Where is the center of the universe?

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Why is it a forgone conclusion that the universe has no edge to it, when we cannot see outside our own observable section? To say there is no edge is absurd in my opinion because our vision it limited.
Because if would violate some of the fundamental laws of physics for the universe to have a physical edge.
 
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Because if would violate some of the fundamental laws of physics for the universe to have a physical edge.
Proof your point.
 

DaveC426913

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Proof your point.
It's not his point, it is generally accepted cosmology.

There's a fair bit of reading, but you could start with the Cosmological principle and the Principle of Mediocrity, though they are not compelling.
 

Drakkith

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Why is it a forgone conclusion that the universe has no edge to it, when we cannot see outside our own observable section? To say there is no edge is absurd in my opinion because our vision it limited.
They don't say there isn't an edge. They say that the model doesn't require there to be an edge for it to work. As far as I know at least.
 

marcus

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They don't say there isn't an edge. They say that the model doesn't require there to be an edge for it to work. As far as I know at least.
There is some truth to that! You can put it in terms of Occam Razor commandment---Thou shalt not make thy models unnecessarily complicated.

We see no evidence of a boundary, so why put it in the model? Plus it would be a mathematical headache. If there is a boundary forces would be unbalanced and expansion would appear asymmetrical unless you put the earth at center. But putting earth at center is "Un-Copernican"

The thing a lot of newcomers don't realize is that cosmology is a mathematical science that is primarily concerned with a math MODEL of the universe and that model runs according to the 1915 GR equation (Einstein Field Equation) which is our current law of gravity. If you have a model which must run according to an equation you don't have a lot of freedom to mess around.

The GR equation describes the evolving geometry of all space. We know it changes and the law of gravity describes how. On page one of the book you are given a manifold which is all space thru all time, and a metric or distance function that describes the geometry---what paths are straight and how distances relate to areas and volumes and how distances change thru time etc.

Personally I find the idea of a boundary UNINTUITIVE. The universe is supposed to be ALL SPACE. So what would a boundary be separating space from?

The GR equation is by far the most accurate law of gravity we've ever had---it gives more precise numbers than the older Newton law. It has been tested repeatedly and checks out every time. And it is a law both of gravity and evolving geometry because they are the same thing (how massive objects influence geometry).
So there is a COMMON SENSE reason to base models of the universe's geometry on the GR equation. Its a no-brainer in fact.

So if you accept to base your model cosmo on the accepted law of gravity/geometry, then the idea of a boundary has no standing. How to implement? Maybe by having the average density of galaxies gradually peter out so that our region is surrounded by a large "void". But then expansion would most likely be decelerating so let's fix that with a larger cosmological constant, and so on. It is not naturally a part of the picture. Just giving the idea of a boundary a meaning seems likely to lead to headaches and a more complex picture.

The discussion gets over into talking about what's called the "cosmological principle". On large scale the universe seems on average uniform. Matter seems uniformly distributed throughout space, at any one time. So we infer looking back in time. At each epoch matter was uniformly distributed at some average density that prevailed at that time.

So people say "homogeneous and isotropic" which basically just means evenly distributed on largescale average.

That makes the model simple and we see no evidence to the contrary so since the job is to get the simplest model with the best fit, and no evidence to contrary, evenness is assumed.

Maybe, as Drakkith suggests, it is at heart an Occam thing--the ancient tradition in mathematical sciences of keeping the model simple.
 
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Rob D

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Personally I find the idea of a boundary UNINTUITIVE. The universe is supposed to be ALL SPACE. So what would a boundary be separating space from?
Precisely. "Bubble theory" as a model for the uber-universe, does not require any membranes around the bubbles but rather they may simply be viewed as cosmological villages in the vast darkness, collections of local activity activated by some localized phenomenon such as a big bang and separated from any other such areas of activity by lots and lots of nothing, or something or what have you. And, of course, the mass and energy making up the village are reorganized every 14 billion years or so, at least in this mind model. It's always been there and always will be there following the various conservation laws.

But, no boundary or membrane encapsulating the universe or universes is needed since the vastness of infinite space pretty much takes care of the isolation question on its own.

Best,
RD
 
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So if you accept to base your model cosmo on the accepted law of gravity/geometry, then the idea of a boundary has no standing. How to implement? Maybe by having the average density of galaxies gradually peter out so that our region is surrounded by a large "void". But then expansion would most likely be decelerating so let's fix that with a larger cosmological constant, and so on. It is not naturally a part of the picture. Just giving the idea of a boundary a meaning seems likely to lead to headaches and a more complex picture.
Right, and what about this 'bounded' universe to be surrounded by similar universes ?
 

marcus

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it gets into semantics and I lose interest. most "other universe" talk seems vacuous, devoid of empirical content. I try to keep language simple and consistent with professional usage---universe is all space and all physical existence.

That seems to be how it is used in 99% of the cosmology research papers that come out daily on the preprint archive.

Have a look for yourself. http://arxiv.org/list/astro-ph.CO/recent
Essentially nothing about "multiverse" in the run of mill professional literature.
More confined to popular media where they stimulate the imagination in order to sell books. Talk about string theory and God and multiverses and stuff.
 
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You obviously don't get my point.
Call our accelerated expaning bubble of galaxies 'A', picture it in space and surround it with 'A2', 'A3', ...
 

Drakkith

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You obviously don't get my point.
Call our accelerated expaning bubble of galaxies 'A', picture it in space and surround it with 'A2', 'A3', ...
What about it? Even if it's possible, there's no way for us to know at the moment. Our current theory is difficult enough as it is without trying to complicate it with unknowable stuff.
 
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What about it? Even if it's possible, there's no way for us to know at the moment. Our current theory is difficult enough as it is without trying to complicate it with unknowable stuff.
At least it can explain the acceleration of expansion, because of attraction to surrounding A2, A3, ... without need for dark stuff, isn't that a simplification ?
 
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How would you see an outer edge or for that matter an inner edge, from our view point we only see signals between objects?
 

Drakkith

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At least it can explain the acceleration of expansion, because of attraction to surrounding A2, A3, ... without need for dark stuff, isn't that a simplification ?
Absolutely not. And it doesn't even explain the accelerating expansion.
 
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One day I may make a GPU simulation out of it, to show how it can work.
 
it gets into semantics and I lose interest. most "other universe" talk seems vacuous, devoid of empirical content. I try to keep language simple and consistent with professional usage---universe is all space and all physical existence.

That seems to be how it is used in 99% of the cosmology research papers that come out daily on the preprint archive.

Have a look for yourself. http://arxiv.org/list/astro-ph.CO/recent
Essentially nothing about "multiverse" in the run of mill professional literature.
More confined to popular media where they stimulate the imagination in order to sell books. Talk about string theory and God and multiverses and stuff.
You might as well say that the cosmos revolve around the earth. That kind of perspective amounts to the very same thing. It could well be true but without proof in either favor, it is speculation and only serves to hinder progress. Nobody will ever find a way to prove it if we refuse to consider the possibilities.

Existing models are useful for practical applications but contemplating what is beyond our knowledge domain is paramount to discovery.
 
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Just to reinforce some previous comments.

The entire Universe has no center, for it to have a center would also preclude a leading edge. This would violate the Cosmological principle and also undermine relativity by applying different and preferential reference frames.

The BB was not a ballistic explosion in a pre-existing space and is entirely background independant.

To try to assume external vantage points "outside" the Universe is pointless and does not provide any helpful understanding IMO.

Now there are edges to the Universe, but these are not spatial; they are temporal. When I stand and look up into the sky I am on the temporal edge of the Universe.

I hope this helps and am happy to discuss this further as sometimes it can help for a layperson to explain this. (My head still hurts if I think about it too much.)

Cosmo
 

Drakkith

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You might as well say that the cosmos revolve around the earth. That kind of perspective amounts to the very same thing. It could well be true but without proof in either favor, it is speculation and only serves to hinder progress. Nobody will ever find a way to prove it if we refuse to consider the possibilities.

Existing models are useful for practical applications but contemplating what is beyond our knowledge domain is paramount to discovery.
We have overwhelming evidence of at least a single universe and zero evidence of more than a single universe. I think in this case we should stick to a single universe model until something tells us otherwise.
 

Chalnoth

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We have overwhelming evidence of at least a single universe and zero evidence of more than a single universe. I think in this case we should stick to a single universe model until something tells us otherwise.
A single universe requires more assumptions than a plethora of universes does.
 

marcus

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I've always found that response to anthropic arguments to be rather pathetic.
Strength/weakness of Steinhardt's statement could be somewhat in the eye of the beholder. He led the charge, and was supported to some extent by David Gross and his Princeton colleague Edward Witten. I think Steinhardt's response was to large extent effective. Multiverse papers were excluded from the "Strings 2008" conference at CERN and have made little or no showing at subsequent Strings XXXX. I give Steinhardt much of the credit for speaking out early on this issue. People should judge the cogency of his argument for themselves.

The question Edge asked in 2005 was "WHAT DO YOU BELIEVE IS TRUE EVEN THOUGH YOU CANNOT PROVE IT?"

==quote Edge 2005 annual question==

Paul Steinhardt
Albert Einstein Professor of Physics, Princeton University.

I believe that our universe is not accidental, but I cannot prove it.

Historically, most physicists have shared this point-of-view. For centuries, most of us have believed that the universe is governed by a simple set of physical laws that are the same everywhere and that these laws derive from a simple unified theory.

However, in the last few years, an increasing number of my most respected colleagues have become enamored with the anthropic principle—the idea that there is an enormous multiplicity of universes with widely different physical properties and the properties of our particular observable universe arise from pure accident. The only special feature of our universe is that its properties are compatible with the evolution of intelligent life. The change in attitude is motivated, in part, by the failure to date to find a unified theory that predicts our universe as the unique possibility. According to some recent calculations, the current best hope for a unified theory—superstring theory—allows an exponentially large number of different universes, most of which look nothing like our own. String theorists have turned to the anthropic principle for salvation.

Frankly, I view this as an act of desperation. I don't have much patience for the anthropic principle. I think the concept is, at heart, non-scientific. A proper scientific theory is based on testable assumptions and is judged by its predictive power. The anthropic principle makes an enormous number of assumptions—regarding the existence of multiple universes, a random creation process, probability distributions that determine the likelihood of different features, etc.—none of which are testable because they entail hypothetical regions of spacetime that are forever beyond the reach of observation. As for predictions, there are very few, if any. In the case of string theory, the principle is invoked only to explain known observations, not to predict new ones. (In other versions of the anthropic principle where predictions are made, the predictions have proven to be wrong. Some physicists cite the recent evidence for a cosmological constant as having anticipated by anthropic argument; however, the observed value does not agree with the anthropically predicted value.)

I find the desperation especially unwarranted since I see no evidence that our universe arose by a random process. Quite the contrary, recent observations and experiments suggest that our universe is extremely simple. The distribution of matter and energy is remarkably uniform. The hierarchy of complex structures ranging from galaxy clusters to subnuclear particles can all be described in terms of a few dozen elementary constituents and less than a handful of forces, all related by simple symmetries. A simple universe demands a simple explanation. Why do we need to postulate an infinite number of universes with all sorts of different properties just to explain our one?

Of course, my colleagues and I are anxious for further reductionism. But I view the current failure of string theory to find a unique universe simply as a sign that our understanding of string theory is still immature (or perhaps that string theory is wrong). Decades from now, I hope that physicists will be pursuing once again their dreams of a truly scientific "final theory" and will look back at the current anthropic craze as millennial madness.

==endquote==
http://edge.org/response-detail/805/what-do-you-believe-is-true-even-though-you-cannot-prove-it
 
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Chalnoth

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Strength/weakness of Steinhardt's statement could be somewhat in the eye of the beholder. He led the charge, and was supported to some extent by David Gross and his Princeton colleague Edward Witten. I think Steinhardt's response was to large extent effective. Multiverse papers were excluded from the "Strings 2008" conference at CERN and have made little or no showing at subsequent Strings XXXX. I give Steinhardt much of the credit for speaking out early on this issue. People should judge the cogency of his argument for themselves.

The question Edge asked in 2005 was "WHAT DO YOU BELIEVE IS TRUE EVEN THOUGH YOU CANNOT PROVE IT?"

==quote Edge 2005 annual question==

Paul Steinhardt
Albert Einstein Professor of Physics, Princeton University.

I believe that our universe is not accidental, but I cannot prove it.

Historically, most physicists have shared this point-of-view. For centuries, most of us have believed that the universe is governed by a simple set of physical laws that are the same everywhere and that these laws derive from a simple unified theory.

However, in the last few years, an increasing number of my most respected colleagues have become enamored with the anthropic principle—the idea that there is an enormous multiplicity of universes with widely different physical properties and the properties of our particular observable universe arise from pure accident. The only special feature of our universe is that its properties are compatible with the evolution of intelligent life. The change in attitude is motivated, in part, by the failure to date to find a unified theory that predicts our universe as the unique possibility. According to some recent calculations, the current best hope for a unified theory—superstring theory—allows an exponentially large number of different universes, most of which look nothing like our own. String theorists have turned to the anthropic principle for salvation.

Frankly, I view this as an act of desperation. I don't have much patience for the anthropic principle. I think the concept is, at heart, non-scientific. A proper scientific theory is based on testable assumptions and is judged by its predictive power. The anthropic principle makes an enormous number of assumptions—regarding the existence of multiple universes, a random creation process, probability distributions that determine the likelihood of different features, etc.—none of which are testable because they entail hypothetical regions of spacetime that are forever beyond the reach of observation. As for predictions, there are very few, if any. In the case of string theory, the principle is invoked only to explain known observations, not to predict new ones. (In other versions of the anthropic principle where predictions are made, the predictions have proven to be wrong. Some physicists cite the recent evidence for a cosmological constant as having anticipated by anthropic argument; however, the observed value does not agree with the anthropically predicted value.)

I find the desperation especially unwarranted since I see no evidence that our universe arose by a random process. Quite the contrary, recent observations and experiments suggest that our universe is extremely simple. The distribution of matter and energy is remarkably uniform. The hierarchy of complex structures ranging from galaxy clusters to subnuclear particles can all be described in terms of a few dozen elementary constituents and less than a handful of forces, all related by simple symmetries. A simple universe demands a simple explanation. Why do we need to postulate an infinite number of universes with all sorts of different properties just to explain our one?

Of course, my colleagues and I are anxious for further reductionism. But I view the current failure of string theory to find a unique universe simply as a sign that our understanding of string theory is still immature (or perhaps that string theory is wrong). Decades from now, I hope that physicists will be pursuing once again their dreams of a truly scientific "final theory" and will look back at the current anthropic craze as millennial madness.

==endquote==
http://edge.org/response-detail/805/what-do-you-believe-is-true-even-though-you-cannot-prove-it
Why did you post this again?
 
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Just to reinforce some previous comments.

The entire Universe has no center, for it to have a center would also preclude a leading edge. This would violate the Cosmological principle and also undermine relativity by applying different and preferential reference frames.

The BB was not a ballistic explosion in a pre-existing space and is entirely background independant.

To try to assume external vantage points "outside" the Universe is pointless and does not provide any helpful understanding IMO.

Now there are edges to the Universe, but these are not spatial; they are temporal. When I stand and look up into the sky I am on the temporal edge of the Universe.

I hope this helps and am happy to discuss this further as sometimes it can help for a layperson to explain this. (My head still hurts if I think about it too much.)

Cosmo

http://www.youtube.com/watch?v=VOz4PkdY7aA&feature=related


Videos like these and many more show animations of the big bang, they show it as an observer somewhere outside of the universe. They put these on all the science channels as well, why would they put false information like this in the public and give them faulty ideas of the big bang if it is not true. From what you stated this animation cannot be valid because there is no edge or outside of the universe, correct?
 
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