Big Bang - No Single point of Expansion

[earamsey]

Cosmologist say that the universe is expanding but from no central point. It seems contradiction to me because the universe also started from a single point and EXPANDED outward. Further, they say if you reverse expansion everything would compress back to a singularity. Seems like expansion is occurred from a single point possibly occurring at one too if you can rewind to a single point!

 

[mgb_phys]

Before the universe there wasn't anything to expand into..
Don't think of the universe as exploding from a point out into black empty space - think of it as the space itself being created as it expands.

A common picture is to think of inflating a balloon. ANy two points on the surface of the balloon are expanding away form each other but there is no point on the surface that is the centre that everything is expanding from

 

[S.Vasojevic]

Space exploded into what?

 

[earamsey]

Intuitively it makes no sense that space is expanding into nothing. Is this something I am to accept and look the other way because no one understands it... like gravity?

 

[mgb_phys]

Intuitively it makes no sense that space is expanding into nothing.

Intuition is a sense of knowledge from your internal experience.
Do you have a lot of internal personal experience of the start of the universe?

In reply to somebody complaining about the confusing terminology of Quantum mechanics - to which one of the founders replied - "yes it's odd that a language invented to tell other apes where the ripe fruit is has difficulty with the notion of a particle as a wave"

 

[earamsey]

No, but I know what nothing is, I have lots of experience with nothing. Nothing is a common human concept and perhaps the problem is trying to explain non-classical events terms of the classical event driven human experience. I know that QM makes no sense until you start to view it in terms of hamilitonian space. Maybe the nothingness is something like that?

I have no problem with expansion but nothing is really abstract and there is actually no true instance of nothing except symbolic. For example, I did nothing to prevent shuttles take off in cold weather. In fact, here nothing means "took no action".

Also, I did not think that space exploded per se. After all "Big Bang" was met to be a derisive term and only stuck because of media like the term and I guess through constant usage made it acceptable. Explosion implies something blew up and BB came from nothing.

 

[russ_watters]

Intuitively it makes no sense that space is expanding into nothing. Is this something I am to accept and look the other way because no one understands it... like gravity?

Intuitively, are you able to visualize a 3 dimensional curved surface (analogous to a two dimensional curved surface of a balloon)? If you can't, then your intuition is failing to help you understand the geometry of the universe and you must learn about a reality that is different from what your intuition tells you. Heck, if our intuition was always right, what would there ever be to learn?!

Trying to understand the balloon analogy would be a big help here.

No, but I know what nothing is, I have lots of experience with nothing.

Ok...well think about how the concept of nothing could apply to the expansion of the universe. You're talking about a spherical universe with an edge and a center, expanding out into empty space surrounding it... so where is this edge? Why don't we see it? Why don't the velocity vectors of galaxies have a preferential direction?

I have no problem with expansion but nothing is really abstract and there is actually no true instance of nothing except symbolic.

Actually, the concept of "nothing" really isn't abstract, but people often use imprecise wording that improperly frames the concept. For example, your quote:

Intuitively it makes no sense that space is expanding into nothing.

...is an improper paraphrase of what people are telling you. They didn't say "space is expanding into nothing", they said space is not expanding into anything. These are two very different things because when people hear "nothing", they think "empty space", but the reality is that the universe is not expanding into empty space...and empty space wouldn't be "nothing" anyway!

 

[justwondering]

Before the universe there wasn't anything to expand into..
Don't think of the universe as exploding from a point out into black empty space - think of it as the space itself being created as it expands.

A common picture is to think of inflating a balloon. ANy two points on the surface of the balloon are expanding away form each other but there is no point on the surface that is the centre that everything is expanding from

Is it best to think of this starting point as containing all of this (our universe) mass/energy/space at some instant, or as a point sized 'entry' location for things to follow? Could we ever know the difference?

 

[earamsey]

This is what I understand of BB. I will use outside observer to help illustrate. At BB this observer would notice some event, a flash of light and then an infinitely small region, a Point, would plop into existence. (I know photons would NOT be able to actually leave region but i say it anyway for illustration).

At this point, the infinitely small region, Point, is fixed in size to observer and will never change. However, internally, the region develops space, time and structure further this space starts to inflate.

So, now I space/time being mysteriously defined inside this region, which is still infinitely small externally. Space time attributes are unique and do not exist outside of region; observer has no concept of space or time only sees a dimensionless point. Now, since space is defined within this region and then the universe itself defines space, it can not expand into space but rather it's space is growing or expanding. At this point I guess I can say that Space/Time is localize to this region and expanding relative to every point within the region.

Now, if I run the process backwards, the space-time within this region would collapse into super dense stuff; but the outside observer not notice anything different until the space inside the point, or region to us, becomes so dense that it collapses and plops out of existence. At this point observer would think he was seeing things because it would have vanish as quickly as it appeared, if it did at all.

But I guess the stuff our universe, region or point, to observer, persists in is of no consequence since we or any law of classical or QM physics could exist there anyway. Our world and laws are inside this infinitely small but vast point. But still I wish I could somehow how see it anyway.

In second to last paragraph I said space-time collapses because, purely intuitively, I think that Time and Gravity were once unified but somehow broke apart.

 

[Nebozilla]

The Big Bang didn't come into existence since nothing existed. Also this observer which I assume is made of nothing but can still interpret things(...some how...i feel kind of bad saying that last sentence) wouldn't see the actual big bang unless he could see pure energy then Gamma rays, X-rays and ultraviolet then finally light which we can see.

 

[earamsey]

he is a pseudo hypothetical being I made up for illustrative purposes. Hmm, i would have met the region of space came into plopped into existence. But citing those few discrepencies I guess my understanding must be nearly correct since you had simple quibbles about post.

 

[Dmitry67]

notice some event, a flash of light and then an infinitely small region, a Point, would plop into existence. (I know photons would NOT be able to actually leave region but i say it anyway for illustration).

If (which is very likely) our universe is infinite now, then it ALWAYS was infinite, and the initial singularity was still INFINITELY BIG in size. Singulary is not (always) a point!

Singularity IS NOT a region. ALL places of the universe were in the same conditions. There were never "in" and "out" of the expanding region. All regions were the same. It is important.

 

[Cryptonic]

If (which is very likely) our universe is infinite now, then it ALWAYS was infinite, and the initial singularity was still INFINITELY BIG in size. Singulary is not (always) a point!

Singularity IS NOT a region. ALL places of the universe were in the same conditions. There were never "in" and "out" of the expanding region. All regions were the same. It is important.

I totally agree with this. Who says "WE" originated in a dimensionless point? A "dimensionless point" (ie singularity) is usually indicative of a flaw in our mathematics & logic.

Either we started with an infinite Big Bang (?), or we are "bouncing" back from a previous (finite) >4D-collapse...(is what I say).

Infinity (like singularities) does not make much cerebral sense. After all, we (our "minds") are part of the universe, and we don't see "infinities" nor "infinitesimal dimensionless points".

I think it's likely that the universe is "bouncing" (breathing) and is an organic entity. We are the neurons/synapses in this Universe's brain. We are the Universe's self-awareness.

The closest I come to this idea theoreticized is Smolin's theories.

Or maybe I'm stoned, who knows.

 

[Jimmy]

If you haven't already, check out the following thread:
Effort to get us all on the same page (balloon analogy anyone?)

 

[Nebozilla]

he is a pseudo hypothetical being I made up for illustrative purposes. Hmm, i would have met the region of space came into plopped into existence. But citing those few discrepencies I guess my understanding must be nearly correct since you had simple quibbles about post.

Those aren't just discrepancies, those are HUGE parts of understanding the Big Bang based on current theory.

 

[S.Vasojevic]

So there must be some kind of boundary between created space, and not yet created space?

 

[sylas]

So there must be some kind of boundary between created space, and not yet created space?

No. "created space" in this context just means that there's more space between things.

On sufficiently small scales (a couple of hundred million light years, perhaps) it is no different to things moving apart from each other in the way we are used to. On larger scales, you have to describe space and movements and expansion with general relativity, which doesn't always fit nicely with initial expectations or intuitions; but in general, it's still just everything moving apart from everything else, with no center, and no boundary apparent or implied.

Cheers -- sylas

 

[S.Vasojevic]

Before the universe there wasn't anything to expand into..
Don't think of the universe as exploding from a point out into black empty space - think of it as the space itself being created as it expands.

So it is expanding into its future self. There must be some propagation front that we can describe. Does GR strictly implies that it does not exist?

 

[sylas]

So it is expanding into its future self. There must be some propagation front that we can describe. Does GR strictly implies that it does not exist?

The term "propagation front" is not well defined. In the normal sense of the word, no there does not have to be a propagation front.

But I guess you might be able to think of "time" as a "propagation front". There is no location of a front in space; but all of space is expanding as time passes. This just means there is more space in between things; subject of course to the fact that objects are also moving with their own peculiar motions and gravitationally bound conglomerations like a galaxy don't expand.

I suspect you are still holding on to misleading metaphors and analogies with an explosion of material out from a point. You have to drop that idea; it's wrong. And you're probably best to forget about trying to shoehorn the idea of a propagation front into cosmological expansion. It's terminology that is bound to mislead.

Felicitations -- sylas

 

[S.Vasojevic]

Thanks sylas. If I understand this correctly galaxies are not moving apart because expanding space is exerting force on them which overcomes gravity, but simply because more space is being "stuffed" in between them?

 

[sylas]

Thanks sylas. If I understand this correctly galaxies are not moving apart because expanding space is exerting force on them which overcomes gravity, but simply because more space is being "stuffed" in between them?

There are better people here than me to answer this. Comment from Wallace would be welcome; and there are a number of others well placed for this also.

I shall try to go a bit further; and I will welcome informed instruction and criticism from experts here present.

Any answer in these terms is necessarily an analogy, or metaphor, for the underlying mathematical descriptions; and I am not sufficiently strong on those to be confident about all the pitfalls, or about identification of exactly how far an analogy works and where or how it breaks down.

My understanding is that things are moving apart because they are moving apart. That is, there's no force required; only an initial impulse. Additional pushes only slow it down or speed it up.

Expansion of the universe kicked off with a burst of inflation in the very very early universe, and since then (for the most part) everything has continued expanding, but gradually being pulled together again by gravity. Recently it has been discovered that the expansion of things is accelerating again; and this corresponds to a small additional kick from "dark energy", which pushes things apart rather than pulling them together as gravity would do.

The key point is that there is no indication of any boundary or edge, and no need for an edge. We can't see all the universe to be sure of what it looks like beyond the limits of telescopes. But the simplest and most straightforward models have all the universe pretty much like the observable universe, with everything expanding away from everything else, and with no limit or edge. If indeed everything is pretty much the same as the observable universe, then whether the universe is finite or infinite depends on the large scale "curvature" of the universe. A positively curved universe would be finite... a bit like the curved 2d surface of a planet is finite without having any edge. Except, of course, that space is 3d rather than a 2d surface.

The thing about relativity is that "Matter tells space how to curve, and space tells matter how to move." (Wheeler) There are small scale examples of how movement of matter leads to changes in spacetime which leads to movement of matter. For example: the http://en.wikipedia.org/wiki/Frame-dragging" effect means that a satellite in orbit around a rotating body (like the Earth) will experience a small "force" pulling it along with the rotation of the planet. I don't know how good a parallel that is; but with an expanding universe, I think that to say there is additional space between things another way of saying they are moving apart.

On the scale of the whole universe you have to deal with space in terms of general relativity; but it reduces on smaller scales to things just moving apart from one another, like a cloud of expanding gas becoming less dense -- although the cloud has no edge or boundary.

Cheers -- sylas

 

[jdz]

(this is a first post, I hope that it is on-topic; no thread-jack intended...)

I have a question about the curved 3-D space and "no edge and no boundary of the universe" idea.

Would it be possable to 'see' far enough to 'see' an edge or front of the universe, or does the curved 3-D space mean that any/every point in the universe is surrounded by the same (aprox the same) observable universe? That is, would the 'sky and stars' be the same, or look the same, from every where in the universe, whether the universe is open or closed?

thanks

 

[WhoWee]

Cosmologist say that the universe is expanding but from no central point. It seems contradiction to me because the universe also started from a single point and EXPANDED outward. Further, they say if you reverse expansion everything would compress back to a singularity. Seems like expansion is occurred from a single point possibly occurring at one too if you can rewind to a single point!

A central point would be possible if the universe first collapsed to a single point - then exploded in a Big Bang (once or cyclically).

 

[sylas]

A central point would be possible if the universe first collapsed to a single point - then exploded in a Big Bang (once or cyclically).

No; there is no distinguished central point in this case. The collapse to a point refers to all of space being reduced to a point; not collapse of all matter into a point in space.

There is no "central" point, in the sense of a point distinguished from other points being in the center. The collapse is when there is no space left between anything; all points are the same point; a singularity.

Felicitations -- sylas

 

[WhoWee]

No; there is no distinguished central point in this case. The collapse to a point refers to all of space being reduced to a point; not collapse of all matter into a point in space.

There is no "central" point, in the sense of a point distinguished from other points being in the center. The collapse is when there is no space left between anything; all points are the same point; a singularity.

Felicitations -- sylas

With no space left to fill after a rapid contraction - the only possible outcome (other than a static space-time) would be an outward expansion.

 

[S.Vasojevic]

My understanding is that things are moving apart because they are moving apart. That is, there's no force required; only an initial impulse. Additional pushes only slow it down or speed it up.

Shouldn't that imply that Universe is gaining gravitational potential energy, at expense of violation of first law of thermodynamics?

 

[sylas]

Shouldn't that imply that Universe is gaining gravitational potential energy, at expense of violation of first law of thermodynamics?

Energy in GR is a bit subtle, but the short answer is no.

Gravity slows the expansion down, as I indicated previously, and this is a bit like a gain in potential energy as things are further apart, and a loss in kinetic energy as the expansion slows. The problem is really that energy depends on the frame of an observer, and you run into difficulties defining energy for the universe. That get beyond what I can explain well.

But there is a correspondence with the normal exchange of potential and kinetic energy for objects moving in a gravitational field.

Cheers -- sylas

 

[sylas]

With no space left to fill after a rapid contraction - the only possible outcome (other than a static space-time) would be an outward expansion.

There's still no central point. The expansion of the universe is not really "outward", but an expansion of matter and energy that fills all of space, at any time slice you consider. No point in space can be distinguished as central. This applies before the hypothetical bounce while the universe contracts, or after as it expands with a hypothetical bounce.

 

[S.Vasojevic]

Gravity slows the expansion down, as I indicated previously, and this is a bit like a gain in potential energy as things are further apart, and a loss in kinetic energy as the expansion slows. The problem is really that energy depends on the frame of an observer, and you run into difficulties defining energy for the universe. That get beyond what I can explain well.

Yes, but I think that expansion is speeding up.

 

[WhoWee]

There's still no central point. The expansion of the universe is not really "outward", but an expansion of matter and energy that fills all of space, at any time slice you consider. No point in space can be distinguished as central. This applies before the hypothetical bounce while the universe contracts, or after as it expands with a hypothetical bounce.

There really is no way to continue the conversation without re-defining the word "point" to mean a place/area/location of an unspecified/unknown size/shape/dimension.