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Author Topic:   Size of the universe
New Cat's Eye
Inactive Member


Message 91 of 248 (600069)
01-12-2011 10:33 AM
Reply to: Message 89 by john6zx
01-12-2011 12:17 AM


Has anyone found any science to give evidence that space is a thing?

Gravity bends light... how do you think that is possible?

All this talk about expanding space is fantasy unless space is a physical thing. In order to expand a thing has to have physical properties.

Oh, I dunno... You can expand a mathematical matrix. You can expand your mind.

Anyway, spacetime is where physical properties reside. Even your own rule here takes place within spacetime. Its kind of its own thing, and not necessarily subject to the rules that take place within it.

So what are the physical properities of space?

That question is nonsensical.


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Iblis
Member (Idle past 1976 days)
Posts: 663
Joined: 11-17-2005


Message 92 of 248 (600078)
01-12-2011 11:03 AM
Reply to: Message 89 by john6zx
01-12-2011 12:17 AM


begging the question
So what are the physical properities of space?

The capacity to act as a medium for matter and energy; curvature, as in expansion and gravitation; and vacuum energy in particular is purely a physical property of spacetime itself.

The fact that this stuff doesn't make sense to you, or fit into your philosophy, has no bearing on its accuracy. Relativity is one of the most thoroughly tested bodies of theory in all of science. If the terms of the mathematical model were less accurate than the piddly bit of "common sense" your brain can produce, any number of those experiments would have failed miserably. The only point where relativity seems to need some work is in describing the very, very small.


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ProtoTypical
Member
Posts: 1777
From: Ontario Canada
Joined: 08-04-2010


Message 93 of 248 (600362)
01-14-2011 6:25 AM


The void
So, then, is the concept of a 'void' only a concept? An impossible one at that. Can we logically conceive a 'place' where no 'thing' exists?

Edited by Dogmafood, : No reason given.


Replies to this message:
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cavediver
Member (Idle past 1724 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 94 of 248 (600365)
01-14-2011 7:01 AM
Reply to: Message 93 by ProtoTypical
01-14-2011 6:25 AM


Re: The void
So, then, is the concept of a 'void' only a concept? An impossible one at that. Can we logically conceive a 'place' where no 'thing' exists?

As we have seen, space-time is itself a thing, and can quite happily exist with nothing else in it.


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Replies to this message:
 Message 95 by ProtoTypical, posted 01-14-2011 7:43 AM cavediver has responded
 Message 98 by ProtoTypical, posted 01-16-2011 8:13 AM cavediver has responded
 Message 125 by ProtoTypical, posted 05-04-2011 8:52 AM cavediver has responded

  
ProtoTypical
Member
Posts: 1777
From: Ontario Canada
Joined: 08-04-2010


Message 95 of 248 (600367)
01-14-2011 7:43 AM
Reply to: Message 94 by cavediver
01-14-2011 7:01 AM


Re: The void
Can I conclude, then, that space must be infinite?
This message is a reply to:
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Replies to this message:
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cavediver
Member (Idle past 1724 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 96 of 248 (600440)
01-14-2011 1:20 PM
Reply to: Message 95 by ProtoTypical
01-14-2011 7:43 AM


Re: The void
Can I conclude, then, that space must be infinite?

No, not at all. It can be either. Space can be wrapped up such that it is finite but with no boundary - in the way that the surface of the earth has no boundary but is finite.


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Seizmik
Junior Member (Idle past 2890 days)
Posts: 2
From: Edinburgh, UK
Joined: 01-10-2011


Message 97 of 248 (600664)
01-16-2011 5:30 AM
Reply to: Message 96 by cavediver
01-14-2011 1:20 PM


Re: The void
cavediver writes:


No, not at all. It can be either. Space can be wrapped up such that it is finite but with no boundary - in the way that the surface of the earth has no boundary but is finite.

To all who read this and get the idea that the universe is a sphere, don't. It very well may be, but that isn't what cavediver was eluding to(I think).

Keep in mind also that since the so-called 'edges' of the observable universe are 14pc away, this doesn't mean that the universe itself is only 14pc in radius. This can easily be thought of with a completely opaque balloon. If you take the balloon before it is inflated and fill it with a multitude of gases, these gases with start to react(possibly) and you could see a multitude of effects going on, if you were inside the balloon. Now if you fill the room you are in with the same gases the same reactions could happen, but you're inside the balloon, so you can't see them.


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ProtoTypical
Member
Posts: 1777
From: Ontario Canada
Joined: 08-04-2010


Message 98 of 248 (600673)
01-16-2011 8:13 AM
Reply to: Message 94 by cavediver
01-14-2011 7:01 AM


Re: The void
As we have seen, space-time is itself a thing, and can quite happily exist with nothing else in it.

OK I have successfully cajoled the little grey cells into accepting this. Having done so, I can no longer imagine a 'place' where there is no space.

...the surface of the earth has no boundary but is finite.

I think I get what you mean by no boundary along the surface. Regardless of it's shape does the word 'surface' not denote a boundary? On the surface or not on the surface. Above or below the surface.

So we exist in a universe that can have a finite space surrounded by an infinite border and infinite space surrounded by a finite border. Am I the only one who has trouble with this?

I am not trying to be obtuse .


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Replies to this message:
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 Message 100 by Percy, posted 01-16-2011 9:41 AM ProtoTypical has acknowledged this reply
 Message 101 by cavediver, posted 01-16-2011 12:27 PM ProtoTypical has acknowledged this reply

  
cavediver
Member (Idle past 1724 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 99 of 248 (600675)
01-16-2011 8:45 AM
Reply to: Message 98 by ProtoTypical
01-16-2011 8:13 AM


Re: The void
Having done so, I can no longer imagine a 'place' where there is no space.

Good.

Regardless of it's shape does the word 'surface' not denote a boundary?

No, not in the mathematical sense of the word 'surface'. When I refer to a surface, the surface is all that exists - there is no above or below. So the surface of the Earth is a 2-dimensional world that is finite but has no boundary. We call it a 2-sphere. If you are a 2d creature constrained to live in this 2-sphere, you can move forwards/backwards and left/right. If you go far enough you will arrive back where you started from without any deviation from your straight path.

The solid Earth is a called 3-ball - it is finite and bounded, and it is bounded by the 2-sphere surface.

A 3-sphere is a 3-dimensional space that is finite and unbounded. It is very difficult to visualise as we cannot build one in space. But if you lived in one, you could move in all three dimensions, and again, if you go far enough you will arrive back where you started from without any deviation from your straight path.

Just to add, a 1-sphere is a 1-dimensional finite unbounded space that similarly loops back on itself. We call them circles. The interior of the circle is the finite bounded 2-ball, or 2-disc. And again, the boundary of the 2-ball is the 1-sphere (i.e. the boundary of a disc is a circle)

So we exist in a universe that can have a finite space surrounded by an infinite border and infinite space surrounded by a finite border.

No! The Universe can be either finite or infinite, and it is without boundary. It could be infinite in all three spatial dimensions, in which case there is obviously no boundary, or it could be finite in all three spatial dimensions but wrapped into a 3-sphere - again, no boundary. It could even be wrapped up into a 3-torus, or something even more exotic, but in each case it is finite with *no* boundary.

Now, there could be boundaries where the Universe as we know it merges into something else, and we consider this in highly speculative theoretical physics... but that's for another day.


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Percy
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Posts: 18312
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.9


Message 100 of 248 (600679)
01-16-2011 9:41 AM
Reply to: Message 98 by ProtoTypical
01-16-2011 8:13 AM


Re: The void
Dogmafood writes:

I think I get what you mean by no boundary along the surface. Regardless of it's shape does the word 'surface' not denote a boundary? On the surface or not on the surface. Above or below the surface.

Yes, the surface of the sphere represents a boundary between the inside and the outside of the sphere, but the analogy is between space and the surface of the sphere itself. You can travel infinite distances along the surface of a sphere and never reach any boundary. If space is unbounded then you can travel infinite distances in space and never reach any boundary.

--Percy


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cavediver
Member (Idle past 1724 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 101 of 248 (600685)
01-16-2011 12:27 PM
Reply to: Message 98 by ProtoTypical
01-16-2011 8:13 AM


Re: The void
Dogmafood writes:

Regardless of it's shape does the word 'surface' not denote a boundary? On the surface or not on the surface. Above or below the surface.

cd writes:

No, not in the mathematical sense of the word 'surface'. When I refer to a surface, the surface is all that exists - there is no above or below.

Percy writes:

Yes, the surface of the sphere represents a boundary between the inside and the outside of the sphere

Typical!

So to clear up the controvercy, Percy is quite correct in that the surface of the sphere (2-sphere) *is* a boundary to the inside and outside of the sphere (3-ball).

BUT we can have the 2-sphere quite independent of any notion of there being a 3-ball to which it would be a boundary. In our everyday experience, this is not possible. Every 2-sphere has an "inside" - but mathematically, and when we are talking about the geometry/topology of space-time, this need not be the case.

AND you were actually asking the more general question of whether a general surface is a boundary between that "above" and that "below". In this case, we can have a finite unbounded 2-dimensional surface that does not form a boundary between an inside and an outside of a 3-dimensional space! This is the famous Klein Bottle, whose inside and outside are joined, yet there is no break in the bottle, no opening... imagine a surreally twisted sphere that somehow manages to join its inside to its outside without any break in the sphere! This is another situation where we cannot actually construct a real Klein Bottle in the boring flat 3d space in which we live.


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 Message 98 by ProtoTypical, posted 01-16-2011 8:13 AM ProtoTypical has acknowledged this reply

Replies to this message:
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zi ko
Member (Idle past 1700 days)
Posts: 578
Joined: 01-18-2011


Message 102 of 248 (601379)
01-20-2011 6:44 AM
Reply to: Message 1 by Calypso
01-29-2010 10:24 PM


good idea

{I haven't a clue of why this was posted, but don't reply to it - Adminnemooseus}

Edited by Adminnemooseus, : Off-topic banner etc.


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NoNukes
Inactive Member


Message 103 of 248 (603822)
02-07-2011 8:55 PM
Reply to: Message 101 by cavediver
01-16-2011 12:27 PM


Re: The void
cavediver writes:

Every 2-sphere has an "inside" - but mathematically, and when we are talking about the geometry/topology of space-time, this need not be the case.

Perhaps a key thing to remember that the 2-sphere represents a two dimensional curved space. An extra dimension that would move you within or without the sphere is not perceptible to a 2-dimensional being. I wouldn't say that a 2-sphere has an inside.

In a flat two dimensional space, it's easier for most folks to accept that questions about what's going on above and below the flat plane have no meaning. You have to treat the 2-sphere in a similar fashion.

Edited by NoNukes, : No reason given.


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Replies to this message:
 Message 104 by cavediver, posted 02-08-2011 6:24 AM NoNukes has responded

  
cavediver
Member (Idle past 1724 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 104 of 248 (603842)
02-08-2011 6:24 AM
Reply to: Message 103 by NoNukes
02-07-2011 8:55 PM


Re: The void
I wouldn't say that a 2-sphere has an inside.

Nor would I except when you quote-mine me:

cavediver writes:

In our everyday experience, this is not possible. Every 2-sphere has an "inside"

Admittedly, there should have been a colon there, not a full stop. And 2-sphere should be in quotes.


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NoNukes
Inactive Member


Message 105 of 248 (603864)
02-08-2011 11:51 AM
Reply to: Message 104 by cavediver
02-08-2011 6:24 AM


Re: The void
"Nor would I except when you quote-mine me"

It wasn't meant to be a quote mine. I just wanted to help others who are having trouble understanding what a two-sphere is.

Edited by NoNukes, : Lighten up the tone a bit.


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