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According to the latest evidence the Universe is expanding at an accelerated rate.

1. What is the void that the Universe is expanding into?

Is it part of the Universe itself? Has it ever been defined?

2. If you reverse the "Big Bang" as if it were a video would it not trace back to the very exact location of where the "Big Bang" initially occured? Would that not

mathemetically be near the very center of the Universe?

Is there such a conceptual "location"?

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Hi msafrin -


these are indeed some of the most fundamental problems of cosmology. There are many theories as to what is "outside" the Universe. It all depends on how you see the Universe in itself. If the Universe originated from "something", then it might indeed be growing "inside" this something. But if our Universe is a closed entity which has no clear beginning and no end (which several scientists actually believe), it would be useless to try to define what is on the "outside".


As for the time reversal idea, there is something in our Universe called entropy. It is a feature (basically, the second law of thermodynamics), which states that any system will fall into gradual disorder as time passes. This is (to put it simply) because it takes energy to keep any organized structure intact, and this energy has to come from somewhere. So the entropy for the Universe as a whole is constantly increasing. Imagine a cup breaking into pieces: indeed, if you film it you can play the film backwards and see the cup become whole again. But there is no way the cup would accidentally put itself back into one piece, even if you somehow "reverse" time - because time is (most likely) not reversible in this way.


Now, the real issue with that is that while it is easy to see time as something flowing "forward", it is not so straightforward to reverse it and expect things to happen backwards. (Se our "Arrow of Time Hypography" for more about this).


But I might be digressing here. You ask if the expansion as we see it originates from the center of the Universe, and that it could theoretically be found.


Well, yes - and no. Theorists do not agree on this issue. Even if the Universe once came from a "singularity", it is important to remember that this singularity <b>was the entire Universe</b> at the time of the Big Bang. What has expanded is the entire Universe. So the center of the Universe does not really exist (what I am trying to say is: the entire Universe does not have a center). For there to be a center, you would have to have a perfectly spherical Universe inside which everything moves away from an absolute center towards the edges. But it all depends on what kind of Universe we live in, really, and this is such a difficult question that I would be ignorant if I try to take this discussion further myself...perhaps other can help out.


Some very interesting books on the topic are:


John Barrow and Frank Tipler: The Anthropic Cosmological Principle


John Barrow: Impossibility (this one is really great)


Stephen Hawking: The Universe in a Nutshell


Martin Rees: Just Six Numbers (Our review: Just Six Numbers)


...and I have just finished reading Martin Rees' latest, "Our Cosmic Habitat", in which he argues that our Universe may indeed just be one among a whole ensemble of Universes in a "Multiverse". But this is _very_ speculative. In essence, he argues that not only does our Universe not have a center - but it is not even a center in itself. It is part of something bigger. Which sort of would be related to both your questions...


Hope this made at least some sense!

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Yes,Tormod your explanation was indeed helpful.Thank you very much for your reply.


I have a provocative comment/suggestion of what it is that may lie beyond our universe that was inspired by an article regarding the latest perspective on the state of our universe that appeared recently at the BBC Science Site and in the Journal,Nature that states how 'Our Universe is so unlikely that we must be missing something'.

Link to the complete article.


I've posted the several paragraphs from the beginning of the article that contains the basis for my provocative supposition regarding what it may be that lies beyond our universe.



Our Universe is so unlikely that we must be missing something.

13 August 2002


In an argument that would have gratified the ancient Greeks, physicists have claimed that the prevailing theoretical view of the Universe is logically flawed. Arranging the cosmos as we think it is arranged, say the team, would have required a miracle.

An ever-more-rapidly expanding Universe is destined to repeat itself, say Leonard Susskind of Stanford University, California, and his colleagues. But the chances that such re-runs would produce worlds like ours are infinitesimal.

So either space is not accelerating for the reasons we think it is, or we have yet to discover some principle of physics, the researchers conclude. Like a guardian angel, this principle would pick out those few initial states that lead to a Universe like ours, and then guide cosmic evolution so that it really does unfold this way.

The incomprehensibility of our situation even drives Susskind's team to ponder whether an "unknown agent intervened in the evolution [of the Universe] for reasons of its own". But creationists should not rejoice: even a god such as this can't explain how things got so strange.

The problem stems from the observation in 1998 that the Universe's expansion seems to be speeding up. The most popular explanation for this is that there is a cosmological constant - a repulsive force that opposes gravity.

As things stand, other galaxies will eventually disappear as they zoom away from us faster than the speed of light. Then nothing that happens in those parts of the cosmos can affect us. Our world - and everywhere else - will be isolated behind a boundary called a de Sitter horizon.

This view holds that the Universe will fragment into a foam of bubbles separated by de Sitter horizons: a de Sitter space. Each bubble would eventually settle into a bland, lifeless uniformity. And that would be the end of history.

MY QUESTION IS:Could it be at all possible that our accelerating universe is but one universe among an infinite number of other universes and that what lays beyond our own universe is a so-called 'de Sitter horizon' separating us from the rest of the Giga-Universe, which in turn is itself accelerating into the vast expansive infinite abyss further beyond-the-beyond,forever for all space/time?



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This is indeed one of the things that Martin Rees discusses in the book I mention above, "Our Cosmic Habitat". Although he calls it a Multiverse, it is basically the same thing: an infinity of universes in which ours is finely tuned for life while many others are not.


The idea may sound radical, but the problem is that it is extremely difficult to prove. Because we are unable to probe anything beyond the de Sitter horizon - simply because light, or anything else which moves at the speed of light will never escape from any other universe and enter our own. Thus we cannot see anything which does not come from our own Universe. So we (might) never be able to observe anything directly.


So it begs the question, how can this be proved? Martin Rees says that since it can be contemplated then it is indeed science - I am not sure this is sufficient for me.


But I agree that the theory is intriguing.

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Thank you for confirming that my supposition regarding

a Multiverse,as proposed by Martin Rees does at least have merit.

You said;

<Because we are unable to probe anything beyond the de Sitter horizon - simply because light, or anything else which moves at the speed of light will never escape from any other universe and enter our own. Thus we cannot see anything which does not come from our own Universe. So we (might) never be able to observe anything directly.>


I totally agree that our chances of ever making any observations from beyond our own universe is nil,but simply as rhetorical conjecture (as 'Devil's Advocate')

I might propose to you that the speed of light,as suggested by some,may not be as immutable as once believed EVEN within our own universe and if for argument's sake, the physics of another universe would allow for a speedier 'speed of light', perhaps the supposition 'that light from another universe might indeed escape and observed by us someday' is a theory that could very well be **contemplated as science**.


<Martin Rees says that since it can be contemplated then it is indeed science - I am not sure this is sufficient for me.But I agree that the theory is intriguing.>


I highlighted the words "contemplated as science" to mock Mr.Rees because I agree with you that his guideline for what he thinks can be constituted as science is not sufficient for me,either.


QUESTION:How does Mr.Rees incorporate the evidence for the

'Big-Bang' into an overall Multiverse? Was the Multiverse

also created by the 'Big-Bang'?


Do you know the basis for the naming of the 'de Sitter horizon'?

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That the speed of light may not be constant in our Universe is indeed exciting, but it is not news at all, I recently posted a link to a news report from New Scientist that Australian researchers have shown that time may indeed be slowing down.


But this discussion is hypothetical to the extreme, because first we must


a) assume that there is a multitude of universes

B) assume that light (or any other source of information) may reach us from this other universe

c) assume that we may be able to probe beyond the de Sitter horizon


I am not a cosmologist so I cannot offer definitions of terms.


To learn more about Willem de Sitter, here is a short bio:

Willem de Sitter biography


What is the de Sitter horizon:

John Gribbin: Inflation for beginners - search this page for "de sitter" and you'll find a brief introduction.


I have read lots of books about cosmology and at work I am doing a feature on John Barrow, one of the brains behind the anthropic principle. I do not agree with the writers of the article in Nature that the Multiverse theory refutes the anthropic principle, rather I see it as a philosophical excercise which actually builds on it. The anthropic principle (which, admittedly, is a rather complex philosophical path) opens up for the possibilities of evolving universes - which would make the Multiverse seem rather necessary in stead of surprising.


But that's just my thoughts on the subject...again, I am not a specialist on this.

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I appreciate the generosity in which you are willing to share your vast encylcopedic repository of knowledge and erudition with the public and your masterful ability to grasp the intracacies of highly complex issues and reducing them into basic everyday laymen's language and understanding.


QUESTION:1.In your reference to Mr.Rees' exotic suppostion, I had asked if you might provide a brief explanation on how he reconciles and incorporates the 'Big-Bang' into his grand vision of a Multiversal cosmos and again I respectfully request your indulgence in this matter.


2. I also hoped to elicit the uncanny powers of your probitive skills and analysis towards an explantion of how it is possible that the physical Universe as we understand it to be is as flat as a three-dimensional shape can possibly be as confirmed by the cosmology commmunity.

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I'll do my very best here (tongue in cheek):


1) If I remember correctly, Rees' suggests that the Big Bang was the beginning of our Universe, but that it was a "local" big bang in what became our part of the Multiverse. There has been and will be an unlimited number of Big Bangs, but for our Universe there will only ever be The One that was the beginning of our time. He does not need to reconcile this with anything, but I think it is obvious to anyone that if you call in a Multiverse to explain the existence of human beings, you kind of push the Causality issue a bit - it's like saying, "okay, there is no God, but there was something before our own Universe. We can never know what it is but it must be there, because we are here."


2) I don't understand your second question, perhaps you need to rephrase it. If you refer to the expansion rate being at the exact level it needs to be to continue expanding forever, well, then I find it rather easy to explain that spacetime is (extremely close to) "flat". If it was not so close to flat, then it would be curved, and the larger the curvation the easier it would be to observe it. In a curved spacetime, time loops should be easier to find, since the distance between two spots in spacetime need not be as far apart as it seems. There is a simple analogy to this - if you take a piece of paper and put one dot on the upper part of the page, and one on the bottom part of the page, then in a flat spacetime the shortest route between the two is a direct line. But in a curved spacetime, the shortest path would actually be to tunnel through the paper from one dot and emerge at the other dot, without moving on the paper at all (because, obviously, the sheet of paper would be curved and not straight).


We do know, of course, that on a local level spacetime is indeed curved, since that is what Einstein proved with his relativity theory. He replaced Newton's idea of attracting bodies with a "gravity well", in which our Sun creates a depression in spacetime, around which our Earth circles. What keeps the Earth from falling into the sun is the speed and momentum of its orbit and (possibly) a repulsive force (the one Einstein called his bigges blunder) which is also the cause of vacuum energy...but on a Universal scale, the local "bumps" in spacetime evens out so in general everything becomes "flat".


But this is written after a long day at work and if it seems totally unreasonable then blame my extreme need for a cup of coffee.



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In reference to my most previous query regarding the flat shape of the universe I have provided a link to the subject and have included the first paragaph of the article and look for your response.


Boomerang backs flat universe

Physics in Action: June 2000

PhysicsWeb - Boomerang backs flat universe


The faint microwave glow left over from the big bang has been measured with unprecedented precision, giving astronomers a new insight into the nature of the universe. The geometry of the universe is Euclidean and space is flat. This has now been confirmed from detailed measurements of the cosmic microwave background - the radiation left over from the big bang - by an international team of astronomers from Italy, the UK, the US, Canada and France. The Boomerang collaboration, led jointly by Paolo de Bernardis of the University of Rome and Andrew Lange of the California Institute of Technology, has measured the angular distribution of temperature fluctuations in the microwave background with unprecedented accuracy. Such fluctuations contain information about the energy density and curvature of the universe.

PhysicsWeb - Boomerang backs flat universe


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2. I also hoped to elicit the uncanny powers of your probitive skills and analysis towards an explantion of how it is possible that the physical Universe as we understand it to be is as flat as a three-dimensional shape can possibly be as confirmed by the cosmology commmunity.


I am not sure we read the same thing into this: "as flas as a three-dimensional shape can possibly be". What do you suggest it means? Three dimensional space is three dimensional space, I don't know if you can talk about "degrees" of flatness.


The paper contains this paragraph:

Boomerang has measured the peak with unprecedented precision and gives confirmation of the primordial origin of the fluctuations. Moreover, the measured peak agrees precisely with the expectation for a flat universe. The location of the peak means that the density of matter is within 10% of the critical value. The universe must therefore be dominated by dark energy - the modern reincarnation of the cosmological constant.


Since the paper is now over two years old, we must take new evidence into consideration. Numerous papers have been published since then, and this summer there has been a lot of attention concerning the amount of not only dark matter but also "dark energy", which has been found (in theory, of course) to reconcile Einstein's relativity theory and the expansion rate of the Universe.


Here are a couple of interesting links to other, more recent articles at PhysicsWeb:

Cyclic universe bounces back


Tuning in to the early universe



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I am no expert by any means in cosmology, but I thought I might add something. You (msafrin) said that there is evidence that the universe is expanding, and indeed that is true. However, with the new theory that the speed of light is not constant, this could have a MAJOR effect on the theories of the rate of the universe's expansion, because we measure the speed at which an object is traveling away from us by its redshift. So if the speed of light is not constant, that could have an effect on the redshift. IF the theory is true, we will have to find the original speed of light, ie, the speed at the beginning of the universe, and figure that into our calculations. However, this might help prove that the expansion of the universe is indeed accelerating.



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The description of the apparent flat shape of the universe as being as 'flat-shaped as possible' was taken from an article I read when this news story first appeared several years ago.


My description of the universe as related in the article 'as flat-shaped as any three dimensional geometric object could be' was used in exercising 'poetic license' to elaborate and explain the description in the simplest words possible but which seems ironically to have created more confusion instead of making it easier to understand.


My reference to the universe being 'as flat as any geometric,three dimensional could be' relates to the conceptual degree of the relative out-of-proportion relationship in comparing its depth to its length and width and can be explained if I used the illustration of a sculptured marble block designed as a pedestal or platform for a statue as a three dimensional model of the universe, the block's dimensions being three feet long,one foot wide and two inches thick it would most definitely be considered flat by any definition of the word.


As an artifact (and three dimensional geometric form),the block could certainly be made relatively flatter by physically chiseling it in half and flatter still until the thickness would remain a sliver of marble up to the very limit in which the marble base retained its physical attributes,or as flat as it could possibly be.


For the purposes of dramatizing how flat a three dimensional object could be relative to its other two dimensions in as precise an incremental measurement as possible let's assume we have a pane of glass one hundred miles long by twenty miles wide and a thickness of one inch, the fact is relative to the admittedly surreal dimensions of this imaginary pane of glass, we could conceivably modify the thickness to one hundredth of an inch creating a flatter three dimensional shape and thus create an ever more flatter three dimensional object so on and so on.


I hope this analogy might explain what I meant when using the term "as flat as possible" when describing the apparent flat shape of the universe which incidentally has absolute no bearing on the question I had originally intended to propose, which is this; Why is the universe indeed flat shaped instead of, let's say,a three dimensional circle? In other words, what specific forces,what physical laws exist in the universe going back to the Big Bang that would result in a flat shape as opposed to any other? Obviously,there must be *some* reason that the universe took this specifc shape.I myself would assume that if the singularity was uniform and the forces that existed at the moment of creation were uniformly applied it should then have radiated out in all directions uniformly and equally into a circular shaped universe.


So,inconclusion what are the specific cosmic forces in the universe that led to the flat shape as opposed to having any other shape???

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I think you are confusing the concepts of flatness in objects with flatness in space.


A one-inch-thick block of marble is not necessarily flatter than a two-inch-thick block. They can both be as flat as the other. Flatness has nothing to do with thickness.


Thus, even the glass plate is no good analogy, because flatness generally will not depend on the size of an object, but on its properties in relation to the spacetime in which it floats.


What I am saying is that it does not make much sense to say that an object is flat just because it has a certain thickness. Consider a sheet of paper - it is also flat in this sense. But if you hold it up by one end, what happens to this flatness? It goes away, because the paper now curves downwards due to the force of gravity. So "flatness" is not a property, it is a state which can only be found by measuring an object. It does not exists as a physical property - there are no true "flat" objects.


If you placed a large, flat, glass plate in space, with the dimensions you specify, it would possibly stay flat for an amount of time. But such a large object, if placed within the vicinity of a planet or a moon, would become attracted to this object (well, in fact, according to Newton the two objects would attract each other), which will make the object curve, most strongly on the part of the object closest to the planet or moon.


So what?

I think it makes no sense to compare the "flatness" of small, physical objects with the flatness of spacetime in itself. I believe that what is referred to when we talk about a "flat" universe, is the curve which can be drawn when you measure the density in our Universe with the rate of expansion.


A "flat" universe is not a universe that is box-shaped with a flat top and bottom. It is a universe in which the density is at a point where the Universe will continue to expand forever.


However, if the Universe is not flat, it must be curved, and that gives us two possibilities:


1. it may be "open", and expand faster and faster (which current observations actually support), in which it will grow infinitely old (read my review of the book The Five Ages of the Universe for an explanation of this)


2. it may be "closed", and expand slower and slower (eventually causing a Big Crunch, where it collapses into a singularity and possibly a new Big Bang).


this web page has an excellent explanation of what "flatness" as related to our Universe really means:

Spatial Curvature; Flatness-Oldness; Horizon

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  • 3 weeks later...

Here is an interesting story regarding Big Bang:


FOUND: Polarization in the Cosmic Microwave Background


Astrophysicists now think they have proof that the Big Bang actually happened, because they can observe a polarization in the microwave background.


Basically what this means is that they can track the ripples in spacetime caused by the expansion which occured after the Big Bang. I think. It's a bit over my head but it's very interesting news.

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Interesting topic, no doubt, and most positive in that it leads to all sorts of speculation. Yet I have to wonder if attempting to explain the origin and ultimate course of the universe (or universes) isn't kind of like trying to read the mind of God. Is it not the symmetries we discover in the process what is of most importance to us as relevant to our past, present and future existance?


I'm a horticulturist (hottotrotulist) and when I consider the apple that drops from the tree what I see is a symmetry. I know (surmise) from all I have experienced of the apple - its hereditary traits and all the observable environmental traits imposed upon it from external sources - that the outer symmetry I view is but a reflection of all its symmetrical possibilities. The apple in particular is interesting because it seldom (never by my experience) comes to true to seed, yet experience also shows that within the seed is all that the apple is, has been, or ever will be. Is not that seed somewhat similar to the cosmologic singularity we derive from observation of the celestial bowl or symmetries observed of the quantum field?


Hey, folks, I'm out of my element here, and no offense meant, okay; but if I were a cosmologist or the quantum physicist I think the tendency might be to make the best I could of the symmetries observed and let the the singularity take care of itself.

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Eugene -


your comments are of course not offensive...but highly welcome.


But I beg to differ. You hold that the seed contains all that is (was, and will ever be) the apple. But this is a vast oversimplifaction in my eyes. How can the seed possibly contain the interactions between the apple and the outer world? How can it possibly foresee when and how the apple will fall, if it will fall at all? Perhaps it will be eaten by an animal or picked by a child.


I believe Cosmology to be the study of the Universe, not what mind is behind it. It is important to question the discoveries astronomers make, but it is also important not to throw everything out the window simply because our intuition tells us otherwise.


Like msafrin pointed out, there are many different views of what the Big Bang was, how it happened, whether it was the beginning of time or not, whether our Universe will expand forever - or not - et cetera, et cetera.


The constants of nature may not be as constant as we think. I am currently reading a very good book by John D. Barrow ("The Constants of Nature") in which he explains many of the very different theories which have come up through the ages to explain the inexplicable symmetry we observe in so many things. And they more often than not turn out to be symmetric simply because of the way we observe them.


But what it boils down to, as far as I can see, is how much we know at any given time, and how much we are able to learn from the mistakes we make. So we see one symmetry today - we might see another symmetry tomorrow.


And that's what makes it all so incredibly exciting for people like me...


And - if I may ask - what is the problem with trying to read the mind of God? Einstein spent most of his life doing exactly that.

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  • 2 weeks later...

I have a friend who once tried to explain how there might be more dimensions beyond the third to someone by saying: "Imagine you are a drawing. You live in two dimensions. There is an up, down, forward, and backwards. If you have lived your entire life only knowing that there are two dimensions, then the thought of a third dimension would never even enter into your mind."


This leads to my question. If there is a multiverse, then couldn't there be another dimension, one that we do not yet know about, that bridges the gap between each universe? This could explain why light can not travel between the universes.


Another question, which has nothing to do with any of these posts, I have read that when matter reaches the speed of light it becomes energy. Then couldn't there be a way to convert the energy back into matter? That really wasn't my question. My question is, is this the basis of the theory of wormholes?

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