no centre to the universe?

[sonic190178]

why does science say there is no centre to the universe?

[JamesF]

In the case of an explosion, there's expansion outwards from the point of the explosion, so it's reasonable to assume that the explosion is the centre of the expansion and everything is expanding away from that point.

The universe doesn't appear to work like that though. Everything appears to be expanding away from everything else, so there isn't anywhere that can be called "the centre". Hubble's classical analogy was with the surface of a balloon (you have to work only in 2D for this analogy to even start to hold up). if you mark a set of points on the surface of the balloon and then inflate it, all the points get further apart. So where's the centre of expansion? Well, in the 2D "universe" that is the balloon surface, there isn't one. Everything is getting further away from everything else.

I'm not sure about this, but I think it may be the case that there could be a centre to the universe, depending on what happens beyond the boundaries of the observable universe, but as we can't observe it there's no way to tell and the "no centre to the universe" model is therefore a reasonable working hypothesis.

James

[sonic190178]

i like to think of the balloon analogy as get a balloon put some confetti inside it then blow it up and the galexies are the bits of confetti inside the balloon

[JamesF]

But even Hubble admitted the analogy is limited and certainly doesn't work if you consider it in 3D. If you want galaxies, they're the dots on the surface of the balloon. Once you put them inside the balloon, the analogy is void. Hubble made the analogy, so he gets to choose how it works. You can't redesign it and claim it's still valid without demonstrating why it should still be valid.

James

[sonic190178]

we live in a 3d universe so an analogy that only works in 2d is void

[Scott]

only 3d?

[sonic190178]

3d because we observe with only human vision

[Keiran]

But if you look through a telescope at the sky, are we still seeing in 3d??

The balloon analogy is just a way to explain how the universe is expanding. Its a simple way of showing how everything is moving away from each other and not away from a single point.

I would like to think, if we came from a big bang, that bang happened somewhere and on earth if we create an explosion everything moves away from that point. So the centre of the universe is where that explosion happened??

[JamesF]

we live in a 3d universe so an analogy that only works in 2d is void

No. It's perfectly valid because Hubble set the frame of reference for the analogy so that it would be. Of course, if you understand more about this than Hubble, feel free to explain.

James

[astrofox]

the 2D analog isn't void, just limited in scope. It points to visions of a 3D univese our brains can't handle. Having said that we should accept our limitations and just accept what the maths tells us. Think of a balloon expanding and from every point on that balloon, there is another ballon at right angles expanding at that same rate. If you can visualise that great, but I can't.

[JamesF]

I would like to think, if we came from a big bang, that bang happened somewhere and on earth if we create an explosion everything moves away from that point. So the centre of the universe is where that explosion happened??

But the Big Bang is not considered to be an explosion. That probably is a poor analogy

James

[sonic190178]

to explain to the universe we need to think in 3d if were thinking in a 2d mind set you will not explain what we observe without big problems

[JamesF]

to explain to the universe we need to think in 3d if were thinking in a 2d mind set you will not explain what we observe without big problems

The purpose of an analogy is not to explain, but to illustrate, and if the illustration works in two dimensions that's just fine. No-one is suggesting that it's all that's required to explain the universe.

James

[sonic190178]

think of it like this are universe is the inside of the balloon not the suface

[JamesF]

Why? That's not the analogy Hubble intended. If you want to set up a new analogy for something different then fine, but don't go confusing it with Hubble's, or with what he was trying to illustrate by it.

James

[sonic190178]

thats the whole point the universe isnt on the suface of a balloon so it a poor analogy

[JamesF]

The sole point of Hubble's balloon analogy was to illustrate how something can expand in all directions at once and have no centre. It achieves that just fine. So well, in fact, that people haven't felt the need to find a better analogy in something like ninety years. To try to draw further conclusions about the way the universe behaves from the way a balloon behaves or to give the analogy any greater correspondence to the universe is wrong and misunderstands the purpose of the analogy.

People are often taught about basic electronics by using an analogy of water flowing through pipes which have valves, constrictions and reservoirs. It's a good analogy for grasping the basics. Would you deny that too because electricity isn't wet, or water doesn't travel at the speed of light (in copper)?

James

[sonic190178]

it dosent because in the balloon analogy the space between the dots expands the same rate all over the balloon and that is not consistent with observations as the galaxies the furthert away are expanding faster then the galaxies near to us

if that was the case and its dark energy driving the expandion then why is there more dark energy by the galaxies the furthest away

and if you take hubbles balloon to the cosmic scale and stand on one of the dots we would look as if we were expanding faster than the dots furthest away from us

[JamesF]

Did I say it was an analogy that was intended to illustrate differential expansion rates? Err, no, I don't think I did. And it wasn't. I said "The sole point of Hubble's balloon analogy was to illustrate how something can expand in all directions at once and have no centre".

You are trying to treat Hubble's analogy as a model of reality. The two things are completely different. An analogy is not a model.

James

[sonic190178]

ok but it dosent match observations so what is the point of it as i said poor analogy

and because it dosnt match observations maybe there is a centre to the universe because hubble was wrong with is analogy

[Auntystatic]

You are trying to treat Hubble's analogy as a model of reality. The two things are completely different. An analogy is not a model.

James

@sonic

Did you miss the above quote or did you just not understand it? Hubble wasn't trying to explain present day observations or explain expansion from a central point of origin, he was just trying to explain how objects could move away from each other in all directions, it has nothing to do with the big bang so as an analogy its a pretty good explanation.

Now as for the big bang, inflation or what ever the current theory is, if it happened from a singularity as thought then as it expands you would think that everything was moving away from everything else and a central point at the same time, at least that's how I currently see it but my application is in for the open university so who knows what I'll bee thinking soon.

As for the furthest objects moving faster, here's my analogy, say you had 6 cars arranged in a star back to back, they all set off at the same speed in a straight line in the direction they are pointing, you are in one car, the cars either side of you might appear to be moving away from you at the same speed, but the car behind you would be moving away faster as it going in the opposite direction, but your all still moving at the same speed relative to the start point , your combined speed with the car behind is double that speed, of course the magic bit here is the furthest objects in the "observable universe" as it is today.

I'm sure my scientific calculator could come up with a neat equation for this analogy if I knew how to use it

[ollypenrice]

Basically I'm with James, especially with regard to the difference between an analogy and a model, something I was going going to say till James beat me to it.

I'm surprized to hear this analogy attributed to Hubble, though. Curiously Hubble himself never comitted to the belief that his distance-velocity relation was the result of the expansion of the universe and he remained agnostic on the matter - though he was happy to ride on a crest of fame when Einstein offered the explanation and praised his work! Perhaps Hubble did create the analogy, I don't know. Fair enough, though, you can have the analogy and not the big bang since Hoyle and co did this with the Steady State theory.

Anyway the anology does not break down because Perlmutter et al have concluded that the rate of expansion is increasing. In fact it holds up perfectly and only requires that the person blowing into it blow with increasing force over time!

The real problem is this; we are graced with 'local brains' for performing 'local tasks.' Our brains did not evolve in the wider universe, they evolved here on earth, and when we want to use them to think about the wider universe we are going to run into difficulty conceiving of what's going in. This is where analogy comes in. There is no reason whatever to believe that our brains can conceive of all that there is, nor is there any reason to believe that all that there is has to be constrained by what our brains happen to accept or reject.

The balloon analogy is good and in one way, at least, it is not an analogy but a straightforward demonstration. A balloon does have a centre. The surface of a balloon does not have a centre. That is not an analogy, it is a straightforward certain fact. If someone were to assert that everythng must have a centre their assertion could be instantly refuted by pointing to the surface of a sphere. Or would you prefer to say that the surface of a sphere has an infinite number of centres? Same difference!

Olly

[JamesF]

I'm surprized to hear this analogy attributed to Hubble, though.

It's entirely possible I've misremembered who created the analogy. It was rather late A quick hunt this morning suggests in may have been Eddington which would make it fairly contemporaneous with Hubble and would make sense because Eddington was committed to the idea of an expanding universe, but you have me doubting myself now. Same argument applies regardless of who created it though.

James

[sonic190178]

Did you miss the above quote or did you just not understand it? Hubble wasn't trying to explain present day observations or explain expansion from a central point of origin, he was just trying to explain how objects could move away from each other in all directions, it has nothing to do with the big bang so as an analogy its a pretty good explanation.

no understand what he was saying but if it does not match present observations why is it still used?

space is expanding at 74kmps mega parsec

the universe is bigger than a mega persec so if you can expand a balloon to the size of the universe the expandion of the dots when be the same no matter how many mega parsec you looked out

and before anyone says you cant expaned a balloon to the size of the universe i know

[ollypenrice]

Did you miss the above quote or did you just not understand it? Hubble wasn't trying to explain present day observations or explain expansion from a central point of origin, he was just trying to explain how objects could move away from each other in all directions, it has nothing to do with the big bang so as an analogy its a pretty good explanation.

no understand what he was saying but if it does not match present observations why is it still used?

space is expanding at 74kmps mega parsec

the universe is bigger than a mega persec so if you can expand a balloon to the size of the universe the expandion of the dots when be the same no matter how many mega parsec you looked out

and before anyone says you cant expaned a balloon to the size of the universe i know

Sorry, I just don't follow this at all. As you expand the balloon the dots move apart. How fast any one dot moves away from any other depends on how much balloon surface there is between them. If they are close on the balloon there is not much expanding surface between them so they move apart slowly. If there is a lot of expanding balloon surface between them they move apart faster. It doesn't matter at all what the rate of expansion is. The balloon analogy holds for any rate of expansion.

Olly