What is at the center of the universe?

[talksabcd]

Talksabcd,
The evidence for a 4th dimension is gravity and time dialation(though there may be more to it that we are unable to observe.

Maxwells Demon,
I'm sorry the last part of my post was so vague. We are in agreement. My point was that an observer on Earth sees everything moving away from him and if he disregards the background radiation, the fact that space and time began with the "Big Bang", and the observations from other places, it would be natural for him to think that he was in the center. Even though this is incorrect.

We are not talking abt Time as fouth dimension but abt spatial fourth dimension. Is there any evidence for a spatial fouth dimension ?

 

[talksabcd]

If there was a center of the universe, then we would find the cosmic background radiation stronger in one direction than another. This is not the case. While NASA's COBE satelite found variations, that is believed to be the beginning of the first structures in the universe, it found the background radiation to be the same in all directions.

The phrase "BIG BANG" leads one to think of the expansion of the universe as an explosion. This is incorrect. An analogy I use is to consider the universe as a loaf of raisinbread expanding as it cooks. The raisins being the galaxies. An observer on one raisin sees all the other raisins moving away. While an observer on a distant raisin sees the same thing. This analogy is 3 dimensional and the universe is expanding in 4 dimensions. This is why it is so difficult for our minds to comprehend.

Some people confuse the "local observable area" of the universe, with the entire thing (As I did until recently). This makes the Earth appear as the center.

If the cosmic background is same in all directions then it doesn't mean that
there is no center to the universe. We see the cosmic background from the
point of last scaterring. If the point of last scaterring is within the finite universe then we should see homogenous cosmic background in all directions irrespective of whether there is a center to the universe or not.

 

[russ_watters]

Why is that? If the universe had a center, wouldn't the point of last scattering appear as a spherical shell in one direction instead of being everywhere?

 

[Maxwells Demon]

If the cosmic background is same in all directions then it doesn't mean that
there is no center to the universe. We see the cosmic background from the
point of last scaterring. If the point of last scaterring is within the finite universe then we should see homogenous cosmic background in all directions irrespective of whether there is a center to the universe or not.

I'm not sure what you're talking about? Is there something you don't understand or? Is there something I don't? If so, could someone explain to me what he's trying to say?

 

[wilgory]

We are not talking abt Time as fouth dimension but abt spatial fourth dimension. Is there any evidence for a spatial fouth dimension ?

Pardon me Talks,

I was talking about time as the 4th dimension. As I understand it, General Relativity also uses time as the 4th dimension. What theory are you using to form your opinion? I tend to go with GR since it has passed many test and as far as I know works perfectly well as far as cosmology is concerned. If you go to Wikipedia you'll find Introduction to Special Relativity and Introduction to General Relativity. I found them both helpful in explaining how current understanding of the four dimensional universe was achieved.

http://en.wikipedia.org/wiki/Introduction_to_special_relativity

http://en.wikipedia.org/wiki/Introduction_to_general_relativity

 

[HeavenTornApart]

can i raise the point of infinite vs finite here as it really is relevant.

if the universe is infinite as some theories try to suggest then it has no central point, its infinite therefore there are no borders for the central point to be established against. so before we hypothesise about where the centre of the universe is, let's find the borders then do the math

 

[talksabcd]

Why is that? If the universe had a center, wouldn't the point of last scattering appear as a spherical shell in one direction instead of being everywhere?

As per my understanding, I have created a picture of the universe with a center.

1) The inner light blue sphere contains only radiation. So its a radiation dominated universe.
2) The outer gray Sphere contains matter.

You can see in both the spheres that boundary of last scattering for Earth (Black dot) is within
the boundary of the universe.

So shoudn't the cosmic background radiation appear homogenous in all directions until the boundary
of last scattering expand and touch the boundary of universe to the left ?

Please correct me if I am wrong.

 

[Maxwells Demon]

I don't understand.. Where do you get this theory from Talks? :)

 

[talksabcd]

I don't understand.. Where do you get this theory from Talks? :)

The diagram depicts radiation filled universe expanding into matter filled universe. We know that the limit of the visible universe is restricted by the
velocity of light. So if that limit has not yet reached the boundary of the universe then shouldn't we see uniform background radiation ?

Here I am not insisting that universe has a center but just trying to understand the cosmic background from a centered universe point of view.

Are you sure that cosmic background wouldn't be homogenous if the universe
has a center ?

 

[wilgory]

As per my understanding, I have created a picture of the universe with a center.

1) The inner light blue sphere contains only radiation. So its a radiation dominated universe.
2) The outer gray Sphere contains matter.

You can see in both the spheres that boundary of last scattering for Earth (Black dot) is within
the boundary of the universe.

So shoudn't the cosmic background radiation appear homogenous in all directions until the boundary
of last scattering expand and touch the boundary of universe to the left ?

Please correct me if I am wrong.

Talks,

It appears to me that you are still thinking of the expansion as a 3D explosion.

I don't know how well you understand the math required to fully understand a 4D expansion. I personally have to rely on the cosmologist due to my ignorance when it comes to the higher levels. I know of no analogy that can truly represent the universe.

When I have questions about the universe I prefer to go to the NASA website for answers (if you search this forum you can find plenty of knowledgeable discussions).

Here are a few links that may help clarify the current understanding of the shape and size of the known universe.

http://spaceplace.nasa.gov/en/kids/phonedrmarc/2003_june.shtml

http://map.gsfc.nasa.gov/m_uni/uni_101bbtest3.html

http://map.gsfc.nasa.gov/m_uni/uni_101shape.html

 

[talksabcd]

Pardon me Talks,

I was talking about time as the 4th dimension. As I understand it, General Relativity also uses time as the 4th dimension. What theory are you using to form your opinion? I tend to go with GR since it has passed many test and as far as I know works perfectly well as far as cosmology is concerned. If you go to Wikipedia you'll find Introduction to Special Relativity and Introduction to General Relativity. I found them both helpful in explaining how current understanding of the four dimensional universe was achieved.

http://en.wikipedia.org/wiki/Introduction_to_special_relativity

http://en.wikipedia.org/wiki/Introduction_to_general_relativity

I have no concerns abt general theory of relativity and I agree with time as
as fourth dimension. But here we are not discussing abt time. We are discussing something abt a Hypersphere (4D Sphere) which is a three dimensional sphere bent in a fourth spatial dimension.

 

[wilgory]

Talks,

This is from the Wiki page on Special Relativity.

The discussion given above has been confined to what is known as "flat space-time". The general, differential form of the space-time interval is given in the article Special relativity. The modern description of the universe uses the term (3+1)D rather than 4D to show how time is not like the spatial dimensions. This corresponds to the difference of the 4D Euclidean metric and the (3+1)D Minowski metric mentioned earlier.

The universe is 4 dimensional with the 4th dimension being time.

 

[talksabcd]

Talks,

This is from the Wiki page on Special Relativity.

The discussion given above has been confined to what is known as "flat space-time". The general, differential form of the space-time interval is given in the article Special relativity. The modern description of the universe uses the term (3+1)D rather than 4D to show how time is not like the spatial dimensions. This corresponds to the difference of the 4D Euclidean metric and the (3+1)D Minowski metric mentioned earlier.

The universe is 4 dimensional with the 4th dimension being time.

Yes I agree with you from the prespective of General relativity. But GR says
that universe is infinite. So is there any evidence for an infinite universe ?

From this thread, we came to know that universe will lack a center if the universe is Infinite or if it is a 4D sphere. To prove that universe lacks center then one should prove that universe is infinite or universe has a fourth spatial dimension. In fact scientists are trying to prove the fourth dimension, a 5D universe (4 Spatial + 1 Time)

http://www.eurekalert.org/pub_releases/2006-05/du-sph052506.php

 

[wilgory]

Talks,

There are none so blind as those that will not see!

 

[talksabcd]

Talks,

There are none so blind as those that will not see!

Here there is no room for philosophy.

 

[Maxwells Demon]

Wilgory I agree...

Talks, this is the General Astronomy room, not the philosophy room..

 

[talksabcd]

Wilgory I agree...

Talks, this is the General Astronomy room, not the philosophy room..

Infinite Universe and extra dimensions do look like philosophy and it is evident
who is supporting.