# Universe Boundaries

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Several theories claim that the universe is expanding, or that at some point it was. My question is (assuming the universe isn't infinite), what could be at the edge of the universe? If I somehow ended up at the boundary of the universe, I presume there would be a sort of barrier where the universe ends, but if the universe is expanding, there must be something outside the barrier for the empty space to even be created? And on that note, what actually defines space itself?

Could it be possible there are an infinite number of universes all within one huge multiverse one one plane (dimension), and while one increases in size, another decreases (Big Bang, Big crunch), like a complex honeycomb formation?

Sorry if this didn't make sense

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And also, what is outside the 'barrier' of space? since outside of the barrier takes up space, it cant be nothing.

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• 2 weeks later...

Think of playing a computer game, when you move over one side of the screen, you appear on the other side. Now increase the area you have to walk until you reach the edge of the screen (although it's not really the edge as you appear on the other side automatically).

That's how the Universe is expanding and also why it dosn't have to expand "into" anything.

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There are no boundaries of the universe (at least in mainstream physics). "The universe expands" means that the distance between two points in space increases with time.

Consider the plane {(x,y) : x,y real}. This plane is infinite. Let the distance between two points P1=(a,b) and P2=(c,d) be defined by d(P1, P2) = t*sqrt[(a-c)² + (b-d)²]. The distance between those two fixed points increases as the time t increases. Therefore one could argue that the plane expands. Also, the distance between any two point is zero at t=0 (which is the big bang, then). But the plane still doesn´t have any boundaries.

If you want to have an example of an expanding finite space without boundaries take a sphere with radius time.

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Several theories claim that the universe is expanding' date=' or that at some point it was. My question is (assuming the universe isn't infinite), what could be at the edge of the universe? If I somehow ended up at the boundary of the universe, I presume there would be a sort of barrier where the universe ends, but if the universe is expanding, there must be something outside the barrier for the empty space to even be created? And on that note, what actually defines space itself?

Could it be possible there are an infinite number of universes all within one huge multiverse one one plane (dimension), and while one increases in size, another decreases (Big Bang, Big crunch), like a complex honeycomb formation?

Sorry if this didn't make sense [/quote']

You are at the boundary now and so you see 3 dimensions and not 4.

Of course you were born on this "3-surface" and have never moved off of it, so no wonder you're puzzled.

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I always had a theory, not backed up by any scientific work, mind you, but just a thought, that what if at the "edge of the universe" there was a two dimensional universe, residing on the very surface of our three dimensional one? And now think, what if our three dimensional universe is on the "edge" of a four dimensional one? (This may be harder to visualize since no one has travelled through the other dimensions) And that fourth universe is on the edge of a fifth one, and so on and so forth?

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Well, isn't the critical density 10^-36 kg (or about that)? Plug this in for the equations involving the mass of the universe divided by its size (supposing its a sphere) that Einstein gave us (with the cosm constant). We can therefore deduce that the universe will expan to be about 9.5*10^22 km in its radius. Huzzah!

But you can't travel there, spacetime will conform itself. Remember, nothing is outside the universe! Its like a fish trying to swim out of a bag but the bag distorts itself to allow the fish to continue swimming.

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Isnt asking whats at the edge of the universe in a way asking if the earth is flat rather than round?

Because "from my point of view," which can always be wrong I'd like to note, an explosion on a 3 dimensional space will expand in 3 dimensions. Now once the big bang happened, the fastest particles we know of are those of light, so that those are on the "edge" of the universe. Now, according to many theories, one cannot travel faster than light. If these three assumptions are all based on correct premises that are true themselves, it is impossible for one to reach the edge of the universe because it will be always be moving away faster than anything that may try to reach it. And not only that, but if one were to reach it, then moving toward the edge of the universe would be much like walking over the surface of the Earth, you would keep walking and walking and reaching the same point over and over again.

Now, like I said before and like to emphasize, none of this, except that the idea that nothing can travel faster than light came from my mind and has no scientific proof, so if it sounds lame to anyone with firther knowledge, excuse me

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I've often heard the universe described as containing billions of galaxies, etc. I guess this imay be a more philosophical question but how can an infinite boundary-less universe contain anything?

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Space Ends

The Universe

http://www.cybcity.com/theuniverse

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Think of playing a computer game' date=' when you move over one side of the screen, you appear on the other side. Now increase the area you have to walk until you reach the edge of the screen (although it's not really the edge as you appear on the other side automatically).

That's how the Universe is expanding and also why it dosn't have to expand "into" anything. [/quote']

The Universe

http://www.cybcity.com/theuniverse

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There are no boundaries of the universe (at least in mainstream physics). "The universe expands" means that the distance between two points in space increases with time.

Consider the plane {(x' date='y) : x,y real}. This plane is infinite. Let the distance between two points P1=(a,b) and P2=(c,d) be defined by d(P1, P2) = t*sqrt[(a-c)² + (b-d)²']. The distance between those two fixed points increases as the time t increases. Therefore one could argue that the plane expands. Also, the distance between any two point is zero at t=0 (which is the big bang, then). But the plane still doesn´t have any boundaries.

If you want to have an example of an expanding finite space without boundaries take a sphere with radius time.

The Universe

http://www.cybcity.com/theuniverse

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Space Ends

The Universe

http://www.cybcity.com/theuniverse

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Space Ends

The Universe

http://www.cybcity.com/theuniverse

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• 2 weeks later...

Well, universe is infinite (cyclic) if you ask me. i believe it's 6 dimensional space, that's my theory which's part is confirmed by last reasearches of star ( our "sun"), it's just a plasma outburst from "somewhere", well most of scientist r blind or dumb if they cant connect those 2 thing : stars emit light and black holes r distorsions that absorb it, so it must be cyclic connection, and crucial thing in any space theory, so on relation star > black hole = space, so nothing can have such energy without any constant source (my oppinion) so that space in relation black hole > star is something else, completely different dimension that I accept to call subspace, so that's my subspace theory in short mode, lol. well if u think something must have a beginning and end, then tell me when time began and when it will end

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any evidence to back your theory up? it has a lot of work to be done on it if you want to get it into the mainstream. Why do stars need a source of energy? can they not make the energy by fusion like most(the reputable ones) scientists and astronomers believe?

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Well, universe is infinite (cyclic) if you ask me. i believe it's 6 dimensional space, that's my theory which's part is confirmed by last reasearches of star ( our "sun"), it's just a plasma outburst from "somewhere", well most of scientist r blind or dumb if they cant connect those 2 thing : stars emit light and black holes r distorsions that absorb it, so it must be cyclic connection, and crucial thing in any space theory, so on relation star > black hole = space, so nothing can have such energy without any constant source (my oppinion) so that space in relation black hole > star is something else, completely different dimension that I accept to call subspace, so that's my subspace theory in short mode, lol. well if u think something must have a beginning and end, then tell me when time began and when it will end

what do you mean 6 dimensions?! there are only 4 dimensions to my knowledge, 2d( x, yflat surface), 3d( x, y,z, coord), 4d(time), please tell me what the 5th and 6th dimension is, and there are a lot of theories i beleive as to howthe universe was started, but i really don't know, its either between big bang or big crunch, i think i'll lean mroe toward, the big bang, it started out as 1 little dot, and exploded, but i wonder where this dot came from, was space, just nothingness, i mean nthing, it was all dark, then a point just appeared, someone or something put it right there, even if there was a big crunch, and the universe just kept exploding and imploding, that means the universe could have been here longer than we think, maybe septillions of years( its an actualy numer, don't believe me , google it)(http://open-dictionary.com/Septillion), but where tdid this "space" come from, its so confusing, that all of this space was just here, and a point came out of nowhere, of course, there could be soething or someone, maybe god, that created everything, and i wonder if there is an afterlife

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that dot started out as an infinite expanse of space. its just that through expansion one side of the universe expanded away from the other faster than c, this means that we simply can't see beyond 13.6 light years (even though it does exist)

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Imagine the universe as an infinite ruler. The ruler was infinite in extent when it came into existence (at t =0) and remains infinite in extent for all very large values of t.

Now, as t increases the ruler 'expands'; this doesn't mean that the extent of the ruler changes (remember it's infinite), what it means is that 'distance' between the notches on the ruler increases. This is what is meant by space-time expanding.

It's also important to remember that locally gravity dominates, it's only on large scales (inter-galactic space) that the universe expands.

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• 2 weeks later...

I think that other universes exist and overlap each other. Much like we have our galaxy, and the distance to the nearest galaxy is huge compared to the distance between stars, the next universe is so distant you could not even fathom it. I think universes form clusters much like galaxies, and when two universes combine, they form a big crunch, which combines the two universes collapse into 1 and then they expand in a violent big bang, forming an even larger universe then the last 2.

Another hypothesis I thought of was giant blobs of anti-matter and matter float around in a plane of existance much larger then we can concieve, and when two of these blobs meet they create a big bang, forming a universe as we know it. (ours being one that consisted of a blob of slightly more matter)

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