a little help needed for an ignorant old man

Brian W (Brian) · #1 25-10-2010, 12:09 PM

Hi all. heres my problem; when I throw a rock into a pond I see circles emanating out from where the rock enters the water. Barring unseen underwater obstructions and until the waves run into something else the rings are concentric and where the rock entered the water is the centre.

To my brilliant but ignorant mind that should also be the case for our universe. The whatever that caused the singularity to morph into our universe must also have had a wherever as well as a whenever.

To my way of thinking this wherever must be the centre of our universe but people keep on telling me everywhere is the centre.

HELP!
Brian

Miaplacidus (Brian) · #2 25-10-2010, 12:21 PM

See, that's the problem with similes. You've got to pick the right one. What you're forgetting is that the rock contains the pool it is thrown into. A marginally more useful analogy is to a balloon that is being blown up with air, with the 3D universe represented by the stretching latex skin of the balloon, with all parts moving away from each other. Ceci n'est pas une pipe...

ballaratdragons (Ken) · #3 25-10-2010, 12:51 PM

Hi Brian,
If there was a 'Big Bang' who's to say it went out in concentric spheres .

Look at any explosion, yes especially in space.

Are you familiar with the shapes of SuperNovae remnants? Notice none of them are concentric.
Yes many Planetary Nebulae look concentric. But they aren't if you look at them properly.

Explosions in space give us a small sampling of how any Big Bang could have reacted. All out of shape.
Personally, I can't see any Big Bang being as neat and ordered as 'rings in a pond'.

Which tells me that it would be fantasy to measure backwards and evenly to find a centre of origin.

Just my Threepence Halfpenny

Brian W (Brian) · #4 25-10-2010, 01:00 PM

Quote:

Originally Posted by Miaplacidus

See, that's the problem with similes. You've got to pick the right one. What you're forgetting is that the rock contains the pool it is thrown into. A marginally more useful analogy is to a balloon that is being blown up with air, with the 3D universe represented by the stretching latex skin of the balloon, with all parts moving away from each other. Ceci n'est pas une pipe...

okay that makes sense but there is still only one centre to the balloon.

Brian W (Brian) · #5 25-10-2010, 01:08 PM

Quote:

Originally Posted by ballaratdragons

Hi Brian,
If there was a 'Big Bang' who's to say it went out in concentric spheres .

I can't see any Big Bang being as neat and ordered as 'rings in a pond'.

Which tells me that it would be fantasy to measure backwards and evenly to find a centre of origin.

Just my Threepence Halfpenny

All-right even if it is not 'concentric' there would still be a spot where it all started and from which everything moved away from. And even today that spot could be findable?

The supernova irregularities make sense to me when I realize that there are any number of gravitational factors involved. But would those same factors be in play at the singularity when things were too hot to coalesce?

Plus as I understand it the 'Big Bang' may not have actually been an explosion but rather an expansion.
Brian

CraigS · #6 25-10-2010, 01:24 PM

The current Lambda CDM model (Standard Cosmology Model) takes into account present Cosmic Microwave Background Radiation (CMBR) measurements which indicate that the universe is flat - not ballon-like in shape. The ballon analogy was invented as an analogue to explain expansion of the universe. Everything expanded all at once including space just after the 'Bang'. An expanding flat rubber sheet is more applicable.

There is no centre. The explosion analogy is not applicable either as explosions do have a centre. They also result in collisions of the exploding particles as well as expansion of the space between others. We only observe expansion (via redshift) at the largest scales of the universe.

Cheers

Brian W (Brian) · #7 25-10-2010, 01:32 PM

Aha! that is just what people keep telling me 'there is no centre' but even on a flat rubber sheet there is a spot that is the centre.

However ... would it change the parameters of the discussion if instead of 'centre' I was to refer to the single place where it all began?
Brian

CraigS · #8 25-10-2010, 01:35 PM

The Cosmological Principle underpins the Standard Model (which includes BBT). The principle states:

Quote:

The two testable structural consequences of the cosmological principle are homogeneity and isotropy. Homogeneity means that the same observational evidence is available to observers at different locations in the universe ("the part of the Universe which we can see is a fair sample"). Isotropy means that the same observational evidence is available by looking in any direction in the universe ("the same physical laws apply throughout"). The principles are distinct but closely related, because a universe that appears isotropic from any two (for a spherical geometry, three) locations must also be homogeneous.

The cosmological principle is consistent with the observed isotropy of the: (i) the celestial distribution of radio galaxies, which are randomly distributed across the entire sky, (ii) the large scale spatial distribution of galaxies, which form a randomly tangled web of clusters and voids up to around 400 megaparsecs in width, (iii) the isotropic distribution of observed red shift in the spectra of distant galaxies, which implies a uniform expansion of space or Hubble flow in all directions, and (iv) the cosmic microwave background radiation, the relict radiation released by the expansion and cooling of the early universe, which is constant in all directions to within 1 part in 100,000.

In other words, there are direct, measurable observations underpinning the Standard Model and the principles underpinning it. The rock in the pond model, ballon analogy, etc are not supported by any combined direct, observational evidence.

Cheers

CraigS · #9 25-10-2010, 01:41 PM

Quote:

Originally Posted by Brian W

Aha! that is just what people keep telling me 'there is no centre' but even on a flat rubber sheet there is a spot that is the centre.

However ... would it change the parameters of the discussion if instead of 'centre' I was to refer to the single place where it all began?
Brian

Correct .. even the flat rubber sheet model is deficient.

There is no geometrical centre in the BBT/expansion model because this still implies that something is not expanding which doesn't align with observations nor the Cosmo Principle.

The rubber sheet model helps to visualise the observable fact that no matter where you are located on the sheet, everything looks as though it is expanding away from everything else as it stretches. This more closely aligns with redshift observations.

Cheers

Brian W (Brian) · #10 25-10-2010, 01:58 PM

Ok Craig I follow your argument with a few questions

(1) when I used to go sailing there were times that I was out of sight of land. Anyone else that was sailing out of sight of land would see basically what I was seeing. I get the idea that it all looks the same.

But I still do not see that that means there is no single spot where it all begins. Unless one was to take ethnocentricity to it ultimate limit.

(2) please explain to me the co-relationship between having a centre and not expanding.

It seems to me that there can be a centre in an ever expanding anything.
Brian

CraigS · #11 25-10-2010, 03:23 PM

Quote:

Originally Posted by Brian W

Ok Craig I follow your argument with a few questions

(1) when I used to go sailing there were times that I was out of sight of land. Anyone else that was sailing out of sight of land would see basically what I was seeing. I get the idea that it all looks the same.

But I still do not see that that means there is no single spot where it all begins. Unless one was to take ethnocentricity to it ultimate limit.

(2) please explain to me the co-relationship between having a centre and not expanding.

It seems to me that there can be a centre in an ever expanding anything.
Brian

Hi Brian;
Please excuse the sharpness of my responses (I'm a bit rushed today).

Ok. So … I guess there can be a centre in an ever expanding 'anything', if one chooses to go with the models originally suggested..

However, two testable consequences of the cosmological principle are homogeneity and isotropy. Homogeneity means that the same observational evidence is available to observers at different locations in the universe. Isotropy means that the same observational evidence is available by looking in any direction in the universe. A universe that appears isotropic from any two locations (for eg), must also be homogeneous.

If the universe is isotropic, the distance to the edge of the observable universe is about the same in every direction (ie: appears as a sphere - confirmed by CMBR observations in different directions). But every location in the universe sees the same view ... which may, or may not, overlap with our Earth centric view.

So, if every observer sees the same expansion (with redshifts) how can one determine where the centre is ? (I don't think this is possible).

I think the point here is, one either goes with the observable evidence, and model, and accepts that there is no identifiable centre, or one believes otherwise, with no observable evidence supporting that belief.

The original model of the BBT suggests that the original universe started from an infinitely small, infinitely hot (energy dense) point. It expanded into nothing. It's location or its centre is not determinable, if one goes with the Standard Model concepts of homogeneity and isotrophy which are based on observations.

Cheers

noswonky (Peter) · #12 25-10-2010, 06:18 PM

Quote:

Originally Posted by Brian W

Aha! that is just what people keep telling me 'there is no centre' but even on a flat rubber sheet there is a spot that is the centre.

However ... would it change the parameters of the discussion if instead of 'centre' I was to refer to the single place where it all began?
Brian

In the balloon analogy, you have a balloon with dots on it representing galaxies. The two dimensional surface of the balloon represents three dimensional space. As the balloon expands, the dots (galaxies) move away from each other. In this analogy, where is the centre?

There isn't one.

Because this is a two-dimensional analogy of three-dimensional space, you can't say that the centre is inside the balloon. That would be the three-dimensional centre and that's not allowed in a two-dimensional model.

So asking where the center is in three dimensional space is like asking where the centre is on the SURFACE of a balloon. There isn't one.

Before the balloon began inflating, all the dots on the balloon's surface were close together - ideally infinitely close together. But once it starts inflating you can't point to a spot on the surface and say 'that's where the balloon started inflating'.

The key is that the expansion on the universe did not start at some point in three-dimensional space. Rather, space itself began tiny and got bigger.

Brian W (Brian) · #13 25-10-2010, 06:45 PM

Craig, I got to go and ponder on this but I will be back.

Peter, couple of points
(1) the balloon is not overly good simply because 'space' is not two dimensional. To my poor way of thinking any three dimensional object must have a centre.

(2) you state that the key is that the universe did not start at some point in three dimensional space but that even 'space' started with the expansion.

To the best of my understanding science makes no claim about what was there before expansion. Nor how it started. And certainly not what it was like at the moment of beginning.

In any case I need to go and ponder cause this is really, at least for me so counter intuitive that I have trouble accepting it.

However I freely admit that the truth of no centre certainly does not rest on my ability to understand it.
bria

Brian W (Brian) · #14 25-10-2010, 06:45 PM

Craig, I got to go and ponder on this but I will be back.

Peter, couple of points
(1) the balloon is not overly good simply because 'space' is not two dimensional. To my poor way of thinking any three dimensional object must have a centre.

(2) you state that the key is that the universe did not start at some point in three dimensional space but that even 'space' started with the expansion.

To the best of my understanding science makes no claim about what was there before expansion. Nor how it started. And certainly not what it was like at the moment of beginning.

In any case I need to go and ponder cause this is really, at least for me so counter intuitive that I have trouble accepting it.

However I freely admit that the truth of no centre certainly does not rest on my ability to understand it.
bria

Archy (George) · #15 26-10-2010, 07:02 AM

Quote:

Originally Posted by Brian W

Hi all. heres my problem; when I throw a rock into a pond I see circles emanating out from where the rock enters the water. Barring unseen underwater obstructions and until the waves run into something else the rings are concentric and where the rock entered the water is the centre.

To my brilliant but ignorant mind that should also be the case for our universe. The whatever that caused the singularity to morph into our universe must also have had a wherever as well as a whenever.

To my way of thinking this wherever must be the centre of our universe but people keep on telling me everywhere is the centre.

HELP!
Brian

Having seen the replies to your sensible question, one can't help but think that in science fiction as in Alice in Wonderland anything is possible

CraigS · #16 26-10-2010, 07:30 AM

Quote:

Originally Posted by Archy

Having seen the replies to your sensible question, one can't help but think that in science fiction as in Alice in Wonderland anything is possible

Care to elaborate on where the "fiction" is ?

Cheers

CraigS · #17 26-10-2010, 08:04 AM

The point to be made here is that there is no 'truth' to be found anywhere on this. We're talking about something ~ 14 billion years old (observable) and (perhaps) infinite in expanse beyond that.

No-one will probably ever know the 'truth' about something as old and as big as this. (At least not in my lifetime).

If there is no truth … then there is no fiction.

The idea is try on: wrapping one's mind around the initial concepts and what follows is extraordinarily logical and rational. Most other alternative starting premises are falsified, pretty quickly, by the observational data.

I'd much rather spend my time pondering the Standard Model than an opinion unsupportable by linked observations.

Cheers

Brian W (Brian) · #18 26-10-2010, 12:21 PM

Hi Craig you have just hit upon my dilemma.

(1) all of my observations tell me that any three dimensional object has a centre.

(2) my observations tell me the universe is three dimensional.

(3) therefore the universe must have a centre.

The above is nothing more or less than basic logic and as such cannot be denied. However as it is a tautology it does not of necessity about reality.

I suppose that I am having the same type of problem that someone who is working on a unified theory faces; how do you make the micro and the macro make sense together?

Oh well, as you say Craig one can only keep on keeping on.

Brian

mswhin63 (Malcolm) · #19 26-10-2010, 12:59 PM

I am tinking in relation to both puddle theory and baloon theory.

BB not yet proved what would happen to the air inside a balloon when you use a powerful compression to blow it up initially, after a while the compressor is turned down and everything inside is settling down. Is it possible the air inside is still moving quickly during this transition and some galaxies or whatever have bounced of the edge and heading towards the centre, air currents or gravity etc are flinging galaxies off in different directions or circulating around the universe. It is just another ignorant man idea.

The same could be said for the puddle as well but in a 2 dimensional.

As the first post is a simple analogy why not me

So if it has already be said in a theoretical mathmatician language then please excuse me.

sjastro · #20 26-10-2010, 01:39 PM

The danger with any analogy is that while it may aid in visualization, taken literally it can lead to false conclusions. One needs to be very careful visualizing mathematical concepts.

The Universe has no centre, the observer is the centre. If a galaxy was receding from the "centre" of the Universe, then any observer in the line of sight of the receding galaxy will measure the same recession velocity.
This clearly violates Hubble's law which shows that the recession velocity is proportional to the distance between the galaxy and observer. This is based on observation.

Hubble's law is explained by having the receding galaxies fixed in space and allowing the space to expand. Hence galaxies recede as a function of the increasing scale of the Universe. In this scenario there is no absolute centre, each observer in the Universe can rightly claim to be the centre.

This leads to the cosmological principle as explained by Craig.

Regards

Steven