The thing is, on a piece of paper, where you’re not perfectly calculating your angles with vet precise instruments, you might be okay. You would be wrong, but you just don’t have precise enough equipment to show you’re wrong.

Kyle Reese came from the future to father John Conner. That’s always been true. And because of that, John grew up and was able to send Kyle back in time.

But even if the universe was closed beyond what we could see, it would still be measurable with what we can see. I don't find it very likely that we just happen to live in a bubble that appears flat throughout all we can observe, but changes beyond that. 

Yes, we do. We just don't know how to define the force that's driving acceleration. Right now they just use "dark energy" or "dark matter" as placeholders. But they do know that's what is driving acceleration. 

I present to you all the current evidence of expansion we have. None of it has ever been disproved.

Technically time isn't a dimension when we're talking about the shape of the universe. It's difficult to grasp, but you gotta not think about the classic 3D model of an object, where time is the fourth dimension. With the shape of the universe, that fourth dimension is another axis, as is the fifth, and so on. But…

Effect comes before cause. It's a paradox. Welcome to time travel. 

Nope.

That’s completely untrue. 

Can you name a few?

We haven't, but I believe we're doing pretty well. 

Skynet sends the Terminator back in time, not because it needs to, but because it already did.

I get that. But there’s absolutely nothing we’ve ever observed or tested that has disproved the current model in any way.

You’re welcome. I used to get bored in the army a lot, so I took to helping some of my friends learn about this stuff. I try my best to be clear, but sometimes you need a white board to draw up some visuals to help.

You’re thinking too 3-dimensionally. A closed universe, by definition, cannot expand infinitely. A closed universe must have enough matter in it to reverse expansion. It has to end in a contraction. If it has the ability to expand forever, that means it’s not closed.

Lines on a globe that meet at the pole aren’t parallel at all, though. Longitudal lines start together, so, by definition, they can’t be parallel.

You’re absolutely right, our model of the universe is constantly evolving. But our current theories are about 99% compatible with what we see. Yeah, there's that 1%, but that 1% isn't going to be something that throws out the other 99%. Our current theories just keep getting proven right over and over, so it's very…

Because we're not in a closed universe. So it doesn't apply to our universe. 

Gravity isn't caused by mass, though. But, you're right in that space curves around everything. It curves around you, around your phone, everything. It's just an incredibly small curve. 

But of the universe isn't infinite, it must contract. It just can't do anything else.