before the big bang,

My two cents:

No one is entirely sure about the "shape" of the universe right now. There are three possibilities, but they all illustrate the same general principle.

1) The universe is "closed." In this case, in principle, if you took a spaceship and flew far enough in one direction you'd end up back where you started. So the universe has no boundaries BUT it has a finite volume. An analogy might be to the surface of the earth--the surface has finite volume, but you can never find an "edge" to it while you're on it.

The fact that the universe is "expanding" does NOT mean that the universe is taking over empty space. It means that the surface on which we live is getting larger. Think of it as if we were all two-dimensional beings that lived on the surface of a balloon. The balloon is the universe to us--we have no idea there's anything but the rubber of the balloon's skin. Then someone starts inflating the balloon. So we see it as the universe "expanding" in that there's more area for us to run around in. If I'm at one spot on the balloon, and someone else is on another spot, then as the balloon inflates we'll get further away from each other. But just because it's expanding doesn't mean that it has a boundary--it's still a sphere, and therefore has no edges.

2) The universe is "flat." In this case the universe would be infinite in a more traditional sense--you could go forever in one direction and you'd never come back to where you started. But even though it's infinite, it still expands. Using a balloon analogy again, say we had an infinite 2-dimensional sheet of rubber. It's total area is infinite, so obviously it can't "expand" in the traditional sense. But if I pull on it, it will stretch, and this will be viewed by the inhabitants of that sheet as expansion--again, if I'm stuck to one piece of rubber and my friend is stuck to another, we perceive ourselves as getting more distant from each other. And this process is occurring simultaneously at every point in the universe.

3) An "open" universe. This is shaped like a 4D hyperbola. It's very hard to visualize. The closest analogy is to a saddle but that really isn't a good enough analogy.

The shape of the universe has implications for our ultimate fate. A closed universe will ultimately collapse back into itself (and maybe oscillate) and the universe will end in an enormous fireball. A flat universe will expand forever, but the expansion will slow down until the rate of expansion equals zero. An open universe will expand forever, but the rate of expansion will remain finite and nonzero. In flat and open universes the universe gets colder and colder forever.

Open is considered the most likely possibility, and if you polled researchers you'd probably get 70% or more who picked this. (In fact, a fair amount of data suggests that the rate of expansion has been speeding up.) Flat is the next most likely. Closed is extremely unlikely--only a few diehards cling to this in the face of the data. The oscillating universe, philosophically appealing as it is, is basically dead.

 

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Well, how about the idea that there is a multiverse--a veritable foam of universes with a whole slew of different properties--which existed before this universe, and out of which this universe was born?

 

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I'm not denying any of this. Read my posts above. The article states:

"we could observe the era when matter was the most important constituent of the universe and the universe was decelerating. At those redshifts, the relation between redshift and flux would bend back toward brighter fluxes, while the effects of gray dust presumably would grow, or at least remain constant. To make accurate measurements of this effect will require discovering and making good measurements of redshift 1 supernovae whose light is redshifted into the infrared. The Next Generation Space Telescope may play an important role in this decisive test."

Anytime: Your "two cents" are worth three. Chess anyone?

Xylene: "a multiverse--a veritable form of universes with a whole slew of different properties--which existed before this universe, and out of which this universe was born?"

Nice point as it is imagined - and even scientifically conjectured - that a previous and future universe would not have the same physics as our's does now.

 

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You say that a flat Universe must be infinite. That's not true, it can also have a finite volume, if is, for example, an hypertorus (other topologies are also possible)
But it's true that the actual paradigm in cosmology, the Lambda-CDM model, postulates that the Universe is infinite

You say that open is considered the most likely possibility. No, the most likely possibility is a flat universe. This is the conclusion drawn from the results obtained by the WMAP satellite. In fact, the Lambda-CDM model is based on a flat Universe

And a closed Universe can avoid collapsing into itself if there exist a cosmological constant. Also, is not true that a flat Universe must necessarily slow down in the future

 

"Lambda-CDM (ΛCDM model) is an abbreviation for Lambda-Cold Dark Matter. It represents the current concordance model of big bang cosmology that explains cosmic microwave background observations, as well as large scale structure observations and supernovae observations of the accelerating expansion of the universe. It is the simplest model that is in agreement with all the observations.

Λ (Lambda) stands for the cosmological constant which is a dark energy term that allows for the current accelerating expansion of the universe. Currently, approximately 70% of the energy density of the present universe is in this form. Cold dark matter is the model where the dark matter is explained as being cold (not thermalized), non-baryonic, collisionless dust. This component makes up 26% of the energy density of the present universe. The remaining 4% is all of the matter and energy that makes up the atoms and photons that are the building blocks of planets, stars, and gas clouds in the universe. The model assumes a nearly scale-invariant spectrum of primordial perturbations and a universe without spatial curvature. It also assumes that it has no observable topology, so that the universe is much larger than the observable particle horizon." http://en.wikipedia.org/wiki/Lambda-CDM_model

Oh, how I love these little wicked Wikipidea definitions. Only joking! But the way they state it seems to end in a contradiction in terms of topography: "assumes no spatial curvature" yet then states "assumes no observable topology." Why not have curves? Look how great they look on girls! And curvatures can come in many shapes:

"An observable Universe that is spatially "nearly flat", from the measured curvature, allows for a simplification, whereby the dynamic, accelerating dimension of the geometry can be separated and omitted by invoking comoving coordinates. Comoving coordinates, from a single frame of reference, leave a static geometry of three spatial dimensions.

Of eight feasible geometries given by the geometrization conjecture, the shape of the observable Universe, or the local geometry, is in all likelihood described by one of the three feasible spacial geometries:

3-dimensional Euclidean geometry, generally annotated as E3
3-dimensional spherical geometry with a small curvature, often annotated as S3
3-dimensional hyperbolic geometry with a small curvature, often annotated as H3

Even if the Universe is not exactly spatially flat, the spatial curvature is close enough to zero to place the radius beyond the horizon of the observable Universe."
http://en.wikipedia.org/wiki/Flat_universe

I interpret this as saying that we can see it as flat, but it can still have curves and/or a curvature at the edges, and thus not make it infinitely flat - maybe folding in on itself at the edges. But also, it may be the current accepted hypothesis of an accelerating expanding universe, but no where does it say that it has to "keep on" expanding. This model can still hold true for the present state of the universe until the universe be shown to start decelerating, thus implying a stop and contraction. It doesn't imply that this is always how it has to be?

 

See that’s not entirely true also. A vacuum is empty. The radiation in space comes from other sources, namely giant balls of plasma (ie stars) which transfer energy off into space in the form of solar radiation (as well as heat and light but that’s another matter).

Space can’t emit energy because it has no energy to transfer. On the other hand it’s perfectly good medium for other sources to transfer energy through. However none of it is coming from the vacuum itself.

Once again, that’s how I remember it.

 

Only an "absolute vacuum" is empty, but physicists don't normally talk about a vacuum as such because it is unobtainable. Therefore, you are right, this is why we receive background radiation, but this is a form of energy. Interstellar space consists of plasma.

 

After reading all the posts, a few thoughts have occurred to me.

First, saying god did it is a copout. Saying we can never know is not the same type of copout (I do not consider it a copout at all). Attributing the start to god pretends to be an answer which requires no further analysis. It says: “problem solved, I know the answer: god did it.” Denying the possibility of finding an answer might be called giving up, but not a copout.

Saying that science will find the answer seems to be a bit of a copout, but at least it is not a claim to be an answer to the question.

There is some reason to suppose that time, space, matter/energy, et cetera are artificial abstractions developed by our minds to help us understand the world of our senses. If the reality is a mix or interaction of these abstractions, then time & space cannot exist independently of matter. This concept might not help us understand, but it compresses the problem to wondering how the matter/energy came into existence. Until matter/energy existed, there was no time and perhaps no space, eliminating the problem of what was happening before the Big Bang.

The above does not help me much, but perhaps it might give others an idea.

It is interesting that Einstein once said: Past, present, & future are very convincing illusions. Maybe he was on to an important concept that most (all?) of us are missing. I think this idea is related to his concept of World Lines.

50 or so years ago the Big Bang, the Steady State (Continuous Creation), and Alternating Bang/Crunch theories were all considered possibilities. The Alternating Bang/Crunch Theory was abandoned very early in the controversy for some (I suppose) good reason. I am sure that the reason was not related to lack of sufficient matter to cause a gravitational collapse. For some time after the Big Bang won out over the other two theories, there was still talk about the possibility of a Crunch.

They might have had some good reason to suppose that after a crunch, there could not be another Bang. They might have thought that Alternating Bangs/Crunches would run down. At any rate, I think the Bang/Crunch theory was untenable before recent discoveries about Dark Matter, Dark energy, and an expansion that is speeding up.

I can think of no reason why the laws of physics in other universes (if any) should be different from the laws of physics here. This concept is mentioned in many contexts, but I have yet to see it as anything more than idle speculation. I will not go on record as denying the possibility of a different set of laws, but consider it highly unlikely due to the absence of supporting evidence.

Many worlds does not seem like a terrible idea if you do not use it as an explanation for Quantum weirdness, but I have yet to see any supporting evidence for the existence of other universes. We have one, so zero universes is not correct. If there is another, I find it hard to imagine that there is not a third, fourth, et cetera. Zero and Two universes seem like the only impossible alternatives, while one seems to the only alternative with supporting evidence.

The anthropomorphic principle does not seem to be an explanation. Our existence seems to be a result of a lot of random processes (Assuming the validity of Quantum Theory). Trying to use such a result as an explanation does not make sense to me.

 

by valich:


I interpret this as saying that we can see it as flat, but it can still have curves and/or a curvature at the edges, and thus not make it infinitely flat - maybe folding in on itself at the edges. But also, it may be the current accepted hypothesis of an accelerating expanding universe, but no where does it say that it has to "keep on" expanding. This model can still hold true for the present state of the universe until the universe be shown to start decelerating, thus implying a stop and contraction. It doesn't imply that this is always how it has to be?
===============================================================

When they say the universe is 'spatially flat' they mean light travels in a straight line, unless bent by some massive object's gravitational field. It has nothing to do with the 'topology' of the observable universe, the 'shape' of the observable universe in other words. When they say the radius of the universe is larger than the observable particle horizon, they are, in effect, saying that there is no possibility of observing the 'edge' of the universe because light from particles beyond this horizon will never reach us because of the tremendous expansion rate. We can never determine the universe's 'shape' by observation of its fartherest reaches. They HAVE estimated the size of the OBSERVABLE universe. Remember we are looking back in time as we look at the most distant objects. By estimating how far those distant objects would be from us NOW due to the expansion, the figure is 154 billion light years in diameter. The most distant objects we have observed were over 13 billion light years from us when the light we see was emitted. That light was emitted 13 billion years ago, and the objects are thought to be receeding from us many times the speed of light due to the increasing rate of expansion, thus they arrive at the estimated size at this present time in its evolution. I have no idea if this is correct, but cosmologists and astronomers much more knowledgable than I have arrived at these conclusions from the analysis of data.

One last point. Current data suggest the universe will continue to expand forever because there is not enough mass, and thus gravity, to reverse the expansion even when dark matter is included. The gap between NEEDED mass and estimated mass is quite large. The only thing I have read of that could possibly reverse the expansion is IF dark energy somehow changed its properties and became attractive instead of repulsive. I am not aware of any accepted mechanism for that to happen, but I believe several theorists are working on such a hypothesis.

 

No, the diameter is believed to be 92 billion light years

A team of cosmologists measured that the universe cannot be smaller than 78 billion ly accross. See
http://www.bioedonline.org/news/news.cfm?art=977

An article in a web of a magazine of popular science mistook the information and declared that the radius was 78 billion ly.

Look page 5 of the following article. it gives the correct estimate
http://www.scientificamerican.com/a...23-1213-852383414B7F0147&pageNumber=5&catID=2

 

I guess it is according to whom you quote. I did make a mistake from memory, the number quoted is 156 billion light years in diameter. The news was all over the web when it came out, also a result of WMAP, 2dF galaxy red shift survey and other collabrations. Here is a cut & paste and link from one of the articles:

"All the pieces add up to 78 billion-light-years. The light has not traveled that far, but "the starting point of a photon reaching us today after travelling for 13.7 billion years is now 78 billion light-years away," Cornish said. That would be the radius of the universe, and twice that -- 156 billion light-years -- is the diameter. That's based on a view going 90 percent of the way back in time, so it might be slightly larger."
http://www.space.com/scienceastronomy/mystery_monday_040524.html
Edit: The correct title of the mission was the 2dF Galaxy Redshift Survey, or the 2dFGRS. The Sloan Digital Sky Survey results were also used in the estimates.

 

That's the article I was referring to: unfortunately is not accurate. It occurs that articles in popular magazines are often wrong. The paper written by Cornish, the man that carried out the experiment, is here
http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310233.pdf

he said in the article that "we will be able to exclude the possibility that we
live in a universe smaller than 24 Gpc in diameter"
24 Gpc is equal to 78 billion ly

in the article is not said that the radius is 78 billion ly

he also says that "with lower noise and
higher resolution CMB maps (from WMAP ’s extended
mission and from Planck), we will be able to search for
smaller circles and extend the limit to 28 Gpc" (28 Gpc is equal to 91 billion light years)

Unfortunately the second year data of WMAP was due to be released more than a year ago, but mysteriously its releasing has been postponed and nobody knows when it will appear

 

I think you may be a little confused about the timeline, Lucas. Cornish was the astrophysicist that was quoted in BOTH articles. Your numbers come from an earlier analysis, soon after the WMAP results were in. The 156 billion light year diameter estimate was NOT misquote or mistake, it was the result of further analysis by Cornish and many other scientists. The 156 billion year diameter is the newest estimate, along with an age of 13.7 billion years, plus or minus .2 billion years. Here is a link to Montana State University that should eliminate any doubts.
http://www.montana.edu/news/1105290436.html

Edit: Seems I did not read the entire article at Montana State Univ. Lucas, you were correct that the 156 billion years diameter quote was a mistake. The correct estimate is 78 billion light years. Discover magazine mistakenly thought the 78 billion light year estimate was the RADIUS of the observable universe, not the diameter. NASA's site on the WMAP mission does not speculate on a diameter of the universe, just the age of 13.7 billion years (+ or - .2 billion years).

 

No, Space is not a vacuum: it is a plasma. It transmits solar radiation - energy.

 

What are you talking about? The rarified interstellar material has nothing to do with the transmission of photons with one exception. The photons emitted by the "balls of plasma" we see as stars interact with gravity only between the point of emission and the point of impact with the back of our retinas.

That one exception occurs when the material is dense enough (e.g., dust nebulae) to dim or even completely obscure the light produced by stars on the other side of the material.