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Author Topic:   Black Holes, for Eta Carinae
Mike Holland
Member (Idle past 483 days)
Posts: 179
From: Sydney, NSW,Auistralia
Joined: 08-30-2002


Message 31 of 53 (82768)
02-03-2004 6:03 PM
Reply to: Message 30 by Sylas
02-01-2004 9:03 PM


Re: response to cjhs
Ye Gods! So it has come to this! You plot to accuse me of being a crank, and have me arrained and publicly flogged or worse!
But all I ask is that you put your eye to the eyepiece.
I looked through those articles/movies about what is seen as you approach and pass through an event horizon, and found them fascinating. But not much new to me. I have no problem with anything said there, except the author's answer to question 2 - that there is no blue shift/speeding up of the world behind you just before you pass the horizon. We see the speeding up when we look at orbiting sattelites, so why wouldn't we in tis stronger gravitational field? The only reason I can think of is that the opposite effect is introduced by the velocity of our fall. Eta Carina said he would calculate the net effect, but he has the problem of what velocity to assume for the falling observer. The observer could go in slowly with his retro-rockets firing all the way! Anyway, I am certain that the GR effect will dominate at the end.
Sheesh... Yes, I do resolve the "problem" of infinite time at the event horizon by choosing a metric where time is not infinite at the event horizon. So does anyone else who knows physics. If you don't even recognize that, I can't help you.
What do you mean by a metric where time is not infinite? In the Finkelstein-Einstein metric the Finkelstein time is our time minus infinity at the event horizon. So you can do anything you like with these changes of metric. Why not choose a metric where time is minus our time. Then you can say that the falling observer passed through the e.h. before he started falling, and that PROVES that it happens!
Going back to that Schwarzschild diagram in your first reference (yes, I am choosing a metric which shows my point best, but is just as valid as other metrics), one can add the world-line of the observer - just to the right of the red line of the e.h., but not sloping as much as the light rays, because he is falling more slowly. Then you can see that the light rays all eventually arrive at his world line - he 'sees' them. And no matter how far you go up the diagram he keeps 'seeing' them - through the future of the universe.
These light rays (photons) hitting his worls lines are events which happen. Can you make them unhappen by changing metrics? I don't think so. You can only change the space and time coordinates used to record them, but the events remain. He 'sees' the future of our universe.
If you want to call me a quack, feel free. I am in very good company on this one. Sticks and stones and all that. In fact I will give you some extra ammunition. I am very partial to the observations and interpretations of Halton Arp regarding quasars and perculiar galaxies. And I also have Hoyle, Burbridge and Narlikar's book 'A Different Approach to Cosmology' in my library, 'though I don't like their cosmology.
Cheers, Mike.
And thanks again for digging out those fascinating web sites.

This message is a reply to:
 Message 30 by Sylas, posted 02-01-2004 9:03 PM Sylas has replied

Replies to this message:
 Message 39 by Sylas, posted 02-04-2004 5:21 PM Mike Holland has replied

  
RingoKid
Inactive Member


Message 32 of 53 (82894)
02-03-2004 10:54 PM


so...
...is this singularity the same singularity of the pre big bang and if so where is it and if not where is it and how can you have two of them ???
[This message has been edited by RingoKid, 02-03-2004]

Replies to this message:
 Message 33 by Sylas, posted 02-03-2004 11:44 PM RingoKid has replied

  
Sylas
Member (Idle past 5260 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 33 of 53 (82905)
02-03-2004 11:44 PM
Reply to: Message 32 by RingoKid
02-03-2004 10:54 PM


Re: so...
quote:
Originally posted by RingoKid:
...is this singularity the same singularity of the pre big bang and if so where is it and if not where is it and how can you have two of them ???
Here are three kinds of singularity.
  • The big bang singularity.
  • The singularity in the Schwarzchild metric at the event horizon of a black hole.
  • The singularity at the center of a black hole.
They are not all the same; they are all very different.
The term singularity is mathematical. It means that a mathematical function becomes badly behaved or diverges. For example, the function y = 1/x has a singularity at x=0.
The mathematical solutions for classical relativity have singularities in the conditions indicated.
For the big bang and the center of a black hole, the singularity indicates a point at which physics breaks down, and fails to give a good description of what is happening. A new physics will be required to handle those conditions; involving an combination of quantum mechanics and relativity. We don't have a theory able to handle those cases just yet.
For the event horizon of a black hole, the singularity is not a consequence of physics failing to work properly, but of one particular metric which could be applied. With a suitable transformation to another metric, there is no singularity.
That is, the singularity at the event horizon is a property of a description; the singularity at the big bang or center of a black hole is a consequence of extreme conditions that modern physics cannot presently model.
Every black hole is a singularity; and includes a region where physics breaks down. There seems to be a large black hole in the center of most galaxies; which indicates that there are many billions of them. There are also many smaller black holes within the galaxy, though these are hard to detect.
The Hubble space telescope has been very useful at finding and studying black holes. Here is a selection of stories about these observations:
NEWS RELEASES

This message is a reply to:
 Message 32 by RingoKid, posted 02-03-2004 10:54 PM RingoKid has replied

Replies to this message:
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RingoKid
Inactive Member


Message 34 of 53 (82914)
02-04-2004 12:05 AM
Reply to: Message 33 by Sylas
02-03-2004 11:44 PM


Re: so...
cheers man...
so what happened to the bigbang singularity, did it all get converted to "everything" or could there still be a whole heap of it left at the frontier of an inflating universe where physical laws also break down ???
and if the inflation is from a hypothetical fixed point could there not also be a singularity at the centre of the universe ???
meaning the universe is finite but the inflation is infinite and cyclic.

This message is a reply to:
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Replies to this message:
 Message 35 by NosyNed, posted 02-04-2004 12:52 AM RingoKid has replied

  
NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 35 of 53 (82924)
02-04-2004 12:52 AM
Reply to: Message 34 by RingoKid
02-04-2004 12:05 AM


Re: so...
and if the inflation is from a hypothetical fixed point could there not also be a singularity at the centre of the universe ???
This is a very common misunderstanding. It comes from having the wrong picture of the nature of the big bang.
The big bang is not and explosion! There is no center. Or equally you could say that everywhere is the center. All the 'places' that there are now, the floor under your feet, the place where Apollo 11 landed on the moon, the point where the Spirit rover is on mars now and a place on a planet in a galaxy far, far away where all right next to each other. NOT the planet, moon or your floor but the place in space where they are now were all crammed side by each. The space expanded carrying those points with them. They were all right there, right close up to the big bang. So they are all near the "center". But there isn't a center.
Refer back to discussions here using the famous (or infamous) balloon analogy. Every point on an expanding balloon moves away from every other. NO point on the surface of the balloon (which is the universe) is the center of the expansion. No where in our universe is a central point.

Common sense isn't

This message is a reply to:
 Message 34 by RingoKid, posted 02-04-2004 12:05 AM RingoKid has replied

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RingoKid
Inactive Member


Message 36 of 53 (82928)
02-04-2004 1:14 AM
Reply to: Message 35 by NosyNed
02-04-2004 12:52 AM


Re: so...
oh, not the balloon again...
if all of those things were right up next to each other then where was this ???

This message is a reply to:
 Message 35 by NosyNed, posted 02-04-2004 12:52 AM NosyNed has not replied

Replies to this message:
 Message 37 by Mike Holland, posted 02-04-2004 5:14 AM RingoKid has replied
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Mike Holland
Member (Idle past 483 days)
Posts: 179
From: Sydney, NSW,Auistralia
Joined: 08-30-2002


Message 37 of 53 (82970)
02-04-2004 5:14 AM
Reply to: Message 36 by RingoKid
02-04-2004 1:14 AM


Re: so...
Where else is (was) there? There was no other space/place.
If you picture the Big Bang as an explosion in pre-existing space, then the universe must have started off as a black hole, and it would still be a black hole - expansion against the mass/gravity of the whole universe would be impossible.
But if you imagine it as space expanding, taking everything with it, them you are imagining things, because I don't believe anyone can really imagine it. We can do the maths, 'though.
Mike.

This message is a reply to:
 Message 36 by RingoKid, posted 02-04-2004 1:14 AM RingoKid has replied

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RingoKid
Inactive Member


Message 38 of 53 (82974)
02-04-2004 5:39 AM
Reply to: Message 37 by Mike Holland
02-04-2004 5:14 AM


Re: so...
quote:
If you picture the Big Bang as an explosion in pre-existing space, then the universe must have started off as a black hole, and it would still be a black hole
exactly...
...black hole singularity in the beginning, on the outside and in the middle with the universe as an inflating membrane and black holes as tendrils rippling thru it becoming wormholes when separated from the edges and acting as counterweights to keep the centre fixed
you still get the expansion of dots/galaxies because the skin of the balloon is the universe...
the analogy would be an expanding plasma ball lamp
possible or not ???
picture yourself on the outside of the universe looking at it, it's so simple to imagine like a big ol' doughnut rolling around on itself

This message is a reply to:
 Message 37 by Mike Holland, posted 02-04-2004 5:14 AM Mike Holland has not replied

  
Sylas
Member (Idle past 5260 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 39 of 53 (83095)
02-04-2004 5:21 PM
Reply to: Message 31 by Mike Holland
02-03-2004 6:03 PM


Mike Holland writes:
Ye Gods! So it has come to this! You plot to accuse me of being a crank, and have me arrained and publicly flogged or worse!
But all I ask is that you put your eye to the eyepiece.
I did not accuse you of being a crank. You might be; I'm not yet sure. We don't flog cranks; or punish them in any way. Here is what I actually said:
cjhs said to michael:
If you approach this under the impression that you have a new theory of physics which resolves all the various breakdowns which are spoken of in the pages cited, then you are doomed to be yet another crank. The relativity groups are full of them.
If you approach this with the recognition that you are student grappling to understand a difficult subject, then you can make progress. I won’t be able to help very much at all; since I am not an expert in relativity. Reading though the tutorials supplied by Professor Hamilton would be a good start. He is an expert.
It would be a good idea for you to clarify in your own mind what it is you are trying to do. If you do think that the mismatches between your ideas and those of Andrew Hamilton are because he lacks your insight; then you are likely to end up as a crank. If you think the mismatches indicate that there is something lacking in your own understanding, then you are right; and you have a chance to learn something. I can help, if you let me.
You do understand some of this material; I endorse your attempts to explain the Big Bang expansion to Ringokid.
I looked through those articles/movies about what is seen as you approach and pass through an event horizon, and found them fascinating. But not much new to me. I have no problem with anything said there, except the author's answer to question 2 - that there is no blue shift/speeding up of the world behind you just before you pass the horizon.
The movies show that someone continues to see light from the rest of the universe even from within the event horizon. That means that the light, and the observer, is all crossing the event horizon. The situations are reached just fine.
The quiz question 2 of Professor Hamilton is actually this:
As you fall freely into a black hole, you see the entire future of the Universe played out before your eyes. True or false?
The correct answer is "false".
The plain prediction of conventional relativistic physics is that an observer who falls into a black hole, will continue to see the rest of the universe as they fall. They fall very quickly, reaching the center in a very short time. Light from the far future does not somehow catch up with them along the way.
As for blue shift, you need to read the pages again. Hamilton says that there is a substantial gravitational blue shift of the rest of the universe as seen by someone falling into the black hole. See his description of Gravitational redshift. He also gives a redshift map which corresponds to a view of the falling observer from about 0.68 Schwarzchild radii; that is, from inside the event horizon. Some parts of the sky are redshifted, and some are blueshifted. The effects are calculated from a combination of gravitational blueshifts, and velocity based red or blue shift.
We see the speeding up when we look at orbiting sattelites, so why wouldn't we in tis stronger gravitational field? The only reason I can think of is that the opposite effect is introduced by the velocity of our fall. Eta Carina said he would calculate the net effect, but he has the problem of what velocity to assume for the falling observer. The observer could go in slowly with his retro-rockets firing all the way! Anyway, I am certain that the GR effect will dominate at the end.
Eta Carina is correct; and Andrew Hamilton has done the calculations and presented them in a pictorial form. The simplest case for velocity is to use the velocity of a free fall from rest at infinite distance. But whatever velocity you use, all the way to the singularity there will be parts of the sky that are blue shifted, and parts that are red shifted. At no point do gravitational blueshifts dominate over the entire sky.
You are incorrect in thinking that you can go in slowly. No matter how good your retro rockets might be, once past the event horizon you will go in very quickly indeed; and it is possible to calculate an upper bound on the time it will take to hit the center singularity. An outside observer will not be able to observe anything from you after you have crossed the event horizon, and from that point you are doomed to hit the central singularity within a tiny fraction of a millisecond, no matter what you do with retrorockets.
quote:
Sheesh... Yes, I do resolve the "problem" of infinite time at the event horizon by choosing a metric where time is not infinite at the event horizon. So does anyone else who knows physics. If you don't even recognize that, I can't help you.
What do you mean by a metric where time is not infinite? In the Finkelstein-Einstein metric the Finkelstein time is our time minus infinity at the event horizon. So you can do anything you like with these changes of metric. Why not choose a metric where time is minus our time. Then you can say that the falling observer passed through the e.h. before he started falling, and that PROVES that it happens!
You mean "Eddington-Finkelstein", not "Finkelstein-Einstein".
It is an error to speak of "our" time. This sneaks in the implicit assumption of a privileged absolute time scale. It is a common mistake. I've tried to point this out several times already. There are many metrics which might be used to give time and space co-ordinates to events which we observe at a distance. In some metrics, the time co-ordinate of events on the event horizon are infinite. In others, it is not infinite. That is what I mean by metrics where time at the horizon is not infinite.
One useful notion of time is the time experienced by a falling observer. In this case, the time metric for an event in spacetime corresponds to that experienced by the falling observer. The corresponding spacetime diagram is displayed at the pages cited previously. You can see clearly that the observer experiences finite time to hit the center; and that the observer crosses a finite number of photon world lines.
The relationship between "Eddington-Finkelstein time" and "Schwarzchild time" is "tF = tS + log|r-1|" (in appropriate units). "r" is distance, which is the same in both metrics.
I cannot make any sense of your last comment about an observer passing through the event horizon before they start falling. If you think you can just do what you like with relativistic metric transformations, then that is another error.
Going back to that Schwarzschild diagram in your first reference (yes, I am choosing a metric which shows my point best, but is just as valid as other metrics), one can add the world-line of the observer - just to the right of the red line of the e.h., but not sloping as much as the light rays, because he is falling more slowly. Then you can see that the light rays all eventually arrive at his world line - he 'sees' them. And no matter how far you go up the diagram he keeps 'seeing' them - through the future of the universe.
This is a simple and unambiguous mathematical error on your part. If you do the math, you can see it is false.
The world-line of a free falling observer will only cross a finite number of world-lines of in-falling light rays. Furthermore, it will cross the exact same finite number of light rays, no matter what metric is used for plotting world lines.
Take a Schwarzchild diagram. Plot world-lines of light rays, and as you say they all diverge upwards at the event horizon. Take a free falling observer, who is falling more slowly than the light. It also will diverge upwards, but not sloping as much as the light rays. But it still only crosses a finite number of the light rays. That is just a mathematical fact.
These light rays (photons) hitting his worls lines are events which happen. Can you make them unhappen by changing metrics? I don't think so. You can only change the space and time coordinates used to record them, but the events remain. He 'sees' the future of our universe.
This is backwards. Only a small number of photons hit the world line of the falling observer, and you can't make them hit the world line of the infalling observer by any transformation. The events don't happen, in any diagram.
Eta Carina is probably better able to manage the maths than I am. I do not know off hand the formulae for the world line of a free falling observer. But we can approximate it.
The diagrams have "r" as the horizontal axis, representing spatial distance from the black hole, and "t" as the vertical axis, representing time. Let "N" be a parameter indicating different photons. The world line for an in-falling photon in the Schwarzchild metric is the line defined by:
t = N - r - log|1-r|
Different values of "N" give different photons.
An infalling observer might have a world line defined by:
t = -2*r - log|1-r|
This is not really a free fall; but some kind of powered descent. It falls more slowly than the photons. You will find that this line diverges upwards to infinity at the event horizon (r = 1); and that it "slopes less" than the photon world lines.
The observer will cross the world line of photons for which "N < -1". Inside the event horizon, this observer crosses the world line of a few more photons, those with "-1 < N < 0". Photons for which "N > 0" will never ever hit the world line of the observer. Those are the photons that hit the central singularity strictly after the observer hits the central singularity.
The observer also crosses the world line of one photon; the "N = -1" photon, right on the event horizon; but of course we can't show that event on the Schwarzchild diagram due to the singularity. We can show it just fine on the Eddington-Finkelstein diagram.
The statement that an infinite number of photons cross a free-fall line which "slopes less" is just false. You would need a line that corresponds to an observer who uses infinitely powerful retro rockets to hold themselves above the event horizon indefinitely, in their own time frame.
If you want to call me a quack, feel free. I am in very good company on this one. Sticks and stones and all that. In fact I will give you some extra ammunition. I am very partial to the observations and interpretations of Halton Arp regarding quasars and perculiar galaxies. And I also have Hoyle, Burbridge and Narlikar's book 'A Different Approach to Cosmology' in my library, 'though I don't like their cosmology.
Shrug. You have a lot to learn before your opinions of maverick cosmologists are meaningful. Halton Arp is a maverick of considerable real ability, but handicapped by a massive blind spot and a bad chip on his shoulder. His observations of peculiar galaxies are interesting, but he does not actually have a good interpretation. He thinks something else must be causing high red shifts for quasars, but does not know what. The rest of the astronomical community considers his claims for the close association of quasars with galaxies of less red shifts to be adequately refuted. The evidence for association he presents is very thin. Be careful also; he has made some serious basic errors in statistical analysis of some of his evidence; which he has since recognized (grudgingly). Alas, many enthusiasts will continue to cite the flawed analysis as if it means something.
But in any case, I am quite sure that Halton Arp would not make the kinds of elementary errors in relativistic analysis seen above.
Cheers, Mike.
And thanks again for digging out those fascinating web sites.
No worries, mate. They are fascinating.
Try to take this in good humour. You may not accept this yet; but you are still making really really basic errors; and I am not going to hide that or pretend that we are discussing this as equals. I'm not an expert, but I know enough to see where you are going wrong, and to point you in roughly the right direction. If you can recognize that you are still learning, there is no reason you can't make progress.
Perhaps I am a bad teacher for not being sufficiently respectful of your ideas; or perhaps you have been handicapped by lack of a teacher who is willing to tell you frankly when you are making silly mistakes. But I am trying to help.
My advice is to focus on your claims about world lines of falling observers and photons in the Schwarzchild spacetime diagram, until you have resolved it. Use some actual maths. See if you can find a mathematical description of the world line for an free fall from infinite distance. I don't know it; if you can figure it out let me know! Seriously. But the fact that it crosses a finite number of photon world lines is definite.
Cheers -- cjhs
[This message has been edited by cjhs, 02-04-2004]

This message is a reply to:
 Message 31 by Mike Holland, posted 02-03-2004 6:03 PM Mike Holland has replied

Replies to this message:
 Message 49 by Mike Holland, posted 02-05-2004 7:19 PM Sylas has replied

  
Sylas
Member (Idle past 5260 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 40 of 53 (83099)
02-04-2004 5:31 PM
Reply to: Message 36 by RingoKid
02-04-2004 1:14 AM


Re: so...
quote:
Originally posted by RingoKid:
oh, not the balloon again...
if all of those things were right up next to each other then where was this ???

The balloon analogy is an attempt to help you answer this question. In the analogy of the balloon, space corresponds to the surface of the balloon, and ONLY the surface of the balloon. Of course, this analogy is not exact, because the surface of a balloon is two dimensional, and the space we experience is three dimensional. But expansion of three dimensional space is not something people find easy to grasp, so we use the ballon analogy to help.
In my own experience, however, it often hinders because students mistake the analogy, and think of the universe including points which are not on the skin of the balloon.
The balloon expands. There is no point on the balloon which is the center of the expansion. The center is back in the past, when the balloon was tiny, and all points on the skin of the balloon were very close to all other points on the skin of the balloon.
Where was the center of expansion for the universe? Right here. And also over there. Every point we see in the universe has equal claim to being a center.
A better analogy may be an infinitely large loaf of rising raisin bread. As the loaf rises, all the raisins are expanding from all the other raisins. Galaxies are like raisins; they are all moving away from each other as the universe expands. In the past, they were all infinite close together. But there is no one point in the loaf, or in the universe, which can be seen as the center. The initial singularity is just a point of infinite density and infinite heat, in which every point in space is infinitely close to every other point in space.
Don't think of a point in space as being the unique center of expansion. That is a common error.
Cheers -- cjhs

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RingoKid
Inactive Member


Message 41 of 53 (83120)
02-04-2004 6:36 PM


yeah cjhs...
...I get all that but even a loaf of raisin bread can be perfectly balanced from some point in the middle of it, a centre of mass
quote:
The center is back in the past, when the balloon was tiny, and all points on the skin of the balloon were very close to all other points on the skin of the balloon
so what shape did this singularity have and where was it ???
...see what i'm getting at, uniform gravity produces perfect spheres, expanding bubbles, sub atomic particles are all spherical aren't they and black holes are round and so are craters no matter what shape the meteor was ???
an infinite universe expanding infinitely in all directions is just a copout for not looking for the centre of mass...isn't it ???

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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 42 of 53 (83123)
02-04-2004 6:45 PM
Reply to: Message 41 by RingoKid
02-04-2004 6:36 PM


the other thing is I'm sure most of you are capable of forming a hypothesis on God that you can test you just don't want to, the hypothesized nature of God is nature itself being the will of God.
The raisen bread analogy is also a bit dangerous. You're thinking of the bread being in a "space" of it's own - the kitchen. So it appears to be an "explosion" out into the kitchens air. But there is not kitchen for the big bang, there is no other "there" that is still part of our universe.
an infinite universe expanding infinitely in all directions is just a copout for not looking for the centre of mass...isn't it ???
I'm not knowledgeable enough to get this right actually. Eta is needed back again.
However, I think that it is true that there is no "centre of mass" either. To find that you would find a point where there was,say, 13.7 G light years of universe on one side and 13.7 light years of universe on the other side (and so on). But the point is the every place in the universe has that much around it. They are all just as good as a centre as anywhere else.

Common sense isn't

This message is a reply to:
 Message 41 by RingoKid, posted 02-04-2004 6:36 PM RingoKid has not replied

  
Sylas
Member (Idle past 5260 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 43 of 53 (83142)
02-04-2004 7:25 PM
Reply to: Message 41 by RingoKid
02-04-2004 6:36 PM


RingoKid writes:
yeah cjhs...
...I get all that but even a loaf of raisin bread can be perfectly balanced from some point in the middle of it, a centre of mass
Always keep in mind that all of these analogies are just analogies, and break down at some point.
The universe does not have a center of mass.
In the analogy of the loaf, I tried to express this by speaking of an infinite loaf. An infinite loaf of bread, like the universe, does not have a center of mass.
However, we don't really know if the universe is infinite, or finite. For the simplest topologies, the most recent results suggest an infinite universe, since it is "open". However, even in this case the universe might be finite if it has a more complex topology. There was, briefly, a newsreport last year about a twelve sided model for the universe. The model was refuted almost as soon as it was published, and it has been discussed in this forum. That was a case of considering a complex topologicial structure for a finite but open universe.
To get an idea of how strange this is, if true it would mean we could see the exact same regions of space by looking in several different directions. It does not mean the universe has a 12 sided edge.
Trying to get reasonable analogies for this that will help give a good mental picture is very difficult. We need to get back to the balloon again. The universe may be like the skin of a balloon. It is unbounded (no edges) but (possibly) finite. Or (as recent observations suggest) it is like the skin of a saddle point in the mountains (negative curvature), which is (in the simplest case) infinite. Mix in a funny topology like a torus or doughnut, and it could still have negative curvature and be finite at the same time. The really tough thing in these analogies is to recognize that the universe is analogous to the skin of the structure; without being embedded in a higher dimensional space..
A common feature of all the models is that there is no center of mass. That is because, as I tried to explain last time, the nature of the expansion of the Big Bang is that there is no point you can identify in space as the point from which expansion occurs. It is an expansion of all space, with all points having equal claim to being a center of the expansion. If the analogy fails to get that across, it is a defect in the analogy.
cjhs:
The center is back in the past, when the balloon was tiny, and all points on the skin of the balloon were very close to all other points on the skin of the balloon
so what shape did this singularity have and where was it ???
It is not meanginful to speak of the shape of the singularity. You can speak of the shape of the universe; but that does not mean what you think. In any case, the universe expands or stretches over time, but the overall shape or topology (which is not known) remains the same.
The singularity is the break down in description back in the past when all points in space were arbitrarily close to all other points in space; but there was never, at any point, a distinguished central point in space.
...see what i'm getting at, uniform gravity produces perfect spheres, expanding bubbles, sub atomic particles are all spherical aren't they and black holes are round and so are craters no matter what shape the meteor was ???
I do see what you are getting at; it is a very common mistake as we start to try and grasp modern cosmology. The problem is that you are still thinking of the universe as a "thing" in space, which has a center and a boundary. That is incorrect. The universe is not like a particle in space. When cosmologists speak of the "shape" of the universe, it is confusing, because they don't mean that the universe has a boundary they can trace. They are talking of the structure of spacetime and intrinsic curvature, with no presumptions at all of an embedding into a larger space.
an infinite universe expanding infinitely in all directions is just a copout for not looking for the centre of mass...isn't it
No, it isn't. The nature of the expansion is that all points in space used to be arbitrarily close together. The ideas of expanding space are really hard to grasp, because expansion of space is not the same as the expansion of a physical object. But that is relativity for you. It's difficult, and it is counter intuitive. But it is not a cop out for avoiding the intuitions you may about a central point.
Cheers -- cjhs

This message is a reply to:
 Message 41 by RingoKid, posted 02-04-2004 6:36 PM RingoKid has replied

Replies to this message:
 Message 44 by RingoKid, posted 02-04-2004 7:57 PM Sylas has replied

  
RingoKid
Inactive Member


Message 44 of 53 (83152)
02-04-2004 7:57 PM
Reply to: Message 43 by Sylas
02-04-2004 7:25 PM


so what are the ramifications for a fixed mass and centre if the universe is finite ???
and is it entirely not possible for it to be embedded in a larger medium ???...not like a "thing" in space but a thing in a nothing/void
as in a singularity in a void that explodes/expands...the singularity becomes "everything" "everywhere" but it is still expanding into the void/nothing

This message is a reply to:
 Message 43 by Sylas, posted 02-04-2004 7:25 PM Sylas has replied

Replies to this message:
 Message 45 by Sylas, posted 02-04-2004 8:41 PM RingoKid has not replied

  
Sylas
Member (Idle past 5260 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 45 of 53 (83169)
02-04-2004 8:41 PM
Reply to: Message 44 by RingoKid
02-04-2004 7:57 PM


RingoKid: writes:
so what are the ramifications for a fixed mass and centre if the universe is finite ???
The ramifications are that a finite universe would have a finite mass, but still no centre.
Again; the balloon. The balloon does not have a center. Recall, in the analogy, you may only consider the skin of the balloon; anything else does not belong in the analogy. That is what a finite universe would be like, in the simplest case. All points in the universe are equivalent, like all points on the surface of the balloon. There is a finite mass in the universe, just like the balloon surface has a finite mass. There is no central point in the universe, just like there is no central point on the surface of the balloon.
We use the balloon analogy simply because it might help to grasp these hard to understand points. The surface of the balloon is an analogy to explain these aspects of the universe. The ultimate reality is the universe; not the balloon.
Of course, science can never be sure about their models. But even if our cosmological models are all fundamentally wrong, this is still not going to restore simple ideas based on particles expanding from a central point in a nice simple flat three dimensional space.
and is it entirely not possible for it to be embedded in a larger medium ???...not like a "thing" in space but a thing in a nothing/void
If you are thinking of the "nothing/void" as a large empty expanse pretty much like what you can find in an empty box, then indeed it is not possible for the models of the universe we are trying to explain to be embedded in such a space.
It is mathematically possible to define higher dimensional spaces in which a curved three dimensional universe might be embedded, in many cases; much like the two dimensional surface of a balloon is embedded in the higher dimensional (three dimensional) space of our normal experience. Nothing is gained by such an exercise. The higher dimensional spaces are far less intuitive than anything you have tried to grasp so far, and they add nothing useful to the models. The higher dimensions are not something we experience, and cannot give you a point in our universe as its center, and do not correspond to anything physical in our universe.
It is likely that there are in fact more dimensions than the three we experience normally; but we would need a whole new set of analogies to try and discuss that idea. These models involve tightly curved dimensions, not higher dimensions in which the space of out normal experience is embedded.
as in a singularity in a void that explodes/expands...the singularity becomes "everything" "everywhere" but it is still expanding into the void/nothing
The models we have for the universe do not involve expansion into a void. Such a notion is in conflict with all the evidence. The evidence we have indicates a Big Bang style expansion -- which is why that is the basis of cosmology.
Cheers -- cjhs

This message is a reply to:
 Message 44 by RingoKid, posted 02-04-2004 7:57 PM RingoKid has not replied

  
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