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Author Topic:   The nature of "space"
Jester4kicks
Junior Member (Idle past 3419 days)
Posts: 33
Joined: 06-17-2008


Message 1 of 15 (502040)
03-09-2009 12:01 PM


Greetings all! It's been a while since I visited, but I always turn to this forum when I've got a puzzle that I simply can't wrap my head around.

With that in mind... the simple question here is this:

Is there "space" outside of the known universe?

What I mean is that, if you were to journey to the outermost edge of the known universe... the point where all matter in the universe had not expanded past yet... would there just be more empty space beyond that boundary?

To give you a little more background, I'm currently in a discussion with a creationist and we are discussing the nature of empty space in the Universe. He is trying to make a point that, as the universe expands, new "space" is "created" between the different stellar bodies.

My point is that space itself is nothing but the void... the medium (if you will) that all matter expands into. It is not tangible, but rather it is only identifiable as a lack of anything between the various stellar bodies. A true void.

My own problem with this understanding is perhaps due to my current understanding of the nature of the universe. I've never understood that whole "balloon" analogy with everything sitting on the surface of the balloon. Instead, I've always thought of the universe more like a "cloud" containing all matter in the known universe that is constantly expanding in all directions outward.

If my own understanding is incorrect, maybe someone here could help put it into better terms.

Thanks!


Replies to this message:
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 Message 4 by Rahvin, posted 03-09-2009 2:46 PM Jester4kicks has responded
 Message 5 by cavediver, posted 03-09-2009 3:16 PM Jester4kicks has responded

    
AdminNosy
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Message 2 of 15 (502072)
03-09-2009 1:41 PM


Thread moved here from the Proposed New Topics forum.
  
Taz
Member (Idle past 1215 days)
Posts: 5069
From: Zerus
Joined: 07-18-2006


Message 3 of 15 (502078)
03-09-2009 2:10 PM
Reply to: Message 1 by Jester4kicks
03-09-2009 12:01 PM


Jester writes:

What I mean is that, if you were to journey to the outermost edge of the known universe... the point where all matter in the universe had not expanded past yet... would there just be more empty space beyond that boundary?


If YOU were to journey there, wouldn't YOU constitute matter.

The point is there's no such thing as the "void" like most people think. Once YOU find it, it's not a void anymore.


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Rahvin
Member (Idle past 1110 days)
Posts: 3964
Joined: 07-01-2005


Message 4 of 15 (502089)
03-09-2009 2:46 PM
Reply to: Message 1 by Jester4kicks
03-09-2009 12:01 PM


Note: I'm not a physicist. Wait for cavediver or Son Goku for the real deal.

Is there "space" outside of the known universe?

What's North of the North Pole?

Your question is the result of attempting to apply human experience to the Universe as a whole. "Space" is a property of the Universe and makes sense only in the context of the Universe itself, much like the direction North makes sense only within the context of a globe.

What I mean is that, if you were to journey to the outermost edge of the known universe... the point where all matter in the universe had not expanded past yet... would there just be more empty space beyond that boundary?

Again, this question misrepresents the actual expansion of the Universe. The Universe is finite and expanding, but it has no boundary. The best available analogy would be to compare the Universe to an expanding balloon, with all three spacial dimensions represented only by the 2-D surface (ie, there is no "up"). As teh balloon expands, the space between two given points increases. The surface is finite, but it has no boundary - there is no "place where the Universe has not expanded yet."

To give you a little more background, I'm currently in a discussion with a creationist and we are discussing the nature of empty space in the Universe. He is trying to make a point that, as the universe expands, new "space" is "created" between the different stellar bodies.

It's more like the existing, finite amount of space stretches in all directions at once, much like an expanding balloon. The farther away two points are, the more expanding space exists between them, and so the more rapidly the two points will move apart. Nothing is being "created." Further, space is a set of three dimensions - asserting that "width" can be "created" misrepresents what dimensions are.

My point is that space itself is nothing but the void... the medium (if you will) that all matter expands into. It is not tangible, but rather it is only identifiable as a lack of anything between the various stellar bodies. A true void.

There's more to it than that...but Ill leave that to cavediver and Son Goku, as I won't be able to comment on it with any degree of accuracy.

I'll say only that space is also affected by mass - mass warps space. This generates the phenomenon of gravitational lensing (and in fact all of gravity). Warped space can change the final direction of a ray traveling in a straight line without causing the ray to bend (an unbent straight bar can be made to have both ends touch, for example). There's a lot more to space than just "void."

My own problem with this understanding is perhaps due to my current understanding of the nature of the universe. I've never understood that whole "balloon" analogy with everything sitting on the surface of the balloon. Instead, I've always thought of the universe more like a "cloud" containing all matter in the known universe that is constantly expanding in all directions outward.

Your analogy is flawed because it posits that there is an "outside" to the Universe. Space, matter, energy, time, all of these are properties [i]of[/]i the Universe. There may well be additional dimensions that our Universe exists in, much the same way the 2-D surface of the balloon or globe exists within the additional spacial and time dimensions, but "space," like "time" has no real meaning outside of the context of the Universe, in exactly the same way that "North" has no meaning outside the context of a globe.

That help at all?


This message is a reply to:
 Message 1 by Jester4kicks, posted 03-09-2009 12:01 PM Jester4kicks has responded

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 Message 6 by Jester4kicks, posted 03-09-2009 3:26 PM Rahvin has responded

  
cavediver
Member (Idle past 1566 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 5 of 15 (502094)
03-09-2009 3:16 PM
Reply to: Message 1 by Jester4kicks
03-09-2009 12:01 PM


Is there "space" outside of the known universe?

Possibly - depends what you mean by "the known universe"

if you were to journey to the outermost edge of the known universe... the point where all matter in the universe had not expanded past yet

No such place - your whole starting assumption is wrong, and your creationist friend is correct: matter is not expanding into space; space is simply expanding between matter, as predicted by General Relativity.

My point is that space itself is nothing but the void...

No, space is as real as the atoms that make up your hand.

My point is that space itself is nothing but the void... ...It is not tangible

Neither are atoms, electrons, photons, etc. Tangibility is a purely macroscopic phenomenon involving near-infinite electromagnetic interactions between near-infinite numbers of photons and electrons associated with the atoms of the toucher and the touchee. Same with visibility...

I've never understood that whole "balloon" analogy with everything sitting on the surface of the balloon. Instead, I've always thought of the universe more like a "cloud" containing all matter in the known universe that is constantly expanding in all directions outward.

The "balloon" analogy was constructed to precisely dispell the erroneous "cloud" analogy :)


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 Message 1 by Jester4kicks, posted 03-09-2009 12:01 PM Jester4kicks has responded

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 Message 8 by Jester4kicks, posted 03-09-2009 3:40 PM cavediver has responded

  
Jester4kicks
Junior Member (Idle past 3419 days)
Posts: 33
Joined: 06-17-2008


Message 6 of 15 (502095)
03-09-2009 3:26 PM
Reply to: Message 4 by Rahvin
03-09-2009 2:46 PM


That help at all?

Kinda... I guess I thought of space as just a sort of medium/non-medium, with planets, gases, and stars all just floating around in it. Kinda like pieces of fruit "floating" in jello.

It sounds more like all space, and the objects in it (stars, planets, etc) are actually interwoven into the same "fabric" of space-time... and the entire thing is expanding.

Is that a little closer?


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Rahvin
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Posts: 3964
Joined: 07-01-2005


Message 7 of 15 (502096)
03-09-2009 3:35 PM
Reply to: Message 6 by Jester4kicks
03-09-2009 3:26 PM


Kinda... I guess I thought of space as just a sort of medium/non-medium, with planets, gases, and stars all just floating around in it. Kinda like pieces of fruit "floating" in jello.

That would be the "aether" model that was held in the middle ages. It's not really very accurate, though "common sense" makes it feel that way.

The problem is that human beings perceive the Unvierse in a very particulay way, and that perception is extremely limited. We don't see things on the subatomic scale, or on the scale of galactic clusters in our everyday lives, and so our perception is flawed.

Our concept of "time" is similarly messed up, and can be even more confusing - time is nothing mroe than a dimension, no different in any way from width or length except in our perception of it.

The Universe is pretty frakking odd to human common sense. Only math starts to make it comprehensible...really complex, long, intricate math.

It sounds more like all space, and the objects in it (stars, planets, etc) are actually interwoven into the same "fabric" of space-time... and the entire thing is expanding.

You could say that.

It would be more accurate to say that the universe is a discrete entity, and that matter/energy and the spacial/time dimensions are all properties of that entity. We are experiencing time as a linear chain of events in the direction of increasing entropy because the electrochemical processes in our brains that constitute thoughts require increasing entropy to function. If you picture the entire Universe as a globe, with the vertical axis represented by time and the 2-D surface as the 3 spacial dimensions, you can start to see what I mean - the North pole would be the "beginning" of time, where the entire Universe existed in a small, hot, dense state. At "later" time coordinates (meaning farther South) the Universe has "more space," meaning that there is greater distance between any two given objects. Questions like "what came before the Universe" or "what's outside the Universe" don't make a lot of sense, given that those questions refer to dimensions that only exist in the context of the Unvierse itself.


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Jester4kicks
Junior Member (Idle past 3419 days)
Posts: 33
Joined: 06-17-2008


Message 8 of 15 (502097)
03-09-2009 3:40 PM
Reply to: Message 5 by cavediver
03-09-2009 3:16 PM


No such place - your whole starting assumption is wrong, and your creationist friend is correct: matter is not expanding into space; space is simply expanding between matter, as predicted by General Relativity.

-shudder- :P

He's actually arguing a point for a "creator" by arguing the "on-going creation" of space between the various planets, stars, etc. It sounds like he actually is incorrect... but only in the sense that space is not "created", but rather that the existing space expands.

Right?

Neither are atoms, electrons, photons, etc. Tangibility is a purely macroscopic phenomenon involving near-infinite electromagnetic interactions between near-infinite numbers of photons and electrons associated with the atoms of the toucher and the touchee. Same with visibility...

I probably should have been a little more clear with that point. I wasn't trying to say that tangibility was the only thing that made something real... but rather that space was the absence of anything, including subatomic particles.

Let me approach it another way... you have a jar filled with a particular compound. You can tests to determine exactly what this compound is, what it is composed of, etc. If your hypothetical jar only had the void (and vacuum) of space "in" it... how would you determine that? How would you identify it as such?

The "balloon" analogy was constructed to precisely dispell the erroneous "cloud" analogy :)

Crap. :P

Does this somehow relate to my comment in the previous response about everything in the universe being "woven" together? If so, maybe I'm starting to understand.... (careful optimism LOL)


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cavediver
Member (Idle past 1566 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 9 of 15 (502103)
03-09-2009 4:47 PM
Reply to: Message 8 by Jester4kicks
03-09-2009 3:40 PM


space is not "created", but rather that the existing space expands.

True - that is like claiming that temperature is "created" in a kettle, or speed is "created" when a ball rolls down a hill. Or better still, that longitude is "created" as you journey south from the North Pole. The distance between any two objects is just a number, and cosmological expansion is simply that number getting larger for all possible pairs of cosmologically sized objects.

but rather that space was the absence of anything, including subatomic particles.

"Empty" space is seething with subatomic particles. But that's beside the point. Take three points in space: A, B, and C. Something we normally call "real" might be the number of photons at each point - say P(A), P(B), P(C). These numbers form a "field" when taken over all points. What we call space is formed by the distance between the points D(A,B), D(B,C) and D(C,A). These numbers also form a "field" when taken over all points. There is nothing more "real" about the photon field than the distance field, they both manifest in our experience, just in different ways.

If your hypothetical jar only had the void (and vacuum) of space "in" it... how would you determine that? How would you identify it as such?

You would mesaure the distance between pairs of points and these would reveal the mass distribution in the jar, possibly a zero distribution of mass. But the existence of the distances would be the "space".

Does this somehow relate to my comment in the previous response about everything in the universe being "woven" together?

The Universe is woven together out of the different fields. That is the sum total of existence as far as we can tell - just interwoven fields.


This message is a reply to:
 Message 8 by Jester4kicks, posted 03-09-2009 3:40 PM Jester4kicks has responded

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Jester4kicks
Junior Member (Idle past 3419 days)
Posts: 33
Joined: 06-17-2008


Message 10 of 15 (502104)
03-09-2009 5:09 PM
Reply to: Message 9 by cavediver
03-09-2009 4:47 PM


Thanks for the explanation (especially the answer to my hypothetical jar scenario)!

One more question...

The Universe is woven together out of the different fields. That is the sum total of existence as far as we can tell - just interwoven fields.

Is there a reason that space expands, but planets and other bodies woven into that space "fabric" do not?


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 Message 11 by Taq, posted 03-09-2009 9:36 PM Jester4kicks has responded

    
Taq
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Posts: 7575
Joined: 03-06-2009
Member Rating: 3.6


Message 11 of 15 (502147)
03-09-2009 9:36 PM
Reply to: Message 10 by Jester4kicks
03-09-2009 5:09 PM


Is there a reason that space expands, but planets and other bodies woven into that space "fabric" do not?

There are two things to consider here. First, the expansion of space. Second, we need to consider gravity. As it turns out, the gravity of a planet overcomes the expansive force where a planet is concerned. As an analogy, it is like comparing the gravitational effects of the Moon and Earth on you right now. The gravity of the Earth overwhelms the gravitational force from the Moon so that you are not drifting towards the Moon.

Edited by Taq, : No reason given.


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 Message 12 by Jester4kicks, posted 03-10-2009 10:11 AM Taq has responded

  
Jester4kicks
Junior Member (Idle past 3419 days)
Posts: 33
Joined: 06-17-2008


Message 12 of 15 (502200)
03-10-2009 10:11 AM
Reply to: Message 11 by Taq
03-09-2009 9:36 PM


There are two things to consider here. First, the expansion of space. Second, we need to consider gravity. As it turns out, the gravity of a planet overcomes the expansive force where a planet is concerned. As an analogy, it is like comparing the gravitational effects of the Moon and Earth on you right now. The gravity of the Earth overwhelms the gravitational force from the Moon so that you are not drifting towards the Moon.

Ok, I kinda follow that...

Let me ask just one more question. (It's another issue being raised by the creationist I'm talking to)

Is there a "center" of the Universe? To expand on that, if space is finite, does it loop around on itself?

I guess I'm just wondering how far that balloon analogy goes. Let's say we draw one line of latitude around the balloon, and one line of longitude. Excluding the poles, we'll have two intersecting points. Let's call point 1 "Earth" and point 2 "Tralfamadore".

If we get in a ship and travel in one direction along our line of latitude to Tralfamadore... can we then continue travelling in same direction, along the same line of latitude, and get back to Earth?

Thanks everyone!


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 Message 11 by Taq, posted 03-09-2009 9:36 PM Taq has responded

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Stile
Member
Posts: 3241
From: Ontario, Canada
Joined: 12-02-2004
Member Rating: 2.6


Message 13 of 15 (502229)
03-10-2009 12:25 PM
Reply to: Message 12 by Jester4kicks
03-10-2009 10:11 AM


I know this one!
Jester4kicks writes:

Is there a "center" of the Universe?

Yes.
And "the centre" is each and every point.
That is, going back to the balloon analogy, think of a perfectly spherical balloon. And remember, the analogy is only the surface of the balloon. So, where is "the centre" of the surface of a perfectly spherical balloon?
Each point on the surface has equal claim to be called "the centre".

And No.
Because every point can be "the centre" of the universe, that means that no point is actually "the centre" of the universe. It means that the universe doesn't really have a unique place you can call "the centre."

Also, we do know that Earth is not at the centre of our solar system. We also know that our solar system is not at the centre of our galaxy.
So, even IF we could (somehow) claim that our galaxy was "the centre galaxy" of the universe... we're still not at the centre of that, so we're still not at the centre of the universe.

To expand on that, if space is finite, does it loop around on itself?

Yes.
In the same way that if you walk along the surface of the balloon, you loop around on yourself.

If we get in a ship and travel in one direction along our line of latitude to Tralfamadore... can we then continue travelling in same direction, along the same line of latitude, and get back to Earth?

My knowledge doesn't go this far. I would say:
As far as we can tell with the information we have so far, IF the theories we have are actually true... then yes.


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Taq
Member
Posts: 7575
Joined: 03-06-2009
Member Rating: 3.6


Message 14 of 15 (502289)
03-10-2009 6:14 PM
Reply to: Message 12 by Jester4kicks
03-10-2009 10:11 AM


If we get in a ship and travel in one direction along our line of latitude to Tralfamadore... can we then continue travelling in same direction, along the same line of latitude, and get back to Earth?

Stile did a great job of explain the other stuff. I thought I might add one thing in response to the above.

If it were not for the expansion of the universe you would end up where you started. The problem here is that over large enough distances the accumulated expansion of the universe is greater than the speed of light. IOW, you would need to travel faster than the speed of light in order to get back to Earth. It's sort of like a treadmill that is spinning faster than you can run. The longer you go the more treadmill you have in front of you.


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cavediver
Member (Idle past 1566 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 15 of 15 (502304)
03-10-2009 8:13 PM
Reply to: Message 14 by Taq
03-10-2009 6:14 PM


The problem here is that over large enough distances the accumulated expansion of the universe is greater than the speed of light.

This isn't actually that relevant. If we were in a closed Friedmann Roberston Walker universe, we could still have the same "superluminal" expansion (for sufficiently large universes), but what would prevent the circumnavigation is the big crunch would occur before the trip could be completed.

Our situation is muddied by the action of the "dark energy" field(s) - in the current phase, the expansion is accelerating, so there is no hope of a circumnavigation. But we don't know the dynamic evolution of the dark energy, and it is possible it could alter such that a circumnavigation is possible.

Of course, all of this presupposes a closed finite Universe. We do not yet know if this is the case. The Universe could well be open and infinite (It could also be open and compactified, but that is a different story...)


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