How can there be an end to space?

What I really mean is, what is space? Is space nothing? What comprises space where there are no stars or planets, etc.? Is it a complete vacuum? If space is nothing, how can there be an end to nothingness? What would prevent someone from flying forever? What I mean is, If I were to fly in a spaceship that could travel waaaaaaaayyyyy faster than the speed of light and could live forever, what would I get to when I reached the end of the universe? A brick wall? Thank you very much.

Not if the universe is a closed system. You would eventually end up where you started, just as if you went around the globe.

Zev Steinhardt

Right! My question exactly. Where did the ‘nothing’ come from? If I’m on the furthest body from the center of the universe (Lets say it is the leading object of the expanding universe)what am I expanding into, how big is it, and where did it come from?

No one knows and, probably, no one ever will.

It appears that there is most likely no “end of the universe” or “furthest body from the center of the universe”.

Warning: balloon analogy approaching

The standard analogy, flawed in many ways but useful in some ways, is to pretend that our universe is like the two dimensional surface of a balloon that is being inflated. The real universe is sort of the three-dimensional version. If you are restricted to measuring and moving along the two dimensional surface of the balloon, you can’t find any boundaries or walls or center of the expansion.

End balloon analogy. Thank you for your patience.

As far as what space is, science hasn’t come up with a complete explanation yet. We have at least two major models of space (relativistic space-time and the quantum-mechanical Standard Model). Each one says different things about what space is, and each fits reality exceptionally well, but they don’t agree when you try to apply them to situations where both (general) relativistic and quantum effects are important.

I don’t think I can give an adequate explanation of what each of these theories says space is, so I’ll leave that to others…

Don’t think of the expansion of the universe like an exploding cartoon bomb expanding outward into space. Space itself is expanding. As far as you, and every other sentient being anywhere in the universe is concerned, the edge of the universe, space and matter, is where the speed of recession is equal to the speed of light.

IF, by some physical miracle, you could be instantly transported to that spot that is receding from you at the speed of light (your perceived edge of the universe from your original location) and looked back at your starting point, it would be receding from you at the speed of light and would be your edge of the universe. However, if you swung around 180 degrees, you would see another point, equally far away, als receding at the speed of light, the other edge of your universe (as perceived from your new location). Repeat ad infinitum.

Apart from the fact that no matter how far, fast and long you travel you can never reach the ‘edge’ of the Universe (since there isn’t one as other posters have pointed out) here’s another way to look at it.

In some ways common sense would say ‘space’ (our space) is expanding into space (i.e. what’s on the other side of the wall?). Turns out not to be the case. Our ‘space’, or vacuum, is anything but empty. Virtual particles are popping into and out of existence constantly in a vacuum. These last less than Planck Time (smallest measuable amount of time…10^-43 seconds) but their existence have been proven (search for stuff on Casimir Effect).

Space outside our universe is true nothingness to the point you can’t even talk about it. When asked what was there before the Big Bang happened Stephen Hawking made some comment to the effect of, “That’s like asking what’s North of the North Pole.” It’s meaningless…no time, no size…in short–NOTHING.

Sure you can talk about what’s outside the Universe… You just can’t talk about it scientifically. If we were able to talk about it scientifically, then it’d be part of the Universe, too, by definition. On the other hand, philosophically, you can say anything you want about what (if anything) is outside, and nobody can say you’re wrong.

Damn, that is just about the best explanation i’ve heard anyone give on the subject. Thanks mipsman!

my $.02:

don’t think of it as the things in the universe expanding away from each other, but the universe itself expanding. that includes you, the chair you’re sitting in, and everything you’ve ever seen. they are all getting “bigger” (more spread out) as i write this.

First off…How many angels can dance on a naked singularity? :wink:

Seriously though…I know there are some theories that allow for many (infinite) Universes out there. Sometimes this stuff is used to explain why our Universe developed life when it would be almost infinitely more likely for our Universe to have initial conditions that would have precluded life (at least our kind of life). Many Universes says basically there are an infinite number of Universes so at least some of them would have conditions suitable for life.

My question isn’t to debate many Universes theory but to ask, philosohpically speaking, how far away these Universes are from each other? I know they can never interact but is it as meaningful to say they are infinitely far apart and less than Planck length close at the same time? Are they piled one atop the other? Also, wouldn’t this imply an edge to universes even if that edge is in the 4th (or higher) dimension so us poor 3-D creatures could never find it?

Not exactly. If everything in the Universe became twice as big - you, me, the chair, wavelengths of light, metersticks, everything, would you notice the change at all? No.

While space is expands, most masses (from molecules to galaxy superclusters held together by gravity) are just coming along for the ride, while keeping the same size.

Thank you for all of the great explanations. However, I have found the answer.

On the outside of the expanding universe is a rather large room.
In the room sits a man named Mel. Mel wears a torn t-shirt, drinks beer 24/7 (Mel time) and wears a hat that says “Who Farted?”

I have no idea what this means, but Mel claims to be God, and says that all of the religions on Earth are in for a rude awakening when they come to visit.

All quotes are from Jeff_42

I’m not sure these could be called theories. One thing that a theory must do is make testable predictions. I don’t see how you could make a testable prediction about somethat cannot (by definition) have any observable effect.

There is a principle (I can’t remember the name of it.) that says "The reason the universe looks the way is does, is that if it were very different we wouldn’t be here to look. In it’s weakest form, it’s undeniable. In it’s strongest form, It really streaches. And I think the only thing they predict is that things are as they are. Not really testable

Distance is a matter of definition. Currently, we define distance by how far light travels in a certain amount of time. Since nothing, including light, can enter or leave the universe, you cannot even talk about distance outside the universe. Our previous definition was direct or indirect comparison with a standard meter held in Paris. Again, distance is not defined outside the universe, for the same reason. For that matter, we cannot talk about time outside the universe. I think it would be impossible to define time or distance outside the universe without making some very arbitrary assumptions.

The Anthropic Principle. Various forms are discussed here and in many other places.

Of course, Terry Pratchett said it best in Hogfather:

"Many people are aware of the Weak and Strong Anthropic Principles. The Weak One says, basically, that it was jolly amazing of the universe to be constructed in such a way that humans could evolve to a point where they make a living in, for example, universities, while the Strong One says that, on the contrary, the whole point of the universe was that humans should not only work in universities but also write for huge sums books with words like “Cosmic” and “Chaos” in the titles.

The UU Professor of Anthropics had developed the Special and Inevitable Anthropic Principle, which was that the entire reason for the existence of the universe was the eventual evolution of the UU Professor of Anthropics. But this was only a formal statement of the theory which absolutely everyone, with only some minor details of a “Fill in name here” nature, secretly believes to be true."

The Anthropic Principle makes me gag.

What is says is this: We’re here because we’re here. If we weren’t here than we wouldn’t be here. But we are here. If we weren’t, then we we wouldn’t even be here. But we are.

By the way, it’s inaccurate to think of space as “nothing.” Space is not merely a container. It has attributes. It can bend, distort, warp and stretch.

It’s both the stage and one of the players.

In its weakest (local) form, the Anthropic Principle is perfectly sound. Example: The Sun has a rather higher proportion of heavy elements than most stars of its type (it’s about 1.5 to 2 sigma above the normal, for you statistics types). Ordinarily, this should be mildly surprising: We generally assume that our location is typical of the Universe. The local anthropic principle, however, explains that since life is more likely to evolve in an overabundant system (probably), it’s therefore no surprise that our system, which has life, is overabundant. This can be applied to any property which can vary in the Universe. Once you start getting up to the really strong forms, though, like that mentioned by Jeff_42, you’re on pretty shaky ground.

::struggling to grasp the ungraspable::

So, is it safe to say that there are two categories of the universe - stuff and nostuff? That is, there are rocks, pencils, dust, light, and the Simpsons. This is stuff, whether you call it energy or matter, it is stuff. Then there is space. This is nostuff, the expanding bit that contains the stuff. Or something like that. So from what I gather from some of the explanations, is that if you were standing on a bunch of stuff at the boundary of nostuff, the nostuff boundary would seem to recede away from you at the speed of light.

So there are two questions that I have. One, is the area of expanded nostuff surrounding a bunch of stuff truly empty? That is, is it free of all forms of light-energy and matter? (Except for that bit of hoo-ha that keeps popping in and out of existence without proper documentation.)

If the universe began with a big kaboom, there is likely to be bits and pieces of dust and whatnot at the edge of stuff. If the dust out there collected, condensed, baked for twenty minutes on high and stabilized to the point of sustaining life, what would that planet’s creatures see when they looked in the night sky? Would the see stars in all directions? Or would roughly half of the night sky look empty (filled with nostuff) and the other half look like you and I?

I have to leave now to go put my stuff away. Thanks for listening,


DrMatrix sez

I read ealier this year in the NY Times (and yes, I know how generally bad the Times’ science reporting is), that one theory holds that gravitons may be able to pass from other multiverses to our own. If the theory is correct (and if the Times didn’t screw it up too much reporting it), effects from multiverses may be observable in our own.


Hmm, well I don’t think anyone can answer the question. For example how do we know that distance remains constant throughout the universe. You describe travelling in terms of speed, which is simply distance travelled over time taken. If distance or time are not constant then we have to look at the concept of either varying from infinitely small to infinitely large, and as we all know it is impossible to visualise infinity either way. If we try to do this we end up imagining very very small or very very large… but not quite infinity. It’s the same concept as us 3 dimensional beings trying to imagine a 4 dimensional universe.

First off–I said in my post to look up Casimir Effect for documentation on the hoo-ha part of your post. Since you didn’t I’ll do it for you:

Also, follow the link on Virtual Particles in the page linked above. Like it or not it is NOT ‘hoo-ha’ but a proven (i.e. not theoretical) part of the Universe.

As for the first part of your question Chronos answered it earlier:

If Chronos is to be believed (and he seems pretty knowledgeable about what this is all about) then I choose to think that the ‘outside’ Universe is filled with beer. My proof being that quantum foam are the bubbles and our Universe is a beer burp.

There is no edge to the Universe…at least not in three dimensions. No matter where you are in the Universe it would appear as if you are at the center and everyone else is moving away from you.

Sphere analogy thing again You’re a 2-D creature living on the surface of a smooth sphere. You have no concept of up or down. No matter where you move on the sphere you’ll never find an edge…each point is indistingiushable from the next. If the sphere is expanding [i.e. a balloon] everything will seem to move away from you no matter where you are).

The analogy only applies to us if we live on a hypersphere (a 4-D sphere) which seems to not be the case. It’s looking like the Universe is flat. Still, it helps visualize how this stuff can work.