Flat..... or not?

[brasileiro]

I'm sorry guys... but I have to ask this. ok... let's say we built a flat wood plank until it touched ends, we could see that the plank isn't flat, but it curves at a very VERY slight angle, but it would seem flat... and if we built a perfectly flat plank, it would seem like it was curving up into the sky... why is that? Someone please elaborate

[jinydu]

and if we built a perfectly flat plank, it would seem like it was curving up into the sky... why is that?

Why do you think that this is the case?

[brasileiro]

The case for what?

[jinydu]

Why do you think that the plank would curve into the sky?

[Twix18]

well it couldnt very well curve into the ground. now if it was built in space it would be a huge flat circling plank... the sky was just a direction.

[brasileiro]

I said it would seem like it did... and why is that? why would the flat one seem like it curved and the curved one seem like it was flat? That's all... and it would be something I would like to see too...

[jinydu]

I still don't understand what you're asking, but I'll take my best guess:

Are you saying that since the Earth is curved, a perfectly flat plank could not stay on the surface of the Earth (otherwise, the plank would curve with the Earth), but would instead have to extend out into space?

[Twix18]

the space thing was my idea not his.. and yea i tihnk that whats hes saying. a plank that spanned the world, while we were on it it owuld be flat, but at the same time curved.

[jinydu]

Hmm, that's not what my last post said.

So basically, you're saying that if we could build a plank that wrapped around the entire planet, it would appear flat to us, but curved to astronaturs in space. What's the problem with that?

[brasileiro]

you know what? I really don't know why i originally posted this.. it was just something I always wanted to say... you know, like something perfectly flat is physically impossible to build... it will always have some kind of curve, no matter how slight.

[wendy]

The universe is flat, since it is an "all-space", and all-space is by definition, flat. Whether the thing has euclidean geometry (ie zero curvature) is what has always been debated.

The experimental evidence suggests that it is on a large scale, zero-curvature, although positive and negative models have both been proposed. A black sky at night is taken as evidence that it is not uniformly packed, regardless of the geometry.

On the other hand, it could be hyperbolic, in which euclidean space itself appears as a proper curve (straight lines do not pass along the surface).