How can there be an end to space?

JonF

Thank you. That is, of course, the word I was looking for. From the link you provided:

This is very subtle. It can be true or false. But you can’t possibly prove that it is false. Is a statement that you can’t possibly prove false necessarily true? I don’t think so. But it is a clever bit of convoluted reasoning. I don’t buy it - I just like twisted reasoning.

Anything that can be observed is by definition part of the universe.

Distance has no meaning until we define it. Distance is not described in terms of speed; it is defined in terms of the speed of light. There are other possible definitions, sure. But, once you define it, asking whether it “remains constant” doesn’t really make sense. The distance between A and B (by some definition) is, say, x meters at some time t[sub]0[/sub]. It cannot change unless you change the definition of distance.

Well, speak for yourself.

I believe that Godel’s proof applies if it’s a mathematical statement; in any mathematical system of sufficient complexity (which isn’t very complex) there are false statements which cannot be proven true within the framework fo teh system, and the converse. I suspect that also applies to the Universe in general.

I may be getting out of my depth here; but my very limited understanding if superstring theory leads me to believe that not only do some theories include a fundamental distance definition that is inherent to the universe (the Plank length), some theories also include two equally valid methods of measuring distance which give wildly different results. In these theories, one scale is greater than the Plank length and one is smaller; we obviously have no practical way today of measuring things using a ruler shorter than the Plank length. However, if the Universe were to stop expanding, and start to contract, when the size of the universe “crosses through” the Plank length the two distance scales interchange and perhaps residents of such a universe would see the universe as “rebounding” from the Plank length and starting to expand again.

The Standard Model seems almost intuitive when compared to superstring theory …

Oh my oh my oh my… I don’t think I was quite clear in my question. First off, I was never questioning the existence of Led Zeppelin related particles. Nosireebob! If you look at my sentence, I was using hoo-ha as a noun, not an adjective. That is, I was not saying ‘those damned virtual particles are a bunch of hooey!’ Grant me the opportunity of asking the question again -

It has been said that space is expanding, expanding at the speed of light. (Or so I understood mipsman. If it (space / nostuff) is expanding at the speed of light, then, for the most part, there can be nothing (i.e. stuff) inside it (it being the newly expanded bit of space.) I don’t believe there could be anything inside it because to keep up with the expansion, they would have to be moving at or close to the speed of light. The only thing that could be inside it are all of the bits and pieces of intertemporal flotsam and jetsam, cosmic hoo-ha, and misplaced wallets, keys and socks that wink in and out of existence.

warning! Impending abuse of the balloon analogy! So that first question really asked if there were two balloons. One representing the nice and familiar compilation of interstellar crap, the other representing the space it can exist in. So sure, the inner (stuff-like) balloon is expanding, but there is a second balloon about that which represents the pure creation of space-time, ever expanding outward. The area between the two balloons would be the newly created space. The only stuff that could exist in that space would be the mysterious particles that come and go like so much fast food.
The other question asked about the border of the stuff balloon and the empty space around that. That is, a few hours or so after the big bang there was a family sized cloud of gunk cooling its jets and coalescing into suns and planets. If there was a bit of heavenly mucus that was closer to the original point of the big bang, a bit that slowed down before others did, than there would have to be some godsnot out at what we would call the ‘edge.’ So why couldn’t life evolve on the bit of cloud that was moving away from the big bang faster than any other bit of dust? And if it did evolve, wouldn’t it be at the edge of the stuff of the universe? Stuff on one side, nothing but relatively recently created space on the other. I don’t get why that bit of edge does not exist.

Rhythmdvl:
Sorry about jumping on the hoo-ha bit. With the added part of the ‘no documentation’ and given this board’s penchant for requiring cites I assumed you meant it as an adjective. Re-reading now I get the joke (man…I need to lighten up).

As for your (our/everyone elses) balloon analogy you are missing a critical point. In your example you have two balloons, one inside the other, and asked what’s it like to live in between. You have to remember, in our analogy, you are a 2-D creature. You have absolutely NO way (and I do mean zero, zip, nada) of looking ‘up’. On a piece of paper your 2-D self could perhaps describe 3-D mathematically but you can never perceive a 3-D world yourself. Hence, you travel across the surface of the sphere forever but never find an edge or anything else. If you travel long and far enough you return to where you started (which is in some views what would happen if you left earth in a rocket ship and travelled in a straight line away from earth…eventually you’d come back without ever turning around). Even if a 3-D creature came along and picked you up you’d still only see the 2-D version of everything.

Now step this up a level. We are 3-D creatures but space is 4-D. Dimension 1 is a line. Dimension 2 is a plane (another line drawn at a right angle to dimension 1). Dimension 3 is a cube(?) (a third line drawn a right angle to dimension 1 & 2 lines). Dimension 4 is another line drawn at right angles to dimension lines 1, 2 & 3. If you can do that you’ll be rich (among other things you could walk into and out of anywhere…includijng bank vaults :)).

Anyway…to see your ‘between the balloons’ you’d need to look into the fourth dimension and that can’t be done…only speculated on.

I just don’t get string theory, but if I understand you, and I think I do, I see no reason why a theory can’t suggest two (or more) different natural definitions of distance. I’d bet they also have two different natural definitions of time that can’t be compared. All I was saying is that the natural way of defining distance under Relativity does not extend to distances outside the universe.

JonF also observed: “The Standard Model seems almost intuitive when compared to superstring theory …”
I gotta agree with that!

Jeff_42:
That was a good explanation. A lot of people seem to think that in the baloon analogy we are inside the balloon and it’s expanding out into something. We are contained in the surface. There is nothing inside or outside the balloon.

The first principle of “edge of universe” discussions is that there is no meaningful difference between “space with nothing occupying it” and “hypothetical, imaginary space with nothing occupying it”.

I’m imagining a universe which does NOT exist (except as a concept in my head) and it has nothing in it. You are trying to tell me about space that exists beyond the bounds occupied by the collection of detritus caused by (or defined as, depending on how you look at it) the “Big Bang” of roughly 15 billion years ago…OK, please explain, WITHOUT reference to the BigBang (edges or otherwise), how YOUR topic matter differs from mine?

I’m not sure I understand exactly what your asking but I’ll give it a shot…

The difference is that our “space with nothing occupying it” can still be defined using a coordinate system (not to mention that it’s not really empty but we’ve been through that recently in this thread…no need to revisit). You can point to a spot and say it has X, Y & Z coordinates and even apply a time coordinate (X, Y & Z at Time-Alpha). Although the vacuum may be nothing in most ways we think about it it does have a presence. For instance it can be warped (much like a tablecloth with a ball in the middle). Put more simply…you can go there.

“Hypothetical, imaginary space with nothing occupying it” is a place you can never (ever, ever, ever) go to. It has no definition in a coordinate system. You can say it is infinitely big or infinitely small or anything in-between and you’d be right on all counts. Also, there is no time there either…no cause and effect, no before and after. In short, nothing in the truest sense of the term.

[Robert DiNero voice] Are you talking to me? You talkin’ ta me? You talkin’ to me?[/Robert DiNero voice]

OK, I do an awful DiNero… If you are talking to me, I don’t see a difference. Distance can be defined in your universe, but this distance is not related to distance as we define it in the “real” universe.

Jeff_42
I just noticed your post. In a space with nothing in it, how could possibly “point to a spot and say it has X, Y & Z coordinates and even apply a time coordinate (X, Y & Z at Time-Alpha)”?

Space has a topology, but without defining distance, you can’t say very much about curvature.

I mean…

Meet me at Doolie’s Pub at 8 p.m… I’d imagine time is another defining characteristic. The pub will be there at many times but I want to describe it a bit more specifically so you don’t get drunk before I arrive.

Now that I think about time can only describe an event and not a location. For an event I can say place X, Y, Z at time Alpha. For just a place I suppose only X, Y and Z will do (no real place for time).

Then again…what if I want to describe a place 20 years in the future (i.e. where the earth will be then)? I’d need X, Y and Z and a time to pinpoint what I’m talking about.

Ahhhh (brain hurts)! I don’t know what I’m talking about. Midnight here…must sleep. Let me know where I’m missing the boat when you get a chance.