If we assume for a moment that the theory of the big bang and onto the expanding universe.

If this is the case then all matter is or has been flung outwards away from the epicentre.

Ok, we take a peek at this expanding universe and true it appears that everything is flying outwards. The question I want to ask is if every thing is outward bound that would mean that the centre of the universe would be void of matter and this void would be getting bigger all the time.

The only answer that I can see is that the bigbang is still ongoing in that at the centre of the universe is the continuous creation of more and more matter thus filling the void created by the outward moving mass.

Has any one got any insights into the above?
What assumptions am I making that are in error if any?

The big bang is responsible for the creation of all matter as well as space-time, but the name appears to have misled you. The expansion of the Universe is due to the 'stretching' of space-time. This causes the matter in the Universe to be more sparsely distributed, and is the reason for the exact temperature of the cosmic background radiation, which is merely the photons from the big bang which have been redshifted as the Universe expands.

Originally posted by Quantum Quack
If we assume for a moment that the theory of the big bang and onto the expanding universe.
yes, lets

If this is the case then all matter is or has been flung outwards away from the epicentre.
the big bang does not state that all matter is flying apart from some epicenter. instead, the distance scale of the universe is itself growing. all parts of the universe are getting farther apart from one another, uniformly throughout the universe.

there is no "epicentre"

Ok, we take a peek at this expanding universe and true it appears that everything is flying outwards.
not "outwards". there is no "out" direction from the universe. instead, i would say that all matter is flying apart

The question I want to ask is if every thing is outward bound that would mean that the centre of the universe would be void of matter and this void would be getting bigger all the time.
no. there is no center. matter is not flying from a single point. instead, space is expanding uniformly in all directions.

in fact, the entire big bang theory rests strongly on the homogeneity of the universe, so the very notion of a central point contradicts big bang theory right away.

The only answer that I can see is that the bigbang is still ongoing in that at the centre of the universe is the continuous creation of more and more matter thus filling the void created by the outward moving mass.
the big bang is over. the universe is cold.

Has any one got any insights into the above?
What assumptions am I making that are in error if any?
i don t know if i have any insigts, but i think you have made an error in your understanding of the big bang, and i hope i helped you to see it.

The Big Bang is not an explosion of matter into an existing space, implying an expanding void and the problems that creates as has been seen. It is the creation of spacetime which itself is expanding. Matter is simply following the expansion of spacetime.

My astrophysics teacher uses the analogy of rasin bread.

If you heat up rasin bread, it doesn't expand from one central point like an explosion. It's all the dought between the rasins that rises and expands, pushing the rasins farther and farther apart.

The universe is like an infinite rasin bread, with the galaxies representing the rasins and the empty space between representing the dough.

Originally posted by Redrover
The universe is like an infinite rasin bread, with the galaxies representing the rasins and the empty space between representing the dough.

No, its like a VERY LARGE raisin bread but I prefer to use the balloon (with marked spots on it) analogy!

But what powers such spreaded expansion? (The only way I manage to visualize this is that only time exploded (on an existing (very small) space) The time was very quick at the beginning so that the distances (the same big as they are now) were "traveled over" in nanoseconds... Now the time is slowing down so that it <i>looks</i> as if the universe were expanding...How can otherwise the expansion be equal on all places with different concentration of matter/energy?)

the question about the raisin bread is whether we eat it quickly or eat it slowly. Hmmmmm...breakfast

The rasin bread view is a much better analogy (in my opinion) for the simple reason it expresses expansion of a 3D volume. The old ballon concept mixes dimensions. I think that is unnecessary and over complicates reality. But my opinion is not the one most scientest seem to prefer.

Originally posted by MacM
The rasin bread view is a much better analogy (in my opinion) for the simple reason it expresses expansion of a 3D volume. The old ballon concept mixes dimensions. I think that is unnecessary and over complicates reality. But my opinion is not the one most scientest seem to prefer.

actually, i think that is a rather astute observation. the balloon analogy often leads to the question of the physical meaning of those extra dimensions....

lethe,

actually, i think that is a rather astute observation. the balloon analogy often leads to the question of the physical meaning of those extra dimensions....

I'm reading your statement to mean you find the extra dimensions being astute. I don't find thinking about those possibilities necessarily bad but I think it is fool hardy to go there unless forced to by evidence. I see no evidence of a 4th dimension much less more.

Further it is not difficult to envision that the extra dimesnions as described in Strings for example are actually 3D artifacts within the basic 3D system.

I think the term dimension is a misnomer. I can visulaize tightly coiled artifacts that would not normally be accessable to us but I don't see them as true dimensions.

Originally posted by MacM
lethe,
I'm reading your statement to mean you find the extra dimensions being astute. I don't find thinking about those possibilities necessarily bad but I think it is fool hardy to go there unless forced to by evidence. I see no evidence of a 4th dimension much less more.

no, i meant that your observation that the balloon analogy is flawed because of extra dimensions was astute.

this analogy (along with the analogy of spacetime as a warped rubber sheet) is confusing for a lot of people, because it introduces extra dimensions, which are not real, not even to string theorists! (string theorists mean physical dimensions. these are not physical)

take it as agreement, and a compliment, that s what it was. you gave the qualifier that your view was not mainstream science, so i thought i would endorse it, since i am mainstream science, and i agree.
Further it is not difficult to envision that the extra dimesnions as described in Strings for example are actually 3D artifacts within the basic 3D system.
there was a time when people worked on string models like this. it is in fact true, that you don t really need 26 physical dimensions for bosonic string theory, you can insert the degrees of freedom into the theory in other ways.

but extra dimensions has proved to be the most promising route. so these days, when string theorists talk about extra dimensions, they really do mean extra dimensions.

I think the term dimension is a misnomer. I can visulaize tightly coiled artifacts that would not normally be accessable to us but I don't see them as true dimensions.
well, like i said above, there are models where the extra degrees of freedom are not really dimensions, and in those cases, the term is a misnomer.

but in most modern string models, the dimensions really are dimensions. when you write down the coordinates of a string, you list 10 coordinates, instead of 4. if that ain t a dimension, i don t know what is.

lethe,

Thanks for the rare compliment. But would suspect that the dimensions you mention are mathematical only describing what will be found to be artifacts below planck scales that are just unobserved (also meaning out of physical contact) by us.

If one defines dimension in those terms I could accept it. But the routine of trying to draw for example a 4D cube or sphere is not how I would see these extra d's.

Originally posted by MacM
lethe,
But would suspect that the dimensions you mention are mathematical only describing what will be found to be artifacts below planck scales that are just unobserved by us.

well there are two ways to look at extra dimensions: you could say that since the math predicts them, and we don t observe, them, then string theory is wrong.

on the other hand, you could just say that they are only observable somewhere near the planck scale. this is the string theorists party line (although there are some scenarios where they might be large enough to be observable). but for the most part, what you said is exactly what the string theorists believe.

Originally posted by MacM
But the routine of trying to draw for example a 4D cube or sphere is not how I would see these extra d's.

i don t know what you mean here. how do you draw a 4D sphere?

lethe,

If that is true (and I'm sure you are right) then I have a greater respect for what strings is attempteing to do but they don't make that clear when they start extrapolating that to multiverses, etc., and seem to relish the idea of making multiple dimensions out to be more than mere microscopic artifacts (physics isolated pockets if you will) within our 3D space.

Originally posted by MacM
lethe,

If that is true (and I'm sure you are right) then I have a greater respect for what strings is attempteing to do but they don't make that clear when they start extrapolating that to multiverses, etc., and seem to relish the idea of making multiple dimensions out to be more than mere microscopic artifacts (physics isolated pockets if you will) within our 3D space.

i guarantee you, string theorists would love it if there were someway to make string theory work in 4 dimensions. the extra dimensions that it requires are a big problem.

it is something that you hear about most often, because it is the result of string theory that lay people find most interesting, i guess because it kind of sounds like sci-fi.

but really, no one relishes those extra dimensions. it just makes everything harder.

lethe,

i don t know what you mean here. how do you draw a 4D sphere?

That was sort of my point about dimensions.:D

I have seen people do all sorts of contortions making representations of a 4D cube but it really has no meaning if you can't also draw a 4D sphere.

Originally posted by MacM
lethe,



That was sort of my point about dimensions.:D

I have seen people do all sorts of contortions making representations of a 4D cube but it really has no meaning if you can't also draw a 4D sphere.

who cares whether you can draw it or not?

The 4-sphere and hypercube you are talking about are abstract mathematical objects, whereas the dimensions of string theory are physical dimensions.

The 4-sphere is a smooth polytope (I'm not quite sure what word to use) whose 'surface' is a 3-sphere, as a hypercube is a 3-cube extended an equal distance into the fourth dimension.

In a sense, any object you interact with is four-dimensional, having a 'length' in time as well as three spacial lengths. Any three dimensional object would either be a two dimensional plane, or an instantaneous object.

Hope this helps seperate the maths from the physics.

When you say "length" in time what do you mean?

To me it implies only the past and the Now but really it is only the now with a past. So length in time is really a continuum of time in the now.

Originally posted by lethe
i guarantee you, string theorists would love it if there were someway to make string theory work in 4 dimensions. the extra dimensions that it requires are a big problem.


However, one of the great triumphs of string theory is that is the first theory that give the dimensionality of the world.

Generally, in physics we are used to say that we don't ask why but we ask how. Untill string theories, we knew we live in a 4D world. We didn't have the answer to why is it like that. String theories (no matter if it is correct or not) shows us that we can also ask the question of why. Finally, we expect that in a theory of everything, the question of why are the interractions what they are, and why does the world look like the way it is,is a legitim question with answer that this is the only consistent theory.

There will always be what I term 'ultimate why questions' though such as why ARE these rules the way they are and why WAS the universe created (if it was) at all. These will never be answered.

John Connellan,

There will always be what I term 'ultimate why questions' though such as why ARE these rules the way they are and why WAS the universe created (if it was) at all. These will never be answered.

That is a very safe bet. :D

Originally posted by 1100f
However, one of the great triumphs of string theory is that is the first theory that give the dimensionality of the world.



yes, i agree with this, although it would be much nicer if the value for D that it predicted were 4 instead of 10. many believe that the equations will eventually show that the 6 dimenional compactification is unique, and then, it really would be quite a triumph. this is a possibility, although it hasn t been shown yet.

also, i should say, lest you think that the 10 dimension prediction is completely bad, it has some benefits. like you need compactifications to get chiral fermions, so if it had only 4 dimensions, there would be no compactification, and therefore no possibility of chiral fermions, which would be bad, since i am made out of chiral fermions.

Originally posted by John Connellan
There will always be what I term 'ultimate why questions' though such as why ARE these rules the way they are and why WAS the universe created (if it was) at all. These will never be answered.
I agree, but the rules would much less restrictive, such as:
Rule number 1: The world is governed by physical laws.
Rule number 2: The rules are the same everywhwere.
Rule number 3: ???

etc.

lethe,

also, i should say, lest you think that the 10 dimension prediction is completely bad, it has some benefits. like you need compactifications to get chiral fermions, so if it had only 4 dimensions, there would be no compactification, and therefore no possibility of chiral fermions, which would be bad, since i am made out of chiral fermions.

Strikes me as a bit ethnocentric and myoptic. :D

Originally posted by MacM
lethe,



Strikes me as a bit ethnocentric and myoptic. :D

is that a joke? if so, i don t get it.

Quantum Quack:
What I meant by a 'length' in time was simply a measurable quantity, like any of the x,y,z components of a 3-vector, just this time, the fourth component is a 'length' of time. I don't know if there's a better word for this, but anyway, you might as well ask what we mean by a length in the x-direction.

lethe,

which would be bad, since i am made out of chiral fermions.

Perhaps I copied to much of your statement and obscured my meaning. :D

the distance scale of the universe is itself growing. all parts of the universe are getting farther apart from one another, uniformly throughout the universe.

In that case, can I ask why lengths here on Earth all stay the same?

Originally posted by Harsh
In that case, can I ask why lengths here on Earth all stay the same?

Local gravitational effects are stronger than the expansion. You only see expansion at lenths greater than several Megaparsec (10's of millions of lightyears).

Originally posted by MacM
lethe,



Perhaps I copied to much of your statement and obscured my meaning. :D

Mac-

you are also made out of chiral fermions.

lethe,

you are also made out of chiral fermions.

Now we agree, it would be bad. :D

I was trying to be cute with your assumption that the world would be at a loss with your demise.

Originally posted by MacM
lethe,



Now we agree, it would be bad. :D

I was trying to be cute with your assumption that the world would be at a loss with your demise.

hehehe... yes, a theory without lethe-particles would be a poor theory indeed.

In that case, can I ask why lengths here on Earth all stay the same?

Relativistically they would stay the same unless observed form some other vantage point as the whole earth would part of the expansion.

A question that comes to my absurd mind is

How far apart can two stars get from each other before their gravitational relationship disappears?

Originally posted by Quantum Quack
How far apart can two stars get from each other before their gravitational relationship disappears?

When two stars are far enough, you can use the classical result that for a potential that goes like 1/r, the total cross section is infinite. this means that the gravitational relationship does not disappear.

Somewhere in Paris the original meter stick is held (in a special vault) . It is held at special temperature (not to change its length). But whatever use it is held there for it is not for the meassuring of the expansion of the universe or its parts. Why? If all is expanding the meter stick is expanding too...

Yeah but we dont rely on that meter stick anymore for standard reference so who cares!

Can I ask why the universe is expanding? And also, if you went out into intergalactic space, would you start expanding as well since there is no gravity holding you together?

Somewhere in Paris the original meter stick is held (in a special vault) . It is held at special temperature (not to change its length). But whatever use it is held there for it is not for the meassuring of the expansion of the universe or its parts. Why? If all is expanding the meter stick is expanding too...

Can I ask why the universe is expanding? And also, if you went out into intergalactic space, would you start expanding as well since there is no gravity holding you together?

No, objects generally do not expand because of the electrostatic forces between them. Molecules stick together because the forces keeping them together have a far greater strength than the expansion of the universe at each point. Hence, as a result, only the distance between objects increases, but not the size of the objects themselves.

Bye!

Crisp

Thanks for the answer, Crisp. However it still seems a little weird to me with respect to what 'the metric expansion of space' actually means. For example, what is the difference between two stationary objects in non-expanding space and two objects moving towards each other in expanding space (and hence remaining at the same difference). Can anyone answer this, as it is really bugging me?

Thanks for the answer, Crisp. However it still seems a little weird to me with respect to what 'the metric expansion of space' actually means. For example, what is the difference between two stationary objects in non-expanding space and two objects moving towards each other in expanding space (and hence remaining at the same difference). Can anyone answer this, as it is really bugging me?

Your confusion is in a simple misunderstanding of "how" the expansion is occuring.
Galaxies are gravitational bound to each other in many different sized 'clusters' of galaxies. Inbetween those clusters of galaxies are many different sized VOIDS (where there are no or very few galaxies) (Largest, IIRC, ~25Mpc).

So, the expansion that is observed is in these voids. The space between the galaxy clusters is expanding.

who cares whether you can draw it or not?

Many thoughtful people are firmly related to the real world of senses including the visual sense.

If you can't figure out how to draw it, it becomes highly suspicious. Maybe if you can't draw it, it DOES NOT CORRESPOND WITH REALITY.

No, objects generally do not expand because of the electrostatic forces between them. Molecules stick together because the forces keeping them together have a far greater strength than the expansion of the universe at each point. Hence, as a result, only the distance between objects increases, but not the size of the objects themselves.

Bye!

Crisp

Do electrostatic forces exist within the real universe or somewhere else? Do electrostatic forces exist in relationship with the "fabric of the universe" or somewhere else? If the "real" universe is expanding, in some magic way whch affects non electric objects, then only neutrons ( if we ignore their electromagnetic moment ), some neutrinos, maybe, and ( maybe ) photons ( if we ignore the Faraday effect ) are exempt.

Not much is left. Are you sure of what you are believing?

Thanks for the answer, Crisp. However it still seems a little weird to me with respect to what 'the metric expansion of space' actually means. For example, what is the difference between two stationary objects in non-expanding space and two objects moving towards each other in expanding space (and hence remaining at the same difference). Can anyone answer this, as it is really bugging me?
In an expanding space the space-space components of the metric have a time dependent function so that test particles at constant coordinate positions have a rigid ruler velocity with respect to eachother that depends on the distance between them. In our expanding universe their rigid ruler velocity is greater the farther away they are because of this. The difference is that two particles drifting apart in flat spacetime won't have a velocity that increases with distance.

i don t know what you mean here. how do you draw a 4D sphere?

You can draw a 4d sphere, its called a movie though.
1/3*PI*R^3=V this is the equation for the volume of a sphere the answer is in cubic inches(cm or whatever) this value is three dimentional.

1/3*PI*(delta time)R^3=v(4d) but for every change in time there could also be a change in R(radius) thus the movie will show the change in V(volume). When you see a movie of someone blowing up a balloon there is your expanding spere.

i don t know what you mean here. how do you draw a 4D sphere?

So 1/3*PI*R=V gives you the 3 dimentional value of the volume of a sphere, and to desribe this we need a picture maybe a wire frame or holigram to describe the 3d represention of this sphere. It is a snapshot in time but none the less our brains know it is a shere.
And in the fourth dimention(Time) we need a multi frame movie to show us if the sphere is changing, right. 1/2*PI*(delta time)R=(delta time)V
But how about two dimentions?
If we take the derivative of 1/3*PI*R^3+V themwe multiply the exponent 3 times the front of the equation and subtract one from the exponent and we get PI*R^2=A or the area of a circle this is inches squared or a 2 dimentional represention of a circle. If we apply the fouth dimention to an expanding circle we would still need a movie though

So if we take the derivative of PI*R^2=A the 2 dimentional representation of a circle . We multiple the exponent (^2) times times the front of the equation and then subtract 1 from the exponent giving us 2*PI*R=C: C being the 1 dimentional representation of a circle or the circumference of the circle and this would be in inches( 1 dementional), and again this could be veiwed in a drawing but to see this in the fourth dimention or time we would again need a movie.

now how about adding another dimention we will call this tempurature of a sphere we could use color, like an infar red picture white as the hottest an black as the coldest and if we wish to see changes of sise and tempurature over time we kneed a color movie.

How about a sixth dimention like the warping of space we can draw this with wire frame and again to see changes in time we again need a movie

I guess it's gravity(? seventh dimention) warping space and time maybe space and time are are distorted to the same degree? If not we can express these as silver and gold wire frame respectively. Maybe teperature has an affect on size,space,time and gravity? We could add the color tint of temperature to the silver and gold of space warp and time warp Gravity wells.
There are other forces elecro magnetic the strong and weak forces of atoms, and who knows what other forces, time dialation, properties of black holes and super conductors and who knows what else.
PS. I like raisin bread myself.

yes, lets


there is no "epicentre"




According to the Bang theiory, the entire mass/energy of the present universe was, once upon a time, for a fleeting instant, growing from the size of, say, an electron, considered by many to be a point particle.

At that time, it had no CENTER?

What does a guy have to do to get a CENTER anyway?

According to the Bang theiory, the entire mass/energy of the present universe was, once upon a time, for a fleeting instant, growing from the size of, say, an electron, considered by many to be a point particle.

At that time, it had no CENTER?

What does a guy have to do to get a CENTER anyway?

Having some sort of outer edge would be nice. It never had one.

The only answer that I can see is that the bigbang is still ongoing in that at the centre of the universe is the continuous creation of more and more matter thus filling the void created by the outward moving mass.

Ha, I can not actually believe that I posted this 3 years ago.Amazing what I haven´t learned since.....ha.

If I could explain this rather intiguing statement of 3 year ago. hmmmmm...what I meant was [hmmmm no I didn´t] that the center of the universe is with in every piece of matter and that as that matter expands could more and more matter be filling in the voids created by outward expansion of that mass, and if not could this mean that the missing 98% of mass that appears to be missing is in fact "inside" the matter and not "outside" the matter....hmmmmm.....well I thought I´d save a little face....ha

Ha, I can not actually believe that I posted this 3 years ago.Amazing what I haven´t learned since.....ha.

If I could explain this rather intiguing statement of 3 year ago. hmmmmm...what I meant was [hmmmm no I didn´t] that the center of the universe is with in every piece of matter and that as that matter expands could more and more matter be filling in the voids created by outward expansion of that mass, and if not could this mean that the missing 98% of mass that appears to be missing is in fact "inside" the matter and not "outside" the matter....hmmmmm.....well I thought I´d save a little face....ha

The universe is expading now but the mass is the same except the mass that is in the form of energy. If all matter and energy were turned to matter it would be a finite amount. We know frome Lavourziay(sp?). we can alter mater and gas the nothing is ever lost or gained.

Many thoughtful people are firmly related to the real world of senses including the visual sense.

If you can't figure out how to draw it, it becomes highly suspicious. Maybe if you can't draw it, it DOES NOT CORRESPOND WITH REALITY.

A little off topic, but...

I often forget that I see the world by combining the 2 dimensional images from each eye. For me, the world sure looks 3d.

You can't really view a 3d drawing. A statue exists in 3 dimensions, but you will always see from a 2 dimensional perspective and create the 3d model in your mind.

All drawings are representations of the reality they mimic. Math is another form of representation which can be used to map/predict reality. Rejecting something just because you can't see it in totality with your eyes shouldn't preclude its existence. But, you can definitely see a 4 dimensional object from a 2 dimensional perspective. This does not imply that such objects exist in reality.

Aside: I would like to see someone create a 3d virtual reality environment containing a 4 dimensional object. Something which you could view with goggles so that each eye would recieve a 2 dimensional persective of the 4d object in a 3d enviroment. I believe this is possible.

If we assume for a moment that the theory of the big bang and onto the expanding universe.

If this is the case then all matter is or has been flung outwards away from the epicentre.

Ok, we take a peek at this expanding universe and true it appears that everything is flying outwards. The question I want to ask is if every thing is outward bound that would mean that the centre of the universe would be void of matter and this void would be getting bigger all the time.

The only answer that I can see is that the bigbang is still ongoing in that at the centre of the universe is the continuous creation of more and more matter thus filling the void created by the outward moving mass.

Has any one got any insights into the above?
What assumptions am I making that are in error if any?

QQ,
The theory of the BB, according to some original theorists, namely Alan Guth, does not describe the expansion as mass flung outward. The inflationary model works as if gravity forces are reversed for a few thousandth of a second. The universe expanded to many orders of magnitude in a very short time period. This was necessary to maintain an even and smooth texture of the univese during early statges of espansion, otherwise the universe would collapse before it reached what we see now. However, as the expansion was so rapid the apparent speed of the individual mass centers would move much faster than c, the speed of light. The theory then goes on by asserting that it was not the mass particles that accelerated from each other, rather the space between the mass centers is what expanded. An observer, whereever located would observe the mass around him as moving away in all possible directions, but really the space was expanding, the mass was stationary,

The COBE satellite measuring the microwave background radiation showed a perfect uniformity of mw radiation in all directions, which posed a huge problem for the BB theorists. So perfect is the background radiation that it would be impossible for the perfectly smooth expanding mass to develop imperfections and allow for the formation of substance. Therefore the COBE data was looked at again and after some juggling of data interpretation a single instance of instability of mass was discovered just slightly within the experimental error of the measurements. Ergo the BB was saved.
Geistkiesel