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Thread: Where did the Big Bang happen?

  1. #1 Where did the Big Bang happen? 
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    'North of the North pole' and 'the question is a category mistake' are answers commonly given. 'Everywhere' tends to be the one given by adherants of scientic orthodoxy. We are told that the Big Bang happened everywhere, after which the universe underwent a period of rapid inflation, and is now continuing to expand.

    How can a universe that is already everywhere inflate or expand?

    Though I tend to accept that the Big Bang happened, I just can't understand or accept that it could have happened everywhere. It only makes sense to say that the universe began everywhere if we define everywhere as 'the place that the universe occupies or occupied at any given time, either now or in the past'. Well in that case 'everywhere' very shortly after the Big Bang was a very small place indeed. Much smaller than today's everywhere. So not everywhere.


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  3. #2 Re: Where did the Big Bang happen? 
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    Quote Originally Posted by nimzo256
    'North of the North pole' and 'the question is a category mistake' are answers commonly given. 'Everywhere' tends to be the one given by adherants of scientic orthodoxy. We are told that the Big Bang happened everywhere, after which the universe underwent a period of rapid inflation, and is now continuing to expand.

    How can a universe that is already everywhere inflate or expand?

    Though I tend to accept that the Big Bang happened, I just can't understand or accept that it could have happened everywhere. It only makes sense to say that the universe began everywhere if we define everywhere as 'the place that the universe occupies or occupied at any given time, either now or in the past'. Well in that case 'everywhere' very shortly after the Big Bang was a very small place indeed. Much smaller than today's everywhere. So not everywhere.
    What you "accept" is irrelevant.

    It happened everywhere. This has nothing to do with orthodoxy. It is based on general relativity, which is supported by a large body of empirical evidence. You need to do some serious reading


    You might start with A Brief History of Time by Stephen Hawking.


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  4. #3 Re: Where did the Big Bang happen? 
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    Quote Originally Posted by nimzo256
    How can a universe that is already everywhere inflate or expand?
    Back then, everywhere was a lot smaller than everywhere is today.

    Quote Originally Posted by nimzo256
    Though I tend to accept that the Big Bang happened, I just can't understand or accept that it could have happened everywhere. It only makes sense to say that the universe began everywhere if we define everywhere as 'the place that the universe occupies or occupied at any given time, either now or in the past'. Well in that case 'everywhere' very shortly after the Big Bang was a very small place indeed. Much smaller than today's everywhere. So not everywhere.
    Yup, very shortly after the Big Bang, everywhere was a very small place indeed.

    The universe is not thought to be expanding into "pre-existing" space. All the space that has ever been, everywhere, has been within the universe, between the stuff of the universe. It is that space that has expanded, meaning that the stuff of the universe has become more spread out.

    If the universe is not expanding into pre-existing space, it must somehow expand within itself.

    If Hawking's book is a little heavy going, you might have a look at the article below, for starters. Actually, the whole of Wikipedia's section on Physical Cosmology is pretty well edited, in my humble opinion.

    http://en.wikipedia.org/wiki/Metric_expansion_of_space
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  5. #4 Re: Where did the Big Bang happen? 
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    Quote Originally Posted by DrRocket
    Quote Originally Posted by nimzo256
    'North of the North pole' and 'the question is a category mistake' are answers commonly given. 'Everywhere' tends to be the one given by adherants of scientic orthodoxy. We are told that the Big Bang happened everywhere, after which the universe underwent a period of rapid inflation, and is now continuing to expand.

    How can a universe that is already everywhere inflate or expand?

    Though I tend to accept that the Big Bang happened, I just can't understand or accept that it could have happened everywhere. It only makes sense to say that the universe began everywhere if we define everywhere as 'the place that the universe occupies or occupied at any given time, either now or in the past'. Well in that case 'everywhere' very shortly after the Big Bang was a very small place indeed. Much smaller than today's everywhere. So not everywhere.
    What you "accept" is irrelevant.

    It happened everywhere. This has nothing to do with orthodoxy. It is based on general relativity, which is supported by a large body of empirical evidence. You need to do some serious reading


    You might start with A Brief History of Time by Stephen Hawking.
    I've read BHOT.
    Along with most of the scientic community, you might be happy to accept something physical that you can't actually conceive, but I'm not - irrelevant though my non-acceptance may be. 'Everywhere' at the time of the Big Bang was a very small space indeed by all accounts. Much smaller than the 'everywhere' of today. And because that's the case we should be able to say where this smaller everywhere was. Quite often the expansion of the universe is compared with a lump of dough with raisins in it spreading out on a table top, the dough representing space and the raisins galaxies etc. Where did the lump of dough first hit the table?

    Your post also fails to learn from the lessons of history. Reminiscent perhaps of some learned physicist 150 years or so ago, determined to defend come what may notions such as absolute time and the luminiferous ether, pointing to all the evidence that they must be correct, and regarding any attacks on them as ignorant. Scientific knowledge changes - and that includes today's scientific knowledge too.
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  6. #5 Re: Where did the Big Bang happen? 
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    Quote Originally Posted by SpeedFreek

    Yup, very shortly after the Big Bang, everywhere was a very small place indeed.
    And in that case why doesn't it make sense to ask where that very small place now is within today's universe? The problem with the answer 'everywhere' to the original question is that today's everywhere is not the same as everywhere 13.7 billion years ago.
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  7. #6 Re: Where did the Big Bang happen? 
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    Quote Originally Posted by nimzo256
    I've read BHOT.
    Along with most of the scientic community, you might be happy to accept something physical that you can't actually conceive, but I'm not - irrelevant though my non-acceptance may be.
    What in the hell is BHOT ? Try something serious, like The large scale structure of spacetime by Hawking and Ellis.

    You have no idea what I can conceive.

    You response simply demonstrates ignorance of the theory and general incompetence with mathematics and physics.

    Yep, your non-acceptance is irrelevant, the more so since you have no foundation for your rejection of the hypothesis.


    '
    Quote Originally Posted by nimzo256
    Everywhere' at the time of the Big Bang was a very small space indeed by all accounts. Much smaller than the 'everywhere' of today. And because that's the case we should be able to say where this smaller everywhere was. Quite often the expansion of the universe is compared with a lump of dough with raisins in it spreading out on a table top, the dough representing space and the raisins galaxies etc. Where did the lump of dough first hit the table?
    Nope. You are simply demonstrating that you don't understand that you don't understand. There is no table.

    Y
    Quote Originally Posted by nimzo256
    our post also fails to learn from the lessons of history. Reminiscent perhaps of some learned physicist 150 years or so ago, determined to defend come what may notions such as absolute time and the luminiferous ether, pointing to all the evidence that they must be correct, and regarding any attacks on them as ignorant. Scientific knowledge changes - and that includes today's scientific knowledge too.
    Wrong. You don't understand the basis for the theory and therefore don't understand which aspects are open to revision and which are not. There are some significant gaps in our knowledge, but they involve the first 10^-33 seconds, the very distant future, the topology of space, and the existence and nature of dark energy and dark matter. Even radically different competing theories show excellent agreement on the basics.

    An open mind is not an empty head.

    It is you, not I that have failed to learn. Your ignorance is quite profound.[/i]
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  8. #7 Re: Where did the Big Bang happen? 
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    What in the hell is BHOT ?
    i think Doc... BHOT stands for brief history of time- stephen hawking, just guessing
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  9. #8 Re: Where did the Big Bang happen? 
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    Quote Originally Posted by nimzo256
    It only makes sense to say that the universe began everywhere if we define everywhere as 'the place that the universe occupies or occupied at any given time, either now or in the past'. Well in that case 'everywhere' very shortly after the Big Bang was a very small place indeed. Much smaller than today's everywhere. So not everywhere.
    The universe is the whole thing, regardless of its "size". "The Big Bang happened everywhere" is just another term for saying that everywhere and everything was generated with the Big Bang. There was nothing there into which the universe was born and is expanding.
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  10. #9 Re: Where did the Big Bang happen? 
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    Quote Originally Posted by Dishmaster
    Quote Originally Posted by nimzo256
    It only makes sense to say that the universe began everywhere if we define everywhere as 'the place that the universe occupies or occupied at any given time, either now or in the past'. Well in that case 'everywhere' very shortly after the Big Bang was a very small place indeed. Much smaller than today's everywhere. So not everywhere.
    The universe is the whole thing, regardless of its "size". "The Big Bang happened everywhere" is just another term for saying that everywhere and everything was generated with the Big Bang. There was nothing there into which the universe was born and is expanding.
    I'll try and put my point in another way:-

    I think that the answer 'everywhere' is confusing because it's used inconsistently. We currently think that the universe has a diameter of approximately 78 billion light years. Nobody I think is suggesting that this was the diameter of the universe shortly after the Big Bang. However if you are going to say that the universe was always everywhere then a structure this size is what people will naturally understand by the statement, 'the Big Bang happened everywhere'. I'm happy with saying that the Big Bang happened everywhere there was at the time, and this everywhere expanded to form today's everywhere. I don't understand what the objection to this is.
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  11. #10 Re: Where did the Big Bang happen? 
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    [quote="DrRocket"]
    Quote Originally Posted by nimzo256
    I've read BHOT.
    Quote Originally Posted by DrRocket
    What in the hell is BHOT ?
    Brief History of Time as recommended by you.

    Quote Originally Posted by DrRocket
    You response simply demonstrates ignorance of the theory and general incompetence with mathematics and physics.

    An open mind is not an empty head.

    It is you, not I that have failed to learn. Your ignorance is quite profound
    I'm not interested in playing a game of argument by insult with you. If you disagree with me then that's fine. But kindly take the trouble to directly address the argument I've put been putting forward - something you so far have manifestly failed to do.

    Quote Originally Posted by nimzo256
    Everywhere' at the time of the Big Bang was a very small space indeed by all accounts. Much smaller than the 'everywhere' of today. And because that's the case we should be able to say where this smaller everywhere was. Quite often the expansion of the universe is compared with a lump of dough with raisins in it spreading out on a table top, the dough representing space and the raisins galaxies etc. Where did the lump of dough first hit the table?
    Quote Originally Posted by DrRocket
    Nope. You are simply demonstrating that you don't understand that you don't understand. There is no table.
    Irrelevant as far as the analogy is concerned.

    Quote Originally Posted by nimzo256
    Your post also fails to learn from the lessons of history. Reminiscent perhaps of some learned physicist 150 years or so ago, determined to defend come what may notions such as absolute time and the luminiferous ether, pointing to all the evidence that they must be correct, and regarding any attacks on them as ignorant. Scientific knowledge changes - and that includes today's scientific knowledge too.

    Quote Originally Posted by DrRocket
    Wrong. You don't understand the basis for the theory and therefore don't understand which aspects are open to revision and which are not. There are some significant gaps in our knowledge, but they involve the first 10^-33 seconds, the very distant future, the topology of space, and the existence and nature of dark energy and dark matter. Even radically different competing theories show excellent agreement on the basics.
    A 19th century physicist would probably have thought that the concept of absolute time was not 'open to revision'. Einstein himself struggled at first.

    Your whole approach seems similar to the one of a university lecturer who, on meeting his students for the first time, tells them how ignorant they are, hands them a booklist, and then instructs them to come back once he deems them worthy of listening to him. A bit of humility might not go amiss. You might find it helpful to read How the Universe got its Spots by Janna Levin. The subject matter should interest you and you might learn some valuable lessons about yourself.
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    I think I get what the OP means

    If you have a single theoretical point with nothing around it. if that point were to explode (or implode) and start expanding because of it, then all matter around it would originate from that point.

    At the time of the explosion (or implosion) the event was everywhere, since the point was everything there was, and the 'entire' point was involved.

    What I think he means though, is where would that point be in the current state of the universe. would it be possible to determine the exact expansion rate (I think I read somewhere they know that allready) and start working back to find where that point was?

    So even though the big bang was everywhere 13.7billion years ago. Where exactly would that point of 'everywhere' be today ?
    That's what I think he means


    The question though I think is irrelevant. Like many posters stated the universe 13.7 billion years ago cannot be compared to the current state. Even if you were to find a coordinate at this exact time. tomorrow that point will describe a plane due to expansion, in which you'd have to redefine a point.
    Due to the expanding nature of the universe, I think it's pointless trying to determine the origin of the big bang, since that point changes every second (or every measure of time really)
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    Quote Originally Posted by toonb
    I think I get what the OP means

    If you have a single theoretical point with nothing around it. if that point were to explode (or implode) and start expanding because of it, then all matter around it would originate from that point.

    At the time of the explosion (or implosion) the event was everywhere, since the point was everything there was, and the 'entire' point was involved.

    What I think he means though, is where would that point be in the current state of the universe. would it be possible to determine the exact expansion rate (I think I read somewhere they know that allready) and start working back to find where that point was?

    So even though the big bang was everywhere 13.7billion years ago. Where exactly would that point of 'everywhere' be today ?
    That's what I think he means
    Thanks. That's exactly what I mean - better expressed than I managed too.

    Quote Originally Posted by toonb
    The question though I think is irrelevant. Like many posters stated the universe 13.7 billion years ago cannot be compared to the current state. Even if you were to find a coordinate at this exact time. tomorrow that point will describe a plane due to expansion, in which you'd have to redefine a point.
    Due to the expanding nature of the universe, I think it's pointless trying to determine the origin of the big bang, since that point changes every second (or every measure of time really)
    If we could build a model of the universe today where we can run backwards in time and continually squash space until it became a point again, then at that point would we not have the location of the Big Bang?
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    Well, the theory is that at the time of the big bang- or at afterwards- the universe itself (space and time) was packed into a 'space' of a volume much less than a grain of sand, the whole universe was in this tiny space and so the big bang happened here- thus it happened everywhere, but everywhere was very small.

    As for what 'everywhere' is today, well, I'd say that it's just the whole universe (however big it is) again- just expanded out very very far, the everywhere today is pretty much the same as the everywhere back then, just bigger.

    That's what I think anyway, I'm only 17- I wouldn't really know, but I am going into astrophysics, so... :-D
    "Nature doesn't care what we call it, she just does it anyway" - R. Feynman
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    Quote Originally Posted by nimzo256
    If we could build a model of the universe today where we can run backwards in time and continually squash space until it became a point again, then at that point would we not have the location of the Big Bang?
    So you are reiterating Dr. Rocket's point that you are indeed ignorant and you haven't learned anything from any answers provided. It is a property of spacetime that produces the apprent motion of galaxies away from each other in the common era and that produced the apparent motion of particles away from each other in the very early era. It is not the case that, in general, these things moved through space away from each other.

    If there was a "big bang" moment, then it happened right here. You can make "right here" be where ever you want, since every point in the universe took part in this spacetime property.
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    Quote Originally Posted by PhysBang
    So you are reiterating Dr. Rocket's point that you are indeed ignorant and you haven't learned anything from any answers provided.
    More argument by insult - sigh. Please point to a single occasion in human history where anyone has successfully explained anything through insult. I'm prepared to accept that I might be wrong, but none of what I've read persaudes me that I am, and that includes your contribution.
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  17. #16  
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    The fact is you can not grasp the concept that the entire space of the Universe was once the size of an atom, and is now billions of light years across. In a way it's OK, because it's a hard concept to get a handle on. But since all the space (not the stuff) in the Universe was in such a point, the fact is the big bang happened everywhere. You are trapped by the common (wrong) concept that it was an explosion. That is not the case. There was nowhere for the explosion to expand in to. There was no explosion of matter spreading out across the Universe. It was an expansion of the entire Universe. Matter didn't form for a long time afterward.

    So despite the fact you don't get it, the expansion started everywhere at the same time, so everywhere is the center olf the Universe.
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  18. #17  
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    Here is a little "toy" model I sometime use in these situations. I am told it sometimes helps.

    So, let's make a model.

    Now to model an expanding space we need to assign coordinates within that space. For the moment, forget about any edges to that space, we don't need edges, we just need coordinates in order to measure the expansion of space. Galaxies come later, so for now just imagine a 3 dimensional grid. At each grid intersection we will assign a coordinate, a point, a dot. Let's say each intersection point is 1 meter apart.

    Put yourself on a point somewhere in this space. Whatever axis you look along you see neighbouring points 1, 2, 3, 4, 5 etc meters away, receding off into the distance. Then we introduce some expansion. Let's say the space grows to 10 times its original size in 1 second! That seems fast perhaps, but this is just a model with easy numbers. The key thing to remember is that the grid expands with the space.

    So, here we are, still sitting on our point (but it could have been any point) 1 second later. Now lets look along an axis. We see those neighbouring points are now 10, 20, 30, 40, 50 etc meters away. The space increased to 10 times its original size, and so did the distance between each intersection point on that grid.

    Our nearest neighbouring point has receded from 1 to 10 meters in 1 second, so it has receded at 9 meters per second. The next point away has receded from 2 to 20 meters in 1 second, so that point receded at 18 meters per second. The fifth point has moved from 5 to 50 meters away in 1 second, so that one has receded at 45 meters per second. The further away you look, the faster a point will seem to have receded!

    And the view would be the same, whatever viewpoint you choose in the grid! There is no "centre" of expansion, no origin point within that grid - the whole thing, the whole space has expanded from something where the spaces between things were really small to something where the spaces between things are much larger. If we imagine an observer at each grid intersection, then the expansion of that space has carried all those observers away from each other.

    Remember I said the grid of points receded off into the distance.. well a point that was initially 33,000,000 meters away will have moved away to 330,000,000 meters in 1 one second, meaning that it has receded at 300,000,000 meters per second - the speed of light! Any point initially more distant than 33,000,000 meters away from another point will have receded from that point faster than the speed of light. That is the distance were an object recedes at light speed in this "little" model of expansion. If you look at a point that has receded at the speed of light, then from that point, the point you are on has receded at the speed of light. But no object would be moving through space faster than light, no photon would ever overtake another photon, it all just gets carried along by the cosmic flow.

    Now I know this is a very simple model, dealing with a simple 10 times expansion in 1 second. This might seem very different from a universe where the rate of expansion was slowing from immense speed and then starting to accelerate, but if you start your grid very small and apply different rates of expansion to that grid, incrementally, over different rates of time, to simulate slowing it down and then speeding it up, when you look at the end result it is essentially the same. (Whenever there is a change in the rate of expansion, it is the rate of expansion for the whole grid that changes).

    You might be asking how useful this model actually is. Well you can substitute different distance measures and time-scales if you like but the principle remains. If you sprinkle galaxies throughout the grid and then expand that grid such that the galaxies move with the expansion, you would find that galaxies interact gravitationally with their near neighbours. The further apart galaxies are when they form, the less the gravitational attraction between them. If they are less than a certain distance apart, the galaxies will move towards each other and cluster together, but if there is enough distance they will be moved apart by the expansion of the universe.

    Galaxies at the edge of clusters might have some attraction to their neighbouring clusters, but that is countered by the gravity of the closer galaxies in their own cluster. Thus, the edges of the clusters seem to stretch out, "filament like", towards others in a manner reminiscent of the spiders web structures of the SDSS survey.

    We end up with clusters of gravitationally-bound galaxies and increasing distance between the centres of those clusters, in a universe where there is no "origin point" or centre of expansion. The whole thing was the origin point and we have no way of knowing how much larger than our observable part of it the whole thing is. We don't even know if it has an edge, and it doesn't actually need one, mathematically.

    It is not quite as simple as saying "if it has an overall shape, it must have a centre", unfortunately. If we trace time backwards until all points on the grid were next to, or even on top of each other, then no point can claim to be the origin point any more than any of the other points can.

    When we look out into the universe, we are looking backwards in time, towards the Big-Bang, whichever direction we look in! And everything we see in the distance seems to be heading directly away from here! We assume the same would be true in all those other places, too.

    I must just reiterate that the above "grid model" is a simple analogy, rather than a rigorous description of Big-Bang theory. It is as valid as the balloon analogy, in educational terms, and it is my attempt to get around some of the inherent problems with that balloon analogy.
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    What you guys don't seem to understand is that the universe is not expanding inside of anything else.
    Or as it was put, what happened when the raisin filled dough hit the table ? THERE IS NO TABLE. In this case the universe is everything and everything means EVERYTHING ! There is no outside.
    And the number you threw out for size is the observable universe which, because of the finite speed of light, is obviously smaller than the actual total universe, which may be finite but unbounded, or infinite.
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    Thank you SpeedFreek. That has been very helpful and I think I'm most of the way there! Your model excellently shows how the expansion is the same from every viewpoint.

    Just one thing still bothering me. Your model (which I appreciate is an anology) begins with multiple points, but my conception of the Big Bang is that it began at just one point. Now maybe mine is a misconception, but if not I think it might present a problem.

    If the Big Bang did start at one point (often called a singularity) then I don't see how it could have moved away from itself. Two points yes - we would then have a line as the points diverged. Three points not in a line would create a plane, and then four points not in a plane would give us space. But how could it all start with just one point? Or did it?

    I await your thoughts with interest.
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    The currently favoured cosmological model of the Big-Bang doesn't go all the way back to the beginning, unfortunately. That model uses the equations of Einstein's theory of General Relativity, our best theory of gravity, which works well for most of the history of the universe but throws out a singularity if we try to go all the way back to the beginning. A singularity in this context is generally taken to mean the theory has stopped working in the situation it is being asked to deal with - it is trying to solve a problem outside its domain of applicability.

    We need a theory better suited to the conditions of the early universe in order to understand what might have occurred. We need a theory that ties gravity in with events occurring at the quantum scale - a theory of quantum gravity, preferably where there is no singular behaviour.

    In cosmology, a universe as a singularity means "we don't really know what is going on there".
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    Thanks. Again very clear - and it confirmed the thought I had just as I was falling asleep last night! We just don't know that the conditions were at the very start and very soon after, and if that is so then we can't know if there was just one point - there may have been more. In fact it might not make any sense to talk about points at all. For me the myth of the singularity is debunked. Also I now know that the general theory of relativity can't be used to explain what happened right at the beginning. Perhaps more importantly I feel that I've now got a much clearer concept of spacetime.

    So many thanks again.
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    It's my pleasure!

    If you are interested, I made a couple of posts in another thread here that might help fill in some of the gaps.

    http://www.thescienceforum.com/Expan...se.-29467t.php
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    We just don't know that the conditions were at the very start and very soon after, and if that is so then we can't know if there was just one point - there may have been more. In fact it might not make any sense to talk about points at all.
    I don't quite see the problem you have with the concept of a single point being the origin of the big bang. In mathematical terms a point has zero dimensions, so the instant any sort of volume exists, you would have infinite points to choose from. The singularity idea results because when you run the clock of expansion backwards, you end up at a single point, i.e. if you keep shrinking a volume it will eventually become a single point. In physical terms, we don't know if a volume existed before the bang, just that a point results if you keep decreasing volume in mathematical terms.

    See my point? *cough*

    Great contribution from SpeedFreak again.
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    Quote Originally Posted by KALSTER
    I don't quite see the problem you have with the concept of a single point being the origin of the big bang. In mathematical terms a point has zero dimensions, so the instant any sort of volume exists, you would have infinite points to choose from.
    I don't see how a single point can be expanded, and because of this I can't see how any sort of volume can exist.
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    Quote Originally Posted by SpeedFreek
    It's my pleasure!

    If you are interested, I made a couple of posts in another thread here that might help fill in some of the gaps.

    http://www.thescienceforum.com/Expan...se.-29467t.php
    Thanks again. The other place we often hear about singularities is in relation to Black Holes. Are cosmologists now moving away from the singularity idea here, as they did with the Big Bang?
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    Quote Originally Posted by nimzo256
    Quote Originally Posted by KALSTER
    I don't quite see the problem you have with the concept of a single point being the origin of the big bang. In mathematical terms a point has zero dimensions, so the instant any sort of volume exists, you would have infinite points to choose from.
    I don't see how a single point can be expanded, and because of this I can't see how any sort of volume can exist.
    Nor can anyone else.

    Simple fact is (as far as I know) that there is nothing known that would stop a singularity from forming during gravitational collapse of a mass great enough to go all the way, nor anything known that says a singularity was not the origin of our universe if you play the tape backwards to the beginning. Our current science simply can't look that far back yet with the big bang or past a certain point during gravitational collapse.

    That is why they talk about singularities. But, AFAIK, as with all things in science, it was never a done deal in the first place. For the moment, we have the science we have and that science tentatively points towards singularities, but we don't know if and how yet. Even if the singularity view is favoured though, it doesn't mean other possibilities aren't being considered. It is just difficult doing much more than speculating at this point AFAIK.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

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    Quote Originally Posted by KALSTER
    Quote Originally Posted by nimzo256
    Quote Originally Posted by KALSTER
    I don't quite see the problem you have with the concept of a single point being the origin of the big bang. In mathematical terms a point has zero dimensions, so the instant any sort of volume exists, you would have infinite points to choose from.
    I don't see how a single point can be expanded, and because of this I can't see how any sort of volume can exist.
    Nor can anyone else.

    Simple fact is (as far as I know) that there is nothing known that would stop a singularity from forming during gravitational collapse of a mass great enough to go all the way, nor anything known that says a singularity was not the origin of our universe if you play the tape backwards to the beginning. Our current science simply can't look that far back yet with the big bang or past a certain point during gravitational collapse.

    That is why they talk about singularities. But, AFAIK, as with all things in science, it was never a done deal in the first place. For the moment, we have the science we have and that science tentatively points towards singularities, but we don't know if and how yet. Even if the singularity view is favoured though, it doesn't mean other possibilities aren't being considered. It is just difficult doing much more than speculating at this point AFAIK.
    The notion of singularities in GR is actually rather subtle.

    1..Singularities are NOT subsets of spacetime, single points or otherwise. The intuitive picture is that a singularity is a point at which curvature or density or some such thing "blows up" and becomes infinite, but this is not the case. Spacetime is presented as a 4-manifold, but in a somewhat unusual way. It is not presented as a given set with a Lorentzian metric, but rather is postulated to be a Lorentzian manifold with the metric determined by a complicated set of partial differential equations (the Einstein field equations) that determine the curvature and thereby the metric. The topology is unknown, and the metric is defined everywhere by the field equations. So a "singular point" at which the curvature tensor fails to exist cannot be a point in spacetime.

    2. The singularity condition for the big bang is that some timelike geodesic cannot be infinitely extended into the past. This is a rather technical condition and tells you essentially nothing about anything that could be interpreted as the topology of a singularity.

    3. Points 1 and 2 notwithstanding there is no such thing as a "center" for the expansion of space. The balloon analogy is applicable here so long as you recognize that the balloon surface represents the entire universe and the universe is not expanding from anything else or into anything else. THE BIG BANG HAPPENED EVERYWHERE.

    4. It is perfectly possible to shrink an infinite space to a point or conversely to "blow up" a point to an infinite space. Consider the map where and . For this maps to a point but for is the identity map. This is what is called in topology a "strong deformation retract of to the point .
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    Quote Originally Posted by nimzo256
    Quote Originally Posted by KALSTER
    I don't quite see the problem you have with the concept of a single point being the origin of the big bang. In mathematical terms a point has zero dimensions, so the instant any sort of volume exists, you would have infinite points to choose from.
    I don't see how a single point can be expanded, and because of this I can't see how any sort of volume can exist.
    The fact that YOU can't understand it is not considered a significant impediment by the Universe...
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    Quote Originally Posted by MeteorWayne
    Quote Originally Posted by nimzo256
    Quote Originally Posted by KALSTER
    I don't quite see the problem you have with the concept of a single point being the origin of the big bang. In mathematical terms a point has zero dimensions, so the instant any sort of volume exists, you would have infinite points to choose from.
    I don't see how a single point can be expanded, and because of this I can't see how any sort of volume can exist.
    The fact that YOU can't understand it is not considered a significant impediment by the Universe...
    Indeed so. However I was asked about the problem I have, so I answered for me. If it's the right question then the universe of course will have its own answer.
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    Very interesting Doc!

    4. It is perfectly possible to shrink an infinite space to a point or conversely to "blow up" a point to an infinite space. Consider the map where and . For this maps to a point but for is the identity map. This is what is called in topology a "strong deformation retract of to the point .
    Would that mean that a contraction or expansion to and from infinity to a point would happen instantaneously? I'm asking, because there is no such thing as half of infinity AFAIK? You either have infinite volume or a single point and nothing in between in that setup. If any sort of non-infinite volume exists, then time would tend towards infinity as volume does.

    That came out muddled. I hope you can make sense of it.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

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    Quote Originally Posted by KALSTER
    Very interesting Doc!

    4. It is perfectly possible to shrink an infinite space to a point or conversely to "blow up" a point to an infinite space. Consider the map where and . For this maps to a point but for is the identity map. This is what is called in topology a "strong deformation retract of to the point .
    Would that mean that a contraction or expansion to and from infinity to a point would happen instantaneously? I'm asking, because there is no such thing as half of infinity AFAIK? You either have infinite volume or a single point and nothing in between in that setup. If any sort of non-infinite volume exists, then time would tend towards infinity as volume does.

    That came out muddled. I hope you can make sense of it.
    Infinity is neither a number nor a place sp you have to be careful how you use the term. Basically he map I showed you is a continuous change of scale and only at scale = 0 does everything go to a point.

    Now, what I showed you is just an example of a mapping and not a model of the big bang based on physics. NOBODY knows what happened in the big bang at t=0. But if the universe is "infinite' (technically non-compact) now it has been infinite ever since t = 0+ . Nobody knows if the universe is infinite or not.
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    But if the universe is "infinite' (technically non-compact) now it has been infinite ever since t = 0+ . Nobody knows if the universe is infinite or not.
    Cool, it is as I thought then. Thanks!
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
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    Many people seem to misunderstand the Big Bang in general... I had many issues with it too at first, but then I learned to accept what the more educated people said. I think everyone should do the same if they want to learn. :wink:
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