The Edge

[Tarantism]

if the universe is expanding constantly, what can hypographers hypothisize is happening at the EDGE? :shrug:

[InfiniteNow]

It's a tough question to answer. When you speak of the "universe," it tends to imply that which encompasses everything. So, to speak of an "edge," would seem to imply something "outside" the universe and the question is like asking "what does water do when it's outside of water?"

 

If there is an edge or boundary condition however (and that's a really big IF), I like to think that it joins up with itself on the other "side." Just don't ask me to define a "side" of the universe and we'll be good. :D

 

 

Cheers. B)

[ronthepon]

You might have heard the earth-being-round analogy... if not here it is.

 

The universe is finite in space, however there is no well defined 'edge'. Just like the earth has a limited amount of surface area, but no edge after which there is no earth.

 

So the universe expanding constantly can be analogous to the radius of the earth increasing.

 

As InfinteNow said, there is no 'side' then.

 

PS: note that it's pretty much what InfiniteNow said.

[Eclogite]

Or, to put it another way, just as the Big Bang happened everywhere, so that we are at the centre of the Universe, we are also at the edge.

[Turtle]

Or, to put it another way, ... we are at the centre of the Universe, we are also at the edge.

 

Exactly! The center is not the middle. The center is always at the edge, or in the case of a line the center is at the end(s).:lol:

 

PS Since the "edge" is a "boundary", the center is always at a boundary.

[Eclogite]

Although, it is interesting to note that while North America is the center of the Universe, the United Kingdom lies at its centre.

:lol:

[Tarantism]

ah, yeah i know about the friedmann(sp?) models. what i was trying to say, i think, is that if the universe is expanding, how can it be expanding onto itelf? wouldnt it overlap?

 

i like friedmann models, just food for thought :lol:

[Tarantism]

Although, it is interesting to note that while North America is the center of the Universe, the United Kingdom lies at its centre.

:lol:

haha!

[CraigD]

Some have proposed that the geometry of the 3-dimensional universe is somewhat like that of the 2-dimensional surface of the Earth – that a line segment projected far enough will form a circle in a 3+1-dimensional space.

 

Although many of these proposals suggest that the circumferance of this hypersphere is so great that the universe has not existed long enough for light to circle it, others have allowed that this may not be the case. I’m aware of one studies of astronomy data that is attempting to detect that stars patterns (allowing for changes over time due the difference in distance) observed in one direction in space correspond to patterns in the opposite direction, as this hypothesis predicts.

 

Others have proposed precise measurement of the angles of a very large triangle – for example, by precisely aligning 3 lasers on 3 spacecraft at distant points in space – to determine if the sum of the angles are not equal to 180°, as is predicted by either circumference-larger-than-age-of-universe-in-lightyears or circumference-not-larger-than-age-of-universe-in-lightyears.

 

Luminet, Starkman, and Weeks describe this far more eloquently than I in the 4/1999 Scientific American cover article “Is Space Finite?”

Looking up at the sky on a clear night, we feel we can see forever. There seems to be no end to the stars and galaxies; even the darkness in between them is filled with light if only we stare through a sensitive enough telescope. In truth, of course, the volume of space we can observe is limited by the age of the universe and the speed of light. But given enough time, could we not peer ever farther, always encountering new galaxies and phenomena?

 

Maybe not. Like a hall of mirrors, the apparently endless universe might be deluding us. The cosmos could, in fact, be finite. The illusion of infinity would come about as light wrapped all the way around space, perhaps more than once-creating multiple images of each galaxy. Our own Milky Way galaxy would be no exception; bizarrely, the skies might even contain facsimiles of the earth at some earlier era. As time marched on, astronomers could watch the galaxies develop and look for new mirages. But eventually no new space would enter into their view. They would have seen it all.

Personally, my only “article of faith” (assertion that I believe but can’t prove) concerning the universe is that it’s finite. I can discern no theoretical or empirical evidence to draw any conclusion about its geometry, including whether it has or hasn’t an edge.

 

I’d love to see the results of that space laser experiment, though :D

[Tarantism]

wow. thanks Craig, great info as always.

[LaurieAG]

Have you thought of considering a gravitational universe with an edge determined by an objects proximity to the universes center of gravity?

 

This type of universe would have a finite mass and a finite size when you restrict the area to its 'edge'. Any object with mass that travels to the 'edge' will increase the size of the universe by the distance of its own gravitational attraction. Multiple universes (independent gravitational systems over a certain size) may be able to coexist in 3D space without causing major problems.