1. ## Big Shell?

The Big Bang discussion on the other forum got me thinking again about a notion I've had for some time. Bear with me... I promise to duck at the end

Originally Posted by KathyNS
There is no centre, presumed or otherwise. The Big Bang was not an explosion that occurred in one place and expanded into the rest, the way we typically picture it.
Okay, that's the standard line... and here's a page that agrees with it.
Cosmology FAQ: Where is center of the Big Bang?
The diagram there shows the spherical shell of an explosion, of which is said the Big Bang is not.

Big shell.jpg

I suggest that our entire observable universe corresponds to that shaded region: a sphere about 30 billion light years across, all contained within the outer shell of a vast explosion. In this scenario, the center of the Bang is in a particular direction, far beyond our view. As the shell expands, other "stuff" within the observable universe would appear to recede from us. Material closer to the center would have less velocity, while material further from the center would have more velocity.

Well, does this make any sense? A mere notion, but could it point to any predictions such that it might become a hypothesis?

2. ## Re: Big Shell?

this is what i've always assumed our situation to be according to the big bang theory, i take it this isn't what the theory implies?

when things 'splode in a vacuum they tend to 'splode in all directions, not sure how big a jump it would be to extend that to something 'sploding in nothing... but there'd have to be another uh, wavefront? shockwave? whatever moving in the opposite direction (and all other directions) if that's the case..

i guess i need to read more on big bang theory, lol..

3. ## Re: Big Shell?

I don't see how the shell idea is useful at all. The uniformity of the Big Bang requires that the universe is homogenous and isotropic. Homogeneity implies that the universe looks the same, on average, from every point. Isotropy requires that in addition the universe looks the same, on average, in every direction. Furthermore homogeneity implies momentum conservation. Isotropy implies angular momentum conservation.

We observe both momentum and angular momentum conservation so we know the universe must be homogenous and isotropic. The big shell is neither homogenous nor isotropic and will not conserve momentum or angular momentum so it's false.

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5. ## Re: Big Shell?

Originally Posted by pointer
this is what i've always assumed our situation to be according to the big bang theory, i take it this isn't what the theory implies?

when things 'splode in a vacuum they tend to 'splode in all directions, not sure how big a jump it would be to extend that to something 'sploding in nothing... but there'd have to be another uh, wavefront? shockwave? whatever moving in the opposite direction (and all other directions) if that's the case..

i guess i need to read more on big bang theory, lol..
Something exploding in nothing makes a universe not homogenous, not isotropic. So be my previous post this thread that idea is already falsified because momentum and angular momentum are conserved.

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7. ## Re: Big Shell?

so the big bang isn't directional in any sense, if homogeneity is a requirement?

doesn't the cosmic background imply a lack of isotropy?

not disagreeing, just wondering. the shell seems to explain our perceived expansion of our observable universe, that's what led me to this conclusion as well..

8. ## Re: Big Shell?

Originally Posted by pointer
so the big bang isn't directional in any sense, if homogeneity is a requirement?
Correct.

doesn't the cosmic background imply a lack of isotropy?
Not at all. The observed dipole anisotropies is consistent with random motion of the Milky Way with respect to the background. Other galaxies will see different dipole anisotropies averaging out to zero anisotropy.

not disagreeing, just wondering. the shell seems to explain our perceived expansion of our observable universe, that's what led me to this conclusion as well..
Well the shell says momentum and angular momentum are not conserved so it's false.

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10. ## Re: Big Shell?

One of the worst things done in Physics is to use a balloon to illustrate the expansion of the universe. If properly interpreted it can be somewhat helpful but not very IMHO.

So we end up with people figuring there is a center to the universe because we consider it to be at least as spherical if not more so than the balloon used to illustrate.

We've even got some Astrophysicists and Cosmologists who are stuck thinking that the universe all began with a sort of quantum smear or some other infinitesimal beginning - which is not at all demanded by the observations/science.

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12. ## Re: Big Shell?

Originally Posted by OleCuss
One of the worst things done in Physics is to use a balloon to illustrate the expansion of the universe. If properly interpreted it can be somewhat helpful but not very IMHO.

So we end up with people figuring there is a center to the universe because we consider it to be at least as spherical if not more so than the balloon used to illustrate.

We've even got some Astrophysicists and Cosmologists who are stuck thinking that the universe all began with a sort of quantum smear or some other infinitesimal beginning - which is not at all demanded by the observations/science.
Yes, it's a tedious error that gets propagated by some popular figures. But General Relativity is experimentally verified and not falsified by any observations and all those observations plus GR say that the universe is the same everywhere and in all directions on average. It also makes clear that any irregularities due to a shell (with two edges, inner and outer) or a ball with only an outer edge violate momentum and angular momentum conservation.

Emmy Noether proved the maths back in 1915 and it's actually more general than General Relativity. Her proof applies to any physical theory classical or quantum, relativistic or not. I suspect that the equation:

homogenous isotropic universe = momentum and angular momentum conservation

has to hold in any physics theory that could be invented.

I'm simply staggered that popularizers of science don't realize this cornerstone of physics applies to and refutes some of their ravings.

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14. ## Re: Big Shell?

Although tough to visualize I've always tried to picture the universe expanding from every point as apposed to "a" point. This would include any "new" points that arise from the expansion. The question I've always had is why the expansion seems to be inhibited near massive structures like a galaxy or atomic nuclei.

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16. ## Re: Big Shell?

Originally Posted by GulfCoastGuy
Although tough to visualize I've always tried to picture the universe expanding from every point as apposed to "a" point. This would include any "new" points that arise from the expansion. The question I've always had is why the expansion seems to be inhibited near massive structures like a galaxy or atomic nuclei.
There is no evidence of which I am aware that expansion is inhibited near galaxies or atomic nuclei. I believe that the statement that there is such an inhibition is mistaken and not based on the numbers.

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