If the universe is expanding, what are we filling up?

[M-CaTZ]

Seeing is that the Universe is expanding at rates that are impossible to duplicate by any machines of mankind, i dont see the purpose in trying to argue what observations can be made at the "edge". I do however have a slightly digressing question about the Universe. Ive read theory's of the Universe possible collapsing at some point in time. A reverse big bang if you will. Although its hard to percieve, what are your thoughts on the end of the universe, and if or when it happens what will happen next. Will the matter disappear, or take a new shape of another form?

[blike]

Originally posted by M-CaTZ

I do however have a slightly digressing question about the Universe. Ive read theory's of the Universe possible collapsing at some point in time. A reverse big bang if you will. Although its hard to percieve, what are your thoughts on the end of the universe, and if or when it happens what will happen next. Will the matter disappear, or take a new shape of another form?

 

 

see this thread and this thread

 

"The 73% density of dark energy means that the universe will keep expanding forever, eventually resulting in a heat death. "Not with a bang, but with a whimper"

[mastersamwise]

not necessarily- the expansion of the universe is essentially depends on the mass (and thus the force of gravity) in the universe.

I dont think that anyone has been able to even hope to approximate the mass of the galaxy, that would be like aristotle knowing the exact distance to the sun- a stab in the dark!

Therefore there are three possible universe endings

1. the value of the universal mass is high- the universe comes to a 'big crunch' after collapsiong in under its own gravity

2. The mass is spread out just enough just enough so that expansion stops, but is not enough to shrink either- the universe goes out in the afore mentioned 'whimper'!

3. The amount of mass is small and thus it is possible the universe will carry on expanding

 

Im not sure of the overall outcome of the last option, i wonder if the mass of the universe has all been created or is it still being created on the edges of the big bang 'shockwave'

any answers anyone?

[Radical Edward]

Originally posted by mastersamwise

I dont think that anyone has been able to even hope to approximate the mass of the galaxy

 

Im not sure of the overall outcome of the last option, i wonder if the mass of the universe has all been created or is it still being created on the edges of the big bang 'shockwave'

any answers anyone?

 

the mass of the galaxy can be calculated by looking at the speed at which objects orbit the centre. there is a discrepancy at large distances though, since the planets out there are moving too quickly. this is one of the hints at dark matter existing.

 

you are viewing the big bang as an explosion from some point, this is not the case. the big bang happened everywhere, and all space was created in it. there is no edge or shockwave, at least according to the standard model.

[Geocentricman]

Originally posted by §lîñk€¥™

This is always a hard one for people to get to grips with (some are lucky and can make the conceptual leap easily).

 

The Universe is expanding but it does not fill anything up. Hard to imagine as it sounds, but the Universe is "making" space whilst expanding not expanding into a space. :scratch:

 

kind regards

Ah no the universe is complete. No expansion required.

[NSX]

Originally posted by Radical Edward

you are viewing the big bang as an explosion from some point, this is not the case. the big bang happened everywhere, and all space was created in it. there is no edge or shockwave, at least according to the standard model.

 

Can you expand on this?

[Clown]

NSX,

 

Where is the edge on the surface of a balloon? What happens if you start to inflate the balloon? Does is have an edge or a center then? That's a pretty good analogy used for the real universe.

[Sayonara]

The balloon clearly still has a center.

 

I think NSX probably meant "boundary" or "inner surface" when he said 'edge'. It's difficult to give something theoretical an appropriate name when there's nothing it directly compares to

[Clown]

The surface of the balloon does not have a boundary though. Of course our eyes can't help but focusing on that, since we are used to everything having an inside and outside.

[Sayonara]

It has a boundary between the air inside and outside the rubber.

 

Are you referring to the point where that surface begins and/or ends?

[Clown]

Well, recall that the surface by definition, is 2 dimensional. It has no center and no edge. You need to go into the 3rd dimension to find an edge, but by then we aren't talking about surfaces anymore, as we've moved onto volumes. Imagining a universe that has a curved volume is not possible with human brains. Much worse, unlike the balloon, there is no "inside" or "outside" in the 4th dimension that universe is embedded in. Useless intuition.

[Sayonara]

The balloon is 3 dimensional in spatial terms, and so is the universe.

[Clown]

The surface is not.

 

And the universe, though having 3 spatial dimensions, has non Euclidean geometry and it would require a 4 dimensional brain to be able to imagine "what it looks like".

[Sayonara]

(1) A 2D surface does not need to be raised into 3 dimensions before you find an edge.

 

(2) I don't see why you see it necessary to imagine the universe as a curved volume. However, if it were, I don't see that as being a problem as - like most people - I am capable of imagining such concepts.

 

(3) A balloon's surface does have an edge - the point where expansion begins, the squiggly bit you tie up. Either locate a related element in the universe model you are using or chose a more suitable analogy.

 

(4) You appear to be considering the balloon's surface as if it were an edgeless plane in 2 dimensions only. Fair enough if you wish to discard one dimension, but that is not an accurate model of the universe.

 

(5) To claim the universe requires a 4D brain to imagine it is a bit vague. Define '4D brain'.

And explain why my puny brain can visualise and manipulate a model of a hypercube if what you say is true.

[Clown]

Originally posted by Sayonara³

(1) A 2D surface does not need to be raised into 3 dimensions before you find an edge.

 

Yes it does. The bit where you tie it up doesn't count - with the analogy you are supposed to imagine it as a completely smooth. Ok, here is a better one. Picture a basketball, and note that the surface is boundless.

 

(2) I don't see why you see it necessary to imagine the universe as a curved volume. However, if it were, I don't see that as being a problem as - like most people - I am capable of imagining such concepts.

Since humans can only see a 2D projection of our 3D universe at any given time, it is not possible to imagnie what a curved volume actually looks like.

 

(4) You appear to be considering the balloon's surface as if it were an edgeless plane in 2 dimensions only. Fair enough if you wish to discard one dimension, but that is not an accurate model of the universe.

 

It's just a 2D analogy. That is, the equivalant in lower dimensions. If you treat the surface as something with only an x y axis, you can see how there is no center. This only applies to a closed universe. Though I suppose the same would apply to a 2D edgeless torus.

 

(5) To claim the universe requires a 4D brain to imagine it is a bit vague. Define '4D brain'.

And explain why my puny brain can visualise and manipulate a model of a hypercube if what you say is true.

 

A model we can imagine is not an actual hypercube. Consider that our ability to imagine objects is based on our visual memory. That is, any dimensional object we are able to see, we should be able to imagine. But when you consider that the retina only displays a 2D image pattern that is sent to the brain, you can clearly see that viewing a full 3D image at one time is not possible. Hence, neither is a curved volume. Depth perception is based on the experience of motion through our 2D viewing area, but we still can't see more than one object at any given x,y coordinate at any given time.

[JaKiri]

Originally posted by Clown

A model we can imagine is not an actual hypercube. Consider that our ability to imagine objects is based on our visual memory. That is, any dimensional object we are able to see, we should be able to imagine. But when you consider that the retina only displays a 2D image pattern that is sent to the brain, you can clearly see that viewing a full 3D image at one time is not possible. Hence, neither is a curved volume. Depth perception is based on the experience of motion through our 2D viewing area, but we still can't see more than one object at any given x,y coordinate at any given time.

 

I've seen a hypercube.

 

It was made in perspective in 3d.

[Clown]

You can only see anything one 2D slice at a time. That's just how the brain works. Unless of course, your mind can somehow transcend the limitations of the eye and the visual cortex.

[JaKiri]

Originally posted by Clown

You can only see anything one 2D slice at a time. That's just how the brain works. Unless of course, your mind can somehow transcend the limitations of the eye and the visual cortex.

 

If you want to argue, take it up with the theoretical physics department at warwick university.

 

ps.

 

Although some people can 'see' it and some people can't.

[Clown]

No one would seriously debate that people perceive objects through a 2D screen. At least not scientifically.

[JaKiri]

Originally posted by Clown

No one would seriously debate that people perceive objects through a 2D screen. At least not scientifically.

 

What?

 

It wasn't a 2D screen, it was through perspective in 3D.

[Sayonara]

Originally posted by Clown

Yes it does. The bit where you tie it up doesn't count - with the analogy you are supposed to imagine it as a completely smooth. Ok, here is a better one. Picture a basketball, and note that the surface is boundless.

"Doesn't count", lol. If you want it to be 2D, open it out so that it's planar. Oh no - that creates an edge doesn't it? Then you'd be wrong, and we can't have that.

 

A basketball has at least one seam, unless it's moulded rubber. Either way it also has a valve.

Since humans can only see a 2D projection of our 3D universe at any given time, it is not possible to imagnie what a curved volume actually looks like.

First off, defined curved volume. Would it be like a banana, or are you adding unneccesary complexity where it is not needed? Secondly, you have not yet explained why the universe volume needs to be curved.

It's just a 2D analogy. That is, the equivalant in lower dimensions. If you treat the surface as something with only an x y axis, you can see how there is no center. This only applies to a closed universe. Though I suppose the same would apply to a 2D edgeless torus.

Reducing a 3D object to 2 dimensions in order to compare it to a 3D object to which it was similar in the first place is stupid.

If you make a balloon 2D, it still has a center as it cannot encapsulate volume and therefore has to be opened up.

A model we can imagine is not an actual hypercube.

Which is why we have models, I wouldn't want one in my brain.

Consider that our ability to imagine objects is based on our visual memory. That is, any dimensional object we are able to see, we should be able to imagine. But when you consider that the retina only displays a 2D image pattern that is sent to the brain, you can clearly see that viewing a full 3D image at one time is not possible. Hence, neither is a curved volume. Depth perception is based on the experience of motion through our 2D viewing area, but we still can't see more than one object at any given x,y coordinate at any given time.

You are now fully in my territory. Hello depth perception, hello perspective, hello "the biology of how the human brain puts together dimensional information to model the environment and objects in it".

 

If you only perceive and process in 2D I suggest you go see a specialist.

 

As far as not seeing more than one object at x,y at the same time goes, I don't see how this is at all relevant to the shape of the universe when considered in any number of dimensions. It also hinges directly on what you consider to be the scope of an object, for instance two glass spheres of differing radius sharing the same center are partially occupying the same space.

[Clown]

Since the visual cortex displays a 2D image based on the retina image, we cannot ever see anything outside this 2D perspective. The only way it would be possible if both things below were true:

 

1. The data for visual perception is not processed in the visual cortex.

 

2. Light could travel freely in 4 spatial dimensions, thereby being able to reach not a 2D retina, but a 3D one.

 

3. Your body would need to be 4D in order to have a 3D retina.

 

Actually, there is an easy way to see this. Take any image of the cube (or anything with depth) any plot an X,Y axis. You'll notice that if there is something behind an object at any specific location, you won't be able to see it. In other words, only one object per X,Y coordinate can be seen. An object at (12,2,3) for expample, would be blocked out by an object at (12, 2, 2).

 

So while we can view the depth of a cube or anything else, we are doing so one 2D slice at a time.

[Sayonara]

Considering the speed with which you replied, I don't think you considered my last post at all.

 

At any one time your retinas 'image' only one 2D slice of an object, CORRECT.

 

However, slices are assembled into models that we can directly manipulate using the magic of thinking. This allows us to perceive dimensions and do things like not trip over our own feet.

 

This is how we are able to perceive the shape of the universe.

 

It's just like being in a really big room. Are you saying you can't work out the shape of a room unless you see it from outside, and from every angle? Or are you just babbling about dimensions?

 

Either way you still haven't proven whatever your point was.

 

And, if you still believe that something in 2D has no edge, I suggest you get a piece of paper and draw a square on it.

[JaKiri]

Originally posted by Clown

Since the visual cortex displays a 2D image based on the retina image, we cannot ever see anything outside this 2D perspective. The only way it would be possible if both things below were true:

 

You have two eyes.

 

Three dimensional vision is implied by their combined use.

[Clown]

Originally posted by Sayonara³

Doesn't count", lol. If you want it to be 2D, open it out so that it's planar. Oh no - that creates an edge doesn't it? Then you'd be wrong, and we can't have that.

 

Don't be silly. The balloon is just an analogy cosmologists use to compare to the idea of a closed, expanding universe. In other words, it's just to show that moving along the x,y axis you will never find an edge or center.

 

First off, defined curved volume. Would it be like a banana, or are you adding unneccesary complexity where it is not needed?

 

Nope, it's required. As you probably already know, the idea of spacetime curvature comes from Einstein's GR. This curvature will give spacetime an overall shape, and if the average density is high enough, space will be warped so much that it folds over itself as in the balloon model. No center, no edge. That is why cosmologists began using the balloon analogy in the first place. Well, the expanding part of it also helps.

 

Secondly, you have not yet explained why the universe volume needs to be curved.Reducing a 3D object to 2 dimensions in order to compare it to a 3D object to which it was similar in the first place is stupid.

 

See general relativity.

 

If you make a balloon 2D, it still has a center as it cannot encapsulate volume and therefore has to be opened up.Which is why we have models,

 

Keep in mind, it's only a geometric analogy used by cosmologists to show the concept of a closed universe. They use it because we cannot visualize 3D curvatures.

 

You are now fully in my territory. Hello depth perception, hello perspective, hello "the biology of how the human brain puts together dimensional information to model the environment and objects in it".

 

Good, then you should know very well how the eye works. Given that, you can see why such clumsy balloon analogies are used.

 

If you only perceive and process in 2D I suggest you go see a specialist.

 

I said we only perceive the 3D world one 2D slice at a time. That is, we see images that have as much light packed into a 2D pattern.

 

As far as not seeing more than one object at x,y at the same time goes, I don't see how this is at all relevant to the shape of the universe when considered in any number of dimensions.

 

It is absolutely relevant when the discussion is that we cannot imagine 3D curvature.

 

It also hinges directly on what you consider to be the scope of an object, for instance two glass spheres of differing radius sharing the same center are partially occupying the same space.

 

The main issue is non Euclidean geometry. So basically, the argument is about the balloon analogy. Let me summarize:

 

Curved spacetime is a result of GR. And since we cannot see curved volumes, cosmologists use the 2D balloon analogy as a way of visualizing a geometric idea.