slightest.

If you're looking for an answer to the question "Why does gravity bend spacetime", the answer is "because".  The mistake people make with physics is assuming there has to be a reason.  Certain aspects of the universe imply other aspects of the universe, sure, but "why gravity" doesn't have an answer.  Gravity bends spacetime because gravity bends spacetime, end of story.

I'm not sure that the time dilation on the scale of a few meters would be measurable before the sun burns out, but dilation a few thousand meters up has definitely been measured, yes. Maybe I missed something more impressive, and they measured the dilation between the top of a skyscraper and the basement, or between the top of the Andes and Death Valley, but I haven't heard of that.
Time dilation is also used in particle accelerator experiments. You can get low mass particles pretty close to c in those things, which means that time slows for them, which is the only way we can measure some of their decays because otherwise they'd happen too quickly to detect.
But time dilation and FTL=time-travel are not quite the same thing, if related. It's more about the weirdness of reference frames. The general rule for minimizing the risk of addressing time-travel is to privilege a reference frame, because Relativity would otherwise result in FTL events preceeding their causes in some reference frames. I still don't get how, though. The only explanations that make any sense are indistinguishable from "it's an illusion caused by looking at it a certain way, but Relativity says that makes it real, so if you did this it would 'violate causality". and I'm pretty sure that's not the actual point.
Like, I'm given the impression that if you could handwave in a way to skip to the fast side of c, Relativity would have it that you'd go back in time by accelerating to relativistic speeds, then going FTL, then stopping and turning around to return to your point of origin. And I have no idea how that's supposed to make sense. I don't remember which equations are relevant, only that they probably involve puting 1-v^2/c^2 in a denominator at least once.

So looking up why FTL implies time-travel on Google, the first arXiv article to come up claims the opposite... but has the same problems I get trying to understand in general:
https://arxiv.org/pdf/1407.2528.pdf
I ran into at least two spots in there where I got lost regarding how they got from A to B. I'm too confused about the first one to be sure, but the second seems like it would be easier to follow with the diagrams. As in, the problem is they randomly switch from explaining things, to pointing to a picture and referencing things in it, without ever explaining what the things in it are.
Somehow, I doubt having all the diagrams in accessible format will resolve the confusion, though. The PBS Spacetime video everyone likes to link did a decent job describing what the diagrams would be like, and it was still like "huh?".

I actually do have issues with the linked paper beyond just the inaccessible diagrams. There's a lot of "let's take as axiomatic that ..." for constructing the scenario, and it kinda feels like they gesture toward Lawrence contraction but mostly ignore it (but maybe that's not the case and I'd know that if I could see it?). It's also written to be as readable as possible without doing a deep-dive into advanced math and physics jargon, which both helps with comprehensibility and makes it harder to identify exactly where it might or might not go wrong.
Idk, maybe if I had coordinates for each labeled point / line / line segment / curve on one of these diagrams, maybe I could reconstruct it in an accessible format ... but I don't want to bug someone into providing those, then go to the trouble of interpreting it, only to wind up exactly as confused as before.