# Where Does Space End? It Must End Somewhere!

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Space ends right behind you. Everything in front of you, which ever way you turn, is the rest of the Universe.

How does that sound?

(The same could be said for the time dimension, too.)

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Ever since I was a young boy' date=' I have wrestled with trying to understand space. In particular, I have never really understood how space is supposed to never end. I really don't see how that's possible. Everything ends somewhere. Where one thing ends the next begins.

Can people please provide thoughts on this?[/quote']

Because you're confusing space as a geometrical construct with content. Content, say length, area or volume, has a boundary. You can say that "space" ends meaningfully simply by clarifying that you mean content. The observable universe is all content within causal communication of itself; the boundary lies where anything outside it is not in causal contact with everything inside.

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Fascinating, even with all the speculation. Today is the first time I came accross this thread and didn't realise it was so old and only just revived.

Nevertheless, I checked out the WMAP data and it is quite compelling however, I do have some questions for the experts.

Severian (or anyone else who is an expert on this), in one of your earlier posts on this subject you put a view accross that space is infinite but most importantly that it was created during the BB (with which I agree) and 'spread out' INSTANT(ANEOUS)LY. AFAIK, there is a consensus that gravitational waves (spacetime curvature) propagates at c, yes? If so, would this not imply that space itself would propagate from the BB at c if it was in fact created during this 'event' ? I am aware that this line of thought may be wrong but we must attribute spacetime to other components of the universe (namely energy) since it does have an intimate link - relativity.

Also, one perhaps disturbing thing that I have noticed on the WMAP site (I found NASA's one) is although there is percentages of what the universe is made of (ie. matter, dark matter, dark energy) there is no mention of 'normal' energy that is NOT locked as ordinary matter! Surely the 'visible' universe is TEEMING with photons/neutrinos/bosons that would account, IMO, for some considerable portion of the universe curvature, or not?

One other matter that may perhaps be beyond the scope of this thread. Although an experimental figure was obtained from WMAP that suggests space is flat rather than open or closed the figure is still positive. Could this not also imply that (keeping in mind that we do not completely and unequivocally understand space) space is just minutely curved overall (ie. not entirely flat) and that the universe still may be closed but ALMOST infinitely large. I know I am definitely wrong with this one and if so, could anyone point me in the right direction to explain why the brightest spots would have to be at least 1.5 degrees accross to make the universe closed AND why we couldn't possibly have gotten our timeline wrong and we're seeing the 'degrees accross' at an earlier stage post BB where the degrees accross were less?

All this WMAP stuff seems to be built like a house of cards, one assumption after another, one dependant on another, that, if one little minute detail is just slightly off, makes the whole house collapse in a heap (or the physicists/astrophysicists are just standing up there supporting the cards so it doesn't fall into a heap).

Why are we so certain about this whole space subject when we cannot even be certain that we have the understanding of space right.

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There is literally nothing at the end of the universe.

If you think you're close to the end of the universe and turn around and can see light you're still nowhere near it. Space ends beyond the reach of all energy. But it's by no means a permanent end, in fact it's barely temporary and easily turns from nothing to space by the invasion of just the smallest little bit of energy.

As an example, you know you've reached nothingness when the temperature is absolute zero. However, just be measuring the temperature you create space that will "never" nothingness again because in order for it to no longer be space it must achieve absolute zero by traveling through an infinite number of negative magnitudes.

If the popular thought is wrong and the speed of light is not the physical limitation for speed in the universe, the real limitation of the speed at which energy must travel in order to violate nothingness before nothingness becomes space would be it, which would result in something like hitting an infinitely strong brick wall (even though this energy would create new space after the "accident").

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Severian (or anyone else who is an expert on this)' date=' in one of your earlier posts on this subject you put a view accross that space is infinite but most importantly that it was created during the BB (with which I agree) and 'spread out' INSTANT(ANEOUS)LY.

[/quote']

That certainly wasn't what I meant. The universe is infinite but it didn't need to spread out to be infinite - it was already infinite when it was created (well, this is supposition, since one can never prove that something is infinite, but you know what I mean). In practice, it did spread out pretty quickly through a mechanism called inflation but since it was infinite before inflation started, it didn't get bigger as such - it was simply that distance scales got bigger.

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I universe could be sphere shaped, when the big bang happened all of the universe was scattered hot. As it expands it cools. Think of a baloon with spirals for galaxys on it, the more you blow the bigger it gets and the longer way the other galaxy is from the other one. When the universe has compelety cooled it might collapse in on itself to make a big crush that could be the start of another universe.

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I just write the whole thing off as incomprehensible. Our minds just aren't advanced enough to truly contemplate the infinite without putting it into finite terms. Take this as an example: Imagine an infinite number of apples. I guarantee, that if we were able to freeze your thought and put it up on a computer screen, we could count the number of apples there. No matter how hard you try, you just can't imagine infinity apples. You would always invasion 5 billion, or 3 trillion, or some other appreciable number. I'm not saying that a biological organism couldn't have a brain capable of conceiving the infinite, ours just don't happen to be wired that way.

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No matter how hard you try, you just can't imagine infinity apples.

I imagine an infinite amount of apples as two things 1) having as many apples as you'd ever need 2) drowining in apples. But that all depends on how you mean infinite. Infinity is not a number, it's a symbol.

Of course we can conceive the infinite, we invented it.

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No, it's not a number, its a concept, which is exactly my point. Numbers are finite and graspable, even if they exist only in the human mind. And certainly the human mind can invent something it can never really grasp. The afterlife for example. Whether it exists or not, it was our little ape brain that was first able to concieve of its existence. But concieving of something's existence does not mean one fully grasps it. I can beleive that the universe is infinite without ever really being able to concieve what infinite is. Like the topic starter stated, everything in our experience has a beginning and an end. That is how our minds are wired. Finitely.

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Our minds just aren't advanced enough to truly contemplate the infinite without putting it into finite terms.

$\lim_{x{\to}0^+}\frac{1}{x}=\infty$

wow, that was hard. infinity basically means expanding without bound

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But do you ever fully grasp it?

I don't suppose my theories (perhaps ramblings would be more appropriate) on the limitations of the human mind are really relevant here, though. I was merely voicing an observation that came to me. You may continue with your regularly scheduled discussion.

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It does end , it just expands. Its a matter of fact that the planets are moving away from each other and so does the space!

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I think he meant visualizing infinity, our thinking about its existence in 'real life' as opposed to an equation on paper or drawn on a graph.

Ilja:

planets aren't moving away from each other. however the space inbetween distant objects in the universe appear to be expanding away from each other.

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Space has an end, it just loops over and over and there is no way of getting to the other side. nothing is on the other side anyways, think of it kinda like RAM in a computer, it is anything, its random, it could be absolutley anything you think of.. but really, who cares? no ones ever going to be able to see whats really there, or if there is really and end and if there is why does it matter? what does it prove?

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I've searched through the thread and apparently no one has mentioned "hyperbolic" which is a possibility for the shape of our universe. This seems to be the most intuitive to me. The universe is an expanding fundamental circle, and as we get closer to the horizon, our metric shrinks to the point that no matter how close we get to the horizon, we can never reach it because our metric keeps shrinking. This is a nontechnical explanation about how hyperbolic metric works, though this picture might help visualize it. http://mathworld.wolfram.com/PoincareHyperbolicDisk.html

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Since there's been so little substantive contribution in this thread, I'm posting below a few relevant links addressing the original question. Hopefully that way people finding this thread will at least have something of value:

Shape of universe:

http://map.gsfc.nasa.gov/m_uni/uni_101shape.html

Cornell astronomer:

If the universe is infinite does that mean there is an infinite number of "me"s?

http://curious.astro.cornell.edu/question.php?number=476

What was there before the Big Bang and what is there outside of our universe?

http://curious.astro.cornell.edu/question.php?number=166

What is the universe expanding into?

http://curious.astro.cornell.edu/question.php?number=274

Why isn't the sky bright at night if the universe has so many stars?

http://curious.astro.cornell.edu/question.php?number=375

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Since I'm the villiage idiot of the Science forums, I don't fear asking this question:

If spacetime is curved, isn't it reasonable to think that the question "where does space end" would be as irrelevant as "where does it begin?" Aren't we the equivelent of a microbe living on the inner walls of a beachball?

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Hi,

The shape of the Universe, its size, length etc. all are just some perceived features. There can be no exact proof for this theory. But still two points are exactly clear, 1. Space is curved 2. It is constantly in acceleration at about the speed of light. Hence all the other theories have been just conjectures made with respect to these 2 points and a few Mathematical theories. We have to somehow accept that space is infinite yet finite.

gagsrcool

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Since there's been so little substantive contribution in this thread,

Ouch, this post right after mine! (#188) And it even has a link in it! Psh.

Happy new year!

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It does end , it just expands. Its a matter of fact that the planets are moving away from each other and so does the space!

My question is what would it expand into then? It has to be taking space from something & therefore making something else smaller, right? I just think the whole question is irrelevant because of the time it would take to find the end if it exsisted. If it's infinite it wouldn't change our view of the space around us & if it's expanding we couldn't catch up with it unless it cooled down & came hurdling back at us & then it wouldn't matter because we'd be hurdling to obliveration ourselves. I view space/time like how longitude & latitude are set up on earth but we keep building on top of it instead of coming back to the same point. That's just my opinion though & opinions are the best answer I think we have right now. It's all in how you percieve it.

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gagsrcool : 2. It is constantly in acceleration at about the speed of light.

Wouldn't it have to be faster than the speed of light or atleast the same speed?

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It will quite obviously be apparent i have little idea about the comparison of fractals to space. but i think i read somwhere that fractals had infinite area but finite perimeter? can someone expand on that, or correct me, or give me some more info?

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My question is what would it expand into then?

"Ask a Cornell University Astronomer: What is the universe expanding into?"

http://curious.astro.cornell.edu/question.php?number=274

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"Ask a Cornell University Astronomer: What is the universe expanding into?"

http://curious.astro.cornell.edu/question.php?number=274

Thank You Joema! That answered some of my questions. Although I disagree with the part about there being no "center" of space. Wouldn't every point be considered a center since every distance around it would be infinite?

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Question: Can we find the place where the Big Bang happened?

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