Suppose you got into a spaceship and flew in a straight line, forever and ever, where would you end up?

I think she’d be flying in a straight line, for all eternity. The universe is supposed to be infinite; I’ve not heard of any theories claiming it curves back on itself.

I think I’d just end up at my mother -in-law’s ;)

@Dr_Dredd: Really? I have. It’s called constant curvature. The theory of a closed, spherical universe posits that traveling in one direction will eventually return you to your starting point. See here especially.

I feel like it would “circle around”.

I don’t think that there’s any such thing as “a straight line” in space. If you stick your finger up in the air right now (and again, according to your rules, you could hold it absolutely steady in relation to the ground that you’re on), that finger is already describing the arc of one circle (the Earth’s rotation about its own axis—“a day circle”), a larger circle around the Sun (a “year circle”) and several others, too, since the Sun is also not stationary.

What’s “straight” in this place?

First you would have to figure out how to fly in a “straight line”. I’m pretty sure it can’t be done without breaking some fundamental rules of space-time.

Jinx, @CW, you owe me a Coke.

If you flew into a Black Hole, that could change your destination drastically. Or maybe not because some people don’t believe they really exist.

@pdworkin, don’t you owe it to me? I really hate to keep disagreeing with you, but I think this is what we both do, isn’t it?

@pdworkin, @CyanoticWasp: Although we are already assuming limitless air, food, and time, so I suppose the ability to travel in a straight line/one direction can be added to the other hypothetical conditionals, no? Or is the possibility of that beyond even the conditional stuff?

@CyanoticWasp where I come from, the person who “calls” it is the person who gets the Coke. P.S. This would not have come up if we hadn’t just agreed.

Ok, I just recently saw another theory or guesswork that stated that they think there may actually be an “edge” to the universe that they are unable to see past yet. It won’t matter to me, of course. I’m not planning on leaving the planet by any other that conventional methods, I wish I had paid more attention now…

@absalom, you need to set up a reference point, then (two, actually) that doesn’t move, so that you can establish what is “straight”. I don’t think it’s possible outside of Plane Geometry, which only exists in books and theory, anyway. (You can’t very accurately navigate using simple plane geometry past “line of sight” even here on Earth.)

@pdworkin, I guess that’s right. I didn’t know ‘the rule’, but I guess that’s the way I’ve seen it work elsewhere. I owe you a Coke.

The other thing is, I believe, that one would never “end up” anywhere if one were to fly forever. (Forever and ever is redundant.) ;-)

@Trillian, along the lines of your last answer, if you “fly forever” you’d never “end up” anywhere, anyway. That’s an oxymoron.

@absalom If you want to “assume” that you can do the impossible, you might as well assume that you know exactly where you are going to end up.

@CyanoticWasp, I know, that’s what I was saying. Or trying to say. Can I have your coke? My coffee is running low..

@Trillian – Is that a cup of genuine Advanced Tea Substitute on your avatar? Can you ask Marvin to make one for me? And say “Hi” to Arthur for me…

@pdworkin: Yes, true, but where’s the fun in that?

@Trillian, I realized that soon after I posted. I don’t know how I was reading your answer to mean other than… what I said. I’m all out of Coke, though. I need to put it on the shopping list just for @pdworkin.

@HungryGuy, um…it’s a cappuccino. Or is Advanced Tea Substitute what you call it? @CyanoticWasp , would you tell him to just toss it to me?

OK. sorry, way off topic. I give up. I’ll keep a closer eye on Discovery Channel, Nat Geo and Nova.

I thought space and time stretched for infinite amount of time, but not completely infinite because eventually it bounce back and starts going back in time after it stretched out to its max?

@pjanaway, but you can’t have it both ways. Something is either infinite or finite. If it’s not completely infinite, then it is by definition, finite. I think that was the point of the question to begin with.

@Trillian – Right. That’s the point of my question. If I had just asked if the universe was open or closed, everybody would have said its closed because the shape of the universe is defined by the sphere of matter produced by the Big Bang that we all know and love.

@absalom

The movie paycheck had a referance to that. It said somebody (not sure who) said that if you could see around an infinite curve, you would see where you are now, but in the future.

And define a straight line. You need to take into accound that space is 3 dimentional, so would it be a straight line 3 dimentionally, or just up and down (of course there is no up and down in space)

@XOIIO – Straight Line: take a meter stick (or yard stick if that’s your thing). That’s a straight line. Now imagine a light year stick that’s perfectly rigid and won’t be bothered by any stars or planets (or even black holes) that it happens to pass through, that’s a straight line one light year long. Now imagine a billion-light year stick, a trillion-light year stick, etc., etc….

Ah, but that’s the thing. Black holes, stars, etc., do mess with your straight line. As in, space curves around them.

@laureth

Perfect answer!

Well, for the sake of argument, imagine that my ship has a nose made out of unobtanium and will just bore straight through any matter that’s in its path…

In a world of hurt.

Never- Never land. Watch out for Captain Hook.

@absalom Interesting! I didn’t know that.

Before you got past mars there’d be someone asking “are we there yet?”

@Trillian – Yeah but I don’t think the “infinite” is supposed to be taken litterally, rather more just a huge amount we cannot estimate instead.

If you flew in a straight line through the universe, odds are you’d hit something. But I’m most comfortable with the idea that the universe is expanding. So you’d probably never reach an end, until the destruction of the universe.

@HungryGuy re: “Well, for the sake of argument, imagine that my ship has a nose made out of unobtanium and will just bore straight through any matter that’s in its path…”

My point is that this is not what happens. Space itself is bent by gravity, and stars (and black holes!) are potent sources of gravity. A straight line curves around them. It would not continue straight, like you’re thinking.

@laureth – Well then, I don’t know how to express myself if I can’t say “straight” when I mean straight…

I’m sure you mean “straight.” It’s not that you don’t mean “straight,” it’s that “straight” doesn’t necessarily happen in reality in space. On the other hand, since you’re punching through black holes with unobtanium, I guess you can make space go straight, too, if you want it to, but you won’t get an answer grounded in reality by ruling out reality as a concern when finding an answer.

Seriously, though, this is one of those questions that physicists can write books about. If you want to know more, Stephen Hawking might be a good place to start. If he takes pages and pages to explain this, there’s no way that I can do it in the space of a quip. There’s a lot of good material out there for the reading!

@HungryGuy, you just don’t want to hear that there is no “straight” in space. But there isn’t. In fact, there isn’t even a “straight line” for you to walk across your living room. If you walk in what appears to you to be a perfectly straight line between any two points, an observer from within our Solar System sees you with one angular momentum as the Earth spins on its daily axis. So from your point of view (and everyone in your living room) you walk a perfect straight line. No cop would accuse you of failing a field sobriety test. But that observer from space sees you walk the same “straight” line… while moving towards the West (on this planet) at up to 1000 miles per hour. He sees you go farther and faster to the side than you could have managed to move on your own. At the same time, he sees you in another angular momentum as you move approximately 1,600,000 miles per hour in an orbit around the Sun.

An observer from outside our Solar System sees even more movement, relative to his position. What seems like a perfectly ordinary straight line to you… is more of a corkscrew motion.

So, fine, you say. I want to start from my living room and move outward in a direct line to that star that you point to and we agree upon.

You still can’t do it in a “straight” line. Whatever star you see is the light from where the star was thousands if not millions of years ago. If you attempt to travel to it, you’ll always be chasing its previous position. (And what do you use to steer with, anyway, when you have no compass, and your sextant is useless?)

So you say, “the hell with that, I just want to go and keep going ‘away from Earth’”. Well, you can do that, more or less. But not in a straight line, with or without your mythical material. Every move you make is dependent upon the move you made before. And if you’re starting from Earth, you will always be starting with the angular momentum of the Earth’s rotation, its revolution around the Sun, the Sun’s revolution around the rest of the Milky Way galaxy, and the Milky Way’s movement relative to other galaxies. “Straight” is a concept that only exists… inside your living room.

If you ever make it to The Restaurant at the Edge of the Universe, please say hello to Douglas Adams for me, please. He’ll probably be sharing a table with Carl Sagan.

Okay then. Let’s assume my spaceship is heading out, dipping through all the gravity wells in its path curving here and there (though it’s going “straight” from its own POV), detouring around stars and black holes, but generally still going away from Earth, the Milky Way, the local cluster, etc., in the same general direction…

- Will it keep on going forever?

- Will it “curve around” and come back to its starting point?

- Will it crash into the “edge” of the universe?

- Will it pass through the “edge” of this universe into the next universe with its own separate big bang?

- Will it do something else?

That’s the gist of my question, irrespective of quibbles over terminology or whether or not space is “flat”...

And of course, I’ll be sure to stop into Milliways, order a cup of Advanced Tea Subsititute, and say “Hi” to Carl Sagan, Einstein, Douglas Adams, et. al..

In that case, while we don’t know for sure, I am leaning with @absalom‘s “curvature” idea in the third quip from the top.

If you can twist the scenario to allow “straightness” how on earth could you “curve around”? I think you are lost in the contradictions of your own question.