Universe Expansion Diagram

[Spyman]

A 'disk' is a solid circular 2D planar shape. There are no 'disks' in the above figure. In the original, 'unaugmented' figure from NASA, space is represented by 1D, and time by 1D, and the curvature of the resulting 2D spacetime is indicated by the 3D perspective -- hence the term (1+1)D in 3D.

I interpret the original picture differently, I see 1D of time and 2D of space, the WMAP spacecraft are placed in the center of the 2D space circle and at the present location on the time scale.

 

In my view the WMAP spacecraft represents our centre position in our observable part of the Universe and each timeslice is therefore a solid planar disk of space, filled with stuff at different locations from the centre.

 

Our observable universe is not hollow, it is a filled spherical volume around us in the centre. The whole Universe could be curved inward on itself and form a hollow hypersphere, but on the scale of our observable limits it's considered to be locally flat.

 

I do definately not think that NASA tries to show somecind of a resulting curvature of spacetime.

 

Note: I am not able to view Widdekind's images from this computer so I am not able to comment on those.

Edited December 8, 2010 by Spyman

[michel123456]

I agree completely with your post #26 Spyman.

I'll put a red cross on my calendar to remember this moment.

[michel123456]

(...) and each timeslice is therefore a solid planar disk of space, filled with stuff at different locations from the centre. (...)

 

I'd like to discuss this point, because I believe the diagram may still be misleading.

 

As I see it, each solid planar disk represents space, full of stuff. Each disk represents the whole space as it is supposed to exist at a certain period of time.So, if we take a disk in the middle of the diagram, it represents space with everything in it. If we take a second disk, it represents again space with everything in it, but at another time. If we take a 3rd disk, again it represents space with everything in it, and so on.

As a matter of consequence, this diagram shows a multiplication of "spaces filled with stuff" along the time-line.

Or, for those who are familiar with space-time diagrams, stars & galaxies on this diagram are not point-like (as represented), but are lines.

[Spyman]

I'd like to discuss this point, because I believe the diagram may still be misleading.

 

As I see it, each solid planar disk represents space, full of stuff. Each disk represents the whole space as it is supposed to exist at a certain period of time.So, if we take a disk in the middle of the diagram, it represents space with everything in it. If we take a second disk, it represents again space with everything in it, but at another time. If we take a 3rd disk, again it represents space with everything in it, and so on.

As a matter of consequence, this diagram shows a multiplication of "spaces filled with stuff" along the time-line.

Or, for those who are familiar with space-time diagrams, stars & galaxies on this diagram are not point-like (as represented), but are lines.

I don't think it was intended to be like a spacetime diagram, it is a simple representation of our observable view and we can only see a star once, in one time slice. We don't see lines or the same stars multiple times in different timeslices.

(Neglecting relativity effects like gravitational lensing and such.)

 

The image doesn't discern between what we actually see and what our model predicts, it is a "representation of the evolution of the universe" with a blend of the rate of expansion and what we are observing at present period of time.

 

As such we can only see a star at one point in time and at one distance corresponding to that time, so the slices doesn't contain everything that has ever been at that distance or everything that has passed through that time period. The slices only contain stars that was both at that distance and in that time period that allowed their light to reach us from there at present time.

[michel123456]

I don't think it was intended to be like a spacetime diagram, it is a simple representation of our observable view and we can only see a star once, in one time slice. We don't see lines or the same stars multiple times in different timeslices.

(Neglecting relativity effects like gravitational lensing and such.)

 

The image doesn't discern between what we actually see and what our model predicts, it is a "representation of the evolution of the universe" with a blend of the rate of expansion and what we are observing at present period of time.

 

As such we can only see a star at one point in time and at one distance corresponding to that time, so the slices doesn't contain everything that has ever been at that distance or everything that has passed through that time period. The slices only contain stars that was both at that distance and in that time period that allowed their light to reach us from there at present time.

 

In this case, each disk is hollow.

Or lets say these are not disks, but circles.

 

Oops, something wrong here.

Edited December 9, 2010 by michel123456

[Widdekind]

If the 3D figure used up 2D for space, it could not then depict both +1D for time and +1D for hyper-spatial curvature (w/in human-visualizable 3Ds). If you use up 2D for space, you must use the remaining 3^rd dimension for hyper-spatial curvature. Then, hyper-curved space (not space-time) looks like a sphere, the 2D closed surface of which represents curved & closed space.

 

If space, in 2D, was a 2D planar disk, it would (1) be flat, not hyper-curved; (2) have an 'edge', not be self-closed. Neither is the case.

[michel123456]

If the 3D figure used up 2D for space, it could not then depict both +1D for time and +1D for hyper-spatial curvature (w/in human-visualizable 3Ds).(..)

 

Correct. As stated by Spyman, here we have space reduced in 2D, and 1D for time. There is no hyper-spatial curvature represented here.

 

If space, in 2D, was a 2D planar disk, it would (1) be flat, not hyper-curved; (2) have an 'edge', not be self-closed. Neither is the case.

 

In this diagram, Space is flat planar disk and have an edge.

 

I don't think it was intended to be like a spacetime diagram, it is a simple representation of our observable view and we can only see a star once, in one time slice. (...)

It is a spacetime diagram.

Once you put T as an axis, and space as the 2 other axes, it is a spacetime diagram.

 

And it is definitely not a representation of the Observable Universe.

In a spacetime diagram, the Observable Universe is a cone.

Edited December 10, 2010 by michel123456

[Spyman]

In this case, each disk is hollow.

Or lets say these are not disks, but circles.

 

Oops, something wrong here.

No, since it's not ment as a spacetime diagram the WMAP spacecraft don't have a worldline through the discs, it has always been where it's located in the image. As such the discs would be like a distant wall, (if space wasn't transparent), and I doubt the walls in your room appear hollow when you look at them.

 

However due to traveltime the distance to all parts of the wall would need to be equal, which if you look carefully in the picture is showed by a slight curving of the CMBR like the bottom of a bowl.

 

The circle you would like to view from the constancy of lightspeed would in this case be in the third dimension which is used to show time in the image.

 

 

It is a spacetime diagram.

Once you put T as an axis, and space as the 2 other axes, it is a spacetime diagram.

 

And it is definitely not a representation of the Observable Universe.

In a spacetime diagram, the Observable Universe is a cone.

Since you seem to be so sure of this then maybe you can explain why the picture apparently doesn't look like a cone with the right side 1100 times larger than the left.

 

The observable universe is a filled sphere surrounding us in the center, but if the image had looked like a huge ball with a CMBR pattern then it wouldn't have showed us the expansion rate, would it?

 

Instead they show us a small slice of the observable universe with the CMBR on the left side, I already mentioned that it's curved, imagine how it would look if you extend the CMBR until it closes in on itself and there is your observable universe with the WMAP in the centre.

 

The image is not a physical representation in scale like a spacetime diagram, it's a composite of several things for a simplified view of the Evolution of the Universe.

[michel123456]

No, since it's not ment as a spacetime diagram the WMAP spacecraft don't have a worldline through the discs, it has always been where it's located in the image. As such the discs would be like a distant wall, (if space wasn't transparent), and I doubt the walls in your room appear hollow when you look at them.

The WMAP is part of the present and is correctly shown in the right part. If instead we put the Earth in place of WMAP, of course Earth has a world line in this diagram.I don't understand what you mean by "the discs would be like a distant wall". We are currently observing the CMBR 13,7 billion years in the past, so all discs in this diagram must be transparent.

 

However due to traveltime the distance to all parts of the wall would need to be equal, which if you look carefully in the picture is showed by a slight curving of the CMBR like the bottom of a bowl.

O.K.

 

The circle you would like to view from the constancy of lightspeed would in this case be in the third dimension which is used to show time in the image.

IMHO it is incorrect to draw a circle or a sphere in this kind of diagram.

 

 

Since you seem to be so sure of this then maybe you can explain why the picture apparently doesn't look like a cone with the right side 1100 times larger than the left.

Good point. I cannot put myself in place of the Nasa scientist who draw this picture. As i see it, each disk represents the situation of space at each interval of time, independently if it is observable or not. The right part should be bigger: maybe the units of space are intentionaly reduced compaired to units of time in order to make more evident the s shape of expansion.

 

The observable universe is a filled sphere surrounding us in the center, but if the image had looked like a huge ball with a CMBR pattern then it wouldn't have showed us the expansion rate, would it?

Correct

 

Instead they show us a small slice of the observable universe with the CMBR on the left side, I already mentioned that it's curved, imagine how it would look if you extend the CMBR until it closes in on itself and there is your observable universe with the WMAP in the centre.

We can't do that. Time is going from left to right, and CMBR is entirely in the past. If you extent CMBR along a circle, you will find CMBR in the present and in the future, which is incorrect.

The image is not a physical representation in scale like a spacetime diagram, it's a composite of several things for a simplified view of the Evolution of the Universe.

I agree it was ment to show a simplified view of the evolution of the universe. I insist it is misleading. And it is a spacetime diagram. Edited December 10, 2010 by michel123456

[Widdekind]

In the OP, the Space-Time (x,t) grid wraps around the surface of the "vase". Only that curved, 2D surface represents Space-Time, everything else is the higher-D 'hyperspace', through which Space-Time can be considered to curve. I would appeal to the original CGI artist.

[alpha2cen]

The diagram assumption is Big Bang occurring far away from here and we are in the CMB.

Our position and Universe expansion speed are reasonable to see that phenomena.---Hidden Universe searching.

No direction deep field searching is right? Every direction far away Universe we can see same phenomena. ?????

Edited December 13, 2010 by alpha2cen

[Spyman]

Good point. I cannot put myself in place of the Nasa scientist who draw this picture.

...

I insist it is misleading. And it is a spacetime diagram.

Well, it's only one image and I can't claim any more knowledge on what or how the people at NASA were thinking when they made the image than you, so lets just accept that we disagree on parts of it.

 

But I want to make a final attempt to explain two parts of my view:

As i see it, each disk represents the situation of space at each interval of time, independently if it is observable or not.

The discs locations are not a simple time position they are also at a distance through space and as such I would say they represents the situation at each interval of a combination of time and space. For instance the objects in any disc once emitted a part of the universal CMBR but we are only able to view it from one disc since those photons from the other discs has already passed us or could reach us in the future and alternatively never reach us if expansion is accelerating.

 

 

We can't do that. Time is going from left to right, and CMBR is entirely in the past. If you extent CMBR along a circle, you will find CMBR in the present and in the future, which is incorrect.

From the timeline on evolution of the Universe time is going from the ignition to the left to the present to the right and it would be incorrect to place CMBR in the future, but from our observational viewpoint we can look in any direction we want and see the timeline going back to the ignition. So we can look to the left and se the timeline as represented in the image but we could also look to the right and see the timeline like a mirror of the left representation.

 

 

A picture are not limited to contain only one motive or purpose, it can have several layers and of course there will be as many interpretations as there are different people looking at it.

[michel123456]

1. "we can look in any direction we want"

In space Yes. In time, no.

2. "So we can look to the left"

Yes we can look the left, but we cannot see everything from the left. The visible left part is a cone. And I support the idea that only the surface of the cone is visible. The inside part of the cone is invisible: for example we can't see in the sky our own world line.

3."but we could also look to the right and see the timeline like a mirror of the left representation"

Ooh I see what you mean. Both arrows of time would be pointing to us. Interesting, but surely nothing to do with the intentions of this diagram.

[alpha2cen]

from our observational viewpoint we can look in any direction we want and see the timeline going back to the ignition.

 

Can we see early Universe in any direction?????

Are we shrinking?

Early Universe was small space and has been expanded continuously.

And we can see it any direction.

Are there any position in the Universe?

If we were shrinking, it would be right.

[Spyman]

Interesting, but surely nothing to do with the intentions of this diagram.

Hmm, obviously if you don't try to understand then you won't succed either...

 

This image from NASA is clearly not a simple spacetime diagram solely intended to show the WMAP spacecrafts worldline extending out from the Big Bang, I have repeated it a few times already and this is the last time, the picture have multiple purposes and shows more than one single thing.

 

 

Yes we can look the left, but we cannot see everything from the left. The visible left part is a cone. And I support the idea that only the surface of the cone is visible. The inside part of the cone is invisible: for example we can't see in the sky our own world line.

IF we assume for the sake of the argument that we can only observe EM-radiation propagating with lightspeed, then the visible part of the surface on the cone you mention would at the observable distance for the CMBR consist of a filled untransparent sphere surrounding us, in every direction around the Earth.

 

¤ If we look the CMBR in the skye, is the image we see hollow?

¤ If you look at the CMBR in the picture from NASA is it hollow?

 

In a spacetime diagram the object has a worldline from the past to the future, but if this image instead is viewed as what the WMAP spacecraft are observing, through the timeline for evolution of the Universe, then the curved disc representing the CMBR, to the left in the picture, is not hollow and even the center line of eyesight is fully observable.

 

 

 

Can we see early Universe in any direction?????

Are we shrinking?

Early Universe was small space and has been expanded continuously.

And we can see it any direction.

Are there any position in the Universe?

If we were shrinking, it would be right.

Yes, in any direction we look, we will see increasingly older views of the Universe when we look further distant.

 

What would be the difference if the Universe is fixed and we are shrinking inside it compared to if we are fixed and the Universe are expanding around us?

 

According to Albert Einsteins theory of relativity the geometry of spacetime is dynamic, so from that viewpoint it's more convinient to think that the geometry is expanding instead of us shrinking.

 

There are no fixed positions in the Universe, everything is relative the observers frame of reference.

Edited December 14, 2010 by Spyman

[alpha2cen]

 

Yes, in any direction we look, we will see increasingly older views of the Universe when we look further distant.

 

 

Problem is the old Universe size was not so large than today.

If we had been shrinking, this size problem would be solved.

But other physical problem would be happen.

What we can see the same figure about the old Universe at all direction in the sky is against the size of the old Universe.

There is something we don't know.

[Spyman]

If we had been shrinking, this size problem would be solved.

You did not answere my question:

 

"What would be the difference if the Universe is fixed and we are shrinking inside it compared to if we are fixed and the Universe are expanding around us?"

 

Please do, your problem with the size might be solved.

 

 

What we can see the same figure about the old Universe at all direction in the sky is against the size of the old Universe.

We are exactly in the center of our observable view of the Universe and as such most parts of it we see have expanded outward from close to our location, everything distant we see was closer to us in the past and is now receding away from us equally in all directions.

 

There is nothing against the size of the old Universe in this argument.

Edited December 14, 2010 by Spyman

[alpha2cen]

You did not answere my question:

 

"What would be the difference if the Universe is fixed and we are shrinking inside it compared to if we are fixed and the Universe are expanding around us?"

 

Please do, your problem with the size might be solved.

 

 

If we had been shrinking, we could see same figure about old Universe at all direction.

We are exactly in the center of our observable view of the Universe and as such most parts of it we see have expanded outward from close to our location, everything distant we see was closer to us in the past and is now receding away from us equally in all directions.

 

There is nothing against the size of the old Universe in this argument.

 

Possible explain is like this.

From the beginning of the Universe, Universe size is very very large , we can't imagine the size.

Later size variation is not so big.

The emitted light at that time has arrived now at all direction in the sky.

[Spyman]

If we had been shrinking, we could see same figure about old Universe at all direction.

And exactly how would that be different from if the Universe would had been growing around us?

(I am very certain that we would still see the same figure about old Universe then too.)

 

 

Possible explain is like this.

From the beginning of the Universe, Universe size is very very large , we can't imagine the size.

Later size variation is not so big.

The emitted light at that time has arrived now at all direction in the sky.

Except that I consider 1100 times to be a rather large size variation, I can't see anything new or against what I posted here.

[michel123456]

Hmm, obviously if you don't try to understand then you won't succed either...

(...)

This image from NASA is clearly not a simple spacetime diagram solely intended to (...)

IF we assume for the sake of the argument that we can only observe EM-radiation propagating with lightspeed, then the visible part of the surface on the cone you mention would at the observable distance for the CMBR consist of a filled untransparent sphere surrounding us, in every direction around the Earth.

 

¤ If we look the CMBR in the skye, is the image we see hollow?

¤ If you look at the CMBR in the picture from NASA is it hollow?

(...)

 

 

I began a new thread to explain my point and forget the NASA diagram for a while.

I don't want to interfere with your interesting question:

"What would be the difference if the Universe is fixed and we are shrinking inside it compared to if we are fixed and the Universe are expanding around us?"

I wonder what is your answer.

Edited December 15, 2010 by michel123456

[Spyman]

I began a new thread to explain my point and forget the NASA diagram for a while.

After reading through that thread, I realize that I have made a somewhat sloppy translation in my post #40 when I said:

 

"IF we assume for the sake of the argument that we can only observe EM-radiation propagating with lightspeed, then the visible part of the surface on the cone you mention would at the observable distance for the CMBR consist of a filled untransparent sphere surrounding us, in every direction around the Earth."

 

Were I instead ment to say "filled untransparent spherical surface surrounding us", in essence that means the CMBR would be like a huge shell or distant wall surrounding us, which is in accordance with what Michel says there:

if we had, in real 3D space, to plot the stars and galaxies that are 1 billion Light Years from us, and only those, we would obtain a sphere. And this sphere would be hollow.

But I don't intend to argue against the 'surface of the cone idea' and in fact did my very best to try to avoid it when I said "IF we assume for the sake of the argument".

 

What I however have been arguing is that Michel seem to claim that NASA made a mistake and should have made the CMBR in the picture hollow, whereas I think that NASA made it like this on purpose.

 

Each "hollow sphere" is represented as a "hollow disk".

And there is nothing weird to that. It is just another way of representing things.

So, does a filled disc of CMBR indicate that the picture is not a spacetime diagram of your cind or that several scientists at NASA faulted?

 

 

-----

 

I don't want to interfere with your interesting question:

"What would be the difference if the Universe is fixed and we are shrinking inside it compared to if we are fixed and the Universe are expanding around us?"

I wonder what is your answer.

Since we don't have any reference to compare against we are not able to discern whether our meterstick is shrinking or distances are increasing, all we can measure is that the scale between them is changing.

 

 

-----

 

For alpha2cen and others, some links that might help understanding expansion of space:

 

http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf

 

http://www.astro.ucla.edu/~wright/Balloon.html

 

http://www.astro.ucla.edu/~wright/Balloon2.html

Edited December 15, 2010 by Spyman

[alpha2cen]

Except that I consider 1100 times to be a rather large size variation, I can't see anything new or against what I posted here.

 

I'm talking about Hubble deep field.

We can see very old galaxy scenery at all direction in the sky.

The light would be started at least 10 bilion years ago.

Important thing is we can see same picture at all direction in the sky.

One possibility is that Universe has been very very large from the beginning.

Thinking about the first point where the light was emitted.

[Spyman]

I'm talking about Hubble deep field.

We can see very old galaxy scenery at all direction in the sky.

The light would be started at least 10 bilion years ago.

Important thing is we can see same picture at all direction in the sky.

One possibility is that Universe has been very very large from the beginning.

Thinking about the first point where the light was emitted.

Read this thread: Picture of galaxy from when expansion only 600 million years old

 

And the follow up: Very old view of the Universe

 

But even more importantly read the explanations in the links I posted in #46.

[alpha2cen]

To finish this argument , we need more data about early Universe.

To use the celestial sphere, we determine more targets for deep field searching, and observe that point more precisely, and analysis the results accurately.

From these results we can estimate the expansion direction of the Universe, and early Universe size ....

[Spyman]

To finish this argument , we need more data about early Universe.

To use the celestial sphere, we determine more targets for deep field searching, and observe that point more precisely, and analysis the results accurately.

From these results we can estimate the expansion direction of the Universe, and early Universe size ....

From careful analysis of the CMBR the scientific consensus is that the Universe has expanded ~1100 times during the traveltime from when this radiation was emitted ~13.6 billion years ago until today when we observe it.

 

We don't know the size of either the early or the present Universe, it could very well have been infinite back then and then it still is infinite but less dense.

 

Our best knowledge and observations indicate that objects inside the Universe, independent of it's total size, has been ~1100 times closer in the past than what they are now.

 

 

[EDIT]

I was rereading this thread an noticed that you said "expansion direction" to which I think I need to clarify that the CMBR is surrounding us equally in all directions and as such the expansion also has been equally large in all directions around us.

 

According to scientific consensus there is no center inside space which the Universe is expanding from.

Edited December 16, 2010 by Spyman