The size of the universe - a question.

[Brian Peacock]

≠========== misquoted, misunderstood, deleted ≠==========

[Brian Peacock]

This one on the topology of the universe is also quite interesting...

[rainbow]

≠========== misquoted, misunderstood, deleted ==========

I agree!

[Brian Peacock]

[NineBerry]

The point about the balloon analogy is that the universe is not like an expanding balloon, but like the skin of an expanding balloon. There is no centre of the universe. And there is no edge that you can cross. If you travel in a straight line, you are actually travelling in a curved line. Imagine travelling on the surface of the Earth.

[Animavore]

Imagine the universe is like a big-ass dick. And that dick is a grower, not a shower. And it's riddled with genital warts from root to tip (Americans might have to use your imagination). Now as that dick becomes more tumescent the farther warts will appear to be moving away faster than the nearer ones to a crab lice living on one of them.

[pErvinalia]

I like to think of the universe like Trump's hair.

That is all.

[Animavore]

Another thing on the centre of the universe question. If the universe had a centre which all things move away from then we are at that centre because everything moves away from us equally in all directions. If we were not at the centre then then things on the side of us away from the centre would be moving away faster while things on the underside would move slower or even towards us.

This isn't accurate, but you might be on the right track. Things closer to the centre are moving outwards at a slower rate than things further out. So we would still be moving away from the things closer in. But, without doing any maths (Jim, can you do some for us?), I'd suspect that you are right that the rates between closer in stuff and further out stuff, in relation to us, would be different. This doesn't fit with observation, so I think you are right that this would explain how there is no centre of the universe. Unless there was some other arrangement. I'm assuming that it's not the case that there's a giant spherical region of nothing in the universe, around which there is a balloon like surface of matter expanding outwards? Matter is fairly evenly distributed throughout the universe, right?

Unless I'm missing some basic maths, this explanation is wrong too. The rate of things receding from us is independent of whether they are X light years away from us 'inwards' vs 'outwards'. It's actually utterly simplistic maths, unless I've missed something. Draw it out on a piece of paper and see what you come up with. I'm pretty sure you'll find it's wrong.

No. You. :p

I'm actually not sure what you're saying here, but another effect you'd see if the universe had a centre with everything moving away from the centre is that matter toward the outside would be more dispersed than matter from the inside. Ie. The same volume of matter would be spread more thinly over each concentric circle.

We don't see that. The CMBR shows equal dispersal in all directions.

[Rum]

OK, got it now. You can all stop posting.

[Brian Peacock]

Imagine the universe is like a big-ass dick. And that dick is a grower, not a shower. And it's riddled with genital warts from root to tip (Americans might have to use your imagination). Now as that dick becomes more tumescent the farther warts will appear to be moving away faster than the nearer ones to a crab lice living on one of them.

[pErvinalia]

Another thing on the centre of the universe question. If the universe had a centre which all things move away from then we are at that centre because everything moves away from us equally in all directions. If we were not at the centre then then things on the side of us away from the centre would be moving away faster while things on the underside would move slower or even towards us.

This isn't accurate, but you might be on the right track. Things closer to the centre are moving outwards at a slower rate than things further out. So we would still be moving away from the things closer in. But, without doing any maths (Jim, can you do some for us?), I'd suspect that you are right that the rates between closer in stuff and further out stuff, in relation to us, would be different. This doesn't fit with observation, so I think you are right that this would explain how there is no centre of the universe. Unless there was some other arrangement. I'm assuming that it's not the case that there's a giant spherical region of nothing in the universe, around which there is a balloon like surface of matter expanding outwards? Matter is fairly evenly distributed throughout the universe, right?

Unless I'm missing some basic maths, this explanation is wrong too. The rate of things receding from us is independent of whether they are X light years away from us 'inwards' vs 'outwards'. It's actually utterly simplistic maths, unless I've missed something. Draw it out on a piece of paper and see what you come up with. I'm pretty sure you'll find it's wrong.

No. You. :p

I'm actually not sure what you're saying here,

It's basic maths. Imagine if you have something towards the middle of a spherical universe and something towards the outer. We are an observer halfway between the two. The universe then expands by a factor of two. The ratio between the outer to us, and us to the inner remains the same before and after the expansion:

Inner = 2
Observer = 4
Outer = 6

Universe expands x 2

Inner = 4
Observer = 8
Outer = 12.

Ratios are the same before and after. So both the inner and outer thing recede at the same speed from us.

but another effect you'd see if the universe had a centre with everything moving away from the centre is that matter toward the outside would be more dispersed than matter from the inside. Ie. The same volume of matter would be spread more thinly over each concentric circle.

We don't see that. The CMBR shows equal dispersal in all directions.

Yeah, it would be more dispersed. I've never really grasped CMBR, either, as I feel like it doesn't make sense in a spherical universe sense. But if we are talking about an infinite universe uniform at the time of the big bang, then yeah I figure CMBR would be uniform in all directions too.

[pErvinalia]

This one on the topology of the universe is also quite interesting...

I didn't understand any of that. Although one thing stuck out - "Plonk time"..

[Brian Peacock]

Jim knows all about 'Plonk time' - to wit, it's always time for plonk!

This one says the same thing as the previous video, in a slightly different way...

[Animavore]

Ratios are the same before and after. So both the inner and outer thing recede at the same speed from us.

The inner circle would be travelling towards us in the same direction, at the same speed. The outer circle away, at the same speed*. The distance between us would remain the same with the outer galaxies red shifted and the inner ones blue shifted. The universe wouldn't appear to be expanding, rather it would appear to be all moving in one direction. Unless you are at the centre or you're near enough that the arc of your sphere creates a universe which curves, in a convex way, around the epicentre on the inside and a concave way towards the out.

*it might even be the case the inner ones travel faster and the outer ones slower as the energy gets dissipated over a larger area.

[pErvinalia]

No, that's wrong. We are moving away faster from the inner one than it is moving towards us. And the outer one is moving away faster from us than we are moving towards it. The ratios are exactly the same. From our reference frame we would see both receding from us at the same rate.