Question about the Big Bang

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Original post by Omegavolt And this has always made me wonder. If the galaxies are all expanding from a central point, the Big Bang Ground Zero in other words, then wouldnt a little calculus tell us what our distance is from said Ground Zero? If the actual velocities are added to the relative velocities (the ones that cause the red-shift for us) then wouldnt that shift the relative velocities so that we could tell the direction that the Big Bang originated?

The traditionaly analogy is that if you draw dots on a balloon and then inflates it, looking at its surface, each dot is moving away from every other, but there is no central point. Or if you prefer, every point is the central point of the expansion.

Mathematically, if you take a plane with (x,y) coordinates and start doubling those (x,y)->(2x,2y), you will find that everything is going away from everything else. The point O (0,0) would seem to be fixed, because its coordinates do not change, but that is just an illusion: you could do a change of frame of reference to any other point and it would now appear to be going away, just like everything else. Wherever you place yourself, everything seems to be going away from you, at a speed that only depends on how far they are from you, not on their direction or "absolute" position -- if there were such a thing.

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Whats bugging me about knowing the direction of the Big Bang Ground Zero is that it is said that no matter what direction we look in, we are looking further back in time, due to the space-time continuum.

We are seeing light that was emitted in the past. How far past is dependent on how far the light source was at that time.

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Some say that the furthest galaxies out are the first ones to form after the Big Bang occurred. The problem is, this should hold true no matter which way in the sky we look, yet there should only be one direction toward Ground Zero.

There is no Ground Zero.

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Furthermore, wouldnt the fact that these first galaxies being 13 billion light years out mean that the universe is even older than this, considering that it simply took 13 billion light years for the light to get to us, which doesnt account for the time it took the galaxies to get that far out?

If you were able to instantly move to one of those galaxies, you would indeed travel more than 13 billion light years, because it is now further away. Yet, if you were to look back at Earth, you would indeed find out that it is 13 billion light years away.

You would also find it considerably different from how it looked in the telescope, since you were seeing how it was 13 billion years ago. Which is why it is said that they were the first one to form - they weren't, everything happened simultaneously, but the light that was emitted during their formation is only reaching us now.

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Am I totally on the wrong track here?

In part. Relativity involves significant mental gymnastic.

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There is no Ground Zero.

There isn't? Isnt the Big Bang explosion itself Ground Zero? I mean, they say the universe began as an infinitely dense golf ball-sized mass, right? When the explosion occurred all matter in the universe expanded, not only away from itself as you stated, but away from the original location of the explosion as well.

I understand that expansion is going on right now from all points in the universe. Thats why all the galaxies are red-shifted. But in addition to that, they should be speeding along away from the original location of the Big Bang explosion right? It wouldnt be much of a 'big bang' if they aren't.

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We are seeing light that was emitted in the past. How far past is dependent on how far the light source was at that time.

Right. So theoretically, if we look back far enough in one direction, we should see a galaxy just as its stars light up. But then how is it possible that we can look in the exact opposite direction and see the exact same thing? The Big Bang theory states that galaxies lit up some billion or so years after t=0, when the galaxies were still relatively close together. Yet our observations tell us that the further back in time we look in 2 directions, the further apart the galaxies were.

Looking back in time should show that universe is smaller, yet we look back in time and the universe is bigger.

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Original post by Omegavolt Quote: There is no Ground Zero. There isn't? Isnt the Big Bang explosion itself Ground Zero? I mean, they say the universe began as an infinitely dense golf ball-sized mass, right? When the explosion occurred all matter in the universe expanded, not only away from itself as you stated, but away from the original location of the explosion as well.

It's not that all the matter in the universe is expanding outward into space, it's that space itself is expanding, "dragging" everything along with it. Hypothetically, initially every single point in space was infinitely close to every single other point; they were all at the singularity. Thus, they all have equal claim to being the center.

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Original post by Agony Quote: Original post by Omegavolt Quote: There is no Ground Zero. There isn't? Isnt the Big Bang explosion itself Ground Zero? I mean, they say the universe began as an infinitely dense golf ball-sized mass, right? When the explosion occurred all matter in the universe expanded, not only away from itself as you stated, but away from the original location of the explosion as well. It's not that all the matter in the universe is expanding outward into space, it's that space itself is expanding, "dragging" everything along with it. Hypothetically, initially every single point in space was infinitely close to every single other point; they were all at the singularity. Thus, they all have equal claim to being the center.

Yeah, I had the same misunderstanding until recently. It doesn't help that people are reluctant to come out and say this. The closest they come is saying things like, "The distance between two objects is increasing". That's true, but that's also true if their momenta are in opposite directions. Here, it's not a question of momentum. It may be helpful to view galaxies as being stationary with space being inserted between them.

The balloon example would be more helpful if it were first explained that it's representing a 2D universe. The example tries to show objects moving apart in a 2D space which is the balloon's surface. What people see is objects moving apart in a 3D space. When you say "There is no central point", people think "Yeah there is, the center of the balloon".

I wrote this back in January but never finished because I dont like finishing things. I even started writing some mathematica stuff to convert into gifs. :(

Most texts which give a lay treatment of the big bang topic fail to impart a thorough picture of what is meant by the whole topic. They tend to leave a misconception that the universe began with the big bang and the big bang was an explosion. That people would think that the big bang was an explosion is not at all suprising. It is after all, called the big bang and Im not sure I know of anything that causes bigger bangs than explosions. But this is a very wrong impression of what occured way back then. The task of this work is twofold, to force help structure a set of free floating concepts in my mind and to give a thorough accounting of the Big Bang. One which would leave little room for assumptions to enter.

The first thing to realize is that the big bang does not deal with the begining of the universe, such explorations are best left to philosophers and theologans, they are not addressable by science. The big bang instead deals with the period of time shortly after what some argue was a singularity. The truth of this though is highly questionable as singularities and point. The universe can have no begining since

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I found some notes I began to make:

The Universe and a set of points. A the space between the points expanded

Cases:

Finite Size and bounded

Infinite but Bounded
---Shape of space time At boundaries, things curve to shape
Examples shapes

Infinite and Unbounded
-No edge just goes on, likely no inherent shape

no begining to time

topological descripyions likely most sensible
Group of topological structutures that are locally euclidean

[Edited by - Daerax on June 13, 2006 5:35:52 PM]

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Original post by Agony It's not that all the matter in the universe is expanding outward into space, it's that space itself is expanding, "dragging" everything along with it.

"Dragging" it from where?

To say that all points in space in our current visible universe can all claim to be the center, then that means that the universe expands infinitely in all directions. If we are the center, and the galaxies 13 billion LY away are also at the center, then there are galaxies 13 billion LYs further out than them, and so on, and so on.

If this is not so, then the galaxies 13 billion LYs away would be considered at the 'edge' of this expanding space, right?

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Original post by Omegavolt Quote: Original post by Agony It's not that all the matter in the universe is expanding outward into space, it's that space itself is expanding, "dragging" everything along with it. "Dragging" it from where? To say that all points in space in our current visible universe can all claim to be the center, then that means that the universe expands infinitely in all directions. If we are the center, and the galaxies 13 billion LY away are also at the center, then there are galaxies 13 billion LYs further out than them, and so on, and so on. If this is not so, then the galaxies 13 billion LYs away would be considered at the 'edge' of this expanding space, right?

Nothing is being dragged, more pulled apart. Difference of vocabulary probably the cause of this confusion. Space itself is being stretched. Nothing else is moving.

Take a rubber band. Make five random dots near each other on it. stretch it. thats whats going on with the unviverse. Also, did you notice how the dots near to each other behave with respect to those that are far apart? There is No explosion (nothing moved!), no centre to expansion. As to your question of ad infinitum boundaries, that may or may not be the case. :)

[Edited by - Daerax on June 13, 2006 6:04:26 PM]

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Original post by Omegavolt I mean, they say the universe began as an infinitely dense golf ball-sized mass, right?

No.

As Daerax says, we don't really have much idea what it might have been the instant before it 'exploded'. Our physical models start to break down too close to such a singularity.

To clarify things, let's expand on the balloon model.

The universe is a balloon, it's fabric being space-time itself. Galaxies and things like that are little dots drawn on the surface of the balloon. There is a rule that you can't move faster than a certain speed across the surface of the balloon.

However, that speed limit does not effect how quickly you can inflate the balloon. You can inflate it so that the dots appear to be moving away from each other faster than the speed limit, however since the dots aren't actually moving across the surface the speed limit is never actually broken.

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Original post by Agony Quote: Original post by Omegavolt Quote: There is no Ground Zero. There isn't? Isnt the Big Bang explosion itself Ground Zero? I mean, they say the universe began as an infinitely dense golf ball-sized mass, right? When the explosion occurred all matter in the universe expanded, not only away from itself as you stated, but away from the original location of the explosion as well. It's not that all the matter in the universe is expanding outward into space, it's that space itself is expanding, "dragging" everything along with it. Hypothetically, initially every single point in space was infinitely close to every single other point; they were all at the singularity. Thus, they all have equal claim to being the center.

Yes, this space that is expanding is known as the fourth dimension (aka space time)

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Nothing is being dragged, more pulled apart. Difference of vocabulary probably the cause of this confusion. Space itself is being stretched. Nothing else is moving. Take a rubber band. Make five random dots near each other on it. stretch it. thats whats going on with the unviverse. Also, did you notice how the dots near to each other behave with respect to those that are far apart? There is No explosion (nothing moved!), no centre to expansion. As to your question of ad infinitum boundaries, that may or may not be the case. :)

Notice something else, and that is that the width of the five dots stretch to match the expansion. I argue that if the universe was to stretch, we ourselves, and our perception of the universe would stretch with it, and we couldn't percieve a difference without another point of reference. The idea of space "stretching", without the objects within it being stretched, sounds like a workaround to try and explain how matter could move faster than light relative to an observer.

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Original post by OmegavoltIf this is not so, then the galaxies 13 billion LYs away would be considered at the 'edge' of this expanding space, right?

No. In fact it gets worse: There is no "edge" of the universe. To say that there was is as silly as saying that there is an edge to the earth that you could fall off of. Notice that, although the earth is finite in surface area, it has no "edge". The universe itself is the same way. It has a finite space, but no edge. You could never travel "out of" the universe. There is no "outside". At least not that us 4D beings could ever understand. God could probably tell you about it, but that's it.

In fact, the universe's edgelessness yields this fun fact: if you set out in a straight line away from earth, you will with enough time eventually come back to earth. And if you had a super-mega-high-powered telescope and you look really really really far away, you would be able to see Earth (from a gajillion years ago).

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Original post by ktuluorion Quote: Original post by Agony Quote: Original post by Omegavolt Quote: There is no Ground Zero. There isn't? Isnt the Big Bang explosion itself Ground Zero? I mean, they say the universe began as an infinitely dense golf ball-sized mass, right? When the explosion occurred all matter in the universe expanded, not only away from itself as you stated, but away from the original location of the explosion as well. It's not that all the matter in the universe is expanding outward into space, it's that space itself is expanding, "dragging" everything along with it. Hypothetically, initially every single point in space was infinitely close to every single other point; they were all at the singularity. Thus, they all have equal claim to being the center. Yes, this space that is expanding is known as the fourth dimension (aka space time)

The fourth dimension is not known as space time, it is commonly simply referred to as the time dimension. The enirety of all 4 dimensions (yes, I said 4,QFT says its so, string theory is not falsifiable as of now, we cant accepts its claims on our universe as being true) is what is known as space time and is what is expanding.

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Original post by Nemesis2k2 Quote: Nothing is being dragged, more pulled apart. Difference of vocabulary probably the cause of this confusion. Space itself is being stretched. Nothing else is moving. Take a rubber band. Make five random dots near each other on it. stretch it. thats whats going on with the unviverse. Also, did you notice how the dots near to each other behave with respect to those that are far apart? There is No explosion (nothing moved!), no centre to expansion. As to your question of ad infinitum boundaries, that may or may not be the case. :) Notice something else, and that is that the width of the five dots stretch to match the expansion. I argue that if the universe was to stretch, we ourselves, and our perception of the universe would stretch with it, and we couldn't percieve a difference without another point of reference. The idea of space "stretching", without the objects within it being stretched, sounds like a workaround to try and explain how matter could move faster than light relative to an observer.

Well actually, locally - the forces are strong enough to hold back the expansion so to speak, although I read somewhere that atoms may in fact be slightly bloated.

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Original post by leiavoia Quote: Original post by OmegavoltIf this is not so, then the galaxies 13 billion LYs away would be considered at the 'edge' of this expanding space, right? No. In fact it gets worse: There is no "edge" of the universe. To say that there was is as silly as saying that there is an edge to the earth that you could fall off of. Notice that, although the earth is finite in surface area, it has no "edge". The universe itself is the same way. It has a finite space, but no edge. You could never travel "out of" the universe. There is no "outside". At least not that us 4D beings could ever understand. God could probably tell you about it, but that's it. In fact, the universe's edgelessness yields this fun fact: if you set out in a straight line away from earth, you will with enough time eventually come back to earth. And if you had a super-mega-high-powered telescope and you look really really really far away, you would be able to see Earth (from a gajillion years ago).

This is not necessarily true. It is only true if you assume an infinite but closed (bounded) universe.

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Original post by Nemesis2k2 Quote: Nothing is being dragged, more pulled apart. Difference of vocabulary probably the cause of this confusion. Space itself is being stretched. Nothing else is moving. Take a rubber band. Make five random dots near each other on it. stretch it. thats whats going on with the unviverse. Also, did you notice how the dots near to each other behave with respect to those that are far apart? There is No explosion (nothing moved!), no centre to expansion. As to your question of ad infinitum boundaries, that may or may not be the case. :) Notice something else, and that is that the width of the five dots stretch to match the expansion. I argue that if the universe was to stretch, we ourselves, and our perception of the universe would stretch with it, and we couldn't percieve a difference without another point of reference.

And you'd be wrong. Suppose, instead of dots on a balloon (or band), you have specks of dust. As the balloon expands, the specks of dust get further apart, but they do not themselves get larger.

The balloon analogy is merely an analogy. It's just a way of thinking about what's really happening, not a strict definition.

In reality, what holds these specks of dust together are the four fundamental forces: gravity, electromagnetism, and the strong and weak nuclear forces. The expansion could, in certain circumstances, be thought of as a fifth force which is much weaker than the other four, but which attenuates less rapidly. Such a force would be almost unnoticable at short ranges (as indeed the expansion of the Universe is), but would dominate at long ranges. Technically, however, it isn't a true 'force' since it doesn't cause masses to accelerate, that being the definition of a force.

Some (untested) theories speculate that the expansion of the Universe may in fact still be accelerating. In such a Universe, the expansion would eventually overcome the other forces and galaxies, stars, planets, people, atoms and hadrons will fly apart faster than the speed of light, leaving the Universe as a 'Cantor dust' of fundamental particles. This highly speculative fate is known as the Big Rip (by analogy with the Big Bang and Big Crunch), although it isn't truly a 'ripping' of spacetime..

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Original post by Nathan Baum Some (untested) theories speculate that the expansion of the Universe may in fact still be accelerating. In such a Universe, the expansion would eventually overcome the other forces and galaxies, stars, planets, people, atoms and hadrons will fly apart faster than the speed of light, leaving the Universe as a 'Cantor dust' of fundamental particles. This highly speculative fate is known as the Big Rip (by analogy with the Big Bang and Big Crunch), although it isn't truly a 'ripping' of spacetime..

Actually it would be experimental data that has forced us to realize that the rate of exapansion of the universe expansion is accelerating. The ways to explain this apparent (or real) expansion, ranging from offerings of dark or phantom energy to posutlations of the failures of Relativity at large scales is what is theoretical. It remains an open question even with this expansion, if these other forces would be overcome and a rip would occur.

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Original post by Omegavolt Right. So theoretically, if we look back far enough in one direction, we should see a galaxy just as its stars light up.

Theoretically. We haven't seen that far yet. We've seen back about 13 billion years, which we believe is about 700 million years after the Big Bang, and we think that galaxy formation would have begun after around 300 million years.

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Looking back in time should show that universe is smaller, yet we look back in time and the universe is bigger.

Looking back we definitely find the Universe is smaller.

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Original post by Daerax Quote: Original post by Nathan Baum Some (untested) theories speculate that the expansion of the Universe may in fact still be accelerating. In such a Universe, the expansion would eventually overcome the other forces and galaxies, stars, planets, people, atoms and hadrons will fly apart faster than the speed of light, leaving the Universe as a 'Cantor dust' of fundamental particles. This highly speculative fate is known as the Big Rip (by analogy with the Big Bang and Big Crunch), although it isn't truly a 'ripping' of spacetime.. Actually it would be experimental data that has forced us to realize that the rate of exapansion of the universe expansion is accelerating. The ways to explain this apparent (or real) expansion, ranging from offerings of dark or phantom energy to posutlations of the failures of Relativity at large scales is what is theoretical. It remains an open question even with this expansion, if these other forces would be overcome and a rip would occur.

Interesting. I wasn't aware (or I'd forgotten) that we knew the expansion was accelerating.

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Original post by Sandman The universe is a balloon, it's fabric being space-time itself. Galaxies and things like that are little dots drawn on the surface of the balloon. There is a rule that you can't move faster than a certain speed across the surface of the balloon.

I think I see now that whats being suggested through these analogies. It is that the 'starting point' of all this matter was stretched, not just the matter thrown out itself, which bends the rules of absolutes. This only makes me think that really, we are seeing the singularity as it was all those billions of years ago, with all of the matter in the same places as they were in the singularity, only now everything is spread out, almost like we were seeing the singularity through a microscope.

All this does is raise more questions for me though.

If the singularity started off hot, why did all the matter cool off, then become hot again? Did something stronger than gravity spread all of this matter apart, only to let gravity bring it back together again to form galaxies, but now the gravity is too weak to keep the galaxies together?

If the singularity started off as a small point, and the space spread out in all directions, how is there not an edge to the universe??? Was there not an edge to the singularity? If not, then the singularity was infinite, right?

Still my unanswered question from before: How is it that looking farther out into space shows galaxies as they were when they were closer together?

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Original post by Nathan Baum Quote: Original post by Daerax Quote: Original post by Nathan Baum Some (untested) theories speculate that the expansion of the Universe may in fact still be accelerating. In such a Universe, the expansion would eventually overcome the other forces and galaxies, stars, planets, people, atoms and hadrons will fly apart faster than the speed of light, leaving the Universe as a 'Cantor dust' of fundamental particles. This highly speculative fate is known as the Big Rip (by analogy with the Big Bang and Big Crunch), although it isn't truly a 'ripping' of spacetime.. Actually it would be experimental data that has forced us to realize that the rate of exapansion of the universe expansion is accelerating. The ways to explain this apparent (or real) expansion, ranging from offerings of dark or phantom energy to posutlations of the failures of Relativity at large scales is what is theoretical. It remains an open question even with this expansion, if these other forces would be overcome and a rip would occur. Interesting. I wasn't aware (or I'd forgotten) that we knew the expansion was accelerating.

If this is not sarcasm then kindly disregard this link : universe is expanding. :)

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Original post by Omegavolt Quote: Original post by Sandman The universe is a balloon, it's fabric being space-time itself. Galaxies and things like that are little dots drawn on the surface of the balloon. There is a rule that you can't move faster than a certain speed across the surface of the balloon. I think I see now that whats being suggested through these analogies. It is that the 'starting point' of all this matter was stretched, not just the matter thrown out itself, which bends the rules of absolutes. This only makes me think that really, we are seeing the singularity as it was all those billions of years ago, with all of the matter in the same places as they were in the singularity, only now everything is spread out, almost like we were seeing the singularity through a microscope. All this does is raise more questions for me though. If the singularity started off hot, why did all the matter cool off, then become hot again? Did something stronger than gravity spread all of this matter apart, only to let gravity bring it back together again to form galaxies, but now the gravity is too weak to keep the galaxies together? If the singularity started off as a small point, and the space spread out in all directions, how is there not an edge to the universe??? Was there not an edge to the singularity? If not, then the singularity was infinite, right? Still my unanswered question from before: How is it that looking farther out into space shows galaxies as they were when they were closer together?

Do not talk about the singularity, too much is fickle there. For one, it could be that we see that point as a singularity simply because that is where relativity, our physics, breaks down. There may be no singularities (naked or otherwise) in nature. Asides, we cant go that far back anyway, big bang theory starts just after that.

Eh? Heated and cooled and then heated again? That didnt happen. And your question, when you look at galaxies far away you are actually looking into the past, seeing them as they were before, at a time when they were closer together.

The "singularity" could have contained an infinite number of points or it could not have, we know nothing on it. What could the edge of the universe be? By definition there can be no outside to the *uni*verse (since everything is inside of it) yet by supposing an edge we imply a place outside the universe. Maybe there is true nothing outside? Maybe the universe is not universal? I do not know.

Read this on cosmology.

[Edited by - Daerax on June 13, 2006 10:55:21 PM]

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Original post by Omegavolt I think I see now that whats being suggested through these analogies. It is that the 'starting point' of all this matter was stretched, not just the matter thrown out itself, which bends the rules of absolutes.

Pretty much, yes.

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If the singularity started off hot, why did all the matter cool off, then become hot again?

Well stars are hot because of the nuclear reactions that get started by gravity, but the rest of the universe has cooled down to about 3K. But yes, theories do include a possible phase of exponential expansion that "moved" things very far apart very quickly (there seem to have been some preliminary experimental confirmation very recently).

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Did something stronger than gravity spread all of this matter apart, only to let gravity bring it back together again to form galaxies, but now the gravity is too weak to keep the galaxies together?

The relative strength of the "expansion force" compared to gravity is very much an open question.

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If the singularity started off as a small point, and the space spread out in all directions, how is there not an edge to the universe??? Was there not an edge to the singularity? If not, then the singularity was infinite, right?

The shape of the universe is also an open question. Note for example that the surface of a sphere is finite, but doesn't have an edge.

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Still my unanswered question from before: How is it that looking farther out into space shows galaxies as they were when they were closer together?

Because it takes time for light to reach you. It is possible for stars to be so far away that the expansion increases the distance between us and them faster than the speed of light. As a consequence, their light will never reach you. This puts an upper limit to how far away we can see things: an horizon.

This paragraph from Wikipedia's Observable Universe is particularly relevant.

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Both popular and professional research articles in cosmology often use the term "universe" when they really mean "observable universe". The reason for this is that unobservable physical phenomena are scientifically irrelevant; that is, they cannot affect any events that we can perceive, and therefore causally do not exist. They also cannot be measured, and therefore hypotheses about parts of the universe that are not observable may be ignored.

Anyway, there is still a lot of work being done to figure out what's going on. All this could very well end up being thrown out of the window. [smile]