Re: endless universe?

From: Jaxtraw (jaxtraw_at_nospamnobigfoot.com)
Date: 06/22/04 

Date: Tue, 22 Jun 2004 03:02:38 +0100

"Joseph Lazio" <jlazio@adams.patriot.net> wrote in message
news:llu0x4v070.fsf@adams.patriot.net...
> >>>>> "J" == Jaxtraw <jaxtraw@nospamnobigfoot.com> writes:
>
> J> "David Staup" <dstaup@ev1.net> wrote in message
> J> news:40D60DE5.78C645C3@ev1.net...
> >> Midjis wrote:
> >>>
> >>> Joseph Lazio <jlazio@adams.patriot.net> wrote:
> >>>
> >>>> So let me rephrase my question. In what direction on the
> >>>> Earth's surface and how far do I have to walk before I reach
> >>>> the edge of the Earth's surface? In other words, I'm
> >>>> restricting you to the 2-dimensional Earth's surface.
> >>>
> >>> If I were to be restricted to a 2D surface then OBVIOUSLY it has
> >>> no boundary. [...]
> >>> The question Tim asked was what would the barrier be if the
> >>> universe was finite in size - we are not asking about its surface
> >>> area, if such it has, but its volume, in however-many dimensional
> >>> space it exists. [...]
> >>
> >> It's can only be described nonrigorusly by analogy. The surface of
> >> the earth is a 2D surface in 3D space. It's not cheating nor
> >> avoiding the question to limit you to the surface for the analogy
> >> to make sense.
>
> J> I'm not so sure. The 2D surface of the earth can only exist in
> J> reality because it has a 3rd dimension to be bent through. You
> J> can't create an edgeless 2D surface in 2-space.
>
> J> There's no evidence that the universe has 4 macroscopic spacial
> J> dimensions. We experience 3, and it seems that 3 are all that
> J> there are. So the analogy doesn't really hold very well.
> [...]
> J> So what I'm really saying is that such analogies are very crude and
> J> rather useless.
>
> I agree they are crude, but I wouldn't agree with useless. Many
> people believe that finite is the same as bounded. The point of the
> analogy is to try to get them to see that finite does not necessarily
> imply a boundary. If they grasp this point, then the analogy is useful.
>

I'm beginning to think tho that all these well-worn analogies do more harm
than good. The surface of *every* object is unbounded. Why does everybody
always use the Earth as an example? It's no more unbounded than the surface
of a refridgerator or a brick. A bounded surface would be rather weird,
really, in fact it's impossible in normal space. Take a complex object, like
a shoe, (chosen at random). An ant can start walking in a straight line in
any direction and never fall off. There you go- your shoes are finite, but
unbounded... :)

My point is, it doest really help explain how one can go in a straight line,
but never hit the edge, whether you use the earth or, er, a shoe. A person
travelling around the earth travels in a curved trajectory, and if not for
gravity they'd soon know it because they'd seperate from the earth. If you
say they are trapped within the surface, then heck, may as well use a brick,
a refridgerator, or a shoe, for all the difference it makes. I know I'm
waffling here, but fundamentally it doesn't really explain anything. If you
understand why the analogy works, you don't need the analogy to explain
it...

It's like those damned rubber sheets. They don't explain GR either. Anyone
who thinks they do ends up suddenly realising they don't, and then ends up
on Usenet "disproving" Einstein.

Bah.

I'll stop ranting now :)

Ian

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