h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

How can the Universe be curved?
I was thinking last night about the theory that the universe is curved and started wondering how they came to that conclusion. I am not sure whether they think we are inside a ball like structure or that we are on the outside, in which case the ball would be required to be somewhat spherical and have a gravitational pull, but how could there be a pull which affects us in no matter what way we where traveling because on earth we only have the four main compass bearing (North, East, West and south) then the ones in-between those i.e. north east. But we can travel up or down as we can in space so it would require a string of spherical gravitational pulls all linked together.

To try and picture what it would be like to traveling in a straight line using this theory, take your one hand and clench it in a fist in front of you then with a finger from your other hand start moving along it as if your were going in a straight line in any direction, this seems like what happens to us on Earth, now try to think if you were to travel up or down off your hand, how could the loop around because you are leaving the gravitational pull so the only way to compensate for this would be to imagine arcs coming off your hand and any direction you go to just travel along this arc. Now what happens if we decide to stray off from our straight line course and make a sharp turn, try to do this with your hand, start going up then make a sharp 90* turn either left, write, back or front, that would either require another arc taking you back to the arc before or just an arc taking your back to the center, no try this process by going up and making several sharp turns, where do you wind up? Very far from your original point. One other thing to try to imagine is instead of going straight into space go with a bit of a curve, the opposite of what we think pulls you back then theoretically you would be going in a straight line right? Well whether it would work or just bring you back to the same point but you take another route well I’m not 100% positive but I think you would probably keep going the “true straight”

Now with things like these to think about it is easy to see why this theory has many floors in it (or maybe mine just does) because you could going and making 90* turns forever and either hit the end of space, just keep on going for eternity and discover that space is infinite or wind up back in the same part as you started which would leave me totally puzzled and annoyed due to the fact that I was awake till 3am thinking about me theory and giving myself one heck of a bad headache.

The only other possibility is that there are more dimensions than we know which would allow for such a complex strain arcs linked together.

Hi Iffy. Curved space can't really be visualised, so this is the closest I can get. A flat 2 dimensional surface can be bent through a third dimension to form a sphere - a finite but unbounded surface. A Euclidean 3 dimensional space can be similarly bent through a fourth dimension to form a hypersphere - a finite but unbounded volume; which is how most physicists think our universe is.

Locally, when light from a distant star passes close to a large object like the sun, the star will appear to be displaced to a slightly different position in the sky. Since light travels in a straight line relative to the space it's in, the apparent curvature of the light can be thought of as a curvature of space itself.

Hope that helps

Noggin

well if i coudld change my my title it would be something like, "a few of the reasons why it might not be curved," not just why it cant be.

Ok, I'm not too great at physics (i do pride myself with the fact that -by using a great book that explained everything very well- at one point i completely understood the theory of relativity and all that stuff. i probably've already fogotten it all again )

I read that entry about 4 times, and i know that u wrote it ages ago, but I would like u to explain something to me: With the arcs, do u mean they sort of start out at the center, or earth, or wherever u're coming from, to form a kind of fountain shape, or do they surround the earth, like a sphere in a sphere in a sphere etc. I still haven't quite understood ur theory, but i think i sort of get the gist of it....if u can explain the arc thing to me.

yes it has been a long time. thing of it as a circle coming for the north pole out around to the south pole, a bit like drawing the magnetic field of the earth, then another one from each point between north and south pole. help that helps a bit


what book is it that explains all this stuff? i love being the person who nows more than the teacher in physics class since we have never done physics before

yeah, that helps, thanks.

The book is in German, sorry. It's kind of like Einstein in the modern world, explaining stuff to his neice....i read it a long time ago. I was especially fascinated by the stuff about how gravity around planets is like heavy balls laying on a thick blanket. (Good thing to know if u ever want to get rid of an extremely annoying stupid person. It should keep their brains so perplexed they can't move)