what is the big bang and how do i understand it?

Great.Now we have a theory that is based on the existence of something that is postulated in order to make another theory work ....epicycles on epicycles on epicycles.perhaps this will lead to refutation of the "dark energy" concept?enjoy.

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

Exacty the same as when you throw a ball into the air... "gravity" decreases as height is gained, but it doesn't necessarily allow the the ball to escape to infinity. As mentioned in my reply to DS, the "sphere" is an output of the model. This is not an output of the model, but just conjecture. It also doesn't make a huge amount of sense given the nature of the singularity. It is possible that quantum gravity could describe what you are imagining, but now there would be no south/north pole, but a thin "neck" connecting each "sphere"... but I find it difficult imagining how this would work. I would have thought we would require a major deceleration of the collapse long before we actually enter the planck scale. But it could be done with quintessence. True, the spherical model is a depiction of the classical closed big-bang scenario. Because it is an excellent model for understanding how to imagine 4d space-time... and up until a few years ago was a primary model.[Edit to correct an infinite number of typos]This message has been edited by cavediver, 08-12-2005 03:45 AM

Well, in a closed big-bang, it's topologically a sphere (minus two points) and that's good enough for me

It's not, unless quintessence evolves in a very strange way... much like what may be required for your oscillating universe. Why? This does not follow...

Not really... string theory (and supergravity before it) suggests several mechanisms for a cosmological constant. The question was always "why don't we see a cosmological constant?". We know think that we do. So it makes total sense to look at some of the implications for our universe, especially as we are looking at a dynamic field providing the "cosmological constant". That field could evolve in a number of ways, and a very simple evolution would be some form of power law. I'm not sure how this follows. As mentioned, the question has always been "why is dark energy zero?" (not that we called it dark energy back then)

I'm sorry if I wasn't more explicit. You are fairly new here and may not have read some of my posts on this topic before.The standard theory of gravity al la Newtonian physics was fine until relativity came along, and the new theory on the block has gotten rave reviews from all concerned, as the evidence mounted it looked like we had a winner ...... except for two small problems The first problem has spawned a number of interesting theories, including several forms of string theories, which call on added dimensions to solve the problems. The concept of added dimensions does solve a lot of little things and leads to some interesting thought experiments. Personally I have always considered more dimensions likely because of the dance of sub-atomic particles both in and out of existence and in and out of different "incarnations" or forms: to me this is similar to something 3 dimensional oscillating in and out of "flatland" and spinning such that it's appearance changes with time as well. Time will tell if extra dimensions bear fruit ... and in the long run that "fruit" will need to be at the galactic scale, or it doesn't solve problem (1). Of course one of the problems with the quantum mechanics side of the gravity equation is the total absence of any observed {particle\field\mechanism} for gravity on the subatomic scale.The second problem has spawned first "dark matter" and then "dark energy" based entirely on the question "if the equations are correct, then what do I need to have in order to make predicted behavior match observed behavior" -- in other words they assume that the latest equations are correct and then "invent" matter and energy to make it work. It seems to me that (almost) nobody is asking, "if the equations are wrong, what do I need to do to them to make predicted behavior match observed behavior" -- and then to look for evidence of that. There have been a couple in recent years, but they seem to be treated as fringe concepts when they have just as much validity as invented "dark stuffs".Note that physicists are comfortable with saying that Newtonian physics are sufficiently accurate that they can be used at small (planet sized?) scales, only requiring General Relativity physics for interplanetary calculations and stuff within the solar neighborhood. They tend to break down when you get outside the solar system (as evidenced by the several satellites that have left the solar neighborhood and which show behavioral anomalies consistent with the effects on large galactic systems ... as if "dark stuffs" were existing within the solar system). And then note that all these theories of gravity are essentially empirical formulas based on observations, and not derived.One of the new string based theories that intrigues me is ekpyrosis, as it minimizes the need for new dimensions, but also explains the anomaly between observation and prediction in the motions of large galactic systems ... without invoking "dark stuffs" ... which is something that I expect from the next generation theory of gravity.That is, of course, my personal opinion.Now to tie this in to the new theory, it takes for granted the existence of the dark stuffs and then theorizes what effect they may have in the next million years plus. Sorry if I find this concept ludicrous at the start, but note that the advantage of such thoughts is that they may develop tests for the existence of the dark stuffs, and we may then learn that it is indeed a house of cards.Enjoy.

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

Agghhh, I don't have time to do this justice... oh well, i can try. Sorry about the piecemeal approach; I'd prefer to reply in kind, but it's quicker this way, if somewhat lacking in eloquence. This "problem" is far more to do with our lack of understanding of time, than any problem with GR or QM. GR leaps way beyond our preconceptions of time, where-as QM is naturally embedded within them. It is not a matter of tweaking GR until it "dovetails with QM". I can easily imagine a world where GR would fit with QM, in the sense that a we had a renormalisable theory of a spin 2 massless gauge field. We would declare that GR fits with QM, but we would not have solved the real issue. But everyone outside of QG would think that everything was fine.But I agree wholeheartedly with your point on "elegant" solutions. The problem is usually the lack of elegance in our understanding... Just as slight quibbles, string theory was not developed to address the GR/QM problem. GR fell out by accident. But even string theory does not in any way even begin to solve the problem of time. It just provides a "solution" in the sense I mentioned above.And string theory does not call upon extra dimensions to solve problems as such. String theory only works in certain dimensions. It is a requirement of the theory, and thus a strength of the theory. GR does not specify a dimension. You can have it in as many dimensions as you like. You're right in that these extra dimensions are very useful in solving various issues. Ok, this ties in with a major point I want to make that covers your entire post: observation... it is very easy to take observation for granted. But our geocentric viewpoint is rather restricted when it comes to the universe as a whole. We are at the limits of observability of predicted grav waves. We are many orders of magnitude away from being able to detect a graviton interaction. This is not exactly a problem.When it comes to dark matter, there seems to be more matter out there than is actively emitting in a remarkably narrow range of the EM spectrum. There even seems to be matter out there that is not active electromagnetically at all (that we can detect). So what? Is this surprising? We are conditioned to observe and think electromagnetically because1) our universe contains a massless abelian gauage field (photon) - if the photon were not abelian, there would be no "sight" possible in the universe2) we have an immense local source of said photons (Sun)And dark energy... I have already explained in my previous post that dark energy is part of GR. It is part of the theory. The question has always been why does it appear to be zero? It is not a new invention or addition to the theory. So the Big Rip study is entirely valid. It would have made sense to relativists any time in the last 70 yrs, but has more interest now after the recent discovery of potential accelerating expansion. It does not minimise the need for extra dimensions. It is routed in string/m-theory so we are still looking at 10/11 target-space dimensions. And it comes from exactly the same maths as the dark energy calculations.More importantly, it is not a new "theory". It is still string theory. Just as with GR, the theory can predict an infinite number of different universe, depending on the parameters set. It is just another output from the theory, with some interesting behaviour. Not sure about this. Apollo was all Newtonian, and I would be very surprised if there has been any need for GR for any probe trajectory calculations, but I may be wrong. I've not seen this. Any references? GR is not empiracally based... in fact, Einstein was beaten to the Einstein Equation by a few days using mathematical reasoning.Anyway, sorry again for this being so slapdash. There are a number of points here we could possibly break off into seperate threads...

Thanks, the problem in understanding may be mine, due to limited exposure (several university courses, but ... was it really 40 years ago? ... updated occasionally by talks with a radio astronomer brother) I don't think of tweaking one or the other so much as of new ways of thinking about them that alleviate the problems -- a new way of thinking about time for instance. One thought that has been on my mind for some time is that we all talk about time being another dimension, but the equations still only have space factors and there is no relationship between gravity and distance in time (that I am aware of as a physics "spectator"). I'm having trouble resolving this apparent contradiction. It seems that string theory does not require dimensions, but when they are developed to explain observations that then they have to be there? But this still does not negate the fact that we do not have any corroborating evidence. That is my problem. This also makes me wonder if we are not blinded to other possibilities as a result of taking the theories as more solid than the evidence justifies. I have no problem with non-radiant matter within the galactic medium: we obviously have evidence of it right here in River City: our planets, asteroids, comets, dust, etcetera ... but it doesn't add up to a significant proportion of the mass of the solar system. With dark stuffs we are talking about the sun representing 4% of the {mass\energy} of the solar system (to put it in the same proportion as the galactic scale calculations on the amounts of dark stuffs), and I have some trouble with that.We are also now finding planets around other stars, and can calculate their masses and orbits and find they apparently are not significantly different from the mass distributions in our solar system. This tends to corroborate the evidence of the solar system.This leaves the space between stellar systems for the {stage of actions} for the dark stuffs, and while some rogue brown dwarfs, black holes and orphaned planets have been found (most by accident it seems) they do not add up to a significant proportion, while the dark stuffs need to be a significant proportion for the equations to work. And had humans on hand to make corrections as needed. More to the point are the {mars landers} of recent fame and misfortune, and they were programmed by GR (IIRC). Several. The easiest is from wikipedia, (and this has the advantage of being updated by those in the field as new information becomes available, but offset by the capability of being edited by someone without a clue): Another is a complete PDF paper (takes some time to load) from some heavy-hitters:
http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf Again, that looks like the effect of dark stuffs right here in River City (and that means trouble, folks). How is the value of {G} determined? What should it be?Note that one of the problems that I have with the ekpyrosis theory is that it explains the gravity anomaly by having a 'mirror' universe in the other sheet(s) and that gravity carries from one to the other. The problem here is that there is no reason for the other universe to end up with the same mass distribution, so there should be anomalies within anomalies.Instead consider that each subatomic particle travels in time (similar to the stacks of earth concept). The existence of particles as lines in time does not affect the observed behavior of particles at a point in time because it is "pulled" equally forward and back by its "time shadows" and the effect of "time shadows" gets absorbed into Newtonian {g} calibrations and Einsteinian {G} calibrations for the scales we are working in (as meager humans in a much vaster universe). But "time shadows" can easily add up to affect gravity on vast galactic scales. And here in River City. This is one of the concepts that I toy with, wishing I had the resources to check it out.Enjoy.

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

A couple questions right off the bat:Is the universe finite or infinite?Does the rate of expansion increase with distance?I don't think the Big Crunch can be possible with an increasingly expanding universe, nor with a horn shaped model.My tall stack of earths model depends on the possibility of the Big Crunch. But the ball is slowing down as height is gained. If the expansion of the universe is increasing, then gravity wouldn't be able to "turn-it-around", like earthly gravity does to the ball. If it is the same as the ball, then the universe couldn't be increasingly expanding. yeah, do you mind? Sorry if you think your wasting your time. I appreciate the replies, though. I don't know much about the nature of the singularity. When you say neck, it seems like it'd be more than one point. Why couldn't it be one point?, where the northernmost point of one sphere and the sothernmost point of the other are the same point, singularity. I realize that the closer you get to singularity the more flat the model becomes, and the harder it would be for this point to exist on both spheres, but I don't see that it can't be done.This message has been edited by Catholic Scientist, 08-15-2005 06:51 PM

Because, if the Big Crunch can happen, then there can be another Big Bang after it, and we would be existing before that big bang. The people after that big bang might say that nothing could exist before it, but what about us? What about the people that existed before the last big bang that we are talking about?

Hmmm, I owe RAZD a big reply, but I'm sure he won't mind if I fit this one in first Yes (I don't know is the less obtuse answer) It appears that it might, contrary to what we believed just a few years ago. True and true True again (I would say rate-of-expansion just to be clear). I thought you were reasoning against collapse even without the recently discovered acceleration factor... however, if the acceleration is dynamic, it might reduce or switch off, in which case we could still have a (delayed) collapse. I think you misunderstand me. Despite what most think (including "science" correspondants), our models of the universe are not observation based but mathematics based (GR), with observations providing the parameters for the model. All of our predictions come from the mathematics. The big bang is simply not a result of running the expansion backwards... it is the output of the mathematics of General Relativity. My picture of the globe representing space-time is not just an analogy but a representation of the actual mathematics. Your picture of the globes on top of each other is a (good) analogy of the oscillating universe conjecture, but it is no longer an accurate representation of any of the mathematics, and actually can create confusion as to the nature of time. Why should there only be one globe touching our original globe at the pole? Why couldn't several globes touch here? The "neck" concept saves this problem. Also, the idea of two globes touching at a point, and expecting some form of sensible propagation across this point (the singularity) is hopeful at best... Unfortunately, [conventional] human reasoning is very counter-productive in this field. What can and can't be done is down to the mathematics. Believe me this is not a restriction. For every idea you have that is shown to be implausible, the mathematics will offer up ten ideas that we could never hope to dream up...AbEThis message has been edited by cavediver, 08-15-2005 08:47 PM

Ok, I see your reasoning. But a big crunch does not imply your "stack of earths" is correct...

What's your opinion, if you had to pick one? Which one do you like more? understood. Well, if I'm wrong then I'm wrong (Does that mean we can't still explore the idea?). Got any suggestions for a book I should read? I've got the math from getting a B.S. in engineering so it might need to be dumbed down a little, but I would be looking for a book that isn't too simplified. Because it represents the UNIverse, of which there is only one. The other globe is the same universe, just earlier in time. Then we would be in one of many uni(multi)verses. How does the neck concept save the problem? Just because of the overlap of multiple spheres touching at one point?

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Because it represents the UNIverse, of which there is only one. The other globe is the same universe, just earlier in time.

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This is actually the crux of the problem.
The other sphere wouldn't be our universe at an earlier time.
All time would end at our south pole.
What you would have is two universes which both become undefined near a singular point.

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Then we would be in one of many uni(multi)verses. How does the neck concept save the problem? Just because of the overlap of multiple spheres touching at one point?

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Because it prevents singularities and also prevents the spheres being two seperate universes.This message has been edited by Son Goku, 08-18-2005 06:32 PM

It would be all the same matter. Or does matter stop existing at singularity too? Thats kinda why I think the singularity would have existed for an infinatlely small amount time, I know i know time ceases to exist, but because its undefined makes me think it didn't really exist as singularity, literally(in reality).Is this question answerable:How long was the universe at singualrity before it began to expand?