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stebini
2005-Nov-09, 07:11 PM
1. It is gererally accepted that the age of the universe is 12-15 billion years old.

2. It is generally accepted that the Big Bang occured 12-15 billion years ago.

Paradox: The light we are seeing from the most distant objects left the position we now see them in some 12-15 billion years AGO. Yet, 12-15 billion years ago they should have been in or near the point of the big bang.

Ken G
2005-Nov-09, 07:16 PM
There is no "point of the big bang". The big bang happened everywhere, including where you are sitting right now, and in all the places that we observe quasar emission and CMB radiation. There is no paradox. But welcome to the forum stebini!

stebini
2005-Nov-09, 07:22 PM
How can it be expanding if there is no point of origon? A singularity implies a specific moment in time and space.

Argos
2005-Nov-09, 07:28 PM
Every "point" can be said to be the home for the big bang because indeed it is. Remember that space has expanded since then, and the "points", once reunited, separated from each other.

stebini
2005-Nov-09, 07:40 PM
OK. Pick any object that is 12 billion light years away from us. We are seeing that object where it was 12 billion years ago. If the universe is 12 billion years old, where was that object at the time the universe began and how could it have been moving for 12 billion years to get to where we percieve it as being now?

Kaptain K
2005-Nov-09, 08:00 PM
The big bang was the creation of spacetime. All of space was contained within the singularity. Everything is moving away from everything else, but nothing is moving away from the center, because everything was (and still is) the "center".

edited to add the last sentence

Ken G
2005-Nov-09, 08:00 PM
Imagine an infinitely large chess board with ants crawling all over it, at the speed that ants crawl. Now imagine the chess board is rubber and is constantly stretching, though the ants don't know it, they just keep crawling in a straight line. If the ants are photons, that's all you need to know to imagine where the photons came from that you are seeing from 12 billion years ago. The squares on the board were originally arbitrarily small, but now they are quite large. But there are still ants all over it, crawling in straight lines. How would you express your paradox in that model? It goes away, just as it does for the Big Bang.

stebini
2005-Nov-09, 08:09 PM
Ken - Hmm. I'll have to think about that for a while.

I really like this place!

2005-Nov-09, 08:33 PM
The idea that everywhere is the center of the universe is an idea that I understand, but am not quite ready to accept yet. And I've been thinking about it for years.

Kaptain K
2005-Nov-09, 08:36 PM
Where on the surface of a sphere is the "center"?

Swift
2005-Nov-09, 08:44 PM
To use a slightly different variant of Ken G's analogy... image the universe is the surface of a ballon and we and everything else are ants on the suface of that ballon. At the big band you had an infinitely tiny ballon, which has been slowly "blowing up" ever since. Even if the ants don't move, they are still moving away from each other. And as Kaptain K said, there is no "center" of the ballon, just the surface.

2005-Nov-09, 08:56 PM
Where on the surface of a sphere is the "center"?This kind of question is why I am still a spot uncomfortable with with the idea. The center would be inside, not anywhere on the surface. Yes, I know you can define a two dimesional geometry which curves around a sphere. Within this definition there would be no center. I'm just not sure it's real.

uniqueuponhim
2005-Nov-10, 12:35 AM
I'm a little bit confused on one issue here:
I realize fully that the amount of matter in the universe is finite, and one definition of the universe might be "all of the matter in existence and the space it occupies," however, when I say universe, I am talking about the total extents of space, even outside of the sphere of matter within the universe.
Now, in a thread I started quite a while ago, I was told that presently, astronomers believe the shape of the universe to be "flat," basically meaning that space extends on forever in all directions; in other words, space is infinite (as opposed to "closed," which would mean the universe would curve in on itself, so that if, for example, you travelled in one direction for long enough, you would eventually wind up where you started, meaning space would be finite; or "open," which I do not know the meaning of.)
However, we do know that space is, and has at least since the big bang been expanding at a finite rate. If these astronomers are correct, and the universe is in fact infinite, and space has always expanded at a finite rate, then it has to have always been infinite, even at the time of the big bang.
Now, this clearly means that space wasn't a singularity at the time of the big bang, meaning that the singularity from which arose the big bang would have to have been made up purely of matter/energy, and actually would have had to have existed in space, rather than be made up of both matter/energy and space.
If the people posting in this thread are to be believed, however, space was in fact a part of that singularity, and did not exist before the big bang. This would mean that space started out as a singularity, and has since been expanding at a finite rate - this implies that space has to be finite, meaning that the shape of the universe has to be closed, contradicting the astronomers from the first paragraph.
Who is right here, and is there any contradiction at all?

Tacitus
2005-Nov-10, 01:08 AM
This kind of question is why I am still a spot uncomfortable with with the idea. The center would be inside, not anywhere on the surface. Yes, I know you can define a two dimesional geometry which curves around a sphere. Within this definition there would be no center. I'm just not sure it's real.

It's not a perfect analogy unless you assume that *only* the surface of balloon/sphere is the entire universe - i.e. it makes no sense to say the center is "inside" the sphere since there *is* no "inside" for a center to be in. (Mind bending, I know, but keep thinking about it!)

And the "surface of a balloon" analogy does illustrate another reality about our universe. If you set off in straight line in *any* direction and keep going-and-going long enough, you will eventually end up exactly where you started. You won't reach the "edge" - there isn't one - either on the balloon or in our universe.

Tacitus
2005-Nov-10, 01:15 AM
If the people posting in this thread are to be believed, however, space was in fact a part of that singularity, and did not exist before the big bang. This would mean that space started out as a singularity, and has since been expanding at a finite rate - this implies that space has to be finite, meaning that the shape of the universe has to be closed, contradicting the astronomers from the first paragraph.
Who is right here, and is there any contradiction at all?

OK, I could be wrong, but I believe astronomers are not talking about the physical shape of the present universe when they say it's "flat" or "closed" or "open". It's more to do with the eventual fate of the universe. A closed universe is one that will stop expanding and eventually fall back in on itself (the big crunch), an open universe is one which will expand at an exponential rate, and a flat one will just keep expanding at the present rate.

I believe that in any of these three cases, what I said in the previous post holds true - if you set off in any direction in a staight line (fast enough, of course) you will eventually end up where you started.

Kaptain K
2005-Nov-10, 01:45 AM
...a flat one will just keep expanding at the present rate.
Not quite. A flat universe is one in which the rate of expansion is slowing down at such a rate that v=0 at t= infinity.

Benign Terrorist
2005-Nov-10, 02:19 AM
uniqueuponhim
If you want to be just a tad more confused than you were before, consider that the rate of expansion has probably changed. Indications now are that it's getting faster than it was before. This sort of crumples up and tosses into a wastepaperbasket the comparison of flat to open universe. It could have been flat before, but has become open sometime ago.

A question I have pondered is whether the big bang banged all at once, or whether it took a discrete segment of time. My initial reaction is to say that it took measurable time, but I am not sure of it.

Tacitus
2005-Nov-10, 02:45 AM
Not quite. A flat universe is one in which the rate of expansion is slowing down at such a rate that v=0 at t= infinity.

Thanks - I knew something wasn't quite right :)

Tacitus
2005-Nov-10, 02:51 AM
uniqueuponhim
A question I have pondered is whether the big bang banged all at once, or whether it took a discrete segment of time. My initial reaction is to say that it took measurable time, but I am not sure of it.

I don't think your question makes sense. As far as we know, time itself did not exist before the big bang. Yes, I know, how can there be a "before" if time did not exist...?. Good question. Suffice to say, the space-time in this universe was created in the big bang, so unless you include the first part of the expansion that resulted from the big bang, by definition the big bang did "bang" all at once.

(And now let me go crawl into a corner and whimper until my brain stops hurting).

Ken G
2005-Nov-10, 04:04 AM
First of all, the singularity is not a part of the Big Bang theory. It is a mathematical extrapolation, useful only conceptually. It has no physical significance whatsoever, as it is well known that the laws of physics as we know them or will ever know them must break down before you reach a singularity. It is a mathematical idealization, and I would give it not another thought. The Big Bang theory actually begins when the physics you know still applies to the universe. So there's never a singularity, and no need for one. It's just an initial condition. Most models try to start at what is called the Planck time, which is very very short but not zero. If the universe is infinite now, it was infinite then also. Ergo the chess board is always infinite in size (so has no boundaries), but the squares are getting bigger. That's probably the best picture to use at present.

By the way, a flat universe does not mean the expansion speed will reach zero at infinite age. It now looks like the expansion speed will only increase, forever, yet the universe could remain flat all that time (it will never be known for sure). The point is, flatness is a geometrical property-- even really huge triangles have angles that add up to 180 degrees. It is plane geometry, Euclidean. That's a fortunate simplification-- we can all sigh in relief, and maybe the textbooks will soon dispense with those infernal "closed" and "open" geometry pictures!

Tacitus
2005-Nov-10, 05:40 PM
Ok, I was beginning to get confused again, so I did a bit of leg work.

The "flatness" of the universe is a property of the observabled or local universe (i.e. the part of the universe that is within the 13.7 billion light years of us, since that is the maximum distance light could have travelled since the big bang). As Ken says, the flatness is a geometric property, and the current understanding is that the observable universe is flat or nearly flat.

But... the flatness, or otherwise, of the observable universe only determines the shape of the whole (global) universe to within certain boundaries. If the local universe was tightly curved, then we would have known that the global universe was also curved and could only be up to a certain size. But because the local universe is flat (or nearly so) then the geometry of the global universe is still open to question. We just don't know whether the size the global universe is finite (bounded) or infinite.

So... even if the observable universe is geometrically flat, if the universe as a whole is finite (bounded) then the "surface of a sphere" analogy still holds - you could still end up back where you started if you travel in a straight line long enough.

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

Grey
2005-Nov-10, 06:34 PM
However, we do know that space is, and has at least since the big bang been expanding at a finite rate. If these astronomers are correct, and the universe is in fact infinite, and space has always expanded at a finite rate, then it has to have always been infinite, even at the time of the big bang.
Now, this clearly means that space wasn't a singularity at the time of the big bang, meaning that the singularity from which arose the big bang would have to have been made up purely of matter/energy, and actually would have had to have existed in space, rather than be made up of both matter/energy and space.You're thinking of a singularity as an infinitely small point. But "singularity" really just means "our mathematical and physical models break down here". There's nothing wrong with assuming that the universe began as a singularity of infinite extent. Indeed, if the universe is now infinite (which is perfectly possible), then it always was infinite, pretty much exactly because of the argument you give.

As far as the geometry questions, when cosmologists talk about the universe being open, flat, or closed, they really do mean its overall geometry. A flat or open universe is of infinite extent, while a closed universe is finite. However, there's been a slight twist in recent years. Without a cosmological constant, the geometry of the universe is also related to its ultimate fate. A closed universe will eventually collapse back on itself, an open universe will continue to expand, but at a rate that approaches zero, and an open universe will continue to expand at a rate that doesn't approach zero. It looks, though, like there's a nonzero cosmological constant, and in this case, the fate is not determined only by the geometry. It's possible in principle to have a closed universe that expands forever, or an open universe that eventually stops expanding. This site has a nice graph showing the possibilities, and how they relate to various values of cosmological parameters.

uniqueuponhim
2005-Nov-10, 06:48 PM
It looks like most of you completely misunderstood my problem.
I'm not talking about whether or not the universe will continue to expand indefinitely, I'm not talking about the future at all, I am simply talking about the present and the past shape of the universe, period.
Maybe I didn't use the correct terminology, but here it is in simpler terms:

The space which the universe occupies is either boundless, stretching on into infinity in all directions, or it is finite, and curves in on itself in some way or another, essentially meaning that if you go in one direction long enough, then eventually you will end up where you started (like on the surface of a sphere.)

If you're confused by this, imagine a two-dimensional universe: the chess-board situation brought up earlier. Imagine you're an ant on this chessboard. Although you do not know right now which is correct, you know that either the chessboard extends infinitely in all directions, or is curved in on itself as a sphere so that if you go on in one direction long enough, you will end up back where you started. So there are your two possibilities: it is flat and goes on forever, and all of the ants on the chessboard(matter in the universe) are located in one small portion of the vast infinity of the board OR the board curves in on itself and there is only a finite amount of it.

Now, the ants on this board are intelligent, and they think they have determined a way to determine whether the board is flat or curved, by somehow measuring the flatness of the board locally. The ants have found that locally, the board is in fact very flat, and so they determine that it is likely that the entire board is flat (either that or it has such a small curvature that it is impossible to detect.) This is what happened in our universe (as far as I can tell:) Astronomers have measured the curvature of the universe locally, seen that it is flat, and from that have decided that it is most likely that the universe is in fact flat and extends infinitely out forever.

So, let's look at the two possibilities (curved and flat) for the big bang:

A) The universe is curved. Space is finite right now. At the time of the big bang, all of the matter/energy in the universe existed in a single point, as did space itself. After the big bang, space expanded from that point at a finite rate, carrying the matter along with it. It continued to expand for 13 billion years at a finite rate until the present (and it continues to expand.) Perfect. This can be likened to the spherical chessboard on which the ants reside expending at a finite rate, and this makes good sense.

B) The universe is flat. Space is infinite right now. Since the time of the big bang, the universe has expanded at a finite rate. We know this because we exist: if space had at any point since the big bang expanded at an infinite rate, then every point in space which existed before that expansion would now be infinitely distant from every other point, and as a consequence, every bit of matter or energy in the universe would be infinitely distant from every other bit of matter or energy. The fact that the molecules from of which I am comprised are not smeared across the infinity of space right now means that space must have always expanded at a finite rate.

So let's rewind now back to the big bang. If space is infinite now, and it has always expanded at a finite rate, then at the instant of the big bang, space must have still been infinite. If at the instant of the big bang, space was infinite, then the entirety of it could not have existed in that one point, on the contrary, that singularity would have had to have existed in space. Note that this does not preclude the big bang from being able to have happened, it simply means that space must have existed before it if we are to take space as being infinite.

So, I ask you, who is right? The astronomers telling us that space is flat(infinite) or the people telling us that space did not exist before the big bang, and that it came into existence as a result of the big bang? Or is it that my logic somehow flawed, and the two are not mutually exclusive?

Grey
2005-Nov-10, 07:01 PM
So let's rewind now back to the big bang. If space is infinite now, and it has always expanded at a finite rate, then at the instant of the big bang, space must have still been infinite. If at the instant of the big bang, space was infinite, then the entirety of it could not have existed in that one point, on the contrary, that singularity would have had to have existed in space. Note that this does not preclude the big bang from being able to have happened, it simply means that space must have existed before it if we are to take space as being infinite.

So, I ask you, who is right? The astronomers telling us that space is flat(infinite) or the people telling us that space did not exist before the big bang, and that it came into existence as a result of the big bang? Or is it that my logic somehow flawed, and the two are not mutually exclusive?I'll repeat my response, which might have gotten lost in the rest of my message. You're assuming that a "singularity" is a single point. There is no such requirement. Under standard cosmology, if the universe is flat, then it's infinite and always was. At the moment of the big bang, the universe was infinite in size, and very hot and dense. As time passed, it became less hot and dense by expanding (I know, I have a hard time envisioning something that's already infinite expanding, too :)). If it's possible for infinitely compressed space to spontaneously appear, why is it any harder for space that's already infinitely extended to suddenly come into existence?

stebini
2005-Nov-10, 07:25 PM
I’ve always been a more than a little confused about this and it seems the more legwork I do the more perplexing it becomes. :confused:

Let’s consider for the moment that most of what has been stated so far is true:

• There was a big-bang or singularity which had no specific point of origin and space/time began at that instant.

• The perceivable universe came into being as a result of that occurrence and has since grown from infinitely small to some state between that and infinitely large.

• It has been in a constant state of consistent or accelerated expansion with the distances between everything increasing relative to that rate of that expansion.

• The universe has or does not have a center, or has a center which may exist in a dimension that is unperceivable to us.

Now if I may also include the following commonly accepted data:

• The age of universe is between 12 and 15 billion years.

• 8 billion years after the big bang the first galaxies started to form.*

• The most distant perceivable galaxies are 12-15 billion years away.

If the most distant galaxies we perceive are 12-15 billion years away;

and, the light we are seeing from those objects originated 12-15 billion years ago;

then, how is it that we are able to see objects such as galaxies at that distance?

They did not exist 12-15 billion years ago.

* Reference: Universal Time Table (http://www.msnucleus.org/membership/html/k-6/uc/universe/6/ucu6_1a.html)

Tacitus
2005-Nov-10, 08:01 PM
Hey stebini - you're not alone in your confusion!

But I believe you have misread the timetable you quote. It says that after 8 billion years "Most galaxies, including the Milky Way have formed". This may be sloppy prose, but it's supposed to mean that after 8 billion years most galaxies have reached middle age - i.e. they are no longer forming.

The Hubble Deep Field photographs have pretty much proved that galaxies started forming very early on (perhaps one billion years after the big bang or even sooner). BTW the latest accepted figure for the age of the universe is 13.7 billion years.

Therefore there is no problem with seeing galaxies 12 billion light years away - they did exist at that time.

Grey
2005-Nov-10, 09:02 PM
Therefore there is no problem with seeing galaxies 12 billion light years away - they did exist at that time.Moreover, there's some confusion in what we mean by how far away a galaxy is, especially as quoted in popular accounts. There are several possible things we could mean by that. We might mean how far away the galaxy was from us when the light was first emitted. We might mean how far away the galaxy is now. What's usually reported is the light travel distance, which is neither of these. It's just the amount of time the light has been travelling, multiplied by the speed of light. So the galaxy we see wasn't that far away when the light was emitted, but we've been moving away ever since.

Part of the reason that it's reported this way is that journalists don't always understand the distinction. But part of the problem is also that, to be able to convert from a light travel time to the distance to the galaxy when the light was first emitted, you have to know some parameters for the universe, like how the expansion has proceeded since then. Ned Wright talks about the difference between these distances here (http://www.astro.ucla.edu/~wright/cosmo_02.htm).

uniqueuponhim
2005-Nov-11, 03:30 AM
Grey, thank you for your clarification, but I'm still not 100% sure I understant it correctly. Let me go back to the ants on a checkerboard illustration and give an example and you can tell me if I'm correct:

At the instant that the big bang occured, the checkerboard existed, and was infinite, and had relatively small squares (say 1 fm across.) all of the ants were packed into an infinitessimally small point which existed on the checkerboard. After the big bang, the checkerboard began to expand, spreading out the squares, and increasing the distance between the ants. It has since continued expanding and the squares are presently a whopping 1km across.

Also, if the universe is in fact infinite, there must be a center of mass for the matter which comprises it, and this center of mass must always move at a constant velocity, and cannot accelerate. Would it be unreasonable to call this center of mass the center of the universe? Would it not also be reasonable to say that this is the point at which the big bang occured? After all, if the big bang had occured at any other point, that point would be the center of mass.

Finally, in response to the poster's original question, say an object starts out 1Gly distant from you, and over the next 2Gy, due to the expansion of the universe, that distance doubles. Now, imagine at time t=0, it is 1Gly distant, and emits a photon which travels toward you. Over the next 1Gy, the photon will have travelled 1Gly, however, due to the expansion of space, the distance between you and the star has increased to 1.41Gly. Now, at this point in time, the photon will be more than 1Gly from the star it originated from, but it won't have reached you yet. It will be a bit less than 0.41Gly from you. The exact distance it has left to travel takes a little bit of calculus to do, which I would be happy to put up here if I knew how to do the fancy shmancy integral signs and stuff, but I don't, so I'll just tell you that the distance it would have left to travel after 1Gy would be 0.219Gly, and it would reach you after a total of 1.228Gy. If it had started at a distance of 2Gly, it would take 3.41Gy for the light to reach you, and if it had started at a distance of 2.8Gly, it would take 10.2Gy to reach you, and if it were 2.9Gly or more away to begin with, it would never reach you. Of course, the universe doesn't expand at this rate, but whatever rate it does expand at, you can see that it can take a lot longer for you to see something that starts out only a couple of billion light years away than it would if space weren't expanding. Thus, objects we are seeing now as being 12Gly away, may only have been 2Gly away when they emitted their photons.

Grey
2005-Nov-11, 02:46 PM
At the instant that the big bang occured, the checkerboard existed, and was infinite, and had relatively small squares (say 1 fm across.) all of the ants were packed into an infinitessimally small point which existed on the checkerboard. After the big bang, the checkerboard began to expand, spreading out the squares, and increasing the distance between the ants. It has since continued expanding and the squares are presently a whopping 1km across.Mostly correct, except one thing. Change your sentence to say that all of the ants (infinitely many of them, of course) were spread throughout the infinite checkerboard. There were enough ants that they were packed really, really tightly.

Also, if the universe is in fact infinite, there must be a center of mass for the matter which comprises it, and this center of mass must always move at a constant velocity, and cannot accelerate. Would it be unreasonable to call this center of mass the center of the universe? Would it not also be reasonable to say that this is the point at which the big bang occured? After all, if the big bang had occured at any other point, that point would be the center of mass.With the change in ant distribution, you should see that this doesn't work out. If I were to assume that ant distribution is more or less isotropic, you can see that no matter which point I pick, the ants will be uniformly distributed around it, so I could call it the center of mass. Since all points are the same, it doesn't make sense to call any specific point the center of mass, to the exclusion of the others.

uniqueuponhim
2005-Nov-11, 02:55 PM
Grey, I'm pretty sure it's been well established that there isn't an infinite amount of matter in the universe.

stebini
2005-Nov-11, 06:11 PM
Finally, in response to the poster's original question, say an object starts out 1Gly distant from you, and over the next 2Gy, due to the expansion of the universe, that distance doubles. Now, imagine at time t=0, it is 1Gly distant, and emits a photon which travels toward you. Over the next 1Gy, the photon will have travelled 1Gly, however, due to the expansion of space, the distance between you and the star has increased to 1.41Gly. Now, at this point in time, the photon will be more than 1Gly from the star it originated from, but it won't have reached you yet. It will be a bit less than 0.41Gly from you. The exact distance it has left to travel takes a little bit of calculus to do, which I would be happy to put up here if I knew how to do the fancy shmancy integral signs and stuff, but I don't, so I'll just tell you that the distance it would have left to travel after 1Gy would be 0.219Gly, and it would reach you after a total of 1.228Gy. If it had started at a distance of 2Gly, it would take 3.41Gy for the light to reach you, and if it had started at a distance of 2.8Gly, it would take 10.2Gy to reach you, and if it were 2.9Gly or more away to begin with, it would never reach you. Of course, the universe doesn't expand at this rate, but whatever rate it does expand at, you can see that it can take a lot longer for you to see something that starts out only a couple of billion light years away than it would if space weren't expanding. Thus, objects we are seeing now as being 12Gly away, may only have been 2Gly away when they emitted their photons.

uniqueuponhim - Thank you. That actually makes sense and I no longer see it as a paradox.

But now something else has me confused: :confused:

If the universe has always been infinite, how can it be expanding? Say it expanded by 1 inch. That would make its size infinity + 1". How can that be? Infinity is already infinite.

eburacum45
2005-Nov-11, 06:21 PM
One thing which might help this discussion is that the universe expanded for a few hundred thousand years before it became transparent, so we would not see anything before that time.

Since that time the universe has expanded by about a thousand times in linear dimension, so the earliest objects we can see were situated very roughly thirteen or fourteen million light years away from our location in those days.

The light from those objects has travelled across expanding space for 13.7 billion years since that time and has only just reached us.

The exact distance of such early objects might be quite a bit different to my rough estimate given above, and I would be interested if anyone had a more accurate figure, but I think it is in the right ballpark.

Grey
2005-Nov-11, 06:57 PM
Grey, I'm pretty sure it's been well established that there isn't an infinite amount of matter in the universe.I can't think of any way that someone would establish that. The mainstream interpretation is indeed that if the universe is infinite in size, then there is also an infinite amount of matter in it, since whatever matter is present should be distributed more or less evenly (with some minor bits where there's a little extra matter, like galaxies :)) throughout space. You may be confusing the universe as a whole with the observable universe, which only includes those parts of the universe which are close enough for light to have reached us since the big bang. The observable universe is definitely finite in size and has a finite amount of matter. And its center, of course, is us, though observers located somewhere else would have a more or less identical observable universe centered around them.

If the universe has always been infinite, how can it be expanding? Say it expanded by 1 inch. That would make its size infinity + 1". How can that be? Infinity is already infinite.As I mentioned above, I have a really hard time envisioning it, too, so I'm hopeful that the universe turns out to be finite so that I don't have to try. :) The best way to try to imagine it is with uniqueuponhim's chessboard. It has squares on it that are really small, extending on forever. Then it starts to expand, and all the squares get bigger. They still extend on forever, of course. How can a given square stretch like that? Well, it pushes the neighboring squares over a bit. And they push the neighboring sqaures over a bit, and so forth. There won't ever be a problem with a square not having enough room to expand by pushing neighboring squares over, because you'll never get to a boundary that prevents you from pushing further out. Mathematically and physically, this works out fine, we just have a hard time conceiving of infinity. Thinking of an infinite universe expanding by 1 inch then being "infinity plus 1 inch" in size is treating infinity like a number that measures the size of the universe, and that's not the case.

stebini
2005-Nov-11, 07:29 PM
I think a plausible explanation might be that we are only seeing a portion of the entire universe. And that the portion of the universe which we perceive is expanding into another dimension which we are not able to perceive.

uniqueuponhim
2005-Nov-11, 10:04 PM
uniqueuponhim - Thank you. That actually makes sense and I no longer see it as a paradox.

But now something else has me confused: :confused:

If the universe has always been infinite, how can it be expanding? Say it expanded by 1 inch. That would make its size infinity + 1". How can that be? Infinity is already infinite.
http://www.astro.ucla.edu/~wright/infpoint.html

Jerry
2005-Nov-11, 10:29 PM
I’ve always been a more than a little confused about this and it seems the more legwork I do the more perplexing it becomes. :confused:

Let’s consider for the moment that most of what has been stated so far is true:

• There was a big-bang or singularity which had no specific point of origin and space/time began at that instant.

False! There is no singularity requirement space grew - space between matter, as we define it today.

• The perceivable universe came into being as a result of that occurrence and has since grown from infinitely small to some state between that and infinitely large.True

• It has been in a constant state of consistent or accelerated expansion with the distances between everything increasing relative to that rate of that expansion.
true

• The universe has or does not have a center, or has a center which may exist in a dimension that is unperceivable to us.
No Center can be defined - growth of space is omi-directional

Now if I may also include the following commonly accepted data:

• The age of universe is between 12 and 15 billion years.

• 8 billion years after the big bang the first galaxies started to form.*

• The most distant perceivable galaxies are 12-15 billion years away.

If the most distant galaxies we perceive are 12-15 billion years away;

and, the light we are seeing from those objects originated 12-15 billion years ago;

then, how is it that we are able to see objects such as galaxies at that distance?

They did not exist 12-15 billion years ago.

We see stars 12-15 billion light years away that may have been only 4 billion years away from us when the light we are looking at was created. But since the space between us and them also expanded, It took the light from these galaxies 12-15 billion years to get to us.

Disclaimer: This is an interpretation of a commonly accept theory, not a personal theoretical preference.

Ken G
2005-Nov-12, 06:15 AM
We see stars 12-15 billion light years away that may have been only 4 billion years away from us when the light we are looking at was created. But since the space between us and them also expanded, It took the light from these galaxies 12-15 billion years to get to us.
Actually, if it was 4 billion LY away when the light was emitted, and it is 12-15 billion LY away now, then the time it would have taken to reach us would have to lie in between 4 billion and 12-15 billion years. Remember, the light did not have to cross all the space in that 12-15 billion LY you are talking about, since some of it "stretched" into existence after the light had already passed! A surprise around every corner, and no calculation is easy in that business, I'm afraid.

Tacitus
2005-Nov-12, 10:06 AM
We see stars 12-15 billion light years away that may have been only 4 billion years away from us when the light we are looking at was created. But since the space between us and them also expanded, It took the light from these galaxies 12-15 billion years to get to us.

Disclaimer: This is an interpretation of a commonly accept theory, not a personal theoretical preference.

I already pointed out earlier in the thread that stebini had misread the original article pertaining to galaxies starting to forming only 8by after the big bang.

heusdens
2005-Nov-13, 12:16 PM
The big bang was the creation of spacetime.

Creation of spacetime from what?

Isn't this just some new form of creationism?

There are no physics laws that can describe creation of spacetime from nonexistence.

stebini
2005-Nov-13, 04:16 PM
I am thinking that our perception of space time and the universe as we know it was "created" from one or more physical dimensions which are invisible to us at our present state of evolution. Our technology and physics only allow us to see as far back as somewhere after the "big bang" so any references to a specific time or point of "creation" is speculation.

Of course this would lead to the next question of when and where did the other dimensions come from and I believe that this is a question that will require substantially more time and evolution for us to even begin to comprehend.

Tacitus
2005-Nov-16, 10:24 PM
I am thinking that our perception of space time and the universe as we know it was "created" from one or more physical dimensions which are invisible to us at our present state of evolution. Our technology and physics only allow us to see as far back as somewhere after the "big bang" so any references to a specific time or point of "creation" is speculation.

Of course this would lead to the next question of when and where did the other dimensions come from and I believe that this is a question that will require substantially more time and evolution for us to even begin to comprehend.

First, if you define "dimensions" in the same way cosmologists and theoritcal physists do, then it is incorrect to say that our universe was created from "other dimensions". According to the latest theories, all the dimensions in this universe, seen and unseen, were "created" as the result of the Big Bang.

What exists outside our universe or existed before our universe, if anything, is of course, merely conjecture at this point. But I think you are forgetting about the important role those theoretical physists sitting in some back room hunched over incredibly complex mathematical equations play.

Our universe is subject to a set of physical rules, a lot of which we know, and many we don't. Those rules can be boiled down into a set of mathematical formulae: F=ma, E=mc2, etc. etc.

By studying those rules through the use and manipulation of these formulae, we have discovered a lot about the universe only later confirmed through experimental means. Quantum physics is a great example of this.

But mathematics can also tell us things about our universe we may never be able to verify through direct measurement or observation, including what happened in the seconds after the Big Bang. So although cosmologists are still arguing about the details, there isn't much debate about the approximate age of the universe - 13.7 billion years.

And as our understanding of the maths improves and new mathematical techniques are discovered, we may one day begin to understand how and why the universe began and what, if anything, lies beyond. (Though if mathematics itself is purely a property of our universe we may hit a dead end!)

The hunt for the elusive "Theory of Everything" (the convergence of all the basic laws of matter and energy) is part of that process, but is not likely to be the end.

Fortunate
2005-Nov-17, 03:32 AM
But now something else has me confused: :confused:

If the universe has always been infinite, how can it be expanding? Say it expanded by 1 inch. That would make its size infinity + 1". How can that be? Infinity is already infinite.

Think of the real number line. Now stretch it so that 1 is now where 2 used to be, 2 is where 4 used to be, -1 is where -2 used to be, etc. This illustrates an infinite manifold expanding. Of course, this expansion is centered somewhere, but the illustration may at least handle one of the many confusing points.

Its old length was infinite, and its new length is infinite, yet it has expanded.

Damburger
2005-Nov-17, 02:20 PM
Regarding the balloon analogy a while back..

The centre of an expanding balloon (sphere) is not in the same plane as anything on the surface of the sphere. You need a dimension inaccesible to the residents of the sphere surface in order to describe where the centre is.

Now, current theories postulate many more dimensions than the 4 we experience in the form of spacetime. My question is, Does the universe have a centre that can be described using these dimensions?

Ken G
2005-Nov-17, 11:36 PM
Now, current theories postulate many more dimensions than the 4 we experience in the form of spacetime. My question is, Does the universe have a centre that can be described using these dimensions?
Personally, I hate the balloon analogy. The current thinking is that the universe is flat, so it's time to dump the balloon in favor of an infinite chessboard. I personally don't have trouble with something that is infinite that can expand, but I prefer to imagine that the chesspieces are shrinking anyway. Note that none of those examples requires a center, in any number of dimensions.
However, if there is some tiny and undetectable positive curvature, then there could still be a center in some other dimension, it seems to me.

stebini
2005-Nov-18, 06:23 PM
Any mathematics I've tried fall apart when trying to prove or disprove the origin of the big bang as arising from our own dimension, or another. However, I perceive a greater probability of at least one more physical dimensions than not. A three dimensional universe requires something arising from nothing/nowhere whereas a fourth dimension introduces a physical place from which it can appear – the outflow of a black hole, perhaps.

Consider the room you are in right now. Look around. Pick an arbitrary point of space somewhere in the room. It could be anywhere but I can visualize it best if I pick a point near the center of the room.

Try to imagine a "big bang" or any matter, for that matter -; being generated out of that place. You can't. Why? Because it is not visible from our perspective. To see it, you would have to pry apart the fabric of space from some random point in your room and look inside. Visualize spreading apart the atoms that occupy that point and looking inside. If you could do that you would be looking into another dimension.

Because there can be no single place where this extra dimension exists, it either exists everywhere, or nowhere at all. Dismissing the latter for the purpose of this discussion let’s assume that it does exist everywhere. Would that make it very large - something we would need to step outside to see; or very small – something that we would need to step inside to see. I am in favor of the latter because it provides answers to some of the most fundamental questions about our universe, marrying the laws of quantum physics with general relativity and offering a single set of principals, which may govern our known universe.

montebianco
2005-Nov-18, 06:28 PM
Think of the real number line. Now stretch it so that 1 is now where 2 used to be, 2 is where 4 used to be, -1 is where -2 used to be, etc. This illustrates an infinite manifold expanding. Of course, this expansion is centered somewhere, but the illustration may at least handle one of the many confusing points.

Its old length was infinite, and its new length is infinite, yet it has expanded.

Good example, generally speaking, intuition often leads one astray when dealing with the infinite. Despite thinking about such things for a lot of years, I can still come up with mathematical statements which seem obvious to me, but which are nonetheless false...

Tacitus
2005-Nov-18, 08:15 PM
Any mathematics I've tried fall apart when trying to prove or disprove the origin of the big bang as arising from our own dimension, or another.

With the greatest respect, any mathematics you or I could bring to the table (unless you have a degree in advanced theoretical physics) is far too simplistic to begin to probe the mysteries of our universe, and its beginnings.

Because there can be no single place where this extra dimension exists, it either exists everywhere, or nowhere at all. Dismissing the latter for the purpose of this discussion let’s assume that it does exist everywhere. Would that make it very large - something we would need to step outside to see; or very small – something that we would need to step inside to see. I am in favor of the latter because it provides answers to some of the most fundamental questions about our universe, marrying the laws of quantum physics with general relativity and offering a single set of principals, which may govern our known universe.

I agree that assuming one or more "extra" dimensions exist, they must exist everywhere. If you go back to the infinite chessboard illustration and add height, then you can place yourself over the chessboard anywhere above it, not just in the centre. However, I disagree that any extra dimensions must be large. In fact, the latest theories indicate that these dimensions must be very, very small, "curled-up", otherwise we would be able detect them (don't ask me how, I'm not a physicist!).

Again, you have to distinguish between other dimensions that (may) exist within our universe and the thought experiment of being able to step outside the universe altogether and look back at it. They are not the even close to being the same thing.

I would recommend that you pick up a copy of a book that explains, in layman's terms, the state of current cosmological research. It can be fun to speculate on the issues like this, but I think it would be wise to at least have a reasonable understanding of what the experts are thinking. I really enjoyed "The Whole Shebang" by Timothy Ferris (though it is a few years old) and I hear "The Elegant Universe" by Brian Greene is also a good primer. I'm sure other posters will list any other books that are worthy of mention.

Finally a fun question. If you could "turn over" a person in a fourth spatial dimension what would they look like? Answer: the same, except they would be the mirror image of what they were before. The heart would be on their right, if their right hand on their left, and so on).

stebini
2005-Nov-18, 10:35 PM
Tacitus - I was not aware that you needed a PhD to advance a theory around here. I do have a degree in Physics and many of the formulas I tested were written by some of the most highly regarded physicists from Newton to Witten. The bottom line is, we don't know.

My theories are based on mathematics and physics and whether or not they agree with your theories or not is of little importance. What matters is whether or not it is conceivable, mathematically possible and can be proven. There is no question that the prevailing theories of the universe are in their infancy and it will be a long process of time and evolution before we as a species even begin to comprehend the most deepest mysteries. In the mean time, a little creative thinking can go a long way towards enlightening ourselves towards a greater understanding of the universe.

It is obvious that you missed my meaning entirely and I never said that the extra dimension(s) must be large or that we had to step outside to look in. Indeed, I stated that my current findings lend a greater probability to the opposite.

stebini
2005-Nov-19, 12:05 AM
I want to add that my findings are not all that far-fetched if you consider the fundamental Kaluza-Klein theory, first published in 1921. Particularly if you replace the similarity equivalent of Maxwell's equations for the electromagnetic field and replace the extra scalar field with the dilaton.

[Moderator edit: wikipedia material on "Kaluza-Klein theory" begins here; I've left only the first sentense; the rest may be found here (http://en.wikipedia.org/wiki/Kaluza-Klein_theory):] A splitting of five-dimensional space-time into the Einstein equations and Maxwell equations in four dimensions was first discovered by Gunnar Nordstr&#246;m in 1914, in the context of his theory of gravity but subsequently forgotten.

[snipped]

[the remaining material is very similar, but not identical, to the wiki article; note that the latter contains the equations (stebini's text, here in BAUT, does not).]

The connection A on the fiber bundle is related to the electromagnetic field strength in such a way that there always exists such a connection, even for fiber bundles of arbitrarily complex topology, is a result from homology and specifically, K-theory. Applying Fubini's theorem and integrating on the fiber, one can easily calculate the varying the action with respect to the component A, which regains the Maxwell equations. Applying the variational principle to the base metric g, one can use simple Einsteinian equations with the stress-energy tensor, sometimes called the Maxwell stress tensor.

The original theory identifies Λ with the fiber metric g55, and allows Λ to vary from fiber to fiber. In this case, the coupling between gravity and the electromagnetic field is not constant, but has its own dynamical field, the dilaton. The size of the loop Λ acts as a coupling constant between the gravitational field and the electromagnetic field. If the base manifold is four-dimensional, the Kaluza-Klein manifold P is five-dimensional. The fifth dimension is a compact space, and is called the compact dimension. The phenomenon of having a higher-dimensional manifold where some of the dimensions are compact is referred to as compactification.

Tacitus
2005-Nov-19, 12:13 AM
stebini - I stand corrected regarding the mathematical knowledge at your disposal, I meant no insult to your education or knowledge. I apologise if I did offend you.

And of course you don't need an advanced degree to express an opinion, far from it. But I got the sense from your posts that the ideas you are putting forward have already been debated and discussed in much greater detail by scientists who have made a career out of studying these issues, and so I assumed that you were not conversant with them.

So when you say things like:

<quote>I perceive a greater probability of at least one more physical dimensions than not. A three dimensional universe requires something arising from nothing/nowhere whereas a fourth dimension introduces a physical place from which it can appear...</quote>

it strikes me, even as a lay person, that you're trying to fathom out stuff that's already been worked out by the theoreticians, and that you seem to be heading down the wrong road. In fact, in this statement you say that you think the universe must have more than three (spatial) dimensions because then there can be a physical place from which it can appear.

On the face of it, this doesn't make sense. The best mathematical models to-date say that there are multiple (very small) extra dimensions, but none of these is anything from which this universe could have sprung. As I said before, these extra dimensions are assumed to be part of our universe and were created at the same moment. So when you refer to a dimension as something from which a universe could have sprung, you are contradicting the established definition of what a dimension is.

Finally, I did misread your last paragraph. On re-reading I don't find anything to object to.... rats! :)

stebini
2005-Nov-19, 06:14 PM
The best mathematical models to-date say that there are multiple (very small) extra dimensions, but none of these is anything from which this universe could have sprung. As I said before, these extra dimensions are assumed to be part of our universe and were created at the same moment. So when you refer to a dimension as something from which a universe could have sprung, you are contradicting the established definition of what a dimension is.
Tacitus – Which models are you referring to? The concept of 4 dimensional space evolving from a 5th physical dimension is the basic premise for virtually all of the popular multi-dimensional theories. I explained that ad nauseam in my previous post with the Kaluza-Klein et.al. geometric representations; and Witten agrees [fundamentally] given additional dimensions and branes. While they all have underlying mathematical dissimilarities, the one collective conformity is that our perceived 4 dimensional universe was derived from one or more extra dimensions.

Look, I didn't come here to pick a fight and if my posts are disturbing to you or the other members, I’ll leave. I already participate in physics discussions and found this to be a more relaxing and informal medium in which to express my thoughts in a more abstract manner without having to justify every sentence with a mathematical equation. The majority of responses to my posts have been enlightening and thought provoking. If everything has already been "worked out by the theoreticians” then what does that leave us to discuss? I believe that there is far more to our universe than anyone yet realizes and that abstract discussion such as this may lead to a greater understanding, or at least offer new and insightful ways of thinking about it.

DrChinese
2005-Nov-20, 05:42 AM
We live in a universe in which spacetime is described by General Relativity, and the expansion of spacetime since the Big Bang is affected by initial conditions. There are substantial indications that there have been inflationary stages since just after the big bang; in fact it appears the inflation of spacetime is continuing today. By some estimates, the diameter of our 13.7 billion year old universe is 156 billion light years.

See for example: Misconceptions about the Big Bang, by CH Lineweaver and TM Davis, March 2005 Scientific American. The ideas they present help explain these 2 facts:

i) why we can see light from an early galaxy 13 billion years ago.
ii) why that light has a red shift indicating that it is receding from us at over 3 times the speed of light.

Tacitus
2005-Nov-20, 06:04 AM
I'm sorry you feel picked on - that was not my intent. No need to go, but I have no interest in upsetting anyone, however unintentionally, so I'm unsubscribing from this thread forthwith.

Ken G
2005-Nov-20, 06:06 AM
I should have said this earlier-- welcome to the forum DrChinese! Your posts are very insightful, and helpful. I hope you will find this a stimulating place to hang out! By the way, if you get the opportunity, I would be curious what your take would be on the exchange I've been having with Tensor on the thread about interpretations of cosmological redshifts, under "Questions and Answers". There I give a pedagogical interpretation of the expanding universe that replaces expansion with shrinking mass. Probably not a new idea, but if you look at the end of the thread, Tensor has forced me to really spell out this alternate view, and that's where I would be curious if you think it is (a) wrong, (b) obvious, or (c) an interesting alternate pedagogy. Perhaps (b) and (c)! Also, it is relevant to the present thread as well, since shrinking mass avoids certain conceptual problems with speeds greater than light, etc.

DrChinese
2005-Nov-20, 04:12 PM
I should have said this earlier-- welcome to the forum DrChinese! Your posts are very insightful, and helpful. I hope you will find this a stimulating place to hang out! By the way, if you get the opportunity, I would be curious what your take would be on the exchange I've been having with Tensor on the thread about interpretations of cosmological redshifts, under "Questions and Answers". There I give a pedagogical interpretation of the expanding universe that replaces expansion with shrinking mass. Probably not a new idea, but if you look at the end of the thread, Tensor has forced me to really spell out this alternate view, and that's where I would be curious if you think it is (a) wrong, (b) obvious, or (c) an interesting alternate pedagogy. Perhaps (b) and (c)! Also, it is relevant to the present thread as well, since shrinking mass avoids certain conceptual problems with speeds greater than light, etc.

Thanks, Ken! I was turned on to this site by Nereid.

I will take a look at that thread, though I must caution I am not very strong in that particular area.

-DrC

Broken Symmetry
2005-Nov-20, 05:17 PM
This kind of question is why I am still a spot uncomfortable with with the idea. The center would be inside, not anywhere on the surface. Yes, I know you can define a two dimesional geometry which curves around a sphere. Within this definition there would be no center. I'm just not sure it's real.

Nobody is sure if there is a 'real' center to the universe. But it is possible, for every point on the surface of a sphere to be an 'observational' centre. If we take the universe to be an N-dimensional sphere, it's possible for every point in that spacetime to be a genuine observational center.

Broken Symmetry
2005-Nov-20, 05:25 PM
It's not a perfect analogy unless you assume that *only* the surface of balloon/sphere is the entire universe - i.e. it makes no sense to say the center is "inside" the sphere since there *is* no "inside" for a center to be in. (Mind bending, I know, but keep thinking about it!)

And the "surface of a balloon" analogy does illustrate another reality about our universe. If you set off in straight line in *any* direction and keep going-and-going long enough, you will eventually end up exactly where you started. You won't reach the "edge" - there isn't one - either on the balloon or in our universe.

A universe with an 'empty centre' (I know the analogy doesn't do justice, because it's misleading) has the topology of a taurus. So the universe could be the shape of a 4 dimensional doughnut

Broken Symmetry
2005-Nov-20, 05:29 PM
A question I have pondered is whether the big bang banged all at once, or whether it took a discrete segment of time. My initial reaction is to say that it took measurable time, but I am not sure of it.
Perhaps the universe is still banging!

The ceaseless procreator!

[and I'm not joking]

Broken Symmetry
2005-Nov-20, 05:52 PM
Since that time the universe has expanded by about a thousand times in linear dimension, so the earliest objects we can see were situated very roughly thirteen or fourteen million light years away from our location in those days.

The light from those objects has travelled across expanding space for 13.7 billion years since that time and has only just reached us.

The exact distance of such early objects might be quite a bit different to my rough estimate given above, and I would be interested if anyone had a more accurate figure, but I think it is in the right ballpark.

What if the rate of expansion of the universe was in fact a bit slower than the speed of light at the early stages of its evolution? (whether during or before the theorized inflation period) Or what if the speed of light is dependent on the rate of expansion, but the rate of expansion is the same everywhere in the universe at any given time (non-local)? - This may provide an illusion that the speed of light is constant and possibly even explain why the universe appears to be expanding.

[I'm just being controversial, although I know these ideas have come up time and time again. There may be more weight to them than BBT cosmologists give them]

stebini
2005-Nov-21, 12:47 AM
Tacitus - I didn't mean that I wanted you to leave. Surely we can coexist peacefully. I will make a better effort to accompany my thoughts with data or prevailing theories from now on.

DrChinese - Thanks for the great read. Lineweaver/TM Davis make some excellent observations regarding the behavior of our perceivable post big-bang universe. I have always had problems with the general relativity assumptions of a fixed speed of light transcending our visible universe and the objects in our universe moving away from each other at the measurable redshift without the objects themselves moving. I understand the reasoning behind a 150Gyr universe but still feel that this might be another observation that is limited by our perspective and could be even much larger than that.

uniqueuponhim – Thanks for the link. It painted a clear distinction between the sizes of the actual universe vs. the part we are able to observe and provided a reasonable explanation to my original "paradox".

Let’s picture our known universe as a small piece of either a very large expanding balloon or chessboard [whichever you prefer] representing the entire universe. Now, taking the Lineweaver/Davis model, extrapolate backwards in time until “we can conceive of the early universe as a pile of overlapping grapefruits that stretches infinitely in all directions”. This is fairly consistent with uniqueuponhim’s Edward L. Wright model, representing only a small portion of the observable universe being concentrated to a single point while the entirety of the universe continues to contract indefinitely. Both theories would seem to indicate an infinitely large universe with no beginning. Now that we have reasonable explanations for the increasing distances between objects and our perception of them, it leads me to contemplate the cause of the big bang, what preceded it and what it is expanding into – other than “itself”.

This would seem to pose at least four possibilities: Either,
1.) there was no big bang; or,
2) it evolved from no specific place into no specific thing; or,
3) it had no beginning and everything exists in an ongoing and infinite perpetual big bang state; or,
4) it evolved from a dimension beyond our perspective.

With all of these being feasible it would tend to come down to ones own preference. Personally, I don’t like the scenarios suggesting everything existing forever because it proposes a quandary without a solution, lacking cause and effect. I am also unable to grasp concepts that require something being derived from nothing. By process of elimination, that makes me the most comfortable with a universe that evolved from an extra dimension. It also offers an explanation for the relatively weak force of gravity, as compared to the strong, weak and EM forces. I like a tidy, explicable universe. :)

Of course this leads to more questions. Not the least of which is where did the extra dimension(s) come from and how big are they? The most popular extradimensional theories such as Witten tend to favor smaller, “curled up” dimensions and much larger extradimensional “branes” that may collide, causing energy sufficient to create an entire universe. There are as of yet no any observations that can prove any of these theories. However it is hoped that the new Large Hadron Collider (LHC) in Switzerland may be able to prove the existence of subatomic particles such as gravitons and sparticles, which will lend additional credibility to these theories. Perhaps they will even detect a graviton at the point of its disappearance into another dimension! Whether they do or not, it would appear that exciting times lie ahead.

And what if these smaller dimensions could also be the pathways to new universes?

Consider a supermassive black hole. It takes enormous amounts of matter and compresses it down to a seemingly infinitely small space, possibly right down into one or more of the tiny curled up dimensions. Suppose all that matter and energy gained sufficient force so as to rupture the very fabric of our universe at a subatomic level and break through to another dimension, perhaps even creating a new universe in that dimension or something else at another place in our own universe. Where else could all that matter and energy go? It is believed that black holes never “die”. If they continue evolving and consuming matter forever, without ever displacing that matter, what does that leave? Eventually all of the matter in the universe would be consumed by black holes. It seems conceivable that black holes - like every other force of nature, might play an intricate role in universal evolution.

Hazza
2005-Nov-22, 02:42 PM
well, this is my maiden post :P, laiden with plenty of ingorance, bound to last the entirety of my duration here.

regardless, heres my opinion (i have only my personal readings and year 11-ish physics to form my basis' :P):

firstly, "The Big Bang" is very misleading - it was much more akin to something like "The Big Pop" - ie, matter just spontaneously appeared from every point possible in a finite space.

i am informed that energy (in one of the reasons still unkown to us) began rapidly converting to matter (perhaps the reversal of when, say, an electron and positron meet for example).

er....i'll finish this later....too much study (stupid exams)

Ken G
2005-Nov-22, 08:50 PM
Welcome Hazza! I agree that the Big Bang is a terrible misnomer, in fact it was originally used (I think by Hoyle) as a term of ridicule of the ideas of LeMaitre (who was originally seen as an ATM type. Correct my history if I'm oversimplifying). But the term stuck, and now the first thing every educator must do is replace the wrong impression that the Big Bang is an explosion, which people have experience with, with the right impression that it is simply a rule about the way the universe is changing dynamically, which people don't have much experience with. But I'll hazard an analogy. The key lesson of Einstein's gravity (even though he himself was slow to realize it!) is that the universe must be dynamic, so the Big Bang is the only possibility that can work. By dynamic, I mean like a ball that is not touching anything, and so the Big Bang is essentially the way a juggler keeps these dynamical objects in the air (as opposed to a bowler, who uses the ground, that is the alternative that doesn't exist for our universe). The juggler analogy works best if the universe will fall back on itself, which it doesn't look like it will do, but I hope you see the idea of "dynamic" anyway.

About the energy conversion to matter-- that part is pretty well understood, although there's still some worry about how we ended up with matter but no antimatter. The really unknown parts are where did the energy come from, and what set off the dynamics, in the first place. That is simply an initial condition, the Big Bang doesn't predict it. In other words, the Big Bang model doesn't know where the balls came from or where the juggler came from. Minor problem there! I think other highly speculative models are trying to handle those issues.