[Airbrush]

Jiggerj, on 31 January 2012 - 09:56 PM, said:

Good point. I also have a problem with the word 'Universe' when used by physicists. Is it just the space that is considered the observable universe, or does it also include what may lie beyond it?

Scientists will make a distinction. The observable universe is called exactly that. "Universe" generally means everything, even beyond the observable limit.

[IM Egdall]

Airbrush, on 1 February 2012 - 09:30 PM, said:

Scientists will make a distinction. The observable universe is called exactly that. "Universe" generally means everything, even beyond the observable limit.

I have found scientists to be sloppy on this point. They often write or say "universe" when they are referring only to the "observable universe". So you have to be careful in trying to understand which one they are referring to.

[PhysicsBurger]

Edisonian, on 6 October 2004 - 03:32 AM, said:

Ever since I was a young boy, 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?

The earth doesnt "end". You just keep going round until you end up right where you started.

[*puffy* japanisthebest]

Edisonian, on 6 October 2004 - 03:32 AM, said:

Ever since I was a young boy, 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?

... i found a little solution of my own... the universe repeats... i think that if you reach the edge... you will emerge into the beginning of the universe that you just crossed..........

PhysicsBurger, on 4 February 2012 - 04:08 PM, said:

The earth doesnt "end". You just keep going round until you end up right where you started.

yep

[Jiggerj]

Edisonian, on 6 October 2004 - 03:32 AM, said:

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?

I'm reading this question as: Where does the realm of Something meet the realm of Nothing?

In a spaceship, we've flown to a place where we can go no further. What is there to prevent us from going ever forward? A wall? The inner surface of a shell? Even so, walls and shells can be cut through.

The only thing that could truly stop us is a big ol' chunk of Nothing. But, what is nothing? What does it look like? Is it impenetrable? No, nothing can't be impenetrable because Nothing can't be hard or solid; hard and solid define Something.

A state of absolute nothing cannot exist. Therefore, the realm of Something cannot end.

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[DrRocket]

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*puffy* japanisthebest, on 6 February 2012 - 03:15 PM, said:

... i found a little solution of my own... the universe repeats... i think that if you reach the edge... you will emerge into the beginning of the universe that you just crossed..........

yep

Believe it or not that is actually one possible model for space in cosmology. It is properly called the flat torus. In Brian Greene's most recent book you will find it called "Pac Man" space.

Greene's name comes from the Pac Man video game, and from the construction of the ordinry 2-torus by indentifying (gluing) opposite edges of a rectangular strip together preserving up, down, left and right. Yoou can do exactly the same thing with a cube, identifying opposite faces, to get what geometers call a 3-dimensional flat torus.

But note that these structures have no real edge, just like an ordinary torus (surface of a donut) has no edge.

This post has been edited by DrRocket: 12 February 2012 - 09:28 PM

[Temporocitor]

There must be an eternal vacuum where within all resides. Negative energenesis ad infinitum is the so-called free lunch. Eventually -A x -B = |C| matter is, but is not infinite. Absolute nothing isn't, but is infinite.

[mertol]

I like to think about the universe like this:

You cannot be at the edge of the matter going away from the center of the big bang at light speed because you can always point a beam of light over that edge. If the laws of physics are the same everywhere and there is no special place in the universe like a place where the big bang happened then this implies that the big bang happened everywhere at the same time. If there is something going away from something at light speed for everything in the universe then the universe is infinite. For every observer in the universe, the space gets progressively distorted the further away from him. Close to the 13.7 billion light years distance everything is going away from the observer at nearly light speed so it is nearly flat. So for every observer, the universe is a sphere with 13.7 billion light years radius where everything near the edges gets infinitely flat and infinitely dense and with infinitely slowed time so you can take this as the limit of the universe although the universe remains infinite nevertheless.

Are my thoughts correct?

As a speculation: if there is infinite mass and density at the edges of the universe wouldn't that be the cause for the accelerating expansion since the gravity of everything on the edge will pull everything inside the sphere and eventually everything will end up on the edges. But everything is also always in the center of the sphere so the pull is always cancelled out... Thinking about this can make you crazy.

This post has been edited by mertol: 21 February 2012 - 04:19 PM

[morgsboi]

Well we can only see as far as the cosmic microwave background. Whether we can see past it or even get past it in the future would be a huge achievement.

[IM Egdall]

mertol, on 21 February 2012 - 03:47 PM, said:

I like to think about the universe like this:

You cannot be at the edge of the matter going away from the center of the big bang at light speed because you can always point a beam of light over that edge. If the laws of physics are the same everywhere and there is no special place in the universe like a place where the big bang happened then this implies that the big bang happened everywhere at the same time. If there is something going away from something at light speed for everything in the universe then the universe is infinite. For every observer in the universe, the space gets progressively distorted the further away from him. Close to the 13.7 billion light years distance everything is going away from the observer at nearly light speed so it is nearly flat. So for every observer, the universe is a sphere with 13.7 billion light years radius where everything near the edges gets infinitely flat and infinitely dense and with infinitely slowed time so you can take this as the limit of the universe although the universe remains infinite nevertheless.

Are my thoughts correct?

As a speculation: if there is infinite mass and density at the edges of the universe wouldn't that be the cause for the accelerating expansion since the gravity of everything on the edge will pull everything inside the sphere and eventually everything will end up on the edges. But everything is also always in the center of the sphere so the pull is always cancelled out... Thinking about this can make you crazy.

Here is my understanding. Yes, according to the big bang theory, it happened everywhere. The "explosion" was the expansion of space itself. But whether the universe is infinite or finite is still unknown.

The rule that nothing can travel faster than the speed of light through space is from special relativity. But per general relativity, space itself can (and does) expand faster than the speed of light.

This post has been edited by IM Egdall: 26 February 2012 - 04:21 PM

[life station]

there are to things in this universe one is space (emptyness) otther is matter or energy both are the same thing known to the science very well ( means mass air gase gravity radiowaves light etc) where there is matter there is no space and where there is space no matter so now you can understand that the end of space is out of question it is endless

[JohnStu]

Space doesn't end, the question is where does the matters end.

Space is just the non-currently-occupied region of matter. If space had a limit then there would be a wall where matters bounce back which doens't make sense because what would be beyond the wall. And no such wall can possible exist unless it is... OMG WE ARE IN A MATRIX!

[owl]

JohnStu, on 29 February 2012 - 01:53 AM, said:

Space doesn't end, the question is where does the matters end.

Space is just the non-currently-occupied region of matter. If space had a limit then there would be a wall where matters bounce back which doens't make sense because what would be beyond the wall. And no such wall can possible exist unless it is... OMG WE ARE IN A MATRIX!

I agree. "Infinite space" is one of my favorite concepts to contemplate. And I've 'thrown in my two cents' on the topic in other threads too. No matter what theoretical "form" one proposes for "the universe," the question/challenge always remains, what lies beyond the defining 'boundary' of any form? Whether there is more "stuff" (matter/energy) or just more space, the concept of an "end" is absurd.

Same applies to the 'surface of earth' model of space-as-endless: more space within and beyond the 'surface of the sphere.' Space is volume, not a "surface" anyway.
Edit; ps:
I liked Jiggerj's cartoon in post 685.
"Oh, crap!" ('space closed beyond this point')

This post has been edited by owl: 2 March 2012 - 07:06 PM

[morgsboi]

JohnStu, on 29 February 2012 - 01:53 AM, said:

Space doesn't end, the question is where does the matters end.

So your saying that space has no matter? Did you take things like light and radiation into consideration?