I remember back in the days, old USS Enterprise would sometimes manage to cross the edge of the universe and go into "outside", where the screen only displays orange geometrical lines and everybody panics. Much fun to be poked at this.

What is the current theory of the edge of the universe though? There is nothing outside the universe, but is the edge possible to reach at all (since the universe is expanding at light speed, I guess the answer to that is no.)?
Would it be solid or would it be like in old flight simulators where you come out on the other side if you go for too long on one side? Would you see the mirrored universe approaching?

Nobody ever writes about those things any more in scifi, I wonder why it has become so silent about it. Everybody saw how silly it was in Star Trek?

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Si tacuisses, philosophus mansisses.

"Half of what I say is meaningless, but I say it so that the other half may reach you."

That's actually a really good question. From what I understand (and I am not a cosmologist) a closed universe would imply that you would in fact reappear on the other side. This is actually a rather appealing concept to me personally. Not because I miss the Atari 2600 necessarily, but it gives one hope that we could explore the whole shebang ... one day. Unfortunately there's that pesky Dark Energy expanding the Universe at ever greater speeds. Also all tests that we are able to make seem to imply a flat universe which may extend out to infinity. Bummer.

Theory:
space=3D version of the surface of a 4Dsphere therefore no edge

Hypersphere(n-sphere)
http://en.wikipedia.org/wiki/N-sphere

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The other day we drove across the border from the Netherlands to Germany, and our TomTom nav device did something very much like what you described. There was no panic, although the kids were a little mystified

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"Ignorance more frequently begets confidence than does knowledge" -- Charles Darwin
"Your right to hold an opinion is not being contested. Your expectation that it be taken seriously is." -- Jason Thompson
Meet the OOONG TOE.

I would think that many of us have thought about this question deeply...

My answer offered here is know more correct than any one Else's explanation.

' There can not be an outside or beyond when talking of the universe'

The very use of that word 'universe' has dictated that its all of everything. That is the meaning of that word.
My understanding of the expansion mentioned also makes getting there never possible., and just in case that has not helped its not there.

We do not know what if or even if there is a edge. Its one of those questions that humanity will never know. So my answer is what will you find at the edge...Nothing. Not even time. For at the edge of the universe where the expansion is so close to C that time its self has no forward motion...

Maybe outside of the edge, if there is one, reality just doesn't exist. Hard to imagine what would happen if you got to the edge though, I mean hitting an invisible wall seems a bit daft.

Maybe you would actually go through the edge, but since there is no other side, no reality, then the part of you that would be coming out of the other side if there was one, would just dissapear, it would just sease to exist.

That comes across as the most realistic thing I can think of.

It matters what you are talking about with the word universe...various theories have made the term confused...

Universe technically means everything so everything you can think of fits into the universe, but what most people talk about when they say universe is more akin to our current perceivable time-space and in this this sense it only takes into account what we perceive and ignores that which we can't such as membranes peabrains and alternate timelines all of which should be included in the word universe, but from our understanding is outside of the universe

Most people i know of have started using the common comic book term which is the "Multiverse" but i'm not sure how this term has caught on in the scientific community.

So what's at the edge of the univese and has anyone covered it lately...
There is nothing really to prove whats there but several things have been...
#1. The star trek one where you are in a non-space where thought becomes reality.
#2. The most recent media one shown in Futurama where you can see across to another universe where they said that is the only other one, but in another episode they jump through boxes and find multiple universes.
#3. If you go to the edge of the universe due to the spherical nature of the universe you would be on the otherside heading back to your originating point.
#4. According to that whole membrane thing we are at the edge of the universe constantly and what happens when we get there is nothing...

these four only take into consideration the perceivable universe and not the all universe which nonoe has ever asked to my knowledge and that was is the one that is 100% unknown, unimaginable, and impossible to measure

What edge?

Whichever "edge" is considered, one should keep in mind that space is intimately linked to time.

All kinds of spatial manifolds and topologies have been analyzed. Observational limitations make it difficult to pick the right one.

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Everyone is entitled to his own opinion, but not his own facts.

Nobody knows if there is an “edge” or not. Nobody knows if “our” universe is infinite or not.

For years, people have been searching for some evidence of an “infinite” universe or maybe a round spherical one that has a spherical outside “edge” to it, but even Hubble hasn’t been able to see far enough out to see anything more than more distant galaxies, with no hint of an outer “edge”.

In the old days, when old-timers used their first crude telescopes to try to see if the universe had an outside “edge” to it, they didn’t even realize we were located in an individual galaxy that did indeed have an “edge” to it, or at least outer limits to it.

The desire to see beyond what we can actually see is apparently an old one. Here’s a guy trying to look “beyond the edge”:
http://i29.tinypic.com/24q93bs.jpg

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Everyone is entitled to his own opinion, but not his own facts.

There is a principle in philosophy called Occam's Razor that asserts that the simplest answer to a question is likely to be the correct one. I see in this and other threads a tendency to argue for unnecessarily elaborate explanations for observed phenomena. Thus, when asked "What is the shape of the Universe?", people frequently offer remarkably complex geometries, overlooking simple ones. Thus, Dr. Gay has, apparently urged us in all seriousness to believe that the Universe has the shape of a doughnut with its central hole an integral feature of its shape. I have offered in rebuttal to that suggestion a thread entitled "The shape of the Universe" that offers a much simpler picture that may at first sight seem complex but is in reality the simplest model that can answer questions of geometry associated with the Big Bang theory. It is a logical extension of the very simple model in which the universe is imagined to be two-dimensional rather than three-dimensional and to be the surface of an expanding spherical balloon. I see our actual Universe as the three-dimensional surface of an expanding four-dimensional hypersphere. In this model, the Universe that we know is finite but unbounded and has the same shape from wherever you view it. This model provides readily understandable answers to many questions regarding the shape of the Universe all the way back to the Big Bang. Among other things, it has no edge.

The USS Enterprise is an aircraft carrier that never leave the water. Star Trek is fiction. Nothing can move faster than light.

The universe has no edge. In fact, the latest evidence is that it is infinite. Which is to say that any attempt to fly to the end of the universe will fail as it is expanding faster than the speed of light and no spaceship will ever be able to go faster.

This is reality...or at less the best guess at what we know is real at this time.

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I came for the astronomy but I do love the physics!

The problem with this idea is that our universe is observationally three-dimensional, and expanding as time passes. There is no evidence of a 4th spatial dimension. We can’t just invent a 4th dimension of space, or a 5th or a 6th for no reason. To do so makes matters more complicated than they really are in nature, and that violates Occam’s Razor.

I have heard there is evidence for the 4th spatial dimension in the cosmic microwave background radiation. Sorry, but I cannot even pretend to understand it.

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I came for the astronomy but I do love the physics!

Please provide a link to what you’ve “heard”.

I’ve “heard” of “ghosts”, “flying saucers”, “Bigfoot”, etc.

I would think that a 4th dimensions is no stranger, or less explainable, than an infinite 3 dimensional space.

So Occam's razor doesn't come into it, I wouldn't have thought.

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I thought that CMB was evidence for a closed system(hypersphere), as the radiation, from the big bang, would just keep going around and around, rather than just dispersing into endless space.

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Then why would the distant galaxies not go “around and around”. Every new Hubble deep field photo of the most distant galaxies shows them going outward in a radial motion. We don’t see any evidence of galaxies going “around and around”.

well, galaxies are much slower than em radiation, anyway, I'm not sure I was correct about the "around and around", perhaps it just indicates that there is no co-ordinate center for the Universe(meaning, where the big bang occured), suggesting a 3D surface of a hypersphere, in the same way that there is no co-ordinate center for the surface of a 3D sphere.

And if there were no co-ordinate center, then you are just as likely to find em radiation, from the BB, on Earth, or 8Billion light years away, which, on Earth at least, is what I think they think they have found.

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Two FAQs are "where is the center of the universe?" and "what happens at the edge of the universe?" At present there seems to be only one FAQ essay, but perhaps this will help:

http://www.math.ucr.edu/home/baez/ph...GR/centre.html

<screech>No, no, nooooo!</screech>

I'd like to know where you heard that, because I have an issue with whoever told you that. (Assuming you didn't simply misunderstand what they said.)

The CMB is evidence for the standard Hot Big Bang theory. Various FRW models can be used as idealized models for studying the consequences of this theory and making zillions of predictions which can be compared with observation (and with great success).

Don't confuse the Hot Big Bang theory with the Inflationary Scenario, or with current speculation about Dark Matter or Dark Energy; these are all later additions, and are not as well established at the Hot Big Bang theory itself. Speculations about possible "additional compact dimensions" (arising most recently in the arena of superstring theory and M-theory) also go beyond gtr and the HBBT.

And don't be misled by the name (due to an early critic): the standard "Hot Big Bang theory" does not say "the universe began with a curvature singularity", it says (in essence), "the universe was once much denser and hotter than it is today". (Much more precise than that, but never mind). It is true that the FRW models, which are perhaps the simplest cosmological models compatible with the Hot Big Bang theory, do exhibit strong spacelike curvature singularities which are often referred to as representing "the Big Bang", but strictly speaking, this goes beyong the HBBT.

I don't really want to talk about this because the lies told by "creationists" who want to "critique" a theory they don't even comprehend on even the most basic level are so...

Can I put it like this without offending anyone? Leave it to the cosmologists; they understand the complexities of the theories and even more important, of the relevant evidence. You don't (unless you are a cosmologist, and have studied a lot of textbooks, read hundreds of papers, made many computations, and so on.)

Please stop and think about what you might mean by saying this.

I hope you didn't misunderstand what I said about Clifford circles in the other thread you started in Q&A. That really has nothing to do with how dust particles (idealized galaxies) move in FRW models, not even the ones which happen to have S^3 hyperslices orthogonal to the world lines of the dust particles.

(Because a timelike congruence with nonzero vorticity cannot admit a family of orthogonal hyperslices, you shouldn't expect any simple notion of "space at a time" for a family of observers who are twisting about their neighbors in a manner similar to points moving along neighboring Clifford circles.)

S^3 and other spheres are surfaces of constant curvature; all points are equivalent.

The CMB is not radiation from a hypothetical curvature singularity, despite the name "Big Bang theory". It is radiation from the epoch in the history of the universe, which was once so dense and hot that EM radiation could not propagate freely (photon's couldn't move very far without running into another photon), when for the first time the universe cooled and attenuated to the densities which allowe light to propagate freely for long distances. Before this epoch, the notion of "optical image" was impossible, for example.

That is not correct. There is no "spherical outside edge" in any of the spatial hyperslices in any FRW model, not even the ones with S^3 hyperslices orthogonal to the world lines of the dust particles.

In a post today to another thread in Q&A, I mentioned work by Cornish and Weeks (and others) which attempts to search for data which could uncover possible nontrivial topology of spatial hyperslices, but which might fail to find such evidence even if nontrivial topology exists, because (roughly speaking) the absolute past corresponding to the event "here and now" is too small.

I am still rather new at BAUT, so I don't know how serious any of you might be with regard to learning about cosmology, but assuming some of you are serious:

With some trepidation, because such knowledgeable posters as Pervect and Spacetiger appear to have left, I recommend asking questions in the Cosmology forum at http://www.physicsforums.com/
Posters like robphy and marcus probably won't mislead you, but be careful about some other frequent posters there who frequently make claims which could easily appear plausible to nonexperts but which are mathematically wrong, or in some cases simply incompatible with current scientific evidence.

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Chris Hillman

Read these PF posts. Avoid Wikipedia--- except for these versions. Read this and this suggested sticky. When asked for advice, I always say: never take advice!

Our Universe is NOT observationally three-dimensional. One of the objectives of WMAP is to detect the curvature that would determine that the Universe is at least four-dimensional. Thus far, WMAP has not been able to do so because any curvature that may exist is too small to be detected in the data collected to date from irregularities in the cosmic microwave background radiation (CMBR). There remains the possibility that curvature may be detected as additional data are collected. Any conclusion that there is no curvature would be premature.

I’m not worried about the “center of the universe” superstition, either way. A superstition of one kind or another is no justifiable reason to either add or subtract spatial dimensions that deviate from actual observation.

Ok, let me know if they ever find any evidence of a 4th-D, so I can add a "w" to the x, y, and z Cartesian coordinate system.

Vandamonde is probably referring to possible evidence for hypothetical compact dimensions, in which (roughly speaking) instead of hyperslices like E^3 we contemplate hyperslices like E^3xK where K is some compact manifold such as circle (but in M-theory, much more complex and interesting than a circle).

I am pretty sure Frog march means S^3 not S^4 when he talks about "4Dsphere". If so, his terminology is nonstandard.

I am pretty sure dcl means that in gtr, spacetime models are four-dimensional Lorentzian manifolds, but it is possible he is reffering to the same thing as Vanamonde.

I think Sam5 is thinking here of a spatial hyperslice with a compact fourth dimension, something like E^3 x S^1.

And to forestall further possible confusion: yet another thing people might have in mind when they mention "higher dimensions" is the idea of embedding Lorentzian manifolds in higher dimensional spaces (typically flat spaces). For example, one can locally embed the Schwarzschild vacuum in E^(2,4), a flat six dimensional space. That is a completely different concept from the aforementioned "compact dimensions". (Although some M-theory inspired stuff involves embedding in higher dimensional de Sitter spaces.)

And having said that, I should stress that, as Gauss first noticed, c. 1830, it is not neccessary to embed Riemannian or Lorentzian manifolds in simpler higher dimensional spaces in order to define and study their intrinsic geometry. Here, intrinsic geometry refers to geometric properties which are "internal" and independent of any embedding. It is also possible to study extrinsic geometry, which involves how submanifolds bend and twist in the parent manifold. (Thanks to publius for suggesting that I mention this!)

Everyone, please try harder to make sure you don't write ambiguously. As you can see, you can easily generate a ridiculous amount of confusion if you write carelessly!

(Assuming that none of you were trying to cause confusion; if that is acceptable behavior at BAUT I am definitely out of place here.)

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Chris Hillman

Read these PF posts. Avoid Wikipedia--- except for these versions. Read this and this suggested sticky. When asked for advice, I always say: never take advice!

I've been outside the universe. I saw a couple of racks of tools, a few crates of spare parts, a repair manual, a console with flashing warning lights, an empty wine bottle, and a technician with a long white beard passed out on the floor.

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Life is like a box of chocolates. All of your choices are bad for you.

I was afraid someone would find something like that.

As far as I know, there is currently no evidence for a fourth spatial dimension. The basis for suspecting that there is a such a dimension is a question that I have been asked on a number of occasions: If the Universe expanded from a single point, in what direction in the night sky musty I look to be looking toward that point? The only answer that makes sense to me is that there is no single point in our Universe of which we can say, "The entire contents of the Universe originated at that point and has been spreading out ever since into the entire otherwise empty infinity of empty space and that space is utterly empty beyond a certain distance from that point. That answer does not make sense to me. For one thing, it implies that some objects are stationary at that point while most are speeding away from it at speeds proportional to their present distances from it. It makes much more sense to me that everything is moving away from that point in all directions at roughly the same speed. All of this suggests that that point that is not in the universe that we perceive at all. What comes to mind for me are marks on the surface of an expanding balloon. The expanding hypersphere is the four-dimensional analog of that.

Well I’m glad somebody know what we are talking about!

Hi, dcl,

I have seen a recent claim of evidence for compact dimensions as per M-theory in the arXiv which has been widely publicized in the popular forums. When I have a moment I'll try to find it for you.

I should add that this claim is very new and I haven't had a chance yet to look into it or to form any judgement about the likelihood that it will pan out. As I am sure BAUTians are aware, these says universities tend to employ overzealous PR reps who are not scientists and who tend to portray every humdrum paper (sometimes even quite silly papers) by their faculty as a "revolutionary breakthrough".

Here I think dcl is also using nonstandard terminology by referring to S^3 as a "four-dimensional hypersphere".

I am getting a bit exhausted by correcting common misconceptions which are covered in the sci.physics FAQ and/or Ned Wright's Cosmology FAQ, and in this case it seems possible that dcl was just writing carelessly, but just to make sure:

The FRW models do not envision that dust particles (model galaxies) are expanding from some distinguished location; rather, they are all moving apart from one another in such a way that there is no distinguished location. With an overlay you can illustrate that this makes sense even for suitable motion in the euclidean plane. Indeed, the hyperslices orthogonal to the dust particles in one subfamily of the FRW dust solutions are copies of E^3.

This is not to deny that there are other exact dust solutions which can be interpreted as alternative cosmological models in which there is a distinguished location (e.g. Szekeres dust, LTB dust, which are inhomogeneous models)) or a distinguished direction (e.g. Kantowski-Sachs dusts or E^2-symmetric Kasner dust, which are anisotropic models). There are also exact solution in which the world lines of the dust particles are twisting about one another (e.g. Goedel lambdadust). Some of these can even be interpreted as "nonlinear perturbations" of FRW models, in which the perturbations introduce some inhomogeneities, or anisotropies, or vorticity, or some combination.

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Chris Hillman

Read these PF posts. Avoid Wikipedia--- except for these versions. Read this and this suggested sticky. When asked for advice, I always say: never take advice!

To me, that has never been a big problem, because I’ve read a lot of history about science and I know that mankind, at different times in the past, has been in the very same situation we are in now, back when we didn’t know where we were located inside our solar system or inside our own galaxy, and further back in time when nobody knew where they were on the earth’s surface or whether the earth was “flat” or not. So, my standard answer to the question about where are we located in the universe is, “We don’t yet know, and we don’t even know if it has a center or not. If it’s infinite in size, it wouldn’t have a center”.

I think the reason people tend to be so demanding regarding an answer to the universe question is because: 1) we know the earth is spherical and we know where each of us is on it, and we know why Australians don’t fall off of it, 2) we know where the earth is located inside our solar system, 3) we know where our solar system is located inside our galaxy (we didn’t learn that until early in the 20th Century), and so, some people impatiently want to know where we are located in the whole universe, although we can’t yet see the whole universe and we might not ever be able to see all of it or be able to determine where we are within it.