How can the observable universe be 46 billion lyrs in size?

[marcus]

And...?
What if the Hubble constant go down even <0?
The big crunch?

That is right, as a "what if". In models where the universe contracts the H is negative. But the change in H has been observed over time and the evidence is that although it has indeed been decreasing it is not tending to zero, or into negative territory! It is leveling out at a positive value.
(that is what is beginning to cause acceleration in individual distance growth speeds)
You can see the leveling out in the plot.

 

[marcus]

... in the paper: http://arxiv.org/abs/1011.5000)

(and I see marcus was faster this time! :) )

I should just keep quiet and not clutter the thread! I really like your explanations. That is a nice picture in post #30. Stephanus notice that increasing z means going back in time, so in the plot Bander showed, the H increases as you go back in time. That means it is decreasing as you go forward in time. (which is also what my picture showed but more confusingly because it uses an untypical time scale)

 

[rootone]

Are you sure?

No not 'sure', since there is no evidence one way or the other.
However the proposal that the observable Universe is identical to the entire Universe implies that the the entire Universe is a sphere with the Earth in the dead center of it.
A lot of people would be very surprised if this somehow became proven to be true.

 

[Stephanus]

No not 'sure', since there is no evidence one way or the other.
However the proposal that the observable Universe is identical to the entire Universe implies that the the entire Universe is a sphere with the Earth in the dead center of it.
A lot of people would be very surprised if this somehow became proven to be true.

And after all Galileo, Copernicus, Kepler, we're back to geosentris. But this is Occam Razor thing I think.

 

[rootone]

But this is Occam Razor thing I think.

Sure. Occams Razor is not infallible, but is a good reason to believe it highly unlikely that the Earth occupies a very special location within the Universe as a whole.

 

[phinds]

... the proposal that the observable Universe is identical to the entire Universe implies that the the entire Universe is a sphere with the Earth in the dead center of it.
.

I think that's a leap of "logic" that does not compute at all. If the universe is infinite, then the observable universe can be identical with the observable universe NOT at the center (or yes, at the center just as is every other point in an infinite universe ... there really is no center to an infinite universe). If the universe is not infinite but rather finite but unbounded, then it is does not need to be true that we are at the center of whatever the topology is.

Either way, your statement does not compute.

 

[rootone]

Must be something wrong with the way I tried to express it, I'll try again.
OK, so the observable Universe is a spherical region of space which is observable by an observer who is at the center of that sphere.
That's a reasonable definition of 'observable Universe' I think, tell me if otherwise.

We can't say whether there is more to the Universe as a whole outside of this observable sphere due to lack of evidence.
However it does seem highly probable that there is more stuff in the Universe then the observable sphere.
The reason being that if there was not more stuff outside of the observable universe, then the term 'observable' becomes redundant, the observer can observe 'everything'.
'Observable universe' and 'whole universe' would be synonyms for the exact same thing.

If this was true, then therefore the observer has the luxury of being located in the exact center of the total cosmos, not just the observable universe but the totality of everything, (which can only be spherical if this is true).
I see no reason for making such an extravagant assumption, it's far more likely that the observer is nowhere special within the entire cosmos, and that more stuff does exist beyond the observable horizon

 

[phinds]

Yes, that's correct except that the assumption that the OU is the entire universe is MUCH worse than just the hubris involved in our making that assumption. Namely, it requires a sharp boundary that defies our understanding of physics and is therefore extremely unlikely. The fact that we cannot collect direct evidence from outside the OU seems somewhat irrelevant to the conclusion that there is something there and that at least for some finite distance (probably huge) the U continues on in the same way. After that it either just keeps going to infinity or it "wraps" in some topology that we do not have evidence of.

 

[bapowell]

Are you sure?

Yes. We know that there was more universe beyond the Hubble sphere at the time of last scattering, so why not now? Unless you think the minimum amount of inflation required to solve the horizon/flatness problems is exactly the amount of inflation we got...