The Direction of Space: Is Light Traveling Around the Periphery?

[Les Sleeth]

Here is something I wonder about:

If the big bang has created spherical expansion, with all resulting galaxies residing on the suface of the sphere, does celestial observation ever involve looking "across" the vast (assumed) empty middle to the other side of the sphere? Does anyone think light might travel around the periphery rather than straight through it? Is there a chance all observed galaxies are only those on the surface all around us, and much further away, on the other side of the expanding sphere, are galaxies we can never see?

 

[maximus]

i see what you're getting at, but i think your error is it the assumtion that "all galaxies reside on the surface of the sphere". you should think of it in terms that all current galaxies reside on the surface, but there are older galaxies further to the center. and remember, that there is no "center of expansion" so there really is no center of the spherical expansion. one could just as easily say we're the center of expansion as they could another point in space.

 

[Les Sleeth]

My understanding is that part of the inflation model explains the universe's matter as expanding away from the big bang point, and existing in a huge spherical shape something like the surface of a balloon.

I could see this "surface" being quite thick, but with inflation there should also be an empty core. I suppose I was asking if light could travel across that core, or if it is too vast and expansion too rapid for that light to ever reach us.

 

[marcus]

Originally posted by LW Sleeth
My understanding is that part of the inflation model explains the universe's matter as expanding away from the big bang point, and existing in a huge spherical shape something like the surface of a balloon.

I could see this "surface" being quite thick, but with inflation there should also be an empty core. I suppose I was asking if light could travel across that core, or if it is too vast and expansion too rapid for that light to ever reach us.

It is quite remarkable how many different visions of space there are!

The "expanding balloon" model of a space with positive curvature was thrown out by cosmologists some time ago

but they apparently did not bother to tell the rest of us!

so people still picture the galaxies as dots painted on the surface of a balloon which is gradually expanding so the dots are getting farther apart----a lovely picture but unfortunately confusing because very wrong.

a better picture, my cosmology professor told me years ago, is of a rising loaf of raisin-bread dough
the galaxies are raisins
and as the 3D loaf of space expands the raisins get farther apart.

as cosmologists talk, for space to be "spatially flat" means that it is ordinary Euclidean 3D space----only expanding in time.

It doesn't mean that it is flat like a 2D thing like a flat piece of paper but it has an analogous 3D flatness in that the sum of the angles in any triangle is 180 degrees

maybe in small scale around stars and black holes etc it is curved by local concentrations of mass-energy but in large scale space has an overall flatness-----or so they tell us the best and most recent observations show.

so ordinary 3D space, like raisinbread dough extending to infinity in all directions, seems by far the best model

and there is no HOLLOW that it curves around and encloses!
that way lies madness. Perish the thought!
Alan Guth, who graciously invented the "Inflation Scenario"
for our edification, never said anything about expanding balloon shape or hollow. This is not part of any currently credible big bang or inflation picture at least that I have heard of.

 

[Les Sleeth]

Originally posted by marcus
This is not part of any currently credible big bang or inflation picture at least that I have heard of.

See, I knew this was a dumb question.

Thanks Marcus/Maximus

 

[meteor]

It doesn't mean that it is flat like a 2D thing like a flat piece of paper but it has an analogous 3D flatness in that the sum of the angles in any triangle is 180 degrees

If the universe is flat, it doesn't mean that it has a center?

 

[Mentat]

Originally posted by meteor
If the universe is flat, it doesn't mean that it has a center?

Not if it's infinite.

 

[Phobos]

LW Sleeth - As already well explained (so why am I repeating it?!?), the Big Bang was not an expanding sphere from a central point with galaxies on the outer edge (that image is the result of an inadequate balloon analogy...the raison bread analogy is slightly better but still incorrectly implies an outer expanding edge). The Big Bang happened everywhere in the universe, not from a central point. The points of space across the universe just used to be a lot closer together than they are now.

meteor - Like Mentat said, a "flat" universe is believed to be infinite (or at least boundless)...no center & no edge in 3D space.

 

[meteor]

Not if it's infinite.

You can't say that. The universe started in a singularity, and has been growing since that, and only can reach an infinite size in an infinite period of time, that is not the case

 

[Mentat]

Originally posted by meteor
You can't say that. The universe started in a singularity, and has been growing since that, and only can reach an infinite size in an infinite period of time, that is not the case

If the entire Universe, all of spacetime, began as a singularity, then you are right, it cannot be infinite now (IMO). However, it didn't necessarily all start out as a singularity, as it could be just "local expansion" (in that there could be many Universes, that "bubbled up" at the beginning of time, and our's just happens to be expanding).

 

[russ_watters]

Originally posted by marcus
It is quite remarkable how many different visions of space there are!

The "expanding balloon" model of a space with positive curvature was thrown out by cosmologists some time ago

but they apparently did not bother to tell the rest of us!

so people still picture the galaxies as dots painted on the surface of a balloon which is gradually expanding so the dots are getting farther apart----a lovely picture but unfortunately confusing because very wrong.

a better picture, my cosmology professor told me years ago, is of a rising loaf of raisin-bread dough
the galaxies are raisins
and as the 3D loaf of space expands the raisins get farther apart.

and there is no HOLLOW that it curves around and encloses!
that way lies madness. Perish the thought!
Alan Guth, who graciously invented the "Inflation Scenario"
for our edification, never said anything about expanding balloon shape or hollow. This is not part of any currently credible big bang or inflation picture at least that I have heard of.

Marcus, the balloon analogy is just that - an ANALOGY. Part of the analogy is that you must translate the 2D balloon surface into 3D space. It requires some mental gymnastics. It was never, AFAIK, meant to say that everything in the universe resides on a thin shell of a sphere - that would not account for Hubble's observations.

The loaf of rasin bread analogy is also flawed because it includes an edge for the galaxy, something that is not observed.

The expanding balloon analogy is often simply misstated and that's why the confusion exists. IMO, the balloon anaogy is the better analogy - it is borderless, finite, and uniformly expanding.

Not if it's infinite.

AFAIK, the universe is not theorized to be infinite.

 

[meteor]

The Big Bang happened everywhere in the universe, not from a central point. The points of space across the universe just used to be a lot closer together than they are now.

I have read that the aparition of the universe is interpreted as a fluctuation of the vacuum, more or less like the appearance of virtual particles in quantum mechanics. Can a fluctuation have an infinite size?

 

[Mentat]

Originally posted by meteor
I have read that the aparition of the universe is interpreted as a fluctuation of the vacuum, more or less like the appearance of virtual particles in quantum mechanics. Can a fluctuation have an infinite size?

First off, that is just one hypothesis on the origin of the Universe.

And, secondly, the fluctuation wouldn't really have size, as their would not yet be any space.

 

[meteor]

The expanding balloon analogy is often simply misstated and that's why the confusion exists. IMO, the balloon anaogy is the better analogy - it is borderless, finite, and uniformly expanding.

Definitely, the balloon analogy is a very bad analogy. It would be a good analogy if the curvature of the universe was different from zero, but it has been showed that the curvature of the universe is zero, and the cake analogy is billions times better. The dream of Einstein of look at a telescope and watch his own back neck is not plausible

First off, that is just one hypothesis on the origin of the Universe.

And, secondly, the fluctuation wouldn't really have size, as their would not yet be any space.

Yes, but this hypothesis first introduced by Tryon is the standard hypothesis. You only have to Google and you will see that the majority of the webs says clearly that the Universe started in a very little fluctuation, and after undergo inflation in a fraction of second, reached the size of a tennis ball

 

[Eh]

Inflation seems to be the standard hypothesis, but is different than the an ex-nihilo varient floating around these days. While inflation doesn't explain the origins of the pre-existing expanding space-time, some like Alexander Vilenkin have proposed that the entire universe was created out of literally nothing at all, as a quantum fluctuation. Inflation occurs after this fluctuation has already brought the universe into existence.

I'm not sure how popular this idea is among physicists.

 

[maximus]

Originally posted by Mentat
If the entire Universe, all of spacetime, began as a singularity, then you are right, it cannot be infinite now (IMO).

how can it ever be infinite? it will always be expanding at the max of a very finite speed (the speed of light). maybe you mean it will exist forever.(if it doesn't recollapse) but at no point in time (now or ever) will somebody observe the size of the universe to be infinite.

 

[Mentat]

Originally posted by maximus
how can it ever be infinite? it will always be expanding at the max of a very finite speed (the speed of light).

First off, it is (according to modern measurement) expanding faster than the speed of light.

Secondly, if all of space is infinite, but our local Universe is expanding, then the whole "Universe" (everything) is infinite, but we would still observe expansion.

maybe you mean it will exist forever.(if it doesn't recollapse) but at no point in time (now or ever) will somebody observe the size of the universe to be infinite.

Well, no one can ever actually conclude that it is infinite (since it could just be really big), but it (spacetime) could still be infinite.

 

[maximus]

Originally posted by Mentat
Secondly, if all of space is infinite, but our local Universe is expanding, then the whole "Universe" (everything) is infinite, but we would still observe expansion.

my understanding is that as the universe expands, space expands with it. so what's beyond it? nothingness: no time/matter, ect...

 

[Draco]

Originally posted by maximus
my understanding is that as the universe expands, space expands with it. so what's beyond it? nothingness: no time/matter, ect...

Thats true.
Scientists already know that the Universe expands. They can see galaxy's spreading far apart, they move out into space. So i guess this means that the Universe does expand.

I doubt whether the Universe if infinite...When i think of it, i get all weird inside for some reason.

I don't think that the Universe if a sphere, if it is, then what is on the other side? Nothing? Some sort of wall? Hmmm!
Or is the Universe just a black hole going in reverse. Well that's what Stephen Hawking said, a massive black hole that's in reverse...you know, time starts to go...and eventually it dies. Well i don't know if it will result in the supposedly 'big crunch'

 

[Les Sleeth]

Originally posted by maximus
my understanding is that as the universe expands, space expands with it. so what's beyond it? nothingness: no time/matter, ect...

I agree with you that time and space are defined by the beginning and, if it happens, the end of the universe. So they are not infinite and can never be.

The question of "nothing" I think is a really important one which has no satisfactory answers. To say nothing does anything whatsoever, even something as apparently insignificant as a quantum fluctuation, means it wasn't "nothing" after all.

In the philosophy area I argued that since everything which exists must be preceded by the potenial to exist, we can look at what exists now and say something about the potentiality it sprang from.

Even being conservative about it, we can say potentiality can produce a universe, life and consciousness. So is that really "nothing"?

 

[maximus]

humanity lacks both the mental and verbal ability to describe absolute nothingness.

 

[Eh]

Originally posted by maximus
my understanding is that as the universe expands, space expands with it. so what's beyond it? nothingness: no time/matter, ect...

There is no beyond. And it's really that simple. Either the universe is finite or infinite. If it's finite, there can be no beyond at all, since that location would neccessarily be defined by space.

 

[Eh]

Originally posted by LW Sleeth
I agree with you that time and space are defined by the beginning and, if it happens, the end of the universe. So they are not infinite and can never be.

Not quite. Spaces are defined by their points, not their edges. The same applies to time when treated as an extra coordinate. Space may well be infinite in spatial extent, and is not incompatible with the big bang theory. There are also some models for a cyclic universe that would allow time to be without beginning.

The question of "nothing" I think is a really important one which has no satisfactory answers. To say nothing does anything whatsoever, even something as apparently insignificant as a quantum fluctuation, means it wasn't "nothing" after all.

The void of pre big bang theories is something - it's a state where spacetime does not exist, but the laws of physics do.

 

[meteor]

The void of pre big bang theories is something - it's a state where spacetime does not exist, but the laws of physics do.

Are you suggesting that the Big Bang is a quantum fluctuation of infinite size?

 

[Mentat]

Originally posted by maximus
my understanding is that as the universe expands, space expands with it. so what's beyond it?

I had the same problem before, the truth is that you are right: if the Universe is finite, it will always be finite. However, if it (spacetime) started out infinite, then it will always be infinite and is not expanding altogether - there are just small parts of it that are expanding ("local expansion"). IOW, if space is infinite, but our local "Universe" is expanding (into that empty space), then our local Universe will never become infinite, but the whole Universe (all of spacetime) is infinite.

nothingness: no time/matter, ect...

"Nothingness" doesn't really mean anything. See the following two threads
Why "Nothingness" Is Not A Word and An Exercise in "Nothing" Semantics.

 

[Mentat]

Originally posted by Eh
The void of pre big bang theories is something - it's a state where spacetime does not exist, but the laws of physics do.

I'll have to disagree with you here. If time doesn't exist, then this state doesn't exist for any amount of time, and thus it doesn't exist. Also, if space doesn't exist, then it (this "void") is no where, and occupies absolutely zero space (obviously), and thus it (the "void") again doesn't exist.

IOW, a "void" has to have some spatial extent, otherwise it wouldn't be "anywhere"; and it has to have temporal extent, otherwise it would "never" exist.

 

[Les Sleeth]

Originally posted by Eh
Not quite. Spaces are defined by their points, not their edges. The same applies to time when treated as an extra coordinate. Space may well be infinite in spatial extent, and is not incompatible with the big bang theory. There are also some models for a cyclic universe that would allow time to be without beginning.

Mostly I just meant that as far as what we actually know, space and time are finite. Obviously infinity scenerios can be imagined.

Originally posted by Eh
The void of pre big bang theories is something - it's a state where spacetime does not exist, but the laws of physics do.

I suspect you mean spacetime for our universe didn't exist pre-big bang, but may for other universes (since that would rule out your suggestion of possible infinity)

Of course, to the hypothesis that the "laws of physics do" exist pre-big bang, I would add, "at least."

 

[meteor]

Mentat, are you an addict of the theory of the "Ekpyrotic Universe"?

 

[Eh]

Originally posted by meteor
Are you suggesting that the Big Bang is a quantum fluctuation of infinite size?

Nope. A universe brought into existence by a quantum fluctuation must be finite, since no fluctuation could ever must up an infinite amount of energy.

 

[Eh]

Originally posted by Mentat
I'll have to disagree with you here. If time doesn't exist, then this state doesn't exist for any amount of time, and thus it doesn't exist. Also, if space doesn't exist, then it (this "void") is no where, and occupies absolutely zero space (obviously), and thus it (the "void") again doesn't exist.

It's not a matter of opinion, but fact. What physicists have labeled as a void in some pre big bang theories, is a state where no classic notions of space or time exist. I'm not arguing that the idea is valid or even coherent, only that it is the definition being used.

 

[Eh]

Originally posted by LW Sleeth
I suspect you mean spacetime for our universe didn't exist pre-big bang, but may for other universes (since that would rule out your suggestion of possible infinity)

No, I mean all of spacetime did not exist. At least, that is the theory.

 

[Les Sleeth]

Originally posted by Eh
No, I mean all of spacetime did not exist. At least, that is the theory.

Well, if it is the theory, then you can see how time and space cannot possibly be eternal/infinite (though I guess one could say time and space might continue on eternally).

 

[Mentat]

Originally posted by Eh
It's not a matter of opinion, but fact. What physicists have labeled as a void in some pre big bang theories, is a state where no classic notions of space or time exist. I'm not arguing that the idea is valid or even coherent, only that it is the definition being used.

Then a true "void" cannot exist.

 

[Eh]

Originally posted by LW Sleeth
Well, if it is the theory, then you can see how time and space cannot possibly be eternal/infinite (though I guess one could say time and space might continue on eternally).

Remember, it's only one theory. In other models, spacetime is fundamental and exists forever.

 

[heusdens]

Originally posted by Draco
Thats true.
Scientists already know that the Universe expands. They can see galaxy's spreading far apart, they move out into space. So i guess this means that the Universe does expand.

I doubt whether the Universe if infinite...When i think of it, i get all weird inside for some reason.

I don't think that the Universe if a sphere, if it is, then what is on the other side? Nothing? Some sort of wall? Hmmm!
Or is the Universe just a black hole going in reverse. Well that's what Stephen Hawking said, a massive black hole that's in reverse...you know, time starts to go...and eventually it dies. Well i don't know if it will result in the supposedly 'big crunch'

You can only talk in a sensical way about space and time in the context of moving matter (anything "material", i.e. particles, energy, fields, etc.)

Space and time just denote the "mode of existence" of matter.

Matter is to be seen as infinite. The infinity of matter means that, while every material form has a finite extend in space and time, it is always preceded and followed by another material form. Nowhere we see "creation" of matter as such, we can only see the transformation of one material form into another, and this transformations go on endlesly, without begin or end.

 

[Les Sleeth]

Originally posted by heusdens
Matter is to be seen as infinite.

You assume too much. As far as what we actually know, matter and the universe is finite and temporal. To assume any more is pure speculation.

Originally posted by heusdens
The infinity of matter means that, while every material form has a finite extend in space and time, it is always preceded and followed by another material form. Nowhere we see "creation" of matter as such, we can only see the transformation of one material form into another, and this transformations go on endlesly, without begin or end.

Right now the universe appears firmly in the grip of entropy, and if that continues one day it will just fizzle out. It seems if you were right, entropic change would not be dominating, but rather we'd see a balance of entropic and anti-entropic change.

Also, how does your idea get around the same problem people have with a god that is infinite and has always existed? They always ask, "but where did god come from?"

 

[Mentat]

Originally posted by Eh
No, I mean all of spacetime did not exist. At least, that is the theory.

But how is it that they can refer to it, using the term "didn't exist". That's a concept of time.

 

[marcus]

Mentat somewhere recently I read a discussion where
someone was discussing with an astronomer and they
compared a black hole to the beginning of the universe.

You might like how the astronomer replied---he drew a
clear logical distinction that bears thinking about. He said no
the two are very different because

a black hole is a singularity that is localized in space but not in time


whereas the beginning is a singularity that is localized in time
but not in space

you know the big bang occurred everwhere, not at some point.

often people think of it wrongly as an explosion outwards from some point

but the universe is infinite as far as we know (altho can only see a finite part) and so the big bang or whatever is imagined as a beginning must be thought of as extending infinitely in all directions also

but nevertheless (in contrast to a black hole singularity) localized to a particular instant.

Now I personally do not declare this. Make of it what you will. I am just reporting how this guy (maybe it was in one of those Cosmology FAQ things on the internet) made this neat logical distinction between Everything and a Black Hole. Explain it I cannot!

 

[meteor]

So Marcus, you dont't think that Big Bang is a quantum fluctuation?
If you say,Big Bang started in all space at the same time being infinite in size at the same begining, you have to provide a mechanism that permit this to happens. I think that even Big Bang has to have a physical explanation

 

[Draco]

Originally posted by heusdens

Matter is to be seen as infinite. The infinity of matter means that, while every material form has a finite extend in space and time, it is always preceded and followed by another material form. Nowhere we see "creation" of matter as such, we can only see the transformation of one material form into another, and this transformations go on endlesly, without begin or end.

I hope s

 

[marcus]

Originally posted by meteor
So Marcus, you dont't think that Big Bang is a quantum fluctuation?
If you say,Big Bang started in all space at the same time being infinite in size at the same begining, you have to provide a mechanism that permit this to happens. I think that even Big Bang has to have a physical explanation

As I said in my post, I wasn't declaring my personal opinion, or offering to explain. Just reporting what somebody else said. I thought you might find it interesting. I checked in ned wright's cosmology FAQ and it was there, in answer to "Is the BB like a BH?" I don't remember where I first came across this pithy utterance, could have been somewhere else, but anyway one place you find it is at Ned Wright's.

I do think that people are getting closer to a reasonable theory of quantum geometry and gravity-------and one thing such a theory ought to do is model the universe back then. The only model we have now----GR----doesnt work. What was it Wittgenstein said? "Of that whereof one cannot speak, thereof one must remain silent."
A good model would allow us to speak about things that, lacking a model, we can't yet talk about coherently.

Abhay Ashtekar has some good analogies about this and talks about-----well the title of his 2001 paper "Quantum Geometry and Gravity: Recent Advances" says what it is about.

the first thing he discusses in the first paragraph of the introduction is this very problem-----how to model the BB, making it not a singularity any more.

His paper is a non-mathematical overview, with references it is 24 pages long, but (curiously enough) it is not a popularization. Even fellow math/physics folk need to have things explained intuitively and figuratively, without equations, now and then and this is one of those rare cases of a non-popularizing non-mathematical survey of a research area.

arXiv:gr-qc/0112038

if you decide to download it and have any trouble getting the PDF to print please let me know. I didnt have any trouble. He is a famous guy because he invented the "new variables" of general relativity which have transformed the subject and he is clearly interested in the same singularity that you are, so maybe there is something to get from it.

 

[Mentat]

Originally posted by meteor
So Marcus, you dont't think that Big Bang is a quantum fluctuation?
If you say,Big Bang started in all space at the same time being infinite in size at the same begining, you have to provide a mechanism that permit this to happens. I think that even Big Bang has to have a physical explanation

But there are many possible explanations (with a quantum fluctuation of empty space being one of them). One of my favorites is the string theory approach, that all of space is not expanding or contracting, but both, at the same time (this is explained through the inverse nature of the use of wound and vibrational strings).

 

[Mentat]

Originally posted by marcus
As I said in my post, I wasn't declaring my personal opinion, or offering to explain. Just reporting what somebody else said. I thought you might find it interesting. I checked in ned wright's cosmology FAQ and it was there, in answer to "Is the BB like a BH?" I don't remember where I first came across this pithy utterance, could have been somewhere else, but anyway one place you find it is at Ned Wright's.

I do think that people are getting closer to a reasonable theory of quantum geometry and gravity-------and one thing such a theory ought to do is model the universe back then. The only model we have now----GR----doesnt work. What was it Wittgenstein said? "Of that whereof one cannot speak, thereof one must remain silent."
A good model would allow us to speak about things that, lacking a model, we can't yet talk about coherently.

Abhay Ashtekar has some good analogies about this and talks about-----well the title of his 2001 paper "Quantum Geometry and Gravity: Recent Advances" says what it is about.

the first thing he discusses in the first paragraph of the introduction is this very problem-----how to model the BB, making it not a singularity any more.

His paper is a non-mathematical overview, with references it is 24 pages long, but (curiously enough) it is not a popularization. Even fellow math/physics folk need to have things explained intuitively and figuratively, without equations, now and then and this is one of those rare cases of a non-popularizing non-mathematical survey of a research area.

arXiv:gr-qc/0112038

if you decide to download it and have any trouble getting the PDF to print please let me know. I didnt have any trouble. He is a famous guy because he invented the "new variables" of general relativity which have transformed the subject and he is clearly interested in the same singularity that you are, so maybe there is something to get from it.

Actually, marcus, I will have to slightly disagree with you about GR. It can be used to explain the origin of the Universe, but it has to be "taken up a few notches". The real problem (according to Hyperspacial theorists, like Michio Kaku) is that Einstein didn't use enough dimensions. He restricted himself to the 3 spatial dimensions and 1 temporal dimension - which is fine to explain gravity (provided one figures out how to unify it's approach with QM (which I think string theory does rather well)), but it isn't enough to explain the other "forces".

So, basically, the General Relativity approach can be used to explain the origin of the Universe, and all of the "forces", but you need to add more dimensions (which makes the math almost impossible for me to comprehend ).

 

[meteor]

But there are many possible explanations (with a quantum fluctuation of empty space being one of them).

Like Eh said before, a quantum fluctuation can't have an infinite size

One of my favorites is the string theory approach, that all of space is not expanding or contracting, but both, at the same time

How can space be expanding and contracting at the same time? That's not possible. Anyways, redshifts of galaxies indicate that space is expanding.
And remember that string theory can't deal with the problem of the cosmological constant

 

[Eh]

Originally posted by Mentat
But there are many possible explanations (with a quantum fluctuation of empty space being one of them). One of my favorites is the string theory approach, that all of space is not expanding or contracting, but both, at the same time (this is explained through the inverse nature of the use of wound and vibrational strings).

I don't think string theory predicts that. If it were the case, the net expansion/contraction of the universe would be zero. The light from distant galaxies would not be redshifted.

From what I've read, it seems that string theory merely puts a minimum size on the universe. Any attempts to define the universe shrinking smaller than the Planck scale, would be equivalent to defining a universe expanding from that scale. So instead of collapsing down to a singularity, the universe bounces at the Planck scale. But I'm not entirely certain on this.

 

[Mentat]

Originally posted by meteor
How can space be expanding and contracting at the same time? That's not possible. Anyways, redshifts of galaxies indicate that space is expanding.

Yes, space most definitely is expanding. But it is also contracting. Like I said, it's because of our use of vibrational strings in measurement.

A basic explanation would first require that I define "vibrational" and "wound" strings. A "vibrational" string is a string that moves along our 3-d space. A "wound" string is a string that is "wrapped around" our 3-d space. Let me use the "Flatland" illustration to try and better explain this:

Imagine a universe of "flat" people. A 2 dimensional universe, kind of like a bunch of drawings on a piece of paper. They have the directions of North, South, East, and West, but they have absolutely no concept of "up" or "down". These things make no sense to them. Now, imagine that their space was actually "curled up" (as if someone had curled the piece of paper they are on into a hollow tube). Now, they still can't concieve of the "up" direction, but it must exist (otherwise, their dimensions couldn't "curl up"). Finally, imagine that they are all made up of 1-dimensional strings, and that they strings move along their space (their Flatland). These would be the "vibrational strings". But there are also "wound" strings, which are "wrapped around" the "hollow tube" that their reality really is.

It is the same with us (according to string theory). We live our lives in 3 dimensions of space, and can't concieve of any higher space dimensions. As far as common sense goes, our space cannot be "curled up" in another direction. But what if it were so? Then there could be strings that were "wound" and strings that were "vibrational", right?

Now, if we measure using vibrational strings, the Universe is expanding (and all of the stars, planets, people, etc are made up of vibrational strings). However, the measurement using wound strings is always inversely proportional to the measurement using vibrational strings, and thus - depending on which you use to measure it - space is both expanding and contracting.

I don't know if I made that clear enough (and I probably didn't), but I hope you got the gist. I suggest Brian Greene's "The Elegant Universe", as it explains it better, and uses illustrations to help you conceptualize it.

And remember that string theory can't deal with the problem of the cosmological constant

You mean the coupling constant, don't you? This was a big problem for string theory, but the operative word is "was", as M-Theory deals with it rather nicely (it's just much to complicated, mathematically, for anyone to actually solve it's equations, and thus it can't be proven yet).

 

[Mentat]

Originally posted by Eh
I don't think string theory predicts that. If it were the case, the net expansion/contraction of the universe would be zero. The light from distant galaxies would not be redshifted.

Please read my previous post, in response to "meteor" (I'd hate to have to re-post all of that).

From what I've read, it seems that string theory merely puts a minimum size on the universe. Any attempts to define the universe shrinking smaller than the Planck scale, would be equivalent to defining a universe expanding from that scale. So instead of collapsing down to a singularity, the universe bounces at the Planck scale. But I'm not entirely certain on this.

This is pretty much correct (you often astound me with the depth and breadth of you knowledge ), however there is a reason why things appear to "bounce back" at the Plank scale. And that reason is that, at those scales, one measure using "wound" strings, instead of "vibrational" ones.

 

[Eh]

Mentat, are you sure about that? Can you cite something? The closet thing it sounds like is the notion that our 3 dimensions expand while the others contract. Our 3D universe, is still expanding only.