Finite universe [Archive] - Physics Forums

Distant

Mar30-06, 02:33 PM

Indeed it is difficult to imagine a finite Universe. It is much easier to imagine what it must have been like to live in a time before it was known that the Earth was round and that gravity kept us all from falling off the surface. In such a time a similar question to the one of the finite Universe was posed about the surface of the Earth. After all, we can see that the surface extends to the horizon in all directions. If we walk towards the horizon then the limit of the horizon moves with us and we can see how the surface extends further. So surely there can be only two possibilities. Either the surface extends on, forever, and if we carried on walking towards the horizon we would forever encounter new lands, or the surface if somehow ‘bounded’. Maybe we would reach some solid impenetrable wall through which we cannot pass – or maybe we would fall off the edge! (to where exactly wasn’t clear!). Of course, sea voyages set out to investigate the truth of the matter and I am not aware of them encountering either of these problems.

Although we may now view such thoughts in a rather patronising manner, without an understanding of the concepts of gravity and the spherical planet they are natural and logical questions. The spherical shape of the Earth ‘squares the circle’. It does not have a bounded edge to its surface, but it is not infinite – magic! (of a sort).

It required new (rather none intuitive) concepts to understand this problem. We are generally not aware of the curvature of the Earth. The planet is too big and we move too slowly to notice it. It would have been hard to convince to old “flat Earthists” that people living in a far off continent were, in effect, “upside-down” relative us!

Now, back to the Universe. Physicists tell me that the 3 dimensions of space are not the whole story. Time itself can be treated as another dimensions to describe something they call “spacetime”. Just as we once had an inability to notice (or comprehend) the curvature of the earth (nowadays we can view photos from space easily portraying this) we ‘similarly’ have an inability to notice or comprehend the curvature of this spacetime. Trying not be be a modern day equivalent of a “flat Earthist” we may choose to accept the word (and mathematics and experimental evidence!) of the physicists on this point. The point being is that it is postulated that spacetime if also curved, like the Earth is in 3 dimensions in order to produce a 4 dimensional spacetime Universe that is neither bounded nor infinite.

I fear that a more ‘natural’ understanding of such a ‘closed’ Universe, in the same way as we understand and experience a 3 dimensional ‘closed’ sphere, may not be possible. Maybe because our brains are not set up to work in 4 dimensional spacetime.

However unsatisfying this explanation maybe to the none physicist like myself, it surely surpasses the cosmological equivalent of the brick wall at the edge of the Universe, or indeed ‘falling over the edge’!
Ahhhhhhhh!…………

wolram

Mar30-06, 03:03 PM

A warm welcomb Distant, it all ways gives me a glow inside when people
answer my some times inane questions, your anology with the flat earthers
is good, but when it comes down to all there is, my mind just can not cope,
i try to understand, but some times these theories are just so unintuitive.

marcus

Mar30-06, 04:15 PM

if you keep telling yourself it is unintuitive you will make it worse.

do a series of "analogy pushups"

start by thinking of yourself as a 1D being living on a straight line
who imagines adding a "point at infinity" to his world, an extra point that fills the gap between + oo and - oo

so that if he goes faster and faster to the east he eventually comes whizzing in from the west

and he doesnt believe this is real, it is just an abstract mathematical idea for him

he has INVENTED THE CIRCLE, never having seen one, as a mathematical idea.

then 1000 years later the 1D astronomers uncover evidence in the CMB that their actually is a circularity of the universe. they discover that what was just a math idea is actually REAL and they are left scratching their onedimensional heads.
====================

push up to the next level analogy, think that you are a 2D being living in a flat plane, or one that looks flat to you. being an abstract thinker you imagine that there is a "point at infinity" so that if you go racing off in a straight line in any direction you will eventually come zooming in from the opposite direction

you have INVENTED THE MATHEMATICAL IDEA OF THE SPHERE as best as you can imagine it with your limited 2D wits.
it is like you are at the south pole and of the earth and it seems like an infinite flat plane, and the point at infinity is the north pole. so any direction you go in, departing from south pole, you eventully return from the opposite direction.

and maybe years later they discover that this idea of a sphere is REAL and actually how nature is.
=====================

push up to the next level analogy, now you are a 3D being living in a regular square-angle normal euclidean 3D space, analogous to the 2D flat plane.........and you imagine a "point at infinity" is added to your 3D space so that if you go off in a straight line in any direction then eventually after a long enough time you come back from the opposite direction.....
you have done something mathematically creative: you have INVENTED THE SOCALLED "THREESPHERE"

and maybe after hundreds of years the astronomers could supply evidence that what you thought was regular 3D space actually was a threesphere all along. All that time you were living in a threesphere, which you thought was a mere abstract concept.
========================

technically the ordinary sphere----the surface of a balloon---can be called a TWOSPHERE because the local neighborhood of a point looks like a normal flat 2D plane

and a circle or a ring could be called a ONESPHERE because the local nbd of a point looks like a bit of an approximately straight line

so all we are doing is imagining this kind of thing with the dimension jacked up, to get a threesphere

and anyway, Wolram, there are SEVERAL kinds of finite 3D spaces possible------the threesphere is not the only one. there are a whole bunch, just like in the 2D situation you can have donut shapes with more than one hole. But this does not matter. It is enough to just imagine one possible spatially finite 3D thing----and the threesphere is good enough.

Before falling asleep every night, try to imagine that you live in a threesphere, and if you shine a light off in one direction then that same beam of light will eventually get back to you from the opposite. (unless the poor lightbeam has been frustrated by having the space go and expand faster than it can cope with but expansion is another business, ignore that for the while)

wolram

Mar30-06, 04:36 PM

Thankyou very much Marcus, what you say in words makes perfect sense,
but to form an image in ones mind is much harder, maybe i am to stupid, i wish i could understand.

marcus

Mar30-06, 05:59 PM

it makes it worse to keep supposing that one is stupid---one is a human and that involves certain brain limitations which one tries cheerfully to overcome.

try to imagine what it would be like to BE IN a certain space

don't try to imagine what it would look like to a God who is somehow on the outside of it.

we are not asked to imagine what it would look like to an higherdimensional being outside of space

just get a feel for what to expect if you are a 3D creature, which we all are, living in a threesphere

all it means, really, is that if you send a lite-beam off in some direction out in front eventually it will come back from behind you

as 2D creatures living on a Twosphere (the surface of the earth) we are ALREADY USED TO THAT kind of behavior-----of being able to head off in some direction and eventually get back to the same place having gone around

so the analog (3D "flat" space with a point at infinity added) can't be so hard to imagine what it would be like to live in

(forget about God's point of view, just imagine living in it)

Chronos

Mar31-06, 01:46 AM

While a spatial finite universe is difficult to imagine, a temporally finite universe is less difficult. It is, for me, easy to picture a universe where you are both at the center and the edge due to the finite speed of light.

wolram

Mar31-06, 04:38 AM

Thanks Marcus, i do have a picture now, it may be a little fuzzy, almost
abstract, but at least i can think about it now.

Silverbackman

Apr1-06, 05:04 AM

Hmmm, so I guess it is impossible to imagine looking a threesphere like we look at a balloon or a ball. Damn I hate being human.:mad:

Then again I know more than a being from a dot, circle, and twosphere world. Is it possible for a foursphere, fivesphere, ect. ect. till infinite? Of course we can't imagine these other spatial dimensions, similar to how a 2D being wouldn't be able to imagine a 3D world or twospere.

But doesn't the known curvature of the universe suggest that we live in a flat universe and not a saddle or sphere universe? If so then how can we be living in a threespere?

SpaceTiger

Apr1-06, 01:15 PM

Then again I know more than a being from a dot, circle, and twosphere world. Is it possible for a foursphere, fivesphere, ect. ect. till infinite?

I don't understand the question...

But doesn't the known curvature of the universe suggest that we live in a flat universe and not a saddle or sphere universe? If so then how can we be living in a threespere?

Measurements of flatness are local. If inflation occurred, then the universe will be much, much larger than the region of space we can observe and, regardless of its true large-scale geometry, it will appear flat to our instruments. It's basically the same reason the ancients thought the earth was flat -- they could only see a very small part of it.

If inflation had not occurred, however, this wouldn't be the case and we should, in principle, be able to measure the curvature of the entire universe.

wolram

Apr1-06, 01:53 PM

I have an idea to call my image the, ( frustrated boomerang), curved space
with expasion.

VikingF

Apr4-06, 10:58 AM

I don't understand the question...

I think he wondered how many dimensions that can possibly exist. If there may be "infinitely many" dimensions... (1D,2D,3D,4D,....,?D). :smile:

-Job-

Apr5-06, 01:17 AM

One second though. The possibility that we live in continuous unbounded universe, the equivalent of a 4D sphere follows rationally and is more plausible than a finite universe or an infinite universe that does not "wrap-around". But regardless, if we live in a 4D sphere, then this 4D sphere is in 4D space. How is this 4D space then bounded? Is it infinite or finite? Does it wrap around? The alternative is that we live in a 4D sphere which does not reside in space, but then the notion of dimensions should not apply, and it's not a 4D surface at all.

Silverbackman

May4-06, 04:48 AM

I have an idea to call my image the, ( frustrated boomerang), curved space
with expasion.

You mean torus?

I think he wondered how many dimensions that can possibly exist. If there may be "infinitely many" dimensions... (1D,2D,3D,4D,....,?D).

Yea, I wonder what a eightsphere universe would look like.:eek: :eek: :eek: Or how about a 1,678,489,986sphere?:surprised :surprised :surprised

Flatland

May4-06, 05:32 PM

I actually have a problem imagining an infinite universe. And a universe with an infinite dimensions? you wouldn't be able to go anywhere.

setAI

May4-06, 05:59 PM

I conjecture that it is possible for a finite AND flat universe without the topology of a torus or similar form- in fact it can have ANY arbitrary topology as long as it is closed-

how? it is a natural result of computational /category theories and some forms of LQG where the metric of spacetime itself emerges from relationships- for instance the universe can be decribed as a 2-dimensional lattice of 2in/2out quantum logic gates- one could construct such a lattice of quantum logic gates on the surface of a sphere- or any other closed shape- yet the topology of the emergent spacetime metric could compute a FLAT spacetime that wraps around-

consider a classical computational analog: the game Asteroids- where the ship flies straight but wraps around when it hits the edge of the screen- the virtual space of the ship is flat- but the edges are connected in the software- so the virtual space is finite yet unbounded

VikingF

May4-06, 06:06 PM

Yea, I wonder what a eightsphere universe would look like.:eek: :eek: :eek: Or how about a 1,678,489,986sphere?:surprised :surprised :surprised

Yeah... Me too! :confused: :tongue:

According to String theory, there exist 10 dimensions, and M-theory says that there exist 11.

Silverbackman

May5-06, 02:16 AM

Yeah... Me too! :confused: :tongue:

According to String theory, there exist 10 dimensions, and M-theory says that there exist 11.

Yea but they say those dimensions may just exist. It doesn't have anything to do with the universe being a tensphere or elevensphere I think. Or does it?:confused: Actually it probably does because I assume 10 or 11 dimensions cannot exist unless is within some sort of nsphere (or something like an nsphere).

If we do live in a threesphere only that would mean there are four spatial dimensions and one dimension of time. That sounds pretty aesthetically perfect considering 5 is a "perfect" number. Both 5 and 10 seem like aesthetically perfect because of their place on the number line. Why an omnipotent God or even randomness of Nature would pick 4, 7, or 11 as the "official" number of one of the most important aspects of our universe is beyond me.:uhh:

Garth

May5-06, 02:28 AM

Why an omnipotent God or even randomness of Nature would pick 4, 7, or 11 as the "official" number of one of the most important aspects of our universe is beyond me.:uhh:
There is an anthroopic argument as to why we are living in a 3D + time universe.

Time is necessary for process, we exist and evolution of complex beings requires process, therefore time.

In a 1D or 2D spatial universe there is not enough topological freedom for complex organic molecules to operate, the 3D geometry is important for proteins etc. to 'do their stuff'. Hence we cannot exist in a spatial 1D or 2D universe.

Keplerian orbits are unstable in a spatially 4D or higher universe. The Newtonian law of gravity becomes F = GMm/r^3 in a 4D universe for example and the Earth would spiral into or away from the Sun. Hence we cannot exist in a spatial 4D or higher universe.

We exist: therefore our universe has 3 space D + time. :smile:

Garth

VikingF

May5-06, 04:10 AM

Yea but they say those dimensions may just exist. It doesn't have anything to do with the universe being a tensphere or elevensphere I think. Or does it?:confused: Actually it probably does because I assume 10 or 11 dimensions cannot exist unless is within some sort of nsphere (or something like an nsphere).

No, if I have not misunderstood it completely, String theory says that our universe is one of infinitely many three dimensional (or four with time) universes in an infinite ten- or eleven dimensional multiverse.

It's like the drawing on the piece of paper in front of me is two dimensional in a four dimensional universe. :smile:

Garth

May5-06, 04:39 AM

The normal understanding is to ask: "If there are more than 3 spatial dimensions why do we not observe them?" The answer given in string theory is that the extra dimensions are 'rolled' up like a 2D sheet of paper rolled up into a 'straw' with length and very little width. The extra widths are too small to observe normally, and do not affect dynamics such as Keplerian orbits as in my post #21 above, but may be observed microscopically, such as by minute changes in Newtonian gravity at very small ranges.

Garth

Silverbackman

May5-06, 10:24 PM

There is an anthroopic argument as to why we are living in a 3D + time universe.

Time is necessary for process, we exist and evolution of complex beings requires process, therefore time.

In a 1D or 2D spatial universe there is not enough topological freedom for complex organic molecules to operate, the 3D geometry is important for proteins etc. to 'do their stuff'. Hence we cannot exist in a spatial 1D or 2D universe.

Keplerian orbits are unstable in a spatially 4D or higher universe. The Newtonian law of gravity becomes F = GMm/r^3 in a 4D universe for example and the Earth would spiral into or away from the Sun. Hence we cannot exist in a spatial 4D or higher universe.

We exist: therefore our universe has 3 space D + time. :smile:

Garth

This maybe true for our universe but I'm sure a 1D or 2D universe may have different laws of nature. In these universes organic molecules may not be needed to create matter that can become conscious. So anything maybe possible even if it is beyond our current reasoning. As human beings we can't imagine how it would be to live in a 2D or 6D universe. But this all sort of enters the realm of philosophy. There is no proof either way one whether conscious beings can evolve in a 1D or 2D universe. We can't exist in these universes but perhaps in another universe matter can adapt to whatever dimension limitations it may have.

If our universe cannot be spatially 4D, how can we live in a finite threesphere? Wouldn't an extra dimension be needed in order for our 3D universe to curve into a round shape where if you go in one direction that you will come back in another direction?

It is similar to the notion of a 1D being living in a round universe. To him reality is only on the X-axis but if his universe is round then his universe is actually a circle. Circles are 2D. Perhaps the some total of our 3 known spatial dimensions add up to a 4th spatial dimension when curving.

No, if I have not misunderstood it completely, String theory says that our universe is one of infinitely many three dimensional (or four with time) universes in an infinite ten- or eleven dimensional multiverse.

It's like the drawing on the piece of paper in front of me is two dimensional in a four dimensional universe.

Yea but how can other universes exist in these other dimensions that are rolled up. And how do we there is an infinite amount in only a 10D or 11D universe.

Balence

Jun9-06, 03:35 PM

Any shape still has space out side of it, therefore the universe is still infinite. As far as extra dimensions most were created because the mathematics in a theory did not add up so they made alternet dimensions to prove their theory right, they have no proof for these dimensions (besides the faulty equations that gave birth to them) and there are 3 spacial dimensions, all of which are abstract. The dimension of time isnt a dimension on dictionary terms but since it is used to measure can be qualified as a dimension. Any thing that exsists must have and can only have length, width, height, and a place in time. Time is also abstract.

SpaceTiger

Jun11-06, 02:15 PM

Any shape still has space out side of it, therefore the universe is still infinite.

There's no necessity for something "outside" of a finite universe. It need not be embedded in another space to reproduce what we observe.

Aki

Jun11-06, 03:08 PM

and anyway, Wolram, there are SEVERAL kinds of finite 3D spaces possible------the threesphere is not the only one. there are a whole bunch, just like in the 2D situation you can have donut shapes with more than one hole. But this does not matter. It is enough to just imagine one possible spatially finite 3D thing----and the threesphere is good enough.

So does the shape of our universe has anything to do with the Calabi-Yau theory?

string querry

Jun12-06, 08:55 AM

remember we are just talking SPATIAL finite

timewise it can still go on forever

what is the problem imagining a spatially finite universe?

it is the old "surface of a balloon" thing except the surface of a balloon is only 2D and you have to think of what would be the 3D analog of that.

the surface of the ballon is 2D, yes, but why do the theorist always use the surface of the ballon. Why not the volume of the ballon, such as a ballon fuill of gel. Something in the volume of the ballon wil still expand away from anything else in the volume, assuming the the ballon is filled with more gel from a central point of origin, and also discounting gravity/and velocity ie: filling the ballon in a zero-G environment.

string querry

Jun12-06, 09:02 AM

I conjecture that it is possible for a finite AND flat universe without the topology of a torus or similar form- in fact it can have ANY arbitrary topology as long as it is closed-
...one could construct such a lattice of quantum logic gates on the surface of a sphere- or any other closed shape- yet the topology of the emergent spacetime metric could compute a FLAT spacetime that wraps around-

consider a classical computational analog: the game Asteroids- where the ship flies straight but wraps around when it hits the edge of the screen- the virtual space of the ship is flat- but the edges are connected in the software- so the virtual space is finite yet unbounded

Exaclty what I've been thinking for years, but nobody on any of the plethora of Education programs every metnions it. I think the closest I've come to finding that idea was a rather bogus documentary where the "expert" decide that were are all living in a "Matrix" virtual universe. Maybe his right, but that's more of a religion than science...but the basic idea of any point in a curvature having flat properties relative to other points if the properties with the curvature are natural to that state--i agree that is possible, but I don't have the math skills to prove it, and the people that do have the skills can't agree with each other and call each other morons, so such ideas are far ahead of their time and currently trapped in science fiction.

marcus

Jun12-06, 10:59 AM

the surface of the ballon is 2D, yes, but why do the theorist always use the surface of the ballon. Why not the volume of the ballon, such as a ballon fuill of gel...

hello querry,

this is a question you should ask directly to cosmology theorists!
fortunately we have some here at PF. Garth is an active cosmologist (I think with a different day job). SpaceTiger is a PhD student in Cosmology at princeton. He could already have his PhD now, since it is Summer and the semester is over.

I forget who else. Anyway I expect they would be happy to tell you why working cosmologists always use the surface of the balloon (notice that the "sphere" has no edges, no boundary, a creature living in it would never need to encounter a barrier or a higher dimension region, which might have some relevance to your question)
but I ALSO expect that they would be happy for you to believe whatever you want about the universe!

You can believe it is a balloon full of gel if that is what you like. I personally see no reason why you should feel obliged to get in contact with the mainstream professional cosmologist picture.

I guess I will pass on this question and let someone else explain the theorist's preference.

Garth

Jun12-06, 12:37 PM

the surface of the ballon is 2D, yes, but why do the theorist always use the surface of the ballon.
It is only a model to help people conceptualize the idea of spherical space.

3D space is a 'space-like' slice or 'foliation' of 4D space-time.

We cannot visualize 4 dimensions - at least I cannot - and therefore in order to get the idea across, and for students to 'see' what we are talking about, it is helpful to reduce the number of dimensions and suppress one of the space dimensions.

Thus a 3D spherical surface becomes the 2D surface of a sphere - i.e. its surface and not its interior.

Reduce one more space dimension and the 2D spherical surface becomes the 1D line of a circle.

In each case 1D, 2D or 3D these hypersurfaces (http://en.wiktionary.org/wiki/hypersurface) share the common property of being finite in extent yet unbounded.

Theorists do not always use the surface of a balloon, which is a model of spherical space.

Space can also be flat (the surface of a flat sheet of paper) or hyperbolic (the saddle point of a saddle). These spaces share the common property of being infinite in extent yet unbounded.

Although we visualize these spaces 'from outside' it is also possible to test to see what kind of space we are living in by its intrinsic geometry. Euclidean geometry only holds for a flat space. A triangle's interior angles sum to 1800. In a spherical space a triangle's interior angles sum to > 1800, and in a hyperbolic space they sum to < 1800, for example.

I hope this helps.

Garth

string querry

Jun12-06, 01:32 PM

It is only a model to help people conceptualize the idea of spherical space.

3D space is a 'space-like' slice or 'foliation' of 4D space-time.

We cannot visualize 4 dimensions - at least I cannot - and therefore in order to get the idea across, and for students to 'see' what we are talking about, it is helpful to reduce the number of dimensions and suppress one of the space dimensions...
A triangle's interior angles sum to 1800. In a spherical space a triangle's interior angles sum to > 1800, and in a hyperbolic space they sum to < 1800, for example.

I hope this helps.

Garth

THanks! Incredible explanation!

One question, from another thread with no asnwer yet:

Am I stretching the accuracy of the illustration if I infer from it that the "shape" of space/time is spherical (I do not mean in terms of three dimensional space, I know that the universe is not an orb, but in the sense that the furthest point from any given point has the same differential as the differntial between any other given point and the point furthest from it--is that making any sense? I'm trying to define the shape with as little 3Dness as possible) Is that extracting something from the illustration after the point that it breaks down. The reason I ask is that, if so, regardless of any expansion or contraction of the universe, the "shape" would not change and wouldn't all points of space time maintain the same ratios of distance/differencial from each other. Also, would this mean that the universe would have no end, center or edges, just as the surface of a sphere has no center, end or edges?

scarecrow

Jun13-06, 01:01 AM

wolram

Jun13-06, 01:07 AM

Cossmology needs occams razor, not pandoras box.:smile:

Thor

Jun13-06, 06:58 PM

How do you imagine a finite universe ? i find it very difficult.
If the universe was finite then for any given point there must exist another point within a finite distance at which motion in any direction will not increase the distance between the two.

Bend it, twist it, tie it in a knot, a finite Universe is hogwash.

SpaceTiger

Jun13-06, 07:03 PM

If the universe was finite then for any given point there must exist another point within a finite distance at which motion in any direction will not increase the distance between the two.

Not if that point is itself moving! Think again about the expanding balloon analogy. Any two points on the surface of the balloon are receding from one another as the balloon expands.

Chronos

Jun14-06, 01:14 AM

The FRW model pretty much excludes that concept, Thor. I do not understand your point. Are you conserving energy, or ignoring it? What I do see is an effort to introduce an Arpian twist into this discussion.

Garth

Jun14-06, 02:03 AM

If the universe was finite then for any given point there must exist another point within a finite distance at which motion in any direction will not increase the distance between the two.

Bend it, twist it, tie it in a knot, a finite Universe is hogwash.
Are you considering spherical space?

In which case your two points would be each other's antipodes.
In a static universe your statement would be true, just as on the Earth's surface any direction moved from the South Pole takes you closer to the North Pole, what is hogwash about that?

In an expanding universe these distances would be increasing, but still the distance between the two antipodean points would be a maximum of all distances in the universe at any one cosmological epoch.

Garth

Balence

Jun17-06, 02:44 AM

There's no necessity for something "outside" of a finite universe. It need not be embedded in another space to reproduce what we observe.
Your absolutly right, it doesnt have to be something. It could be nothing, empty space, going on infinitly. Our observations are limited by our finite knowledge.

Balence

Jun17-06, 03:02 AM

The universe we live in is probably like a membrane (finite of course, but expanding nonetheless)...like an expanding balloon. But then you ask, "what's outside the membrane?" Well, my answer would be the higher dimensional universes. Overall, it would seem that it would be infinite, but then we'd have to go into religion.
Please define higher dimension. I know the proper definition of dimension is: A measure of spatial extent, expecially width, heigth, or length. Its not feasable for their to be any further dimensions, unless you count time, which isnt spatial but has a relationship to distance none the less. As from what Ive learned of many of the theorys of extra dimensions, the extra dimensions are mathimatical fillers for theory equations that did not make sense. (string theory for example) Like me saying two plus two equals five because of the other dimension. Also how is an infinite universe religion? Higher dimensional universes sounds much more religious. Wheres occams razer when you need it?

SpaceTiger

Jun17-06, 12:25 PM

Your absolutly right, it doesnt have to be something. It could be nothing, empty space, going on infinitly.

In GR and QFT, "empty space" is something. I'm saying that there need not be anything other than the universe we observe and that this universe could be finite in size.

Balence

Jun17-06, 02:44 PM

In GR and QFT, "empty space" is something. I'm saying that there need not be anything other than the universe we observe and that this universe could be finite in size.
There either has to be something or nothing out side the observable universe, if theres nothing, it stretches on infinitly having the potential to be filled by something. Also nothing must have the potential to produce something, or we will never find a complete answer to the beggining of the universe, thus the nothing out side our obserable universe has or will give way to new matter or energy. As nothing stretches on infinitly given infinite time mean that probally theres "stuff" out side our observable universe and its impossible to know what because its unubservable. Much like trying to see beyond the horizon.

SpaceTiger

Jun17-06, 03:13 PM

There either has to be something or nothing out side the observable universe, if theres nothing, it stretches on infinitly having the potential to be filled by something.

Nothing is just nothing, it doesn't stretch out infinitely and it's not the same as empty space. The concept of "outside" isn't even necessary here. The universe, by definition is all that there is. It doesn't make sense to talk about anything outside of it and there's no reason that it can't be finite.

As nothing stretches on infinitly given infinite time mean that probally theres "stuff" out side our observable universe and its impossible to know what because its unubservable.

Most current theories do suggest that there is stuff outside of our observable universe, but when we talk about a finite vs. infinite universe, we're usually talking about the entire universe, even that which is unobservable.

This will be hard for you to understand without a little background in general relativity. You might want to browse the "Special and General Relativity" forum a bit.

Balence

Jun18-06, 07:28 PM

Anything that is finite has boundries. It would seem logicaly that this conflicts with the universe being all there is, as that definition should include whats inside, outside, and the boundries themselves. Even with the curvature of space creating a finite boundry for humans or any other form of matter or energy to travel, does not make the universe finite. Perhaps the limitations due spacecurvature is whats ment by the term universe, and im taking it a bit literally. Though I still believe an "outside" would be more than relevant and logical.

Garth

Jun19-06, 01:55 AM

Anything that is finite has boundries.
Not true - otherwise sailors would still be worried about 'falling off the end of the world'.

Garth

Balence

Jun19-06, 07:19 AM

Not true - otherwise sailors would still be worried about 'falling off the end of the world'.

Garth
Sailors never were astronauts though, "the world" is still finite and still has its boundries which have been crossed.

setAI

Jun19-06, 12:37 PM

VikingF

Jun20-06, 04:37 PM

In the paper "Philosophical Implications of Inflationary Cosmology" by Joshua Knobe, Ken D. Olum and Alexander Vilenkin, there is a theory saying that the universe actually is infinite (see ch 2.2). I am no cosmologist, but the way I understand it, this is somehow a consequence of the inflation theory. I don't quite understand this, because I thought it almost was a "proven fact" that our universe is finite, and not infinite...? :confused:

Anyway, here is the paper:
http://arxiv.org/pdf/physics/0302071

SpaceTiger

Jun21-06, 05:52 PM

In the paper "Philosophical Implications of Inflationary Cosmology" by Joshua Knobe, Ken D. Olum and Alexander Vilenkin, there is a theory saying that the universe actually is infinite (see ch 2.2).

You might want to check out this paper by Linde (a big name in inflationary theory):

http://arxiv.org/abs/hep-th/0408164

People often assume, for simplicity, that the universe would have trivial topology. If this is not the case (and Linde's paper suggests that it shouldn't be), then an inflationary universe can be finite.

Keep in mind that much of this stuff is a long way from experimental testing -- science is probably a long way from providing a definitive answer to the finite/infinite question.

Chronos

Jun21-06, 11:20 PM

The betting window is still open on the finite vs infinite universe. The universe may be finite, but appears to be fairly huge. Some additional papers worth considering:

CMB Anisotropy of the Poincare Dodecahedron
http://www.arxiv.org/abs/astro-ph/0412569

A Cosmic Hall of Mirrors
http://www.arxiv.org/abs/astro-ph/0509171

Extending the WMAP Bound on the Size of the Universe
http://www.arxiv.org/abs/astro-ph/0604616

Balence

Jun25-06, 05:50 PM

ultimately I think that the very idea of a universe finite or infinite with a 'boundary' is wrong-headed- a thing like a universe emerges from the relationships of a causal network- the metrics of distance/duration are established by the relationships of the elements in the network- a boundary is only an arbitrary concept of where one can fit the abstract map of such a causal set in an imaginary mathematical space- but there is no reason for that map-space to exist in any physical way- the elements and events that arise in a causal network don't connect to any kind of outside boundary- causality and the metrics of space and time that emerge from it propagate locally through the elements/events in the network ONLY- there is no spatial/temporal analog of a 'boundary' to be fenced-in by-

given this- my thinking is that emergent systems of relationships that arise form causal networks -like universes [whether they are infinite or finite]- are boundary invariant
Theories for finite univeres I've researched have a shape whether its a hypersphere or a dodecahedron and a way for it to seem boundless whether its mirrors or traveling so far you return to where you started. A good example I feel is a pac man game (no offense). It has a shape and is boundless for pac man. As pac man travels he notices he always returns to his starting point even if traveling in a strait line, he correctly concludes that the curvature of digital space must be the cause. He also assumes the universe must be finite. However one day he tries an experiment. He finds a large dot and specialy marks it then travels in a strait line counting all the small dots till he returns to his large dot. He counted 1000 dots so he can rightfully assume that the distance across his universe is 1000 dots. He then repeats the experiment with other large dots and compares his finding thus being able to pin point where the warp occurs, or where the boundry of his possible travels. He can then do a thought experiment in which he travels 10,000 dots from the large one with out traveling through the warped space. He then can consider the possibility of an infinite universe. My point is that a finite universe by nature has boundries. In the end I come to the same conclusion of universes being boundry invairiable and since a finite universe must have a boundry I personaly conclude that the universe must be infinite. Additionaly the hyperspere uses multiple dimensions to prove it correct. For one pac man is not 2D he is made of pixels which are 3D, they have length width and height regardless of how small. Second its impossible to conceive these dimensions because we are 3D (the theories own argument) therefore it seems scientificly unsound.

Balence

Jun25-06, 05:59 PM

I don't quite understand this, because I thought it almost was a "proven fact" that our universe is finite, and not infinite...? :confused:

Finite universes is taught as almost proven fact by many teachers and professers. The idea of a finite universe is very comforting vs an infinite one because we can fully understand (over time) a finite universe. A infinite universe can have a large number of possible contradicting laws and is very chaotic thus limiting what we can hope to understand. Though I personaly believe over time we will find laws to explain the chaos. Additionaly history has shown man prefers to be as important as can be, an infinite universe makes us even smaller and more insignificant.

Balence

Jun25-06, 06:01 PM

Keep in mind that much of this stuff is a long way from experimental testing -- science is probably a long way from providing a definitive answer to the finite/infinite question.
I agree, only time will tell for sure. Hopefully though it will be rather soon so I can start my victory dance.

Teecher

Jun26-06, 12:40 AM

...He counted 1000 dots so he can rightfully assume that the distance across his universe is 1000 dots. He then repeats the experiment with other large dots and compares his finding thus being able to pin point where the warp occurs, or where the boundry of his possible travels.

Care to explain how Mr. Pac-Man made this last deduction?

SpaceTiger

Jun26-06, 01:53 AM

I agree, only time will tell for sure. Hopefully though it will be rather soon so I can start my victory dance.

Your ideas are not falsifiable and can't really be called science. Basically, it sounds like you're asserting that any self-contained finite universe must be embedded in a larger space (as per the "boundaries" you speak of). I disagree with you on philosophical grounds, but we can never disprove your assertions any more than we can disprove the existence of a "creator". If this infinite space you speak of is out of causal contact with our universe, then there's nothing we can do to detect it.

Balence

Jun26-06, 03:13 AM

Care to explain how Mr. Pac-Man made this last deduction?
He conveniently has a living space in which every straight line of dots going horizontaly have 1000. Conveniently each big dot is one small dot down and to the right of the first big dot. Conveniently the horizontal dots are equal to the vertical so both dimensions are 1000. Using the big dots as markers packman can create a map that would show a declining line of big dots slanting through the center of his finite space. From this he can conclude where the warp is. You can also try drawing it out on graph paper. If this doesnt work then he kept getting digispace sick and figured it must be that warped space. I really wanted to get to the point and wanted to get off pac man so I skiped how he might figure this out.

Balence

Jun26-06, 03:36 AM

Your ideas are not falsifiable and can't really be called science. Basically, it sounds like you're asserting that any self-contained finite universe must be embedded in a larger space (as per the "boundaries" you speak of). I disagree with you on philosophical grounds, but we can never disprove your assertions any more than we can disprove the existence of a "creator". If this infinite space you speak of is out of causal contact with our universe, then there's nothing we can do to detect it.
At this point my theory does loose scientific value due to the fact we can not currently detect this infinite space. However, many current finite theories have even less scientific value and are widely accepted as known truth despite the inability to properly test them thus making them even more unscientific. According to occams razor an infinite universe is more feasable than a finite one. I only assume one thing that is rational, and keep it simple. Finite theories assume alot, much of which is "inconcievable" to us, (irrational) have simular instances in history, (earth being in the center, spontaneous generation) finnaly, and coinciding with my last point, the idea is very alluring as the universe is more predictable if its finite. Additionaly there are several different finite universe theories out there. My point is that while infinite universe theory can be compared to theories of a "creator" its much more closer to compare "creator" with finite theories.

SpaceTiger

Jun26-06, 12:02 PM

He conveniently has a living space in which every straight line of dots going horizontaly have 1000. Conveniently each big dot is one small dot down and to the right of the first big dot. Conveniently the horizontal dots are equal to the vertical so both dimensions are 1000. Using the big dots as markers packman can create a map that would show a declining line of big dots slanting through the center of his finite space. From this he can conclude where the warp is.

How does he know where to put the big dots such that they pass through the center?

Let's try a simpler example to ensure that we're on the same page. Suppose Pac-Man is confined to one dimension (a line). You see him on the screen, moving along the line. From your point of view, he keeps moving to the edge of your screen until he reaches the "warp" point and then comes out the other side. But does this warp point have any significance to Pac-Man? On an initially unmarked line, is there any point along the line that is different from the other? No, from his point of view, it's just a line seeming to extend off infinitely in either direction. He can determine the size of his finite universe by simply marking a point and seeing how long it takes to come back to it. However, there's way for him to know if that point is on the edge or the center of your screen.

The situation is similar in 2-D. The initially unmarked landscape is just a plane seeming to go off inifinitely in all directions. He can mark any set of points that he likes, but there's no way for him to know where these points lie in relation to the center of your screen or the "warp", as you put it.

SpaceTiger

Jun26-06, 12:10 PM

At this point my theory does loose scientific value due to the fact we can not currently detect this infinite space.

We could never detect infinity to start with, but what's worse is that there is no hypothetical observation that could prove your theory wrong. You could always just say that we're out of causal contact with this extra universe.

However, many current finite theories have even less scientific value and are widely accepted as known truth despite the inability to properly test them thus making them even more unscientific.

All current scientific theories are hypothetically testable, but many are beyond the reach of current technology. Your theory is not falsifiable even in principle.

According to occams razor an infinite universe is more feasable than a finite one.

Actually, occam's razor says nothing about an infinite versus a finite universe. If, however, we discovered that the universe was finite, one could invoke occam's razor to support the case for a universe with no boundaries.

My point is that while infinite universe theory can be compared to theories of a "creator" its much more closer to compare "creator" with finite theories.

I think you've misunderstood. I'm not comparing infinite theories to theories of a creator, I'm comparing your "universe with boundaries" idea to that of a creator. Infinite universes are commonplace in mainstream science.

setAI

Jun26-06, 01:26 PM

an odd thing- you can in principle prove the universe is finite- if it is- but can you EVER prove or even know if it is infinite? I would think that locality makes it impossible even in principle-

SpaceTiger

Jun26-06, 01:38 PM

an odd thing- you can in principle prove the universe is finite- if it is- but can you EVER prove or even know if it is infinite? I would think that locality makes it impossible even in principle-

To the best of my knowledge, there's no way to prove (or even find evidence for) an infinite universe. However, a proper scientific model can still be disproven even if it predicts an infinite universe.

Intuitive

Jun26-06, 02:26 PM

Hi SpaceTiger.

My intuition would say that the Universe is infinite in diameter although I know it could never be proven so it would always remain a mystery, A Universe with infinite Super Galaxies that never end.

I tend to believe this because to my knowledge an edge has never been found and that Nature abhores a Vacuum and likes to fill it's space.

I wanted to ask if Scientist are steering more to the infinite Universe concept?

SpaceTiger

Jun26-06, 03:36 PM

A Universe with infinite Super Galaxies that never end.

Infinite Super Galaxies? Where is that coming from?

I tend to believe this because to my knowledge an edge has never been found

There is a definite "edge" to the observable universe, but right now there's no way to know how much lies beyond that.

and that Nature abhores a Vacuum and likes to fill it's space.

That's not really relevant, the question concerns the amount of space, not what fills it.

I wanted to ask if Scientist are steering more to the infinite Universe concept?

Not to my knowledge. I think the majority view is that the universe is much larger than we can currently observe, but it's still unclear how large.

Intuitive

Jun26-06, 03:59 PM

Hi SpaceTiger

Infinite Super Galaxies? Where is that coming from?

It was a general self belief only, I don't believe a vast void exists with nothing in it, Strictly empirical.

There is a definite "edge" to the observable universe, but right now there's no way to know how much lies beyond that.

Is Science saying that the observabale Universe is thinning out?
I never realized that Science had come that far as to see an edge, My apollogies if this is the case.

That's not really relevant, the question concerns the amount of space, not what fills it.

But doesn't the Universe follow the same rules as the rules of a Vacuum?

Not to my knowledge. I think the majority view is that the universe is much larger than we can currently observe, but it's still unclear how large.

I understand, Thanks.

P.S
I really do respect your knowledge and position in this forum, I do look up to you.

Balence

Jun27-06, 12:00 AM

How does he know where to put the big dots such that they pass through the center?

Let's try a simpler example to ensure that we're on the same page. Suppose Pac-Man is confined to one dimension (a line). You see him on the screen, moving along the line. From your point of view, he keeps moving to the edge of your screen until he reaches the "warp" point and then comes out the other side. But does this warp point have any significance to Pac-Man? On an initially unmarked line, is there any point along the line that is different from the other? No, from his point of view, it's just a line seeming to extend off infinitely in either direction. He can determine the size of his finite universe by simply marking a point and seeing how long it takes to come back to it. However, there's way for him to know if that point is on the edge or the center of your screen.

The situation is similar in 2-D. The initially unmarked landscape is just a plane seeming to go off inifinitely in all directions. He can mark any set of points that he likes, but there's no way for him to know where these points lie in relation to the center of your screen or the "warp", as you put it.
He doesnt place the big dots, theyre "convienently" placed. Pac man is still 3D, you cant see 1D with out the other two. If nothing else he kept getting space sick at the same point.

Balence

Jun27-06, 12:26 AM

We could never detect infinity to start with, but what's worse is that there is no hypothetical observation that could prove your theory wrong. You could always just say that we're out of causal contact with this extra universe.

My theory isnt falsifiable so far because I could pose the question of what lays beyond.

All current scientific theories are hypothetically testable, but many are beyond the reach of current technology. Your theory is not falsifiable even in principle.

Its based on principle.

Actually, occam's razor says nothing about an infinite versus a finite universe. If, however, we discovered that the universe was finite, one could invoke occam's razor to support the case for a universe with no boundaries.

A rule in science and philosophy stating that entities should not be multiplied needlessly. This rule is interpreted to mean that the simplest of two or more competing theories is preferable and that an explanation for unknown phenomena should first be attempted in terms of what is already known. Also called law of parsimony.

By deffinition occam razor doesnt directly state anything about infinite vs finite. However it applies to all theories of science and philosophy which include infinite vs finite. An infinite universe is much more simpler and goes by what has been observed for ages.

I think you've misunderstood. I'm not comparing infinite theories to theories of a creator, I'm comparing your "universe with boundaries" idea to that of a creator. Infinite universes are commonplace in mainstream science.

I did misunderstand. However the universe with boundaries is not my idea, it is the neccessity of a finite universe. Infinite universes is an oxymoron. If the term universe means all there is and it is infinite or even finite, there could never be more than one.

Balence

Jun27-06, 12:28 AM

To the best of my knowledge, there's no way to prove (or even find evidence for) an infinite universe. However, a proper scientific model can still be disproven even if it predicts an infinite universe.
I guess logic and thought experiments dont count?

Balence

Jun27-06, 12:30 AM

an odd thing- you can in principle prove the universe is finite- if it is- but can you EVER prove or even know if it is infinite? I would think that locality makes it impossible even in principle-
You cant prove a finite universe by principle. You cant disprove an infinite one by principle.

SpaceTiger

Jun27-06, 02:55 AM

It was a general self belief only, I don't believe a vast void exists with nothing in it, Strictly empirical.

Empirical implies that it has been observed...and it hasn't. In fact, galaxies never get any bigger than a hundred or so kiloparsecs (an observational fact). Larger gravitationally bound objects are known as galaxy clusters.

Is Science saying that the observabale Universe is thinning out?

No, the edge of the observable universe is the maximum distance light could have travelled since the beginning of time (or recombination).

SpaceTiger

Jun27-06, 03:06 AM

He doesnt place the big dots, theyre "convienently" placed. Pac man is still 3D, you cant see 1D with out the other two.

And he receives the meaning of those dots from "on high"? Come on, this is getting ridiculous.

If nothing else he kept getting space sick at the same point.

You can't be serious...

By deffinition occam razor doesnt directly state anything about infinite vs finite. However it applies to all theories of science and philosophy which include infinite vs finite. An infinite universe is much more simpler and goes by what has been observed for ages.

Nope, the number of free parameters in the finite models can be made to be the same as in the infinite ones.

I did misunderstand. However the universe with boundaries is not my idea, it is the neccessity of a finite universe.

There is no need for a boundary anymore than there is need for a creator. It's just a human concept being unnecessarily forced on the natural world.

Infinite universes is an oxymoron. If the term universe means all there is and it is infinite or even finite, there could never be more than one.

The plural was referring to theories of infinite universes -- "Infinite universes are commonplace in mainstream science". That means there are many mainstream theories of the universe that are infinite.

Balence

Jun27-06, 10:05 AM

And he receives the meaning of those dots from "on high"? Come on, this is getting ridiculous.

It is getting ridiculous. I never intended to debate it in the first place.

You can't be serious...

This is my serious face...:yuck:

Nope, the number of free parameters in the finite models can be made to be the same as in the infinite ones.

How so?

There is no need for a boundary anymore than there is need for a creator. It's just a human concept being unnecessarily forced on the natural world.

Finite- Having bounds; limited + Universe- All matter and energy, including Earth, the galaxies and all therein, and the contents of intergalactic space, regarded as a whole. Obviously words cannot describe a finite universe because by definition it contradicts its self.

The plural was referring to theories of infinite universes -- "Infinite universes are commonplace in mainstream science". That means there are many mainstream theories of the universe that are infinite.

Ah, I see what your saying, sorry bout that.