expansion of universe vs looking direction

[ramparts]

Sure, but that stops being relevant on the largest scales. In a universe like ours - that is, homogeneous and isotropic, or everything the same, at large scales - the expansion of spacetime is linked to the expansion of the stuff. As spacetime goes, so does the matter. It just doesn't make much sense to talk about spacetime as expanding while everything else isn't. Even if there were some stuff called spacetime which expanded independently of the stuff on it, it would be unobservable, meaningless.

Imagine, for example, that we lived in a universe where the total density was greater than the critical density - we'd say that the spacetime described a closed universe, and eventually it would recollapse on itself. You could counter that spacetime is not collapsing but actually expanding in the background (and somehow not affecting anything), but what would be the point? It would be both impossible to disprove and completely useless.

In fact, there's an interesting result in standard cosmology that the spacetime in an overdense patch of the universe - such as the kind that forms galaxies - behaves mathematically like the spacetime in a closed universe, or one whose expansion slows down and eventually leads to a collapse. That collapse is what forms galaxies

 

[FlatEarth]

Sure, but that stops being relevant on the largest scales. In a universe like ours - that is, homogeneous and isotropic, or everything the same, at large scales - the expansion of spacetime is linked to the expansion of the stuff. As spacetime goes, so does the matter. It just doesn't make much sense to talk about spacetime as expanding while everything else isn't. Even if there were some stuff called spacetime which expanded independently of the stuff on it, it would be unobservable, meaningless. Imagine, for example, that we lived in a universe where the total density was greater than the critical density - we'd say that the spacetime described a closed universe, and eventually it would recollapse on itself. You could counter that spacetime is not collapsing but actually expanding in the background (and somehow not affecting anything), but what would be the point? It would be both impossible to disprove and completely useless. In fact, there's an interesting result in standard cosmology that the spacetime in an overdense patch of the universe - such as the kind that forms galaxies - behaves mathematically like the spacetime in a closed universe, or one whose expansion slows down and eventually leads to a collapse. That collapse is what forms galaxies

Your explanation is the accepted mainstream view, but I don't agree that the view I propose is meaningless by any means! Certainly what happens at the farthest reaches of the universe isn't useful to us, but if spacetime does behave in the manner I propose, that could lead us to a different understanding of what spacetime is, and perhaps to different discoveries. It's a worthy thesis. Please develop this idea without delay.

 

[ramparts]

haha. Will do. But I'm not talking about the farthest reaches of the universe - remember, in a universe that's the same everywhere, far and near aren't any different. Anyway, this wouldn't be meaningless because it's not useful, but because it's untestable.

Also - and this is something I'm less certain on - but that view would almost certainly violate general relativity. What I'm less certain about is whether or not the current precision tests of GR would have anything to say about it - that is, whether the violations of GR are restricted by experiment. But according to GR, in a homogenous and isotropic universe spacetime traces out the matter distribution, and the idea that it expands "past" the matter is mathematically meaningless. But at this point I'm just throwing out ideas, as I'm tired

 

[FlatEarth]

haha. Will do. But I'm not talking about the farthest reaches of the universe - remember, in a universe that's the same everywhere, far and near aren't any different. Anyway, this wouldn't be meaningless because it's not useful, but because it's untestable.

Also - and this is something I'm less certain on - but that view would almost certainly violate general relativity. What I'm less certain about is whether or not the current precision tests of GR would have anything to say about it - that is, whether the violations of GR are restricted by experiment. But according to GR, in a homogenous and isotropic universe spacetime traces out the matter distribution, and the idea that it expands "past" the matter is mathematically meaningless. But at this point I'm just throwing out ideas, as I'm tired

The thought that it wouldn't show up mathematically actually crossed my mind, although I must admit I don't have the background to do the math myself. Still, I appreciate your thoughts and those of SpeedFreek. This serves as my online astronomy and cosmology class.
Rest up, study hard.

 

[Woggles]

Hi Flat. Thanks. Sure if they like to add to the many questions I have they are more welcome too. I am looking for answers to questions. It doesn’t matter who or where they come from. Hey I work underground most of the time in the NDE (NDT) field. Never taken any course on most subjects talked about here. Only courses I've taken are to research thing I'm interested in, such as topics here on this site. So please Flat keep them coming!! What I don't understand I will try to find out by looking them up or ask other questions. I hope my questions aren't to simple mind for any one here, well maybe they are, but for that to change I need teachers!! Flat I like how you express your self to my questions. You have the ability to allow us lay people to gain a great understand of this world (ok universe) we live in!!

Paul

 

[FlatEarth]

Woggles, please keep in mind that my views are not shared by mainstream science! If you are looking for accepted concepts, Speedfreek, ramparts, and the Mods are the ones to listen to! My ideas amount to conjecture and thought experiments!

Hi Flat. Thanks. Sure if they like to add to the many questions I have they are more welcome too. I am looking for answers to questions. It doesn’t matter who or where they come from. Hey I work underground most of the time in the NDE (NDT) field. Never taken any course on most subjects talked about here. Only courses I've taken are to research thing I'm interested in, such as topics here on this site. So please Flat keep them coming!! What I don't understand I will try to find out by looking them up or ask other questions. I hope my questions aren't to simple mind for any one here, well maybe they are, but for that to change I need teachers!! Flat I like how you express your self to my questions. You have the ability to allow us lay people to gain a great understand of this world (ok universe) we live in!!

Paul

Thanks, Paul, but I am also a lay person, which means I don't know what I'm talking about. I post so that I can learn from others who care to respond.