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| Author |
Message |
| 17 new of 85 responses total. |
rcurl
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response 69 of 85:
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Jul 12 16:47 UTC 1998 |
Quite right, but that doesn't stop me from doing it conceptually.
If the big bang is spread out around the edge of the universe, it must
be very dilute, and now just a sort of hiss, not a bang.
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dang
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response 70 of 85:
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Jul 16 17:16 UTC 1998 |
resp:67 You're right, there would be a fairly limited number of
geometries that ended up with that effect. However, if you can
conceptually jump anywhere, I can conceptualize the universe as a
hypersphere. :P
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srw
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response 71 of 85:
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Jul 21 05:41 UTC 1998 |
In resp:69 you said "hiss not a bang." Well, due to the compression of
time, the universe there is only a few seconds old, so if you squeeze all that
hissing into a few seconds, it's probably more like a bang.
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rcurl
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response 72 of 85:
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Jul 21 19:05 UTC 1998 |
It is only a few seconds old, but it is spread over the outer "surface" of
the universe, which dilutes it greatly.
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lilmo
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response 73 of 85:
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Aug 24 23:43 UTC 1998 |
If you lived on the surface of a sphere, and started walking in what seemed
to you to be a straight line, you would eventually end up at the point
"opposite" of where you started. (Think of where you started as the North
Pole: Any direction you walk is south, along a meridian, and you eventually
end up at the South Pole.) If you keep going in the same direction, you end
up back where you started. Is there any particular reason that some
directions would work, and others would not?
In the real universe, there are stars, so, for practical reasons, not every
direction is suitable. But conceptually, there is no reason any direction
ought to be better than any other.
"Unbounded" just means "without an edge". The Universe can be of limited
volume while still being unbounded for the same reason that the surface of
a sphere can be (and is) unbounded (where is the "edge" of a sphere?) and yet
of limited (and, indeed, calcuable) area.
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rcurl
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response 74 of 85:
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Aug 25 05:53 UTC 1998 |
It is the consequences of those general questions I've been asking about.
A reiteration of the theory doesn't help. I would like an explanation of
how earth could be still "straight ahead" if we went in a straight line to
the "edge" of the universe and beyond (by edge, I mean the point to which
the universe has expanded since the Big Bang. Of course, I am approaching
this conceptually so that I can reach any point instantaneously as
measured by earth time.
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lilmo
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response 75 of 85:
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Aug 31 23:03 UTC 1998 |
Because the universe is curved in the fourth space dimension, just as the
surface of a sphere is curved in the third, a path which seems to be straight
to us, is actually curved.
Personally, the only way I keep track of the discussion is by bouncing back
and forth between the 2-D sphere surface, and the "real world", hoping the
extensions to the analogy still fit. Does this help?
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dang
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response 76 of 85:
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Sep 27 18:51 UTC 1998 |
Rane, according to this theory, the universe does not have an "edge" to
which it has expanded since the big bang. It is expanding in 3
dimensions, certainly, but the edge is in the fourth (or higher)
dimension. In the sphere equivilant, the surface of the sphere has no
"edge", because the expansion is coming in the third dimension, namely
the radius of the sphere. Certainly, the surface area of the sphere is
increasing, but it has no "edge" to which it has increased.
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rcurl
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response 77 of 85:
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Sep 28 05:50 UTC 1998 |
Did it have an "edge" at a couple of nanoseconds into the Big Bang? They
speak of its "size" at that time. By the way....what was outside the
universe at that time? :) [I understand the sphere analogy, but I
don't understand the universe....]
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lilmo
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response 78 of 85:
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Sep 29 01:15 UTC 1998 |
The Universe has a "size", just as the surface of a sphere does, and it can
even be measured, by looking at the curvature of space (or the surface),
soemthing that can be done indirectly by measuring the angles of large
triangles.
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dang
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response 79 of 85:
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Oct 5 05:11 UTC 1998 |
Presumably, no it didn't have an edge a couple of nanoseconds after the
Big Bang, it was just a really small hypersphere. (Incidentally, at that
point it likely was a hypersphere, rather than the bizarre shape it now.
:) I don't understand the universe either, but I sort of understand the
basics of one of the current theories about it.
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rcurl
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response 80 of 85:
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Oct 5 16:34 UTC 1998 |
It does sort of dawn on me that at a couple of nanoseconds we are not
talking about the space and time we "know" today. I'll live with that.
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dang
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response 81 of 85:
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Oct 5 19:03 UTC 1998 |
As to what is outside the universe, think of it this way. There isn't
anything, in the two dimensional sense, outside the surface of the
sphere. Likewise, there isn't anything in the 3 dimensional sense
outside our universe. There *is* outside, but only in higher
dimensions.
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rcurl
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response 82 of 85:
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Oct 5 22:18 UTC 1998 |
Now what's this about the universe being *10* dimensional?
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lilmo
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response 83 of 85:
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Oct 14 00:43 UTC 1998 |
Actually, it is theorized that the Universe originally had 26 dimensions, of
which I think four were time axes, but they quickly collapsed into the three
space and one time dimensions with which we are familiar. The 10-dimension
stage was of longer duration than any other stopping points, I believe.
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srw
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response 84 of 85:
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Dec 23 04:04 UTC 1998 |
I don't know about the 26 dimensions. I think you are referring to
string theory (and superstring theory). Here is some interesting text I
found on this subject (source:
http://www.lassp.cornell.edu/GraduateAdmissions/greene/greene.html
where the author was talking about incompatibilities between general
relativity and quantum echanics at the scale of elementary
particles....)
-----begin quote-----
String theory solves the deep problem of the incompatibility of these
two fundamental theories by modifying the properties of
general relativity when it is applied to scales on the order of the
Planck length. String theory is based on the premise that the
elementary constituents of matter are not described correctly when we
model them as point-like objects. Rather, according to
this theory, the elementary ``particles'' are actually tiny closed loops
of string with radii approximately given by the Planck
length. Modern accelerators can only probe down to distance scales
around 10^(-16)cm ( 10^(-17) in) and hence these loops of
string appear to be point objects. However, the string theoretic
hypothesis that they are actually tiny loops, changes drastically
the way in which these objects interact on the shortest of distance
scales. This modification is what allows gravity and
quantum mechanics to form a harmonious union.
There is a price to be paid for this solution, however. It turns out
that the equations of string theory are self consistent only if
the universe contains, in addition to time, nine spatial dimensions. As
this is in gross conflict with the perception of three
spatial dimensions, it might seem that string theory must be discarded.
This is not true.
-----end------
The author goes on to explain how this conflict can be resolved by
assuming that 6 of the spatial dimensions are curled up at scales too
small to be measured by experiment. I think physicists prefer the term
"curled up" rather than "collapsed," although this may not be an
important distinction.
I found this site clearer than most on the subject, although still this
is a very difficult subject.
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lilmo
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response 85 of 85:
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Apr 17 00:00 UTC 1999 |
Yes, "curled up" is what I meant, but I used a term that came more easily to
mind, for those less familiar with that kind of physics. (like me! *grin*)
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