Does a straight line actually exist?

If you travel in a straight line around the Earth, you will end up at your original starting point because the Earth is curved.

It's said that the same thing would happen in the universe if one could travel long enough.

Therefore it seems that a "straight line" is relative to one's point of view.

So I ask you-

Does a straight line actually exist?

2PacSade-


[edit on 19-12-2007 by 2PacSade]

reply to post by 2PacSade


I am intrigued at the idea about going "around" the whole universe in a straight line,have you got a link about that?

It is hard to comprehend from our tiny pinpoint perspective on Earth.
I have found a few different looks at the "shape" of our universe:

curious.astro.cornell.edu...

This one is very interesting:

www.newscientist.com...

The wiki version:

en.wikipedia.org...

And the "theory of everything" version:

www.universaltheory.org...

All are quite different from each other.
I am not sure any of the above would have a bearing on your straight line idea though.



en.wikipedia.org...(mathematics)

I'm sure a strait line does exist, conceptually. And, in 4D space I believe light travels in a strait line, unless diverted by a gravitational field or something.
I'm sure that somewhere in the universe, there are 2 points that when connected will form a strait line.

Maybe....

In my knowledge, a straight line is a 1-dimensional object that connects two points. In a sense, it does vary with perception -- only if one moves into higher dimensions before observing the line again. A straight line is a straight line on a two dimensional plane. It only curves around circles in three-dimensional objects.

As to what straight lines become in space -- I don't know. I've never been there, and I unfortunately have no further information on the subject. Last I heard, the Universe was either a dodecahedron -- or an interesting cylindrical object.

But before I go any further, I discovered this video yesterday. It should lend more valuable insight on this topic than I can. Hope it helps

reply to post by Silcone Synapse


Here one I found SS. It explains it in easy terms about halfway down the page-

here

2PacSade-

reply to post by 2PacSade


Man,thats a top page there.
Nice one,I will read the lot after I finish working.

Good stuff.

Originally posted by 2PacSade
Does a straight line actually exist?

A straight line is a hypothetical construct in Euclidean geometry. There are all kinds of other non-Euclidean geometries around that don't share this concept.

For instance, Euclidean geometry assumes an observer external to the concept space, which is ridiculous, because it real life, there's always an observer. In fact, in order to observe a line stretching between two points, you have to be external to it, and viewing it from 90 degrees away.

If you put yourself in the concept space, and move 90 degrees relative to the line, it becomes a point. So it all depends where the observer is.

Euclidean geometry doesn't address this at all. It's an okay way to do some things, but it's not a very accurate representation of reality, because you're not in it!

[edit on 19-12-2007 by Nohup]

a straight line? yes, according to one of the non-euclidian forms of geometry (always mix up their names and can't remember how to spell them) it's a straight line. you're thinking of a straight line in euclidian terms, which don't apply to spheres.

You guys keep talking about a line being a space between two points but everything ive ever read or learned about a line says thats not possible because a line goes on forever. It can have points along the line if that is what you are trying to say but it cant end, thats why its called a line.

Originally posted by Seiju
You guys keep talking about a line being a space between two points but everything ive ever read or learned about a line says thats not possible because a line goes on forever. It can have points along the line if that is what you are trying to say but it cant end, thats why its called a line.

Depending on what kind of geometry you're talking about, yes, a line between to designated points does actually consist of an infinite number of points between the two you designate. An infinity within a greater infinity of all the points that the line is not. And, of course, designating two points requires the implication of a third observer point not in line with those two points. Which creates another set of infinities.

All right thanks for clearing that up.

Some excellent posts here!

I jsut want to add that if you decide to remodel your home and do some carpentry, you will soon discover that straight lines most certainly do not exist and we live in a very warped space.

reply to post by Mr Jackdaw


Thanx for the video. If you tried to explain what was going on there in text format most would probably not comprehend, but to experience a visual interpretation allows a lot of it to explain itself.

2PacSade-

reply to post by Nohup


Thanx for the input. Seems that gravity is the killer of the Euclidian geometry. It's the reason for my OP. Even if you shoot a laser out into space it will be bent when encountering a gravitational force.

2PacSade-

Originally posted by madnessinmysoul
a straight line? yes, according to one of the non-euclidian forms of geometry (always mix up their names and can't remember how to spell them) it's a straight line. you're thinking of a straight line in euclidian terms, which don't apply to spheres.

I read a bit on these you mention;

hyperbolic, elliptical, absolute, analytic

source

I'm sure more will probably be invented as we discover inconsistencies in what we hold as truth in present day. Thanx for your thoughts.

2PacSade-

Originally posted by 2PacSade
If you travel in a straight line around the Earth, you will end up at your original starting point because the Earth is curved.

Well you wouldn't travel in a straight line would you ~ you may not deviate left or right, but unless you and me and everything we know only exists in 2 dimensions then you cannot possibly travel ROUND the planet in a STRAIGHT line . If you were to start at a point on the surface of the earth and were to walk in a straight line very soon your feet would be at an ever increasing distance from the ground. Then if you plot your course with for instance the sun as your point of reference instead of the Earth then your straight line would be possible, but to an observer on the Earth it would not appear as a straight line.

Originally posted by buddhasystem
Some excellent posts here!

I jsut want to add that if you decide to remodel your home and do some carpentry, you will soon discover that straight lines most certainly do not exist and we live in a very warped space.

Been there & done that! Try to find a straight piece of wood!

This is so true. Everything construction project is a tradeoff between actually being straight, and "eyeballing".

2PacSade-

Originally posted by Now_Then

Originally posted by 2PacSade
If you travel in a straight line around the Earth, you will end up at your original starting point because the Earth is curved.

Well you wouldn't travel in a straight line would you ~ you may not deviate left or right, but unless you and me and everything we know only exists in 2 dimensions then you cannot possibly travel ROUND the planet in a STRAIGHT line

. If you were to start at a point on the surface of the earth and were to walk in a straight line very soon your feet would be at an ever increasing distance from the ground. Then if you plot your course with for instance the sun as your point of reference instead of the Earth then your straight line would be possible, but to an observer on the Earth it would not appear as a straight line.

I couldn't agree more. That's my whole point. The straightness of the line is relative to the observer. Therefore, if the model of the universe is curved or cylindrical you would follow suit.

"straight lines" exist in geometric theory only???

2PacSade-

Originally posted by 2PacSade
"straight lines" exist in geometric theory only???

2PacSade-

How about "a straight line is in the eye of the beholder" I like that better

Originally posted by Now_Then

Originally posted by 2PacSade
"straight lines" exist in geometric theory only???

2PacSade-

How about "a straight line is in the eye of the beholder" I like that better

Very good! Yes that statement is much more apropos. You get a star to put on your fridge for that one N_T.

2PacSade-