>> Finite? Maybe.
>> Must have a border? Maybe not. Or it may just be that there is no way to
>> perceive it, even if you are almost "touching" it...
>
>  If there is a border, it's probably impossible for us to ever reach it.
> There's this thing called "cosmological horizon" which, if true, means
> that there's just no way, even theoretical, for as to "see" it in any way.
>
>  But that doesn't mean there is no border.

Einstein postulated a finite universe as part of his formulation of
relativity. He said that, since space-time can curve, eventually if
you travel in a straight line far enough you will come back to your
starting point. This would mean that there is no well defined edge.

Modern astronomers can find no evidence of such a large scale
warping of space-time. This is part of why the theories of parallel
universes are in vogue, if the universe is infinite, then if you
travel in a straight line far enough you might reach a region
that is very similar to earth, but isn't quite. It would be "parallel".

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Warp <war### [at] tagpovrayorg> wrote:
> Alain <ele### [at] netscapenet> wrote:
> > Just looking at the night sky, you can hardly say
> > if you are at the center of the galaxy or not.
>
>   If you were at the center of the galaxy you wouldn't be looking at the
> sky. I think you would be infinitely small.

I think he'd be dead, actually... :P

But if you're not exactly in the center of that supposed massive black-hole,
you'd likely be astounded by the huge number of very bright stars at the sky.
You'd definitely feel as being in the center of something...

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Tim Attwood <tim### [at] comcastnet> wrote:
> Einstein postulated a finite universe as part of his formulation of
> relativity. He said that, since space-time can curve, eventually if
> you travel in a straight line far enough you will come back to your
> starting point. This would mean that there is no well defined edge.

  I understand how GR describes the curvature of space-time in relation
to masses, and given the enormous amount of experimental evidence which
corroborates this, I see no reason to doubt it.

  However, I don't understand why GR would predict a curved universe
where each geodesic line is closed. What would cause it? Certainly not
the mass in the universe. I don't think it would be even nearly enough.
(Because if it was caused by mass, it would mean that the entire universe
is actually inside its own Schwarzschild radius, which is clearly not the
case.)

> Modern astronomers can find no evidence of such a large scale
> warping of space-time. This is part of why the theories of parallel
> universes are in vogue, if the universe is infinite, then if you
> travel in a straight line far enough you might reach a region
> that is very similar to earth, but isn't quite. It would be "parallel".

  I don't find any kind of logic in that. Why would there be a "similar",
"parallel" version of anything if you travel far enough? It doesn't make
any logical sense.

-- 
                                                          - Warp

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nemesis <nam### [at] gmailcom> wrote:
> >   If you were at the center of the galaxy you wouldn't be looking at the
> > sky. I think you would be infinitely small.

> I think he'd be dead, actually... :P

  Being infinitely small kind of implies being dead.

> But if you're not exactly in the center of that supposed massive black-hole,
> you'd likely be astounded by the huge number of very bright stars at the sky.
> You'd definitely feel as being in the center of something...

  Assuming that the staggering amounts of radiation and tidal forces don't
rip you into separate atoms.

-- 
                                                          - Warp

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nemesis wrote:
> 
> perhaps our own Universe is nothing but a side-effect of something bigger...

Some of the new theories point an explanation regarding this. According 
to the theories, only certain particles can pass between dimensions, or 
branes. Two of these particles are tachyons and gravitons (not sure if 
the latter have been identified yet though).

It would be interesting if alternate realities were someday discovered. 
Might explain some things.

Sam

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stbenge wrote:
> 
> It would be interesting if alternate realities were someday discovered. 
> Might explain some things.
> 

My dad the math teacher used to say cool things sometimes.  I remember 
one time he said to me, "What if what we think of as the solar system is 
really a carbon atom...it's clinging onto the exhaust manifold of a 
car...and, ten seconds from now, the driver is going to rev the engine 
really, really hard..."

That sort of thing will really jack around with your mind when you're, 
like, five years old...

Yeah, I probably ought to be in therapy.....

--Sherry Shaw


-- 
#macro T(E,N)sphere{x,.4rotate z*E*60translate y*N pigment{wrinkles scale
.3}finish{ambient 1}}#end#local I=0;#while(I<5)T(I,1)T(1-I,-1)#local I=I+
1;#end camera{location-5*z}plane{z,37 pigment{granite color_map{[.7rgb 0]
[1rgb 1]}}finish{ambient 2}}//                                   TenMoons

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Sherry Shaw wrote:
> stbenge wrote:
>>
>> It would be interesting if alternate realities were someday 
>> discovered. Might explain some things.
>>
> 
> My dad the math teacher used to say cool things sometimes.  I remember 
> one time he said to me, "What if what we think of as the solar system is 
> really a carbon atom...it's clinging onto the exhaust manifold of a 
> car...and, ten seconds from now, the driver is going to rev the engine 
> really, really hard..."

My dad once told me about a science fiction story he read once. It was 
about a man who discovered a way to shrink himself. The man kept 
shrinking, past the molecular, atomic and even subatomic level. He then 
noticed that his surroundings looked like galaxies, star systems and 
then matter as we see it now. He kept shrinking, and the pattern 
repeated itself...

> That sort of thing will really jack around with your mind when you're, 
> like, five years old...

I suppose. Or it could just give you a difference perspective on things.

> Yeah, I probably ought to be in therapy.....

Over that? Nah!

Sam

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stbenge wrote:
> Sherry Shaw wrote:
>> stbenge wrote:
>>>
>>> It would be interesting if alternate realities were someday 
>>> discovered. Might explain some things.
>>>
>>
>> My dad the math teacher used to say cool things sometimes.  I remember 
>> one time he said to me, "What if what we think of as the solar system 
>> is really a carbon atom...it's clinging onto the exhaust manifold of a 
>> car...and, ten seconds from now, the driver is going to rev the engine 
>> really, really hard..."

Maybe 10 seconds at the larger scale equals 10 billion years at ours...

> 
> My dad once told me about a science fiction story he read once. It was 
> about a man who discovered a way to shrink himself. The man kept 
> shrinking, past the molecular, atomic and even subatomic level. He then 
> noticed that his surroundings looked like galaxies, star systems and 
> then matter as we see it now. He kept shrinking, and the pattern 
> repeated itself...

"He Who Shrank" by Henry Hasse.  I read it about 30 years ago in a 
collection
of classic SF stories edited by Isaac Asimov.

Not to be confused with the book and film "The Man Who Fell To Earth".

> 
>> That sort of thing will really jack around with your mind when you're, 
>> like, five years old...

Had a similar effect on me to what you describe.

> 
> I suppose. Or it could just give you a difference perspective on things.
> 
>> Yeah, I probably ought to be in therapy.....
> 
> Over that? Nah!
> 
> Sam

Then there is the same concept expressed thus:

"Great fleas have little fleas upon their backs to bite 'em,
And little fleas have lesser fleas, and so ad infinitum.
And the great fleas themselves, in turn, have greater fleas to go on,
While these again have greater still, and greater still, and so on."

by the mathematician De Morgan.

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stbenge <stb### [at] hotmailcom> wrote:
> Some of the new theories point an explanation regarding this. According 
> to the theories, only certain particles can pass between dimensions, or 
> branes.

  Theories are usually devised to try to explain otherwise unexplained
observed phenomena, or in some cases, some consequence of an existing
theory if it is true (eg. the black hole theory is a consequence of GR).

  Exactly which phenomena are these theories trying to explain?

  A theory which doesn't even try to explain some observed phenomenon
is pure speculation and useless.

-- 
                                                          - Warp

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On Sun, 30 Dec 2007 18:16:07 +1100, Paul Fuller <pgf### [at] optusnetcomau>
wrote:

>
>"He Who Shrank" by Henry Hasse.  I read it about 30 years ago in a 
>collection
>of classic SF stories edited by Isaac Asimov.

I remember that. I also remember a story line in Garth from the 60's that was
the same.
Garth? 
http://en.wikipedia.org/wiki/Garth_(comic_strip)


Regards
	Stephen

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