The size of the universe - a question.

[pErvinalia]

No, I'm not talking about an explosion. I've always been referring to the expansion of spacetime. You even make the same point as me in this post, which I somehow forgot to address.

That only works if the universe expands at the same rate everywhere at once, again like a 3-D version of the balloon skin, or the infinite raisin cake. In a sphere which is expanding you have different lines of expansion from the centre along the radius than you do the circumference. In this case its more like the balloon as a whole. Growing in volume at a cubic rate while its surface area increase at a squared rate.

I'm not following. Volume doesn't come into it. We are talking about linear distances. When I say expansion x2, I literally mean that the distance between two points doubles.

If you blow up a balloon does the distance between the inner surface and outer surface double as it expands to twice its former size?

You're still talking about volumes. I just said that I'm talking about linear distances.

[Animavore]

No, I'm not talking about an explosion. I've always been referring to the expansion of spacetime. You even make the same point as me in this post, which I somehow forgot to address.

That only works if the universe expands at the same rate everywhere at once, again like a 3-D version of the balloon skin, or the infinite raisin cake. In a sphere which is expanding you have different lines of expansion from the centre along the radius than you do the circumference. In this case its more like the balloon as a whole. Growing in volume at a cubic rate while its surface area increase at a squared rate.

I'm not following. Volume doesn't come into it. We are talking about linear distances. When I say expansion x2, I literally mean that the distance between two points doubles.

If you blow up a balloon does the distance between the inner surface and outer surface double as it expands to twice its former size?

You're still talking about volumes. I just said that I'm talking about linear distances.

Answer the question then understand the answer and figure out why we are not in a bubble universe in which everything is moving from a central point.

[pErvinalia]

I've got a couple of thoughts on this:
The gravity thing first. That makes no sense to me as it implies that gravity is independent of spacetime. But it's a theory of spacetime. It appears independent, as you'd expect gravity to weaken as spacetime got bigger. But if gravity is maintaining the clumping of matter independent of the expansion of spacetime, then that doesn't really gel in my brain.

I was thinking about this earlier and I wanted to correct myself. The gravity-well would presumably expand with the expansion of space-time, which would result in stronger gravity (helping matter to stay together and not elongate). Which then raises the seeming contradiction of the inverse square law of gravity. If metres aren't growing, but gravity is, then the inverse square law would break, wouldn't it?

How would gravity grow stronger unless the mass of things was increasing?

Because gravity, in this case is a function of spacetime. As spacetime grows, so too must gravity. But as you identify, this leads to a nonsensical outcome (which is why I mentioned the breaking of the inverse square law). So how does spacetime expand without effecting gravity?

Gravity is dependant on the mass of an object.

Stop with the retarded smilies. Gravity, as per Einstein, is a curvature of space time. If spacetime grows, then the gravity well by necessity must grow. But this leads to a contradiction.

[pErvinalia]

That only works if the universe expands at the same rate everywhere at once, again like a 3-D version of the balloon skin, or the infinite raisin cake. In a sphere which is expanding you have different lines of expansion from the centre along the radius than you do the circumference. In this case its more like the balloon as a whole. Growing in volume at a cubic rate while its surface area increase at a squared rate.

I'm not following. Volume doesn't come into it. We are talking about linear distances. When I say expansion x2, I literally mean that the distance between two points doubles.

If you blow up a balloon does the distance between the inner surface and outer surface double as it expands to twice its former size?

You're still talking about volumes. I just said that I'm talking about linear distances.

Answer the question then understand the answer and figure out why we are not in a bubble universe in which everything is moving from a central point.

The question is irrelevant. The movement we have been talking about is an expansion of spacetime. Not a giant explosion pushing things around in the universe. You correctly state that both the volume and the surface area of a sphere grow at a faster rate than the linear growth of the radius. But that's irrelevant.

[Animavore]

I was thinking about this earlier and I wanted to correct myself. The gravity-well would presumably expand with the expansion of space-time, which would result in stronger gravity (helping matter to stay together and not elongate). Which then raises the seeming contradiction of the inverse square law of gravity. If metres aren't growing, but gravity is, then the inverse square law would break, wouldn't it?

How would gravity grow stronger unless the mass of things was increasing?

Because gravity, in this case is a function of spacetime. As spacetime grows, so too must gravity. But as you identify, this leads to a nonsensical outcome (which is why I mentioned the breaking of the inverse square law). So how does spacetime expand without effecting gravity?

Gravity is dependant on the mass of an object.

Stop with the retarded smilies. Gravity, as per Einstein, is a curvature of space time. If spacetime grows, then the gravity well by necessity must grow. But this leads to a contradiction.

Why 'must' It?

[pErvinalia]

Because the well is a spacetime "surface". If spacetime grows, then the well must grow.

[Animavore]

I'm not following. Volume doesn't come into it. We are talking about linear distances. When I say expansion x2, I literally mean that the distance between two points doubles.

If you blow up a balloon does the distance between the inner surface and outer surface double as it expands to twice its former size?

You're still talking about volumes. I just said that I'm talking about linear distances.

Answer the question then understand the answer and figure out why we are not in a bubble universe in which everything is moving from a central point.

The question is irrelevant. The movement we have been talking about is an expansion of spacetime. Not a giant explosion pushing things around in the universe. You correctly state that both the volume and the surface area of a sphere grow at a faster rate than the linear growth of the radius. But that's irrelevant.

No it's not.

You can fuck off now wasting my time with this obstinate rubbish. I've spent far too much time on this bullshit only to have it thrown back in my face with deliberate trolling.

Fucking eejit.

[pErvinalia]

Jesus, settle petal. What's got up your arse? I've explained many times why many of your points are off the mark. You literally haven't addressed a lot of what I've said. If you can't address it, fine. You don't need to spit the dummy, though.

[pErvinalia]

Regarding the actual point you aren't addressing in that tanty, it's not being obstinate. You are literally referring to something that is irrelevant. If the context is spacetime expanding and how that relates to distance between objects and their change over time, then the rate of volume and/or surface expansion of the whole sphere is irrelevant. The only thing that is relevant is linear distances. It is indisputable, unless I've got the maths somehow wrong (and you've not shown that I have), that as spacetime expands, linear distances expand by the same amount.

[Animavore]

I'm sorry. I shouldn't have wrote that. I definitely shouldn't have pressed "post bollocks".

Brian, suspend my for a week. I've real life issues I should be focused on.

[pErvinalia]

You don't need to be suspended. Just get a fucking grip.

[Rum]

It would seem that the universe is, after all, an expanding bubble of hot air.

[pErvinalia]

The best hypothesis to answer your initial query, Rum, would appear to be the "infinite universe" thingy. That is, the universe always(?) existed and was infinite in size when the big bang happened everywhere equally. So not being a sphere, we therefore don't need to link the size of the universe to the age of the universe. And therefore every point can see 13.7 billion light years, even though that leads to an infinitely sized universe.

That alone still doesn't explain how an infinitely sized thing expands, in a way that makes sense. There's also a few lingering questions for me regarding why space (i.e. metres) and time (i.e. seconds) don't expand to match spacetime expansion, and how gravity as an Einsteinian concept is affected or not affected by expanding spacetime.

[Rum]

Well there is clearly something missing in our picture - and I suspect it is the human inability to visualise more than three dimensions plus time. The 'shape' of the universe may possibly only be understood mathematically in the end and us feeble mortals will have to suffice with the like of Brian Cox doing his best to help us out.

One point - not sure if has been raised here yet (too many posts to wade through) is the notion of what happens eventually when the universe has expanded so much that one won't be able to see the light from other galaxies -
and other stars in the end - and then after more billions of years all the energy in the 'system' has expired and all that is left is an almost endless sea of photons swimming about - that there will be no way for information to exist within the system. At that stage the universe could be immensely massive or infinitesimally small - nothing within it will 'know' in terms of the relations between the surviving sub atomic particles. Physics as we know it and the laws it plays by will break down - or not exist in the same way - just as during the big bang.. At that point, I have read, it is possible that a futher big bang could emerge. The universe could be both infinitely large and infinitely small at the same time - or neither.

And no Anim - I don't confuse lightyears with a measurement of time and/or distance. I'm not a total buffoon. Just a bit of one.

[pErvinalia]

Well there is clearly something missing in our picture - and I suspect it is the human inability to visualise more than three dimensions plus time. The 'shape' of the universe may possibly only be understood mathematically in the end and us feeble mortals will have to suffice with the like of Brian Cox doing his best to help us out.

Yeah, I think this is definitely the case. And additionally, infinity falls into the same category. There's nothing natural (that I'm aware of) at our scale of existence that could give us the experience to understand infinity.

One point - not sure if has been raised here yet (too many posts to wade through) is the notion of what happens eventually when the universe has expanded so much that one won't be able to see the light from other galaxies -
and other stars in the end - and then after more billions of years all the energy in the 'system' has expired and all that is left is an almost endless sea of photons swimming about

This gets back to the points about nonsensical (in a 'common sense' context) notions of infinity and it expanding. For the total energy in the system to "expire" or at the very least disperse to such an extent so as to be more or less equivalent to being non-existant, would require that there was a finite amount of energy in the universe when it was created (either 'before' or after the big bang). I.e. If there was infinite energy, then the amount of energy could never disperse away. But how do you have finite energy in a universe that is both infinite and uniformly dense?

The universe could be both infinitely large and infinitely small at the same time - or neither.

I'd like to see someone explain that state of affairs in lay terms and claim with a straight face that they understand it. Yet you'll get lay people on forums and in the media doing just that.

And no Anim - I don't confuse lightyears with a measurement of time and/or distance. I'm not a total buffoon. Just a bit of one.

The thing is, it IS a measure of time, because we know the speed of light is constant (variably, depending on what medium it is travelling through). It's just not a coherent measure of time, like you've tried to describe in the OP, in an infinite universe.